frame comunication arhitecture

Programme name: Information Society Technologies (IST)

Sector:

Project ID: IST-2000-29663

Project acronym: FRAME-S

Project name: Framework Architecture Made for Europe - Support

Deliverable Type: Public

Deliverable Number: D3.3 - Annex 2

Contractual Date of Delivery: N/A

Actual Date of Delivery: November 2004

Title of Deliverable: European ITS Framework Architecture Communication Architecture

Work package: WP 6

Nature of Report: Public Report

Author(s): Richard Bossom (STC)

Project manager: R.A.P. Bossom (STC)

Abstract: This document provides a description of the Communication Architecture that forms part of the European ITS Framework Architecture. It also includes some background on methodology for the Communication Architecture.

Keyword list: Communication Architecture, Framework Architecture, System Architecture © European Communities, 2004 Reproduction is authorised provided the source is acknowledged

Neither the European Commission, nor any person acting on behalf of the Commission is responsible for the use that might be made of the information in this report. The views expressed are those of the authors and do not necessarily reflect Commission policy.

European ITS Framework Architecture Communication Architecture

Annex 2 - Details of ITS related Communications Technologies

Issue 2, November 2004

Produced by: ERTICO

FRAME Communication Architecture - D 3.3 Annex 2

August 2004 Page i Issue 2

Document Control Sheet

Activity name: FRAME

Work area: Architecture Updates – WP6

Document title: Communication Architecture

Document number: D3.3 – Annex 2

Electronic reference:

Editor: R.A.P. Bossom (STCL)

Main author(s): K. Hartwig (ERTICO)

Dissemination level1: Public usage

Version history: Version number

Date Editor Summary of changes

Issue 1 August 2000 R.A.P. Bossom Final Public Issue

Issue 2 February 2004 K. Hartwig Wireless Communication

Approval: Name Date

Prepared K.Hartwig February 2004

Reviewed R.A.P. Bossom September 2004

Authorised R.A.P. Bossom September 2004

Circulation: Recipient Date of submission

CEC November 2004

1 This is either: Restricted (to the programme, to the activity partners) or for Public usage


August 2004 Page ii Issue 2

Table of Contents

EXECUTIVE SUMMARY 1

1 INTRODUCTION 2

1.1 Purpose 2

1.2 Where the document fits in the Architecture Documentation 2

1.3 Document Structure 2

1.4 Abbreviations 2

2 WIRELESS TECHNOLOGIES 4

2.1 Introduction 4

2.2 Short Range communication 5

2.2.1 Introduction 5

2.2.2 Microwaves 5

2.2.3 Infrared (IR) 6

2.2.4 Wireless LAN 7

2.2.5 Bluetooth 8

2.2.6 Dedicated Short Range Communication (DSRC) 9

2.2.7 Digital Enhanced Cordless Telecommunication (DECT) 9

2.3 Long Range Communication 13


2.3.2 Global System for Mobile Communication (GSM) 13

2.3.3 3G Third Generation 23

2.3.4 TETRA/TETRAPOL 27

2.3.5 Satellite Communication 31

2.4 Broadcast 39

2.4.1 Radio 39

2.4.2 Television 45

2.5 Positioning 48

2.5.1 Global Positioning Systems 49


August 2004 Page iii Issue 2

2.5.2 European Systems 53

3 WIRED TECHNOLOGIES 55

3.1 Introduction 55

3.2 Telephone 55


3.2.2 POTS (analogue) 55

3.2.3 Integrated Services Digital Network (ISDN) 56

3.3 Digital Subscriber Line (DSL) 57


3.3.2 Types of DSL 57

3.3.3 Overview and Description 58

3.3.4 Asymmetric Digital Subscriber Line (ADSL) 58

3.3.5 Consumer DSL (CDSL) 59

3.3.6 G.Lite or DSL Lite 59

3.3.7 High bit-rate DSL (HDSL) 59

3.3.8 Single pair HDSL (S-HDSL) 60

3.3.9 ISDN Digital Subscriber Line (IDSL) 60

3.3.10 Rate-Adaptive DSL (RADSL) 60

3.3.11 Single-line DSL (SDSL) 60

3.3.12 Unidirectional DSL (UDSL) 60

3.3.13 Very high data rate DSL (VDSL) 61

3.4 X.25 (Packed Switched Data) 61

3.5 Frame Relay 62

3.6 Asynchronous Transfer Mode (ATM) 63

3.7 Internet 64

3.7.1 Overview 64

3.7.2 Technology 64

3.7.3 Use in Telematics 65

4 OPTICAL NETWORKING 66


August 2004 Page iv Issue 2

4.1 Introduction 66

4.2 SDH/SONET 67

4.3 Packet over SONET (POS) 67

4.4 Wavelength Division Multiplexing (WDM) 68

5 SYNTHESIS TABLE 70

5.1 Introduction 70

5.2 Synthetic Table 71

6 SHORT INTRODUCTION TO THE OSI MODEL 76

7 REFERENCES 78

Figures

Figure 1 DECT transmission – frequency allocation and time spectrum............................... 10

Figure 2 TETRA Illustration of Channel Organisation .......................................................... 27

Figure 3 TETRA Frame Structure .......................................................................................... 28

Figure 4 xDSL speed vs copper pair length............................................................................ 61

Figure 5 Evolaution of Infrastructure ..................................................................................... 66

Figure 6 Comaprison of different types of SDH/SONET....................................................... 67

Figure 7 Graph of network capacity for different WDM sppeds............................................ 69

Figure 8 OSI Model Layer Structure ...................................................................................... 76

Tables

Table 1 Broadcast Radio Cuumincations - Available Types.................................................. 39

Table 2 Allocation of DAB Bands.......................................................................................... 43

Table 3 Values of the Synthesis Table.................................................................................... 70

Table 4 Synthetic table on telecommunication technologies linked with ITS ....................... 72


August 2000 Page 1 of 84 Issue 2

Executive Summary

Telecommunications is one of the fastest developing technologies today. The main driving force for this is the permanent growing demand for more and better services by the customers. The government bodies with deregulation and the opening of national telecommunication markets met this. This led to increasing competition with the result that new developments took place in both the use of hardware and technologies.

As a result of these changes, ITS deployments are faced with new telecommunication equipment and new telecommunication standards with an ever increasing speed. The best example for this situation can be seen at the mobile handset market. Today’s state of the art mobiles equipment will be outdated in a short time. And each new family of mobile handsets shows changes in the interfaces, both in electrical and mechanical sense. Thus changes in ITS-applications (for example using GSM) must be done by each improvement of the product family of the mobile handset manufacturers.

This report offers a brief overview of the currently used telecommunication standards that are linked with ITS-applications and mentions some possibly emerging future standards.



1 Introduction

1.1 Purpose

This Document provides the second Annex to the main part of European ITS Framework Architecture Deliverable Document D 3.3, which provides a description of the European ITS Communication Architecture. This Annex Document includes additional and supporting information to the Main Document. It contains a description of the various technologies being currently used for ITS communications, an analysis of their main characteristics and a description of the OSI Model.

1.2 Where the document fits in the Architecture Documentation

The document is one of a set of two Annexes to the main European ITS Framework Architecture Communications Architecture Deliverable Document (D 3.3). The other Annex in the set is:

D3.3, Annex 1 - Communications Architecture - Supporting information for Communications Analysis

1.3 Document Structure

This Annex Document has been divided into six chapters. They provide information and data supporting the analysis of “example Systems” in the Main Document.

The following Chapter (2) provides an overview on Wireless technologies. It is divided into short-range communication, long-range communication, broadcast and positioning technologies. Chapter 3 deals with wired technologies. It provides information on wired telephony and different means and protocols for wired data transfer. There is then a Chapter (4) on optical communications technologies, after which there is a Chapter (5) containing a table summarising the main characteristics of all the technologies described in the three previous Chapters. Finally the last Chapter in this group (6) provides an overview description of the OSI Models. In all of these Chapters, the main emphasis is on the aspects of the technology that are relevant to ITS and the communications links that it requires.

The update to this deliverable carried out in 2004 in the context of the FRAME-S project focuses mainly in the emerging wireless technologies

1.4 Abbreviations

The following abbreviations have been used in this Document and their meanings may not be included in the adjacent text.

3G 3rd Generation

AuC Authentication Centre



DSL Digital Subscriber Line

DTE Data Terminal Equipment

EFC Electronic Fee Collection

FRAME-S Framework Architecture made for Europe - Support

FSK Frequency Shift Keying

Gbps Giga bit per second

GHz Giga Hertz

IMEI Internet Mobile Equipment Identity

ISL Inter-Satellite Link

ITS Intelligent Transport Systems

ITU International Telecommunications Union

KB Kilo byte

Kbps Kilo bit per second

Mbps Mega bit per second

MFO Multi-Function Outstation

MoU Memorandum of Understanding

OSI Open System Interconnection

PMR Private/Professional Mobile Radio

PSK Phase Shift Keying

RF Radio Frequency

TCH Traffic Channel

TD-CDMA Time Division – Code Division Multiple Access

TETRA Terrestrial Trunked Radio

UMTS Universal Mobile Telecommunications System

W-CDMA Wideband - Code Division Multiple Access



2 Wireless Technologies

2.1 Introduction

In most cases, one important point in ITS communication is the fact, that often at least one user of an ITS system is on the move. The best (and usually only) way to communicate with the moving user is using wireless technologies.

Since radio spectrum is a limited resource shared by all standards and users, the wireless part of the communication within ITS systems can be seen as the most critical one in terms of bandwidth, security or costs.

Thus choosing the best fitted means of wireless communication may determine the overall success of any ITS application. And best fitted is not only restricted to considerations in a technical sense. Nowadays many marketing and commercial aspects must be taken into account before the technology decision can be done.

Wireless communication technologies can be split into a number of different categories, for example:

• By Communications means: Point-to-Point, Point-to-Multipoint vs. Broadcast communications

• By Communications bandwidth: narrow vs. medium vs. wide bandwidth

• By Communications distance: Short-range vs. long-range communications

• By Communicated content: voice vs. video vs. data communications

For wireless communication different frequencies can be used. Their use in telematics applications depends on the law, the used protocol and the propagation characteristics of the bearer, as e.g. reflection and diffusion. The following table gives an overview about frequencies and their range of use.

Figure 1 Allocation of Frequencies Abbr. Name Frequency range Wave length Use ELF Extremely Low

Frequency < 300 Hz > 1000 km Submarine

communication VF Voice Frequency 300 Hz – 3000 Hz 100 – 1000 km (wired) Telephony VLF Very Low Frequency 3 kHz – 30 kHz 10 – 100 km Audio, acoustic noise LF Low Frequency 30 kHz – 300 kHz 1 – 10 km Radio Broadcast MF Medium Frequency 300 kHz – 3 MHz 100 – 1 000 m Radio Broadcast HF High Frequency 3 MHz – 30 MHz 10 – 100 m Radio Broadcast VHF Very High Frequency 30 MHz – 300 MHz 1 – 10 m Radio + Television

Broadcast, Radar UHF Ultra High Frequency 300 MHz – 3 GHz 10 cm – 100 cm Television Broadcast,

GSM, DECT Phones, WLAN, Bluetooth, Microwave Oven



Abbr. Name Frequency range Wave length Use SHF Super High

Frequency 3 GHz – 30 GHz 1 cm – 10 cm Satellite Television,

Radar, EHF Extremely High

Frequency 30 GHz – 300 GHz 1 mm – 10 mm Beam Radio

IR Infrared 300 GHz – 400 THz 780 nm – 1 mm DSRC, Medical Equipment

Visible Light has a wavelength between 400 nm (violet) and 750 nm (red). With the decrease of the wavelength the optical characteristics of the radio waves increase. That means e.g. the use of microwaves (Frequency > 1 GHz) desires intervisibility of the communicating partners.

The following chapters give an overview of technologies for variant purposes.

2.2 Short Range communication

2.2.1 Introduction

For the use in ITS there are several short-range communication technologies available. They can be used for vehicle-to-vehicle communication, e.g. Bluetooth, or for transmitting information from roadside equipment to cars passing the beacons, as used in public transport or tolling systems.

2.2.2 Microwaves

Microwaves are all Frequencies higher than 1 GHz. They are used for Wireless Data Networks, Tolling Systems, scientific and medical devices and Satellite Television as well. More information about Spectrum Utilisations can be obtained at the ERO Frequency Information System (EFIS) of the European Radiocommunications Office (ERO) at www.efis.dk/search/general.

The use of microwaves requires an inter-visibility (complete line of sight) of the communicating partners. Because of the curvature of the earth and buildings or trees between the communicating partners, for communication over long distances large antennas are necessary. Another reason for the use of large antennas is, that rain affects the microwaves, because it absorbs and scatters the radio frequency energy. Using microwaves the communication on earth over a distance up to 50 km is possible. Via satellites the communication around the world is possible.

There are several unlicensed radio bands (ISM band2), different from country to country. Only the 2.4 band is licence-free world wide. Other bands can be used too, but the system needs to be licensed then.

2 Industrial, Scientific and Medical band, for licence-free use for industrial, scientific and medical use; requirements concerning transmitting power and disturbance of other frequency ranges



2.2.3 Infrared (IR)

The use of infrared light transmission allows the wireless communication between IR-equipped devices. The Infrared Data Association, a group of device manufacturers, developed a standard for the transmission of data, using infrared light waves. The IR communication system allows a data transfer rate comparable with the rate of the parallel ports. For the communication the devices must be in a clear line of sight and only a few centimetres away from each other. 3Regarding present publications on IrDA features, IrDA Data is recommended for high-speed short range, line of sight, point-to-point cordless data transfer - suitable for HPCs, digital cameras, handheld data collection devices, etc. If IrDA is supported, it must be targeted at the 4 Kbps per second components. IrDA Control is recommended in-room cordless peripherals to hostPC for lower speed, full cross range, point-to-point or to-multipoint cordless controller - suitable for keyboards (1 way), joysticks (2 way & low latency) etc. IrDA Data and IrDA Control requires designer attention to ensure spatial or time sharing techniques so as to avoid interference.

Since 1994, "IrDA DATA" defines a standard for an interoperable universal two way cordless infrared light transmission data port. IrDA technology is already in over 300 million electronic devices including desktop, notebook, palm PCs, printers, digital cameras, public phones/kiosks, cellular phones, pagers, PDAs, electronic books, electronic wallets, toys, watches, and other mobile devices.

IrDA Data Protocols consist of a mandatory set of protocols and a set of optional protocols.

Mandatory protocols:

• PHY (Physical Signalling Layer)

• IrLAP (Link Access Protocol)

• IrLMP (Link Management Protocol and Information Access Service (IAS)) Characteristics of Physical IrDA Data Signalling

• Range: Continuous operation from contact to at least 1 meter (typically 2 meters can be reached). A low power version relaxes the range objective for operation from contact through at least 20 cm between low power devices and 30 cm between low power and standard power devices. This implementation affords 10 times less power consumption. These parameters are termed the required maximum ranges by certain classes of IrDA featured devices and sets the end user expectation for discovery, recognition and performance.

• Bi-directional communication is the basis of all specifications

• Data transmission from 9600 b/s with primary speed/cost steps of 115 Kbps and maximum speed up to 4 Mbps

• Data packets are protected using a CRC (CRC-16 for speeds up to 1.152 Mbps and CRC-32 at 4 Mbps).

3 Source: http://www.irda.org/standards/standards.asp



Characteristics of IrDA Link Access Protocol (IrLAP)

• Provides a device-to-device connection for the reliable, ordered transfer of data.

• Device discover procedures.

• Handles hidden nodes.

Characteristics of IrDA Link Management Protocol (IrLMP)

• Provides multiplexing of the IrLAP layer. Multiple channels above an IrLAP connection.

• Provides protocol and service discovery via the Information Access Service (IAS).

Optional IrDA Data Protocols:

Tiny provides flow control on IrLMP connections with an optional Segmentation and Reassembly service.

IrCOMM provides COM (serial and parallel) port emulation for legacy COM applications, printing and modem devices.

OBEX™ provides object exchange services similar to HTTP.

IrDA Lite provides methods of reducing the size of IrDA code while maintaining compatibility with full implementations.

IrTran-P provides image exchange protocol used in Digital Image capture devices/cameras.

IrMC specifications on how mobile telephony and communication devices can exchange information. This includes phonebook, calendar, and message data. Also how call control and real-time voice are handled (RTCON) calendar.

IrLAN Describes a protocol used to support IR wireless access to local area networks.

More information about specifications and guidelines can be obtained at the website of the Infrared Data Association (IrDA) www.irda.org.

2.2.4 Wireless LAN4

A Wireless Local Area Network (W-LAN) uses radio as carrier, i.e. the last link between the user and the network of a building or a company is wireless. It shows its advantages where the use of a cabled LAN is rather difficult or more expensive. For the wireless LAN the variations of the standard IEEE5 802.11 and HomeRF6 specify the communication technology.

4 Source: http://de.wikipedia.org 5 IEEE: Institute of Electrical and Electronics Engineers, http://www.ieee.org

6 Home Radio Frequency: designed specifically for wireless networks in homes, while IEEE 802.11 was created for use in business



IEEE 802.11a defines the communication on the 5 GHz band with a gross transfer rate of 54 Kbps. Devices applying to the IEEE 802.11b standard work within the (world wide) licence free band of 2.4 GHz (ISM band) with a transfer rate of 11 Kbps, while IEEE 208.11g defines the transfer within the same band with 54 Kbps.

The standard IEEE 802.11 comprises the security standard WEP (Wireless Equivalent Privacy), a 40 bit ciphering, which is not sufficient to protect the system from, attacks. Therefore additional ciphering and a firewall are indispensable. A better protection offers the WPA (Wi-Fi Protected Access) standard, the successor of WEP. It is said to be not to decipher as long as the used passwords are not trivial.

Wi-Fi (Wireless Fidelity)7, a set of standards for W-LAN, is based on the IEEE 802.11 specifications. It is also often used for Internet access, e.g. with a PDA. Within a certain area around a “hotspot” (access point) the connection to the internet can be free of charge or for a fee, e.g. with a pass for a limited time. Certified products can use the official Wi-Fi logo that shows compatibility with other Wi-Fi certified products.

There are many reliable Wi-Fi products on the market, to reasonable prices, but there are many devices using the 2.4 GHz spectrum, which may cause a degradation in the performance. Another problem may be the high power consumption.

2.2.5 Bluetooth

Bluetooth is a wireless technology for the bidirectional short-distance (10 m – 30 m) communication among portable devices, such as mobile phones, computers and PDAs, with a low power consumption (1 mW – 100 mW). It is a small and cheap wireless interface using the bandwidth of 2.4 GHz, developed by the Bluetooth Special Interest Group (Bluetooth SIG). The data transmission speeds are between 1 Kbps (Bluetooth 1.0) and 2 Kbps (Bluetooth 2.0).

The Bluetooth technology is a global standard that facilitates both data and voice communication. With this technology users are enabled to connect a wide range of computing and telecommunications devices easily and simply, without cables. That means the connected devices can move independent from each other while they are connected. It delivers opportunities for rapid ad hoc connections, and the possibility of automatic, unconscious, connections between devices.

The transmission is secured by built-in encryption and authentication methods. Bluetooth mainly uses the FHSS (Frequency Hopping Spread Spectrum) transmission method. All of this together with an automatic output power adoption to reduce the range exactly to requirement makes the system difficult to eavesdrop. The fast acknowledgement and frequency-hopping scheme makes the link robust, even in noisy radio environments.

Bluetooth wireless technology provides a universal bridge to existing data networks, a peripheral interface, and a mechanism to form small private ad hoc groupings of connected devices.

7 Wi-Fi: Trademark of the Wi-Fi Alliance, trade organisation that defines the Wi-Fi Standards; see: http://wi-fi.org



2.2.6 Dedicated Short Range Communication (DSRC)

Dedicated Short Range Communication is a common component of practically all existing Electronic Fee Collection (EFC) systems. Its ability to support other ITS services such as Traffic and Travel Information (TTI) and access control has also been widely demonstrated.

The 5.8 GHz frequency band is allocated for short-range communication. The standardisation of short-range communication is already far advanced and several pre-standards have already been approved (EN 12253 - DSRC physical layer using microwave at 5.8 GHz, EN 12795:2002 – DSRC Data Link Layer: Medium access and logical link control, EN 13372 – DSRC profiles for RTTT8 applications, EN 12834:2002 – DSRC Application Layer). The European standardisation body CEN has a specific technical committee assigned to the issues of road transport and traffic telematics, namely CEN TC 2789.

The working groups of TC278 have elaborated a set of pre-standards which may be amended in the next few years before they will be changed to proven standards. There are approved pre-standards for some parts of the DSRC specification. These comprise the following:

• layer 1, defining the physical characteristics of the DSRC interface;

• layer 2, describing the procedures for transmission medium access and for logical link control between the Road Side Equipment (RSE) and the On Board Equipment (OBE);

• layer 7, defining the basic application services that the DSRC communication offers to all the specific telematics services that want to make use of the DSRC communication stack.

For EFC, there is already a pre-standard in place, the Application Interface Definition for EFC that defines the structure of the communication as well as the functions and data elements available to perform an EFC transaction between the RSE and the OBE via the DSRC link. Although a lot of standardisation work has been done, it has to be highlighted that these standards are only enabling interoperability but not providing interoperability automatically.

2.2.7 Digital Enhanced Cordless Telecommunication (DECT)

Introduction

DECT is a common standard for cordless personal telephony established by ETSI (European Telecommunications Standards Institute). Its micro cellular concept basically aims on the indoor use of mobiles in an environment with a high subscriber density, approximately up to 10000 Erlang (“talkers”) per square kilometre.

8 RTTT: Road Transport Traffic Telematics 9 http://www.nen.nl/cen278



The maximum distance between base- and mobile station is estimated to be 50 meters indoors and up to 300 meters outdoor. The maximum movement speed is between 20 and 50 km / h.

The main benefits of DECT are:

• Robust self organising real time radio channel selection

• Coexistence

• Multiple access rights

• Seamless hand-over

• Mobility

• High subscriber densities

• Inter operability

• High quality voice

• Cost efficient

• High level of security

• Standard inter networking profiles

• Multimedia terminals

• Flexible bandwidth

Description

A DECT system comprises a fixed part, utilising one or more base stations, and one or more portable parts. In first way the DECT standard only defines the air interface between a fixed part and a portable. The radio interfaces uses a Multi Carrier, Time Division Multiple Access, Time Division Duplex (MC/TDMA/TDD) access method with a continuous Dynamic Channel Selection and Allocation capability. This enables a high capacity for pico-cellular systems. DECT can even be utilised in busy or noisy radio environments. These methods enable DECT to be used without the need of expensive frequency planning. DECT makes efficient use of the assigned radio spectrum, even when multiple operators and applications share the same frequency spectrum.

Figure 2 DECT transmission – frequency allocation and time spectrum

Basic DECT frequency allocation uses 10 carrier frequencies in the 1880 to 1900 MHz range. The time spectrum for DECT is divided into time frames repeating every 10 ms. Each frame consists of 24 time slots each individually accessible that may be used for either transmission or reception. For the basic DECT speech service two time slots - with 5 ms separation - are paired to provide a full duplex bearer capacity of up to 32 Kbps. For easy implementation the 10 ms time frame is split in halves. The first 12 time slots are used for the downlink; the other 12 are used for the uplink. This structure allows up to 12 simultaneous basic DECT (full duplex) voice connections per transceiver.


March 2004 Page 11 of 84 Issue 1

Services

Data transmission

DECT is able to combine several channels into one single bearer. For data transmission purposes a throughput rate of n x 24 Kbps (with error protection) can be achieved, up to a maximum of 552 Kbps with full security.

Hand over

DECT portables can escape from an interfered radio connection by establishing a second radio link on a newly selected channel to either the same or to another base. Both radio links are temporarily maintained in parallel with identical transmissions. The quality of these links is analysed. Then the base station finds out the radio link with the best quality. The other one is released.

If the portable is moving from one cell area into another, the received signal strength of the two base stations are changing. When the new base stations signal becomes stronger than the signal from the old base station, a seamless hand over (see above) will be performed. The seamless hand over is a fully autonomous initiative from the portable. The user will not notice this procedure.

Although a hand over is always initiated by the portable, it may also be the uplink that suffers from poor quality. For this case, the signalling protocol enables the base station to signal the link quality to the portable. Then the portable can initiate the hand over procedure.

Technology

Dynamic Channel Selection and Allocation

All DECT equipment is recommended to scan its local radio environment at least every 30 seconds. This means that the local RF signal strength on all idle channels is measured. Scanning is done as a background process and produces a list of free and occupied channels to be used in the channel selection process. With the aid of the information of this list a DECT station is able to select the best-fitted (least interfered) channel to set up a new communication link. In a portable part, the channels with the highest signal strength are continuously analysed to check if the transmission originates from a base station to which the portable has access rights. The portable will lock onto the strongest base station. Channels with lowest signal strength are used to set up a radio link with the base station if the portable user decides to establish a communication or when an incoming call is signalled to the portable. Thus the communication links are established on the channel with lowest actual interference.

Security

The use of a radio access technology providing mobility includes considerable risks with respect to the security of the system. The DECT standard provides several measures to counteract these technological flaws in security. Special subscription and authentication protocols have been included to prevent unauthorised access to the DECT system. In addition



a ciphering concept can be used that will provide protection against many methods for eavesdropping.

Subscription

The subscription procedure is the procedure where the DECT network opens the service to a portable.

The network operator provides the user of any portable with a PIN code. This PIN will be entered into the fixed and the portable part before the procedure starts. Next to that the portable must know the identity of the fixed part it will subscribe to.

This subscription procedure can be done "over the air": A radio link is established and both ends verify that they use the same subscription key. Portable and network identities are exchanged. Then both sides calculate the secret authentication key that should be used for authentication at each single call set up. This authentication key is only known to the portable and the fixed part, it is not transferred over the air.

A portable may have several possible subscriptions with different authentication keys for each DECT network. All keys and network identities are stored in a list within the portable. Any portable will only communicate within a network where it has valid access rights.

Authentication

Authentication of a handset may be done as a standard procedure at each call set up. During the authentication procedure, the base station checks the secret authentication key by a challenge-response-procedure:

The base station sends a random number to the handset. The handset calculates a response by using the authentication key and the challenge number as input parameters. This response is transmitted to the base station. The base station also calculates the expected response and compares it with the received response. If successful the call set up is continued, otherwise the call attempt is rejected.

Encryption

During authentication, both sides also calculate a cipher key. This key can be used to cipher the data sent over the air. At the receiving side the same key is used to decipher the information. The ciphering process is an optional part of the standard.

Profiles

Application profiles contain additional specifications defining how the DECT air interface should be used in specific applications. The most important profiles are:

• GAP: Generic Access Profile, minimum mandatory set of technical requirements

• GIP: GSM / DECT Inter-working Profile

• IAP / IIP: ISDN Inter-working Profile



• RAP: Radio local loop Access Profile, profile for the “last mile”

CAP: Cordless terminal mobility Access Profile, profile for the roaming of DECT portables.

2.3 Long Range Communication

2.3.1 Introduction

For many telematics applications the communication over long distances is essential. These applications have different requirements, e.g. regarding the data transfer rate, the data security, the ability to charge for content or the special and temporal availability of the service. Another requirement may be the ability to address special user groups. GSM, par example, allows addressing single users, but also a group of users, e.g. all users in a certain cell of the network. FM radio broadcast allows to address a wide range of users, but not to send a message to only one terminal or a certain group of terminals. DAB might offer a possibility to do so, which is important for location based or commercial services. Therefore the communication technology has to be carefully selected by means of the requirements of the telematics application.

2.3.2 Global System for Mobile Communication (GSM)

Introduction

GSM is a digital personal mobile communication system based on a cellular network. Its main goal is to offer both the user and the operator the technical base for mobile speech and data communication.

During the development of this standard one main task was to secure interoperability and inter-working. By this the user should be enabled to use a service that today is called “International Roaming”. Looking at the active GSM networks this goal is reached for speech services, whereas the data services and several supplementary services still have many problems to solve.

For more information about GSM Technology you can also see the website of the GSM Association at http://www.gsmworld.com.

Data services

Data (circuit switched data)

The GSM standard supports different types of circuit switched data services. These bearer services can be transparent and non transparent, synchronous and asynchronous. This duplex service usually offers a bit rate between 300 and 9600 bit/s. During the usage of the service the achievable bit rate depends on the quality of the radio link, thus in many cases the bit rate will be below the achievable maximum. Some networks even have implemented a data service that offer a bit rate up to 14400 bit/s, but the result is an increased bit error rate in non ideal communication situations.



GPRS

See below: General Packet Radio Service (GPRS)

High Speed Circuit Switched Data (HSCSD)

HSCSD is a technology that bundles several timeslots (channels) of one cell and uses them for the data communication of one customer. Thus the HSCSD-user can increase its maximum usable bandwidth according to the amount of timeslots used. Theoretically there can be eight channels assigned to one connection. However due to the existing network architecture the current maximum is four. Thus the network provider can offer a bandwidth of up to 38,4 Kbps (on a base of 9,6 Kbps per channel).

Next to the bundling of timeslots some network providers are implementing a new channel coding. As an advantage this coding increases the usable bandwidth per channel from 9,6 Kbps to 14,4 Kbps. Thus these networks will offer a total bandwidth of 56 Kbps to their HSCSD customers. On the other hand the new coding reduces the robustness of the transmission. The result is a higher bit error rate if the quality of radio reception is poor.

One problem occurs when the user in a multi-timeslot environment performs a handover (dynamic call transfer between neighbouring cells). In such situation the bandwidth may drop due to lower number of unused timeslots in the new cell during the handover.

From the commercial point of view a direct trade-off between increased speed and the costs from using more radio resources can be seen. However at least one network provider announced tariffs with no difference between HSCSD and normal circuit switched data.

Currently only a few GSM-networks are implementing this technology, most networks and handset manufacturers prefer GPRS. Thus the possible use of HSCSD for ITS may be seen in the market development of the future.

Short Message Service (SMS)

General, Point-to-Point

A special feature of GSM is the Short Message Service (SMS). This feature can be summarised:

• SMS is a bi-directional service for short alphanumeric messages (up to 160 characters using a special 7-bit alphabet) or transparent data (up to 140 byte per message).

• Short messages are transported in a store-and-forward fashion, they are not sent directly from the sender to the recipient. The messages are sent via a special entity within the GSM-network, the so-called SMSC (Short Message Service Centre). Thus if the recipient has switched off the mobile the message becomes available to him as soon as the mobile station is switched on again.

• The notification of the reception of a message can be send by the SMSC if this is asked for by the sender.



• SMS can be sent and received simultaneously to GSM voice, Data and Fax transmission. This is possible because SMS are transferred via signalling channels. Thus SMS can be used when both voice and data communication is needed to perform a service.

• Typically short messages are stored within the GSM SIM-card. Most mobile phones offer a serial interface. Usually one of the features of this interface is the transfer of short messages to terminal equipment. Special parameters can define the SMS to be transferred directly to this terminal equipment.

• The transfer of short messages between different GSM-networks (roaming or recipient in an other network) is defined within the GSM-standard. However, this possibility is sometimes blocked by some network provider.

• For larger customers (e.g. service centres in the sense of ITS) direct access to SMSCs is supported. However, in most cases different access protocols are used by the SMSC manufacturer.

For point-to-point SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt can be provided to the sender.

SMS - Cell Broadcast (CB)

The Short Message Service can also be used in a cell-broadcast mode. In this mode only mobile terminated message up to a length of 82 bytes can be sent. Thus this service is perfectly fitted for sending short messages such as traffic updates or news updates to a huge amount of recipients.

Two different kinds of cell broadcast information can be defined: static and dynamic information. Implementing static CB information within the networks can be done within the BTS itself. For dynamic CB information a Cell Broadcast Centre (CBC) is needed where the permanent change of transmitted information is managed.

ETSI defined this service only to be optional within the GSM networks. Thus only some networks have implemented this service. In addition many older mobile handsets may not be able decode and display the CB information.

Supplementary Services

When GSM was initially planned, ISDN compatibility in terms of the services offered and the control signalling used was one of the main goals. However, radio transmission limitations, in terms of bandwidth and cost, made it too difficult to allow the ISDN B-channel bit rate of 64 Kbps to be achieved practically. Today, this situation is about to change and technical improvements will rise that limitations up to 2 Kbps (see UMTS).

Next to the speech services GSM offers a variety of data services. GSM customers can send and receive data to and from users on POTS (Plain Old Telephone Service), ISDN, Packet Switched Public Data Networks, and Circuit Switched Public Data Networks.

Supplementary services are provided on top of teleservices or bearer services. At the moment, the following supplementary services are defined within the specification:



• CLIP / CLIR Calling Line Identification Presentation / Restriction

• COLP / COLR Connected Line identification Presentation / Restriction

• MPTY Multi Party

• CF Call Forwarding (different conditions possible)

• CW Call Waiting

• CUG Closed User Group

• AoC Advice of Charge

• CB Call Barring (different conditions possible)

• HOLD Call Hold

It must be noted that even if most of the European GSM networks have implemented many different supplementary services no customer can be assured that the supplementary services he is used to in his home network will work the same way in other networks. The reasons for that can vary from technical problems via commercial difficulties up to legal differences between these countries10.

Internet Services through WAP11 The Wireless Application Protocol is a hot topic that has been widely hyped in the mobile industry and outside of it. WAP is simply a protocol- a standardised way that a mobile phone talks to a server installed in the mobile phone network.

The Wireless Application Protocol (WAP) is an important development in the wireless industry because of its attempt to develop an open standard for wireless protocols, independent of vendor and airlink.

Mobile information services, a key application for WAP, have not been as successful as many network operators expected. WAP is seen as a way to rectify this situation.

WAP also has its detractors and controversies:

• It is very difficult to configure WAP phones for new WAP services, with 20 or so different parameters needing to be entered to gain access to a WAP service.

• Compared with the installed base of Short Message Service (SMS) compliant phones, the relative number of handsets supporting WAP is tiny. WAP is a protocol that runs on top of an underlying bearer. None of the existing GSM bearers for WAP- the Short Message Service (SMS), Unstructured Supplementary Services Data (USSD) and Circuit Switched Data (CSD) are optimized for WAP.

• The WAP standard is incomplete, with key elements such as Push (proactive sending of information to mobile devices) and wireless telephony (updating address reports and the

10 An example for legal differences can be seen in the rules for data protection. Whereas in Germany operators must pay attention to data protection regulations when implementing the supplementary service CLIP / CLIR comparable regulations do not exist in other European countries. 11 Source: http://www.gsmworld.com



like) included in the WAP 1.2, standardized in late 1999 and first expected to be implemented in the Spring of 2000.

• There are many WAP Gateway vendors out there competing against each other with largely the same standardized product. This has led to consolidation such as the pending acquisition of APiON by Phone.com.

• Other protocols such as SIM Application Toolkit and Mobile Station Application Execution Environment (MexE) are respectively already widely supported or designed to supercede WAP.

• WAP services are expected to be expensive to use since the tendency is to be on-line for a long Circuit Switched Data (CSD) call as features such as interactivity and selection of more information are used by the end user. Without specific tariff initiatives, there are likely to be some surprised WAP users when they see their mobile phone bill for the first time after starting using WAP.

The Wireless Application Protocol takes a client server approach. It incorporates a relatively simple microbrowser into the mobile phone, requiring only limited resources on the mobile phone. This makes WAP suitable for thin clients and early smart phones. WAP puts the intelligence in the WAP Gateways whilst adding just a microbrowser to the mobile phones themselves. Microbrowser-based services and applications reside temporarily on servers, not permanently in phones. The Wireless Application Protocol is aimed at turning a mass-market mobile phone into a "network-based smartphone". As a representative from Phone.com (formerly Unwired Planet) on the board of the WAP Forum commented "The philosophy behind Wireless Application Protocol's approach is to utilize as few resources as possible on the handheld device and compensate for the constraints of the device by enriching the functionality of the network".

The Wireless Application Protocol is envisaged as a comprehensive and scaleable protocol designed for use with:

• any mobile phone from those with a one line display to a smart phone

• any existing or planned wireless service such as the Short Message Service, Circuit Switched Data, Unstructured Supplementary Services Data (USSD) and General Packet Radio Service (GPRS).

Indeed, the importance of WAP can be found in the fact that it provides an evolutionary path for application developers and network operators to offer their services on different network types, bearers and terminal capabilities.

The design of the WAP standard separates the application elements from the bearer being used. This helps in the migration of some applications from SMS or Circuit Switched Data to GPRS for example.

• any mobile network standard such as Code Division Multiple Access (CDMA), Global System for Mobiles (GSM), or Universal Mobile Telephone System (3GSM). WAP has been designed to work with all cellular standards and is supported by major worldwide wireless leaders such as AT&T Wireless and NTT DoCoMo.

• multiple input terminals such as keypads, keyboards, touch-screens and styluses.



The Wireless Application Protocol embraces and extends the previously conceived and developed wireless data protocols. Phone.com created a version of the standard HTML (HyperText Markup Language) Internet protocols designed specifically for effective and cost-effective information transfer across mobile networks. Wireless terminals incorporated a HDML (Handheld Device Markup Language) microbrowser, and Phone.com's Handheld Device Transport Protocol (HDTP) then linked the terminal to the UP.Link Server Suite which connected to the Internet or intranet where the information being requested resides. The Internet site content was tagged with HDML.

This technology was incorporated into WAP- and renamed using some of the many WAP-related acronyms such as WMLS, WTP and WSP. Someone with a WAP-compliant phone uses the in-built microbrowser to:

1. Make a request in WML (Wireless Markup Language), a language derived from HTML especially for wireless network characteristics.

2. This request is passed to a WAP Gateway that then retrieves the information from an Internet server either in standard HTML format or preferably directly prepared for wireless terminals using WML. If the content being retrieved is in HTML format, a filter in the WAP Gateway may try to translate it into WML. A WML scripting language is available to format data such as calendar entries and electronic business cards for direct incorporation into the client device.

3. The requested information is then sent from the WAP Gateway to the WAP client, using whatever mobile network bearer service is available and most appropriate.

The published WAP standards can be freely downloaded from the WAP Forum web site www.WAPforum.org.

More information about WAO can be obtained at the website of the Open Mobile Alliance at www.openmobilealliance.org/tech/affiliates/wap/wapindex.html and at the GSM World website in the Technology section at www.gsmworld.com/technology/wap/index.shtml .

Technology

Speech coding

GSM is a digital system, so speech, which is analogue, has to be digitised. The method employed by ISDN, and by current telephone systems for multiplexing voice lines over high speed trunks and optical fibre lines, is Pulse Coded Modulation (PCM). The output stream from PCM is 64 Kbps. This rate is too high to be feasible over a GSM link. The 64 Kbps signal, although simple to implement, still contains much redundancy.

Several speech-coding algorithms were studied on the basis of subjective speech quality and complexity (according to cost, processing delay, and power consumption) before a Regular Pulse Excited -- Linear Predictive Coder (RPE--LPC) with a Long Term Predictor loop was chosen. Basically, information from previous samples, which does not change very quickly, is used to predict the current sample. The coefficients of the linear combination of the previous samples, plus an encoded form of the residual, the difference between the predicted and actual sample, represent the signal. Speech is divided into 20 millisecond samples, each



of which is encoded as 260 bits, giving a total bit rate of 13 Kbps. This is the so-called Full-Rate speech coding.

Enhanced Full-Rate (EFR) speech coding algorithm has been implemented by some European GSM1800 operators and North American GSM1900 operators. This offers an improved speech quality using the existing 13 Kbps bit rate.

A Half Rate (HR) speech-coding algorithm was defined by ETSI, too. This coding offers the possibility of effectively double the customers served within one cell by cutting in halve the needed bit rate. But this coding is said to show a poorer speech quality to the customer, thus the network providers have not implemented it yet.

Inter-working with supplementary services

Most of the supplementary services are applicable on the speech service of GSM.

Hand-over

When a call is in progress, the mobility of a GSM user may cause the need to switch the serving cell of the network especially if the quality of transmission drops below a certain value. Thus GSM defines a procedure called hand-over where a call (or any other connection) can be transferred from one cell to another. For this procedure quality parameters are defined so that this hand-over will not be noticed by the user or the disturbance will be kept to a minimum.

Hand-over procedures are defined for changes between cells that belong to the same and to different BSC / MSC regions of one network. The hand-over between different networks (e.g. between two different countries) is not possible yet.

Multiple access and channel structure

The method chosen by GSM is a combination of Time- and Frequency-Division Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the total frequency band into several carrier frequencies. Each of these frequencies is spaced 200 kHz apart. Next to that different frequency bands are used for the uplink (communication leg from the mobile station to the base station) and for the downlink (communication leg from the base station to the mobile station). Due to the duplex communication of GSM there is always one uplink frequency dedicated to one downlink frequency.

The following frequencies are reserved for GSM within Europe (in USA, a frequency band by 1900 MHz is defined instead):

• uplink: 890 – 915 MHz downlink: 935 – 960 MHz

• 1710 – 1785 MHz 1805 – 1880 MHz

One or more carrier frequencies, depending on the expected load within the range of the cell, are assigned to each base station. Each of these carrier frequencies is then divided in time, using a TDMA scheme.



The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 ms (approximately 0,577 ms). Eight burst periods are grouped into one TDMA frame (120/26 ms, approximately 4,615 ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame.

Channels are defined by the number and position of their corresponding burst periods. All these definitions are cyclic. The entire pattern is repeated in a period of approximately 3 hours. Channels can be divided into dedicated channels, which are allocated to a mobile station, and common channels, which are used by mobile stations in idle mode.

Traffic channels

A traffic channel (TCH) is used to carry speech and data traffic. Traffic channels are defined using a 26-frame multi-frame, or group of 26 TDMA frames. The length of a 26-frame multi-frame is 120 ms, which is how the length of a burst period is defined (120 ms divided by 26 frames divided by 8 burst periods per frame). Out of the 26 frames, 24 are used for traffic, 1 is used for the Slow Associated Control Channel (SACCH) and 1 is currently unused. TCHs for the uplink and downlink are separated in time by 3 burst periods, so that the mobile station does not have to transmit and receive simultaneously. Using this method the electronic components of the mobile station can be simplified.

In addition to these full-rate TCHs, there are also half-rate TCHs defined12. Half-rate TCHs will effectively double the capacity of a system once they are implemented. For doing this specific half-rate speech coders must be implemented both within the GSM-network and the mobile stations using it. Next to the half rate coders enhanced full rate coders are defined. These coders offer a better speech quality to the users, thus this coders are implemented by several networks.

Control channels

Common channels can be accessed both by idle mode and dedicated mode mobiles. The common channels are used by idle mode mobiles to exchange the signalling information required to change to dedicated mode. Mobiles already in dedicated mode monitor the surrounding base stations for handover and other information. The common channels are defined within a 51-frame multiframe, so that dedicated mobiles using the 26-frame multi-frame TCH structure can still monitor control channels. The common channels include:

• Broadcast Control Channel (BCCH) - Continually broadcasts, on the down-link, information including base station identity, frequency allocations, and frequency-hopping sequences.

• Frequency Correction Channel (FCCH) and Synchronisation Channel (SCH) - Used to synchronise the mobile to the time slot structure of a cell by defining the boundaries of burst periods, and the time slot numbering. Every cell in a GSM network broadcasts exactly one FCCH and one SCH, which are by definition on time slot number 0 (within a TDMA frame).

12 They are not yet implemented within a live network.



• Random Access Channel (RACH) - Slotted Aloha channel used by the mobile to request access to the network.

• Paging Channel (PCH) - Used to alert the mobile station of an incoming call.

Access Grant Channel (AGCH) - Used to allocate an SDCCH to a mobile for signalling (in order to obtain a dedicated channel), following a request on the RACH.

Authentication and security in GSM networks

For the authentication procedure two functional entities of GSM-systems are involved, the SIM card located in the mobile, and the Authentication Centre (AuC) located in the network. Each subscriber is given a secret key. One copy of the key is stored in the SIM card and the other one is stored in the AuC. During the authentication procedure, the AuC generates a random number that it sends to the mobile. Both the mobile and the AuC then use this random number together with the subscriber's secret key and a special ciphering algorithm (called A3), to generate a signed response (SRES). This SRES is sent from the mobile station to the AuC. If this number is the same as the one calculated by the AuC, the subscriber is authenticated.

The same initial random number and the same subscriber key are also used to compute the ciphering key using an algorithm called A8. This ciphering key, together with the TDMA frame number, use the A5 algorithm to create a 114 bit sequence that is XORed with the 114 bits of a burst. Enciphering is an additional security option, since the signal is already coded, interleaved, and transmitted in a TDMA manner, thus providing protection from all but the most persistent and dedicated eavesdroppers.

Another level of security is performed on the mobile equipment itself, as opposed to the mobile subscriber. Each GSM mobile station is identified by a unique International Mobile Equipment Identity (IMEI) number. A list of IMEIs in the network is stored in the Equipment Identity Register (EIR). The status returned in response to an IMEI query to the EIR is one of the following:

• White-listed: The terminal is allowed to connect to the network.

• Grey-listed: The terminal is under observation from the network for possible problems.

• Black-listed: The terminal has either been reported stolen, or is not type approved (the correct type of terminal for a GSM network). The terminal is not allowed to connect to the network.

Thus the network provider is given a possibility to prevent the use of irregular (e.g. stolen or defective equipment) within its network. However, this method is not implemented by all network providers or some providers do not exchange their black list with other networks. In some countries this method is even used to block mobiles where the import duty is not paid from working within the local networks.



General Packet Radio Service (GPRS)

13GPRS is a packet-linked technology with a maximum transmission rate of 170 Kbps, which is more than fifteen times faster than GSM. GPRS, the 2.5G technology, only uses network resources and bandwidth during data transmission, so the operator saves network extension costs. It is therefore well suited for a range of personalized applications and value-added services that require bulky and bursty data transfer such as mobile Internet, electronic banking, and location-based services.

With GPRS, the users are charged for the amount of data they transmit and not for the duration of their call. They benefit from ‘always on’ Internet access as no dial-up is necessary, making new services such as real-time messaging viable. Since packet-switched GPRS operates alongside existing circuit-switched services in mobile networks, the users have seamless access to both voice and data services.

The technology enables high data rates by combining up to eight timeslots together with new coding schemes. Thus GPRS uses the radio spectrum more efficiently by utilizing unused cell space. GPRS terminals can download data at speeds of up to 24 Kpbs. When 8 slots are assigned at the same time to a single user 171.2 Kbps are possible, theoretically.

Multimedia Messaging Service (MMS)

14MMS is a universally accepted standard that lets users of MMS supportive mobile phones send and receive messages with formatted text, graphics, photographs, audio and video clips. Video sequences, audio clips and high-quality images can be downloaded to the phone from WAP sites, transferred to the phone via an attached accessory (e.g. a digital camera) or received in an MMS message. MMS messages can be sent either to another MMS-enabled mobile phone or to an e-mail address. Photos, sound and video clips can also be stored in the phone for later use.

MMS supports standard image formats such as GIF and JPEG, video formats such as MPEG 4 and audio formats such as MP3 and MIDI. Multimedia messaging requires high transmission speeds, which can be provided by GPRS and 3G. To support the MMS technology, existing GSM networks need an MMS-C (Multimedia Messaging Service Centre).

The Multimedia Messaging Service can be used for news flash services (pictures, audio files, advertising)) by the service provider. There are many different MMS enables mobile phones on the market and many service provider have launched their Multimedia Messaging Service. The basis of mobile-to-mobile multimedia messaging consists today of 5 content classes, defined in MMSv1.2 OMA15 specifications:

Text (≤ 30 KB), Image basic (≤ 30 KB), Image rich (≤ 100 KB), Video basic (≤ 100 KB), Video rich (≤ 300 KB)

13 Source: http://www.siemens-mobile.com 14 Source: http://www.ericsson.com/technology/tech_articles/MMS.shtm l 15 Open Mobile Alliance, http://www.openmobilealliance.org



GSM-Railway (GSM-R)

GSM-R is a special improvement of the GSM-Standard to fulfil the requirements of PMR-services for railways.

The standard GSM services are added with special Features (usually named “Advanced Speech Call Items”). Some of these Advanced Speech Call Items are:

• Group Calls

• Emergency Calls with priority handling and pre-emption

• Addressing via train numbers (special service for railways)

• very high network availability (> 99,9 %)

• short call establishment (< 5 s)

• low call cut ratio

• support of speeds up to 500 km/h

Using these features special applications can be implemented that fulfil the needs of railway organisations. Some examples for these applications are train security and safety, train control systems, facility management or special travellers information services.

In Germany the Deutsche Bundesbahn is implementing a GSM-R system. This system is using 19 duplex channels at the frequencies between 876 to 880 MHz (uplink) and 921 to 925 MHz (downlink).

The main disadvantages of GSM-R are:

• The system cannot be used by the public GSM-users. Thus public GSM users still must use the public networks when their telephone is used within a train.

GSM-R does not support direct mode. Direct mode is a feature offered by the new digital PMR-systems like TETRA and Tetrapol where mobiles can communicate with each other without the support of any network infrastructure. This feature is very important for emergency organisations like police, ambulance and fire brigade.

2.3.3 3G Third Generation

Introduction

3G is the name of the third generation of mobile communication systems. They offer enhanced services, such as multimedia and video. The main 3G technologies include UMTS and CDMA2000™.



Figure 3: Evolution of 3rd Generation Technology16

17Code Division Multiple Access (CDMA) technology provides excellent voice capacity and data capability for mobile and fixed wireless networks. Because of its advantages, CDMA serves as the foundation for 3G services worldwide.

CDMA works by converting speech into digital information, which is then transmitted as a radio signal over a wireless network. Using a unique code to distinguish each different call, CDMA enables many more people to share the airwaves at the same time — without static, cross-talk or interference.

Commercially introduced in 1995, CDMA quickly became one of the world's fastest-growing wireless technologies. In 1999, the International Telecommunications Union (ITU) selected CDMA as the basis for 3G wireless systems. Many leading wireless operators have commercially launched or are now upgrading to 3G CDMA networks in order to provide more capacity for voice traffic, along with high-speed data capabilities.

Key Attributes of CDMA:

• Direct sequence spread spectrum

• Universal frequency reuse

• Seamless soft handoff

• Multipath propagation for diversity

• Variable-rate transmission

• Unique forward and reverse links

EDGE EDGE (Enhanced Data Rates for Global Evolution) also EGPRS, builds on the GSM infrastructure with minor additions relating to the air interface. It is a 3G radio technology

16 Source: http://www.qualcomm.com 17 Source: http://www.qualcomm.com



standardized by ITU and 3GPP18. It offers a high Quality of Service and a high bandwidth. It allows operators without a 3G licence to deliver data services comparable to those offered via UMTS. 19EDGE capability can be easily upgraded to existing GSM/GPRS networks using appropriate software. GPRS on average triples the current GPRS data rates and the capacity of each hardware and frequency channel, enabling lower usage cost for existing end-user services, as well as the new advanced services delivery over GSM bands, such as video streaming.

EDGE enables advanced mobile services to all end-user segments, creating revenue generation over a wide customer base. Due to its high data rates, EDGE has been adopted as part of ITU's family of 3G technologies. Currently, EDGE is standardized by the same 3GPP standardization body as the other 3G technology, WCDMA, harmonizing the development of both EDGE and WCDMA, and bringing the service delivery capabilities of 3G to EDGE as well.

All major operators and equipment vendors support GSM/EDGE standardization. 20EDGE allows the operator to offer his users 3G-like applications. Compared to GPRS, however, fewer time slots need to be combined in order to provide the same data rate, giving a higher capacity per cell so that more users can be served.

Data rates ultimately depend on the radio access conditions, the coding scheme used and the number of combined timeslots (channels). EDGE combines eight timeslots, with data rates per timeslot (channel) of between 8.8kbit/s (MCS-1) and 59.2kbit/s (MCS-9). Moreover, EDGE offers sustained data rates of 384 Kbps, with a theoretical limit of almost 480 Kbps (i.e. 8 timeslots * 59,2 Kbps).

Other features include:

• RF output power is the same as for current GSM: -47 dBm/900 MHz and 45.5 dBm/1800 and 1900 MHz

• New RF modulation scheme: GMSK21 + 8PSK on the PDTCH, 9 Modulation, and Coding Schemes (MCS)

• Multislot capability, with one to eight time slots combined

• Dynamic allocation by multiplexing GPRS and EGPRS22 on the same PDTCH23

18 3rd Generation Partnership Project, http://www.3gpp.org 19 Source: http://www.nokia.com 20 Source: http://www.siemens-mobile.com 21 GMSK: Gaussian Minimum Shift Keying is the modulation technique used in GSM networks. It employs a form of FSK (Frequency Shift Keying). 22 EGPRS: Enhanced General Packet Radio Service 23 PDTCH: Packet Data Traffic Channel - a channel allocated for data transfer. It is temporarily dedicated to one Mobile Station or to a group of mobiles in the Point to Multipoint - Multicast case. In multislot operation, one MS may use multiple PDTCH in parallel for individual packet transfer



• EGPRS burst access, using a new definition of the 11-bit Packet Channel Request on PRACH and two new training sequences

• New measurement parameters for Link Quality Control (LQC): LA, IR, and Bit Error Probability (BEP)

More information about EDGE and its Network Architecture can be obtained at http://www.siemens-mobile.com

W-CDMA (UMTS)

W-CDMA stands for Wideband Code-Division Multiple-Access, the technology used in UMTS. It is the leading 3G standard in the world and was adopted by the ITU under the name “IMT-2000 direct spread”. It’s the predominant radio interface technology of UMTS for pair band operation and runs on the Frequency Division Duplex mode FDD. As a so-called Direct Sequence CDMA, W-CDMA links the digital, binary subscriber information with a spreading code, which is generated by a special code generator. This spreading code consists of a high bit rate code sequence, of which the smallest unit is a chip (called chip to terminologically separate it from bits). The higher the chip rate, i.e. information rate of the transmission, the wider the bandwidth of the resulting signal. With a maximum of 3.84 Mchips/s (fixed), the width of each frequency band extends to 5 MHz in W-CDMA, that’s a 25 times larger bandwidth compared to GSM. Giving the technology its name "wideband", this higher bandwidth then again supports higher user data rates and also shows performance benefits.

Just like CDMA, the W-CDMA technology encodes every subscriber signal individually. Users can simultaneously use one and the same frequency channel without interfering with one another. Along with the higher spreading, W-CDMA provides an increase of processing gain and a higher multi-path resolution. It moreover fully operates both with circuit and packet-switched high-bit-rate services, ensures the simultaneous operation of mixed services, and supports highly variable user data rates.

What makes W-CDMA the choice for 3G transmission technology is the fact that it evolves perfectly into the most successful pedigree in the mobile world: the GSM family. Most European operators have followed the GSM track by enhancing their system to GPRS and HSCSD, and even American operators like Cingular Wireless and At&T Wireless have left the IS-95 in favor of the 3G equivalent EDGE. So it's at the merit of W-CDMA that the GPRS/EDGE core network can be reused with UMTS. Multimode terminals are being specified, which are capable of supporting GSM/GPRS/EDGE and W-CDMA, and handover as well as cell re-selection will be established between these systems.

TD-SCDMA24

Time Division Synchronous Code Division Multiple Access (TD-SCDMA) was incorporated by the 3rd Generation Partnership Project 3GPP in March 2001 as part of the UMTS Release Phase 4. It will initially be deployed in China.

24 Source: http://www.siemens-mobile.com



Via Time Division Duplex (TDD), the UMTS transmission mode, traffic is sent and received over the same frequency band, but using different time slots. The synchronous "S" signifies that TD-SCDMA can master both synchronous circuit-switched services (speech or video services) and asynchronous packet-switched services (Internet access).

Together with the GSM's Time Division Multiple Access (TDMA), TDD performs an unprecedented duet, significantly improving network performance by processing traffic in both directions, via uplink and downlink. Uplink and downlink resources are assigned according to the individual user needs. Data rates can range from 1.2 Kbps to 2 Mbps. The third companion in this performance is the encoding transmission mode CDMA (Code Division Multiple Access), equipping TD-SCDMA with most efficient capacity and spectrum usage.

2.3.4 TETRA/TETRAPOL

Introduction

TErrestrial Trunked RAdio (TETRA) is an open digital trunked radio standard which is defined by the European Telecommunications Standardisation Institute (ETSI) to meet the needs of most professional mobile radio users.

The TETRA Memorandum of Understanding (MoU) was founded in 1994. It represents a forum for all interested parties, which are professional users, manufacturers, network operators, test houses and telecom agencies.

Description

TETRA supports voice, circuit switched data and packet switched data services with a different data transmission rates and several levels of error protection. TETRA uses TDMA (Time Division Multiple Access) technology with four user channels interleaved into one carrier with 25 kHz carrier spacing. Higher data transfer rates up to 28,8 Kbps are implemented by reserving up to four channels for the same user connection. The needed bandwidth is allocated on demand.

Figure 4 TETRA Illustration of Channel Organisation

TETRA is designed as a trunked system that effectively and economically supports shared usage of the network by several organisations. However privacy and mutual security is supported by this system. Virtual networking inside the TETRA network enables each organisation to operate independently, but still enjoy the benefits of a large, high-functionality system with efficient resource employment.



TETRA is a high security technology that inherently includes encryption of voice, data, signalling and user identities. Two encryption mechanisms are defined:

• air interface encryption; the radio path between the terminal and the base station is encrypted by the network provider.

• end-to-end encryption; the most critical applications can use encryption methods for the transmission throughout the system to the other terminal.

TETRA provides a fast call set-up time (approximately 300 ms). This feature is crucial especially for the public safety and emergency services. TETRA supports both semi-duplex operation for efficient group communication and duplex operation for telephony type individual calls. The feature “Advanced Group Call” and “Announcement Call” included in TETRA meet the needs of the most critical user applications. “Multiple Call Priority Schemes” ensure effective resource allocation to very urgent traffic in the network that may be generated by emergency services.

The TETRA frame structure has four time slots per TDMA frame. This is further organised as 18 TDMA frames per multi-frame. In circuit mode both voice and data traffic from approximately 1 second (= 1 multi-frame length of time) is compressed and transmitted in 17 TDMA frames. Thus the 18th frame can be used for control signalling without interrupting the flow of user data. This 18th frame is called the control frame and provides the basis for slow associated control channel (SACCH). The SACCH provides the background control channel signalling.

Figure 5 TETRA Frame Structure

1 2 3 4 17 18

1 2 3 4

508 509 5101 2 3 4 5

1 hyperframe = 60 multiframes (= 61.2s)

1 2 3 4 605

1 multiframe = 18 TDMA frames (= 1.02s)

1 TDMA frame = 4 time slots (= 56.67ms)

1 time slot = 510 modulating bits duration (= 14.167ms)

controlframe

The gross bit rate of one channel is 9 Kbps, into which speech is coded with 4,8 Kbps net bit rate using ACELP coding. The modulation method used in TETRA is π/4-DQPSK (Differential Quaternary Phase Shift Keying).

Within the TETRA standard direct mode operation between mobile radios without the need for network infrastructure is defined, too. Also repeater and gateway functions are defined. These features will extend the coverage of hand portable radios in both direct mode and network operation.

The defined power classes of TETRA radio equipment are 25 W, 10 W, 3 W and 1 W. TETRA radios can automatically adjust the output power according to the needed field strength. Thus energy consumption is reduced and operation time is increased.



Several teleservices provide complete communication capability for between users, including all terminal functions. In TETRA standards teleservices cover voice communications services.

TETRA Teleservices

• Individual Call

• Group Call

• Acknowledged Group Call

• Broadcast Call

A bearer service provides communication capability between terminal network interfaces, excluding the functions of the terminal. TETRA bearer services are defined for data transfer.

TETRA Bearer Services

• Circuit mode data 7,2/14,4/21,6/28,8 Kbps

• Circuit mode protected data 4,8/9,6/14,4/19,2 Kbps

• Circuit mode heavily protected data 2,4/4,8/7,2/9,6 Kbps

• Connection oriented packet data

• Connectionless packet data

In addition, the standard defines supplementary services for very flexible system applications. Supplementary services modify or supplement the above-mentioned services. Some supplementary services are essential others are optional:

Supplementary Services

Essential Supplementary Services

• Access Priority: The uplink access of a radio unit can be handled with a higher priority when the serving network is congested.

• Priority Call: The access to the network resources can be prioritised, too.

• Pre-emptive Priority Call: This call has the highest uplink priority and highest priority access to network resources. If the system is busy the communication with the lowest priority will be dropped to allow this call to continue.

• Call Authorised by Dispatcher: A dispatcher verifies the validity of a call request before the call is allowed to proceed.

• Area Selection: Areas of operation within the network are defined for the user. It can be redefined on a call-by-call basis.

• Late Entry: Latecomers may join a call in progress

• Discrete Listening: Authorised radio unit may monitor a communication without being identified



• Ambience Listening: Dispatcher may turn on the transmitter of a radio unit without any indication being provided on radio unit.

• Dynamic Group Number Assignment: The dispatcher is able to program new group numbers into the radio units over the air interface.

Optional Supplementary Services

• Calling Line Identification Present: The unit ID of calling party is presented.

• Connected Line Identification Present: The unit ID of the called party is presented.

• Calling/Connected Line Identification Restriction: Either party may prevent the presentation of its unit ID.

• Call Report: Displays calling party ID on a busy radio unit.

• Talking Party Identification: radio unit automatically identifies itself when it is in a group call.

• Call Forward Unconditional: Allows a radio unit to forward all calls to another radio unit.

• Call Forward on Subscriber Busy: Allows a radio unit to forward calls if the radio unit busy.

• Call Forward on Subscriber Not Reachable: Allows a radio unit to forward calls when it is out of service or switched off.

• Call Forward on No Reply: Allows a radio unit to forward all unanswered calls.

• List Search Call: Incoming call will sequence through a user defined list until the call is answered.

• Short Number Addressing: Short number dialling

• Call Waiting: Notification of an incoming call to radio unit which is busy.

• Call Hold: Allows user to interrupt an existing call and re-establish the call when required.

• Call Completion Busy Subscriber: An incoming call will wait until subscriber is free before calling back.

• Call Completion No Reply: An incoming call will wait until the subscriber has made a call before calling back

• Include Call: Ability to include a radio unit in an existing call

• Advice of charge: Call charge information at start, during or end of call

• Call Barring: Ability to bar a call from/to a user defined list

• Call Retention: Ability to prevent call being pre-empted

• Transfer of Control: Initiator of a group call can transfer ownership to another party



TETRAPOL (PMR-System)

TETRAPOL is a digital trunked radio system comparable to TETRA above. Nevertheless TETRAPOL’s primary target market were the public safety organisations

2.3.5 Satellite Communication

Introduction

Satellite Communication Systems offer a family of services that enables the users to make personal (mobile) communications all over the world (or in huge areas) with the same communication system. The availability of current ground-based cellular communications is limited, for geographical and technical reasons. New systems like Iridium, Globalstar and ICO have begun to complement these networks and by extending their coverage across the globe

Iridium

25The IRIDIUM system is a satellite-based Personal Communication Services (PCS), or Mobile Satellite Services (MSS) system, supporting global, wireless digital communications, covering the earth including the Polar Regions. IRIDIUM provides voice, messaging and data services to mobile subscribers using handheld user terminals. Iridium Satellite launched commercial global satellite communications services on March 28, 2001 with enhanced products and services. Service enhancements include improved voice quality and simplified pricing plans. Soon after launch, Iridium expanded the service portfolio to include data services.

At the beginning Iridium was planned to consist of 77 satellites26, later the system was redesigned to use only 66 satellites. Iridium is a so-called LEO-system (Low Earth Orbiting), where the satellites orbit at 780 km altitude in circular orbits. LEO-satellites were chosen because they offer both low path delays and global coverage.

Iridium uses Inter-Satellite Links (ISL), a telephony architecture based on GSM and a geographically controlled system access process. Each satellite can utilise up to 48 beams (‘footprints’), making a total maximum of 3168 beams for the Iridium system. Out of these only approximately 2150 will be active at one time, because some beams are switched off when the satellite crosses the polar region (here beam overlap may occur).

Connections between the Iridium system and the public switched telephone network are provided via gateway installations. Each satellite is connected to its four neighbouring satellites by inter-satellite links (ISL). These ISLs provide flexibility in where the gateways can be located. Thus an Iridium call can be routed within the satellite network and connected to any mobile located anywhere, or it can be connected to the public network through any gateway.

25 Source: http://www.iridium.com 26 77 is the atomic number of the element iridium. This way the name for this system was found.



The Iridium system patterns its call processing architecture after GSM, and the gateways incorporate a GSM MSC with the associated databases (EIR, HLR, VLR). Additional functions required for the Iridium system and not accommodated by the GSM MSC are also taken care of in the gateways.

When a mobile originates a call, the Iridium system will calculate the user's location. Each gateway is associated with a location area, which the gateway controls, and the mobile location is used to assign the home (or visited) gateway, which controls all aspects of the call. If required, a PSTN/PLMN connecting gateway is chosen based upon the mobile’s location and the location of the PSTN/PLMN party at the time of call set-up. Using the position of the mobile, the gateway will ensure the compliancy with national laws enforcing call restrictions on mobiles.

The Iridium satellite system provides multiple services including telephone transmission voice with 2,4 Kbps, data with 2,4 Kbps, fax, or paging.

The following frequencies are assigned to the Iridium system:

user frequency: 1,616 GHz to 1,6265 GHz.

feeder uplink frequency: 29,1 GHz to 29,3 GHz.

feeder downlink frequency: 19,4 GHz to 19,6 GHz.

Inter-satellite cross-links frequency: 23,18 GHz to 23,38 GHz.

Iridium offers the following Services:

• Data • Crew Calling • Paging • International SOS • Short Burst Data

• Voice • Paging • SMS • Fax and Enhanced Messaging

• Ship Security & Alert Systems

Data services:

Dial-Up Data Service provides dial-up connectivity from a PC, through your Iridium phone to another computer, a corporate network/LAN or an Internet Service Provider (ISP). This service offers a data rate of up to 2.4 Kbps. Direct Internet Data Service provides connectivity from a PC, through your Iridium phone, directly to the Internet through dedicated servers at the Iridium gateway. This service utilizes transparent compression, resulting in a data rate of up to 10 Kbps, depending on content.

For more information about iridium and its services please see the Iridium website at www.iridium.com .

Globalstar

Introduction

Globalstar, which was established in 1991 and began commercial service in late 1999, currently offers service from virtually anywhere across over 100 countries, as well as from



most territorial waters and several mid-ocean regions. Signals from a Globalstar phone or modem are received by the company's constellation of 48 Low Earth Orbiting (LEO) satellites and relayed to ground-based gateways, which then pass the call on to the terrestrial telephone network.

As a result, Globalstar is able to provide a variety of telephone services to users who live, work, and travel in areas far beyond the reach of cellular networks. In addition to normal voice communications, these services (Availability of individual services may vary by location) include:

• Internet and private data network connectivity

• Position location

• SMS (short messaging service)

• Call forwarding

These services are supported by a growing range of products and accessories designed to make Globalstar service productive and easy-to-use in almost any situation or environment, including aviation and maritime applications. The company's data modem products can also be used for asset tracking and environmental telemetry applications.

Looking ahead, Globalstar intends to continue expanding its operations to provide service in the few remaining land areas not covered today, as well as across mid-ocean regions. Products and accessories will also continue to be developed and upgraded to make the service even more useful.

Globalstar offers a wide range of products and services, designed to support almost any voice or data communications application wherever you live, work or travel.

Mobile Phones Globalstar mobile phones function as both cellular and satellite phones, allowing to stay in touch from virtually anywhere with reliable voice and data services.

Fixed Phones Globalstar fixed phones offer an innovative solution for remotely-located offices or worksites where stationary installations are required.

Data Communications Simple data kits allow to connect a PC or PDA to the Internet via a Globalstar handset. Specialized modem products are also available for higher bandwidth or customized telemetry applications

Encryption Devices Commercial and Type 1 approved encryption devices are available for use with Globalstar phones ensuring both voice and data communications are sent securely.

Market Specific The Globalstar product suite includes products tailored for use in the air, at sea and on the ground.

Globalstar offers data services with speeds from 19.2 Kbps up to 144 Kbps. Technologies with a data transfer rate of up to 256 Kbps over the Globalstar network are in field trial.



Technology

The Globalstar system is designed to provide satellite-based telephony services to a broad range of users. Globalstar meets the needs of cellular users who roam outside of coverage areas, people who work in remote areas where terrestrial systems do not exist, residents of under-served markets who can use Globalstar's fixed-site phones to satisfy their needs for basic telephony, and international travellers who need to keep in constant touch.

Globalstar's phones look and act like mobile or fixed phones. The difference is that they can operate virtually anywhere, carrying the call over a Code Divisional Multiple Access (CDMA) satellite signal.

The 48 Low Earth Orbiting (LEO) satellites picks up signals from over 80 % of the Earth's surface, everywhere outside the polar regions and some mid-ocean regions. Several satellites pick up a call simultaneously, and this "path diversity" assures that the call does not get dropped even if a phone moves out of sight of one of the satellites. If buildings or terrain block the signal, a handover takes place, and the call's transmission is switched to an alternative satellite with no interruption. This satellite now maintains transmission of the signal to one of several terrestrial gateways.

The Gateways process calls, then distribute them to fixed and cellular networks.

Satellite Constellations

The satellites are placed in eight orbital planes of six satellites each, inclined at 52 degrees to provide service on Earth from 70 degrees North latitude to 70 degrees South.

Gateways

Gateways are an integral part of the Globalstar ground segment, which also includes Ground Operations Control Centres (GOCCs), Satellite Operations Control Centres (SOCCs), and the Globalstar Data Network.

A gateway may service more than one country. Gateways consist of three or four dish antennas, a switching station and remote operating controls. Because all of the switches and complex hardware are located on the ground, it is easier for Globalstar to maintain and upgrade its system, more than it is for systems, which handle switching in orbit (like Iridium).

Gateways offer seamless integration with local and regional telephony and wireless networks. Encryption ensures voice and signalling security for individual transmissions.

Globalstar Advantages

Low Voice Delay: The use of Low Earth Orbiting (LEO) satellites, moving at an altitude of 1,414 kilometres, means the customer is almost not able to make out the voice delay.

Reliability: The Globalstar system's software resides on and is monitored from the ground, not from satellites, which means easy and fast system maintenance and upgrades.



Fewer Dropped Calls: Globalstar's smart system design is based on overlapping satellite coverage, so that several satellites can be available from any location to handle a call. This "path diversity" results in a greater likelihood of establishing calls for customers and far less chance of dropping calls than other systems.

Lighter, All-in-one Handsets: Mobile phones manufactured by Ericsson, Qualcomm, and Telit are lightweight and can be used for either cellular or satellite-based calls. The phones are available with many accessories, such as car and marine kits, which extend the phone's reach still further.

More information about Globalstar can be obtained from the Globlstar Corporate Site at www.globalstar.com.

Inmarsat27

Inmarsat was the world's first global mobile satellite communications operator and is still the only one to offer a mature range of modern communications services to maritime, land-mobile, aeronautical and other users.

Formed as a maritime-focused intergovernmental organization over 20 years ago, Inmarsat has been a limited company since 1999, serving a broad range of markets. Starting with a user base of 900 ships in the early 1980s, it now supports links for phone, fax and data communications at up to 64 Kbps to more than 250,000 ship, vehicle, aircraft and portable terminals. That number is growing at several thousands a month.

Inmarsat Ltd is a subsidiary of Inmarsat Ventures Ltd. It operates a constellation of geostationary satellites designed to extend phone, fax and data communications all over the world. The constellation comprises five third-generation satellites backed up by four earlier spacecraft.

The satellites are controlled from Inmarsat's headquarters in London, which is also home to Inmarsat Ventures as well as the small IGO created to supervise the company's public-service duties for the maritime community (Global Maritime Distress and Safety System) and aviation (air traffic control communications). Inmarsat has regional offices in Dubai, Singapore and India.

Today's Inmarsat system is used by independent service providers to offer a range of voice and multimedia communications. Users include ship owners and managers, journalists and broadcasters, health and disaster-relief workers, land transport fleet operators, airlines, airline passengers and air traffic controllers, government workers, national emergency and civil defence agencies, and peacekeeping forces.

The Inmarsat business strategy is to pursue a range of new opportunities at the convergence of information technology, telecoms and mobility while continuing to serve traditional maritime, aeronautical, land-mobile and remote-area markets.

27 http://www.inmarsat.org



Keystone of the strategy is the new Inmarsat I-4 satellite system, which from 2005 will support the Inmarsat Broadband Global Area Network (B-GAN) - mobile data communications at up to 432 Kbps for Internet access, mobile multimedia and many other advanced applications.

Inmarsat Satellites

Inmarsat's primary satellite constellation consists of four Inmarsat-3 satellites in geostationary orbit. Between them, the main ("global") beams of the satellites provide overlapping coverage of the whole surface of the Earth apart from the poles. So, thanks to Inmarsat, it has become possible to extend the reach of terrestrial wired and cellular networks to almost anywhere on Earth.

A geostationary satellite follows a circular orbit in the plane of the Equator at a height of 35,600 km, so that it appears to hover over a chosen point on the Earth's surface. Three such satellites are enough to cover most of the globe, and mobile users rarely have to switch from one satellite to another.

A call from an Inmarsat mobile terminal goes directly to the satellite overhead, which routes it back down to a gateway on the ground called a land earth station (LES). From there the call is passed into the public phone network.

The Inmarsat-3 satellites are backed up by a fifth Inmarsat-3 and four previous-generation Inmarsat-2s, also in geostationary orbit.

A key advantage of the Inmarsat-3s over their predecessors is their ability to generate a number of spot-beams as well as single large global beams. Spot-beams concentrate extra power in areas of high demand as well as making it possible to supply standard services to smaller, simpler terminals.

Inmarsat Network

To deliver its services Inmarsat operates a worldwide network of ground stations in addition to the satellite constellation. The satellites are controlled from the Satellite Control Centre (SCC) at Inmarsat HQ in London. The control teams there are responsible for keeping the satellites in position above the Equator, and for ensuring that the onboard systems are fully functional at all times.

Data on the status of the nine Inmarsat satellites is supplied to the SCC by four tracking, telemetry and control (TT&C) stations located at Fucino, Italy; Beijing in China; Lake Cowichan, western Canada; and Pennant Point, eastern Canada. There is also a back-up station at Eik in Norway.

Traffic from a user terminal passes via a satellite and then down to a land earth station (LES), which acts as a gateway into the terrestrial telecoms networks. There are about 32 LESs, located in 29 countries.

The flow of communications traffic through the Inmarsat network is monitored and managed by the Network Operations Centre (NOC) at Inmarsat HQ. The NOC is supported by network co-ordination stations (NCS). Their primary role is to help set up each call by assigning a



channel to the MES and the appropriate LES. There is one NCS for each ocean region and for each Inmarsat system (Inmarsat A, B, C, etc). Each NCS communicates with all the land earth station operators in its ocean region, the other NCS and the NOC, making it possible to distribute operational information throughout the system.

Inmarsat Services

INMARSAT REGIONAL BGAN

Regional BGAN is a revolutionary communications system that enables you to surf the web, send e-mail and transfer a host of other data from anywhere within the satellite footprint.

INMARSAT GLOBAL AREA NETWORK (GAN)

Inmarsat's Global Area Network offers voice telephony, as well as a high-speed 64 Kbps data service - Mobile ISDN - and the internet protocol-based Mobile Packet Data service.

INMARSAT FLEET Inmarsat Fleet F77, F55 and F33 provide high-quality mobile voice and flexible data communications services, e-mail and secure internet access for the maritime industry

INMARSAT MINI-M Inmarsat mini-M satphone service enables users to make phone calls to and from virtually anywhere on Earth. With mini-M you simply open the lid of the terminal, point the antenna at the satellite and dial.

INMARSAT SWIFT64 Inmarsat's Swift64 offers the high quality and speed of full Mobile ISDN and global Mobile Packet Data service to aircraft.

INMARSAT B Digital successor to Inmarsat A

INMARSAT B HSD High-speed data at up to 64 Kbps via Inmarsat B

INMARSAT C Store-and-forward data messaging terminals

INMARSAT A Inmarsats original phone, fax and data system

INMARSAT E Global maritime distress alerting via Inmarsat radio beacons

INMARSAT AERO I Inmarsat's latest service for aircraft operators and passengers

INMARSAT MINI-M AERO

Communications for small corporate aircraft and general aviation

INMARSAT D+ Messaging and data broadcasts to pager-sized terminals

INMARSAT MINI-M (Technical Sheet)

Voice, fax and data through desktop-sized phones

INMARSAT AERONAUTICAL SERVICES

Overview of Inmarsat aeronautical services

INMARSAT AERO H Provides simultaneous two-way digital voice and real-time data communications

INMARSAT AERO L Real-time two-way, data communications

INMARSAT AERO C Messaging and data reporting service providing store-and-forward communication



For more information about Inmarsat please see the Inmarsat website at www.inmarsat.org.

Orbcom

ORBCOMM provides two-way monitoring, tracking and messaging through the first commercial low-Earth orbit satellite based data communication system. The possibility to integrate ORBCOMM into existing communications platforms was one of the primary targets when designing the system.

The network operates with up to 36 Microstar satellites in orbit 825 kilometres above the Earth, which utilise the VHF band for communication with subscriber communicators. The Gateway Earth Station (GES) and Gateway Control Centre (GCC) act as the interface between the subscriber communicator, the satellites and the recipient by routing messages and data accordingly.

The system has 35 satellites in 6 orbital planes and at least 15 Gateway Earth Station. The links have the following characteristics:

Subscriber Links Gateway Links

Uplink VHF, 148-150 MHz 2,400 bps

VHF, 148-150 MHz 57.6 Kbps bps

Downlink VHF, 137-138 MHz 4,800 bps

VHF, 137-138 MHz 57.6 Kbps

Orbcomm markets and applications

Transport / Logistic Fleet management Two-way communication World-wide tracking and tracing

Research / Environmental Data transmission from remote locations Weather station monitoring Ocean research

Security Applications Search and rescue services Alarm transmission Theft recovery

Asset Management Pipeline monitoring Heavy equipment monitoring Remote meter reading

Personal Messaging world-wide two-way email communication

Orbcom is a satellite communication system that only offers data services to the customers. Theses services are messaging, email, fax and GPS. The commercial service began on 30 November 1998. In total 48 LEO satellites are used by the system. They are orbiting at



825km altitude and are offering a worldwide coverage. Eight additional satellites are kept as spares on the ground and may be added if there is sufficient demand.

The lifetime of each satellite is estimated to four years. The receiving frequency is between 148 MHz and 149,9 MHz, the transmitting frequency are both between137 MHz and 138 MHz and between 400,05 MHz and 400,15 MHz.

The used data rate is up to 2,4 Kbps (typically 0,3 Kbps).

For more information and the latest developments of Orbcomm please see the Orbcomm website at www.orbcomm.com or http://www.orbcomm.de/e/index_e.html.

2.4 Broadcast

2.4.1 Radio

Introduction

The term “Broadcast Radio” is used to encompass radio transmissions that provide entertainment and other forms of listener services. Prime examples are the national broadcasting services that are provided in most Countries and funded centrally either by governments or by some kind of national licensing arrangements. However there are also now increasing numbers of commercial services that survive on the income from sponsorship or advertising.

Only three types of broadcast radio communications are presently used for the transmission of transport related data. The first two are Frequency Modulated (FM) and Digital Audio Broadcasting (DAB). In both cases, the facility to provide traffic and travel information is seen as an addition to the main purpose of the broadcasting service. The third type of communications (DARC) has yet to make significant inroads into the market, albeit that some new networks are being set up – it appears that DARC will be more appropriate for niche markets.

Table 1 Broadcast Radio Cuumincations - Available Types

Type Data Rates Mobile Use Uni-/Bi-directional Projected Life-span

DAB 1,7 Kbps yes uni-directional >20 years

FM 1,1875 Kbps yes uni-directional another 10 years?

DARC 10 Kbps yes uni-directional another 10 years?

AM radio28

AM stands for "Amplitude Modulation", which refers to the means of encoding the audio signal on the carrier frequency.

28 Source: http://www.fcc.gov and http://en.wikipedia.org



In many countries, AM radio stations are known as "mediumwave" (MW) stations. AM Radio is broadcast in frequency bands ranging from 530 to 1700 kHz.AM stations are also sometimes referred to as "standard broadcast stations", since AM was the first form used to transmit broadcast radio signals to the public. This was the dominant system of radio in the first two thirds of the 20th century, and remains important today.

AM radio technology is simpler than other types of radio, such as FM radio and DAB. Amplitude modulation is a method used to modulate a signal, typically using radio. In the case of an analog signal to be sent, the amplitude of the radio wave is modulated to be directly proportional to the value of the analog signal at the time. An AM receiver detects the power of the radio wave, and amplifies changes in the power measurement to drive a speaker or earphones.

So the broadcast signal consists of the carrier wave plus two sinusoidal waves each with a frequency slightly different from the carrier wave frequency Ω. These are known as sidebands. In general a signal of frequency ω (the signal to broadcast) broadcast with a carrier wave frequency Ω will produce waves of frequency Ω +/- ω and, as long as the broadcast (i.e. the carrier wave) frequencies are sufficiently spaced out so that these side bands do not overlap stations will not interfere with one another.

For the long and medium wave bands, the wavelength is long enough that the wave diffracts around the curve of the Earth by ground wave propagation, giving AM radio, in particular long wave and medium wave at night, a long range.

Short wave is used by radio services intended to be heard great distances away from the transmitting station; the far range of short wave broadcasts comes at the expense of lower audio fidelity. The mode of propagation for short wave is different. AM is used mostly for broadcast uses - other shortwave users may use a modified version of AM such as SSB29 or an AM-compatible version of SSB such as SSB with carrier reinserted.

FM radio

FM stands for "Frequency Modulation", which refers to the means of encoding the audio signal on the carrier (centre) frequency. There are two systems operating for data services on VHF/FM: RDS and DARC. The Radio Data System has been on the market since 1987 and is standardised by CENELEC (EN50067). Applications for RDS include allowing a receiver to search for the strongest frequency or for a particular programme within a transmitter network, the programme service name shown on eight-character display and travel information. The Traffic Message Channel (TMC) is the latest development using RDS.

30Frequency modulation requires a wider bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission: hence the term "FM radio" (although for many years the BBC insisted on calling it "VHF radio").

29 SBB: Single-sideband modulation 30 Source: http://en.wikipedia.org



An FM signal can also be used to carry a stereo signal: see FM stereo. This is done by using multiplexing and de-multiplexing before and after the FM process.

Digital Audio Broadcast (DAB)

Description

The EUREKA-147 DAB system is a novel digital sound broadcasting system intended to supersede the existing analogue Frequency Modulation (FM) systems operating in Band II. As a broadcasting system, it is unidirectional. It is designed as a rugged, yet highly spectrum and power efficient sound and data broadcasting system. It has been designed for terrestrial and satellite as well as for hybrid (co-channel satellite and terrestrial delivery of the same multiplex in the same geographical area) and mixed delivery (same multiplex on different frequencies in different geographical areas).

DAB is considered as the future of radio as it makes more efficient use of crowded airwaves and provides CD-quality sound that is more robust and noticeably better than an FM analogue broadcast. DAB broadcasts are virtually immune to interference and fading; programmes are not suddenly degraded or even lost when the car passes through a tunnel or under power lines.

One of the principal advantages of switching to DAB is that a single frequency called a "Multiplex" can carry a combination of stereo and/or mono audio programmes. DAB allows to go beyond audio and may provide some or even all of the Multiplex capacity to transmit data that is not related to audio programming

The DAB system is an open, stable, fully proven and standardised system which was developed by the EUREKA-147Consortium. It is normalised as a European Telecommunications Standard ETS 300 401 (see ETSI web site http://www.etsi.org). It was first published in 1994 and revised in 1998. This standard describes the DAB emission signal and defines DAB as a system to provide mobile, portable; and fixed reception. The standard is based on the overall system and service requirements adopted by the ITU-R Recommendations 774 and 789.

The DAB system is recommended on the world-wide level by the ITU-R 1114 , as Digital System A, for terrestrial and satellite delivery. The audio coding algorithm used by the DAB system has been subject to the standardisation process within the ISO/Moving Pictures expert Group (MPEG), see ISO/IEC 11172-3 and ISO/IEC 13818-3. The layered ISO open system interconnected model ISO 7498 has been used to the extent possible, and interfacing to information technology equipment and communications networks has been taken into account where applicable.

DAB Standards

Complementary ETSI standards are as follows31:

31 The Eureka 147 Project has also finalised a specification on the return link to be used to provide an interactive channel (PSTN; ISDN, GSM).



• EN 301 234: DAB Multimedia Object Transfer (MOT) protocol

• EN 300 797: DAB Distribution interfaces; Service Transport Interface (STI)

• EN 300 798: DAB Distribution interfaces; Digital baseband In-phase and Quadrature (DIQ) interface

• ETS 300 799: DAB Distribution interfaces; Ensemble Transport Interface (ETI)

DAB receiving equipment standards are adopted by TC 206 of CENELEC as follows:

• EN 50248: Characteristics of DAB receivers

• EN 50255: Digital Audio Broadcasting system - Specification of the Receiver Data Interface

Receivers are becoming available and although currently much more expensive than those currently available for FM, within a few years are likely to cost only marginally more.

DAB is now entering the implementation stage; there are large scale trials in eleven other European countries as well as in other parts of the world. DAB regular services are now available in Sweden and the UK, and Germany has announced regular services. Once regular services are introduced, the broadcasters cannot simply switch them off.

DAB Frequency Management Aspects

The EUREKA-147 System is capable of operating in any frequency band between 30 and 3000 MHz. The required spectrum planning parameters for the EUREKA System are well defined and are available in the public domain (see for example the ITU Special Publication on Terrestrial and Satellite Digital Sound Broadcasting to vehicular, portable and fixed receivers in the VHF/UHF bands, Geneva, 1995). The System has been implemented in various parts of the world at frequencies in the region of 50, 80, 100, 210-240, 600, 800, and 1452-1492 MHz.

Generally the higher the frequency the higher the cost of the coverage will be. Also, building attenuation increases with the frequency. Nevertheless, all the experiments, and recent operational services in L-band) have shown that the EUREKA System performs very well at higher frequencies, including in L-Band. Lower frequencies such as Band I are characterised by a high level of man-made noise and should be avoided.

The introduction of DAB requires a forward-thinking long-term plan. To this end, sufficient radio-frequency spectrum is required to prevent significant co-channel and adjacent-channel interference between DAB services. Non-occupied spectrum is required in blocks of about 1.75 MHz bandwidth. In Europe, such spectrum slots are normally not available in Band II, which is extensively used by FM services. Most of the countries opted to start their DAB services in Band III which is heavily used by terrestrial television or in L-Band which is used by fixed services, radio astronomy, mobile and telemetry / aero-navigational services in many countries.

A three-week Planning Meeting was convened in July 1995 by the European Conference of Postal and Telecommunications Administrations (CEPT). The aim of this Meeting was to produce a Special Arrangement for the introduction of terrestrial transmissions of the



EUREKA-147DAB system in the frequency bands 46 – 68 MHz, 174 – 240 MHz and 1452 – 1467,5 MHz, as well as to prepare an associated Frequency Block Allotment Plan, taking into account the final requirements of the CEPT member countries.

The Allotment Plan drawn up at the Meeting provides practically all the member countries of the CEPT with two sets of frequency blocks, each of width 1,536 MHz. This is a vital prerequisite to the wide-scale launch of terrestrial DAB services in Europe. Most of the CEPT countries opted for frequency block allotments in VHF Band III and in L-Band. This table gives the overall number of all allotments agreed or subject to an agreement in all CEPT countries:

Table 2 Allocation of DAB Bands

Band Frequency Range No of Wiesbaden allotments

No of allotments with a reference to an agreement

Band I 47 – 68 MHz 1 0

Band II 87 – 108 MHz 1 0

Band III 174 – 240 MHz 278 205

Part of L-Band 1452 – 1467,5 MHz 467 177

Part of L-Band + Above 1467,5 MHz 4 0

Total 751 382

Eighty-five frequency blocks can potentially be used for current and future DAB services in Europe. These blocks are located in VHF Band I (47 – 68 MHz), Band II (87 – 108 MHz), Band III (174 MHz – 240 MHz) and in part of L-Band (1452 – 1492 MHz). In September 1998, the CEPT identified a need for 7 additional frequency blocks at L-Band so that the total number of blocks available for terrestrial DAB at L-Band will be 16 (out of 23). This extension should allow for a third frequency block to become available at any given location.

It should be pointed out that the currently available DAB blocks are insufficient to accommodate all the existing national, regional and local broadcasters using FM and to covert them in DAB. To this end, further blocks will be needed. An attractive option, subject to agreement with the military, is the 230 – 240 MHz band (i.e. Channel 13).

All broadcasting bands are subjected to a regulation that defines the content, i.e., audio or data. Today, data services are allowed but the level varies from country to country depending of national regulatory broadcasting arrangements where available. However, the process of convergence of broadcasting and telecommunication already started in various countries thus paving the way towards full data broadcasting.

Each frequency block carries a two- or three-character label that is convenient for receiver manufacturers and consumers to use when initially programming their receivers. The labelling system of the frequency blocks in VHF Band I and Band III is fully compatible with the existing VHF television channel numbers (i.e. Channels 2 to 13). Each of these television channels can accommodate four DAB blocks; six blocks in the case of Channel 13.



Digital AM – Digital Radio Mondiale (DRM)32

The DRM Consortium formed in 1998 when a small group of pioneering broadcasters and manufacturers joined forces to create a universal, digital system (also called DRM) for the AM broadcasting bands below 30 MHz – short-wave, medium-wave and long-wave. Since then, DRM has expanded into an international consortium of more than 70 broadcasters, manufacturers, network operators, research institutions, broadcasting unions and regulatory bodies.

DRM’s membership is global in scope, with members representing more than 25 nations. DRM’s membership is rich in its diversity, with members from countries as varied as Ecuador, Tunisia, Germany, China, the U.S.A., Nigeria, Finland, India, the U.K., Japan, Spain and Australia.

The DRM (Digital Radio Mondiale) on-air system will propel the AM broadcasting bands below 30 MHz – short wave, medium wave and long-wave - to the next level. DRM is the only universal, non-proprietary digital AM radio system with near-FM quality sound available to markets worldwide.

The quality of DRM audio is excellent, and the improvement upon analogue AM is immediately noticeable. DRM can be used for a range of audio content, including multi-lingual speech and music. Besides providing near-FM quality audio, the DRM system has the capacity to integrate data and text. This additional content can be displayed on DRM receivers to enhance the listening experience.

Unlike digital systems that require a new frequency allocation, DRM uses existing AM broadcast frequency bands. The DRM signal is designed to fit in with the existing AM broadcast band plan, based on signals of 9 kHz or10 kHz bandwidths. It has modes requiring as little as 4.5 kHz or 5 kHz bandwidths, plus modes that can take advantage of wider bandwidths, such as 18 or 20 kHz.

Many existing AM transmitters can be easily modified to carry DRM signals.

DRM applications will include fixed and portable radios, car receivers, software receivers and PDAs. Several early prototype DRM receivers have been produced, including a software receiver. The DRM system uses a type of transmission called COFDM (Coded Orthogonal Frequency Division Multiplex). This means that all the data, produced from the digitally encoded audio and associated data signals, is shared out for transmission across a large number of closely spaced carriers. All of these carriers are contained within the allotted transmission channel. The DRM system is designed so that the number of carriers can be varied, depending on factors such as the allotted channel bandwidth and degree of robustness required.

The DRM system can use three different types of audio coding, depending on broadcasters’ preferences. MPEG4 AAC audio coding, augmented by SBR bandwidth extension, is used as a general-purpose audio coder and provides the highest quality. MPEG4 CELP speech coding is used for high quality speech coding where there is no musical content. HVXC speech coding can be used to provide a very low bit-rate speech coder.

32 Source: http://www.drm.org



The robustness of the DRM signal can be chosen to match different propagation conditions.

More information about DRM can be obtained at the website http://www.drm.org.

2.4.2 Television

Overview

The use of television is currently confined to the dissemination of traffic and travel information. This is because at the moment there is no mechanism for its safe use in vehicles, and because it does not allow user (Traveller) interaction. This may change with the advent of Digital Video Broadcasting (DVB – see below).

Analogue

Analogue television has been used as a mechanism to disseminate of traffic and travel information for some time. This is particularly true in the UK, where both the British Broadcasting Corporation (BBC) and the Independent Television companies have both supported information systems called Ceefax and Oracle respectively.

Both the UK systems work by using “spare” parts of the analogue television signal that is used to transmit programmes. Television sets interrogate this signal and store the information that it contains. The television viewer can select “information pages” for display instead of the television programmes, and can navigate through the “pages”. Some “pages” are in fact multiple displays that scroll automatically. The scrolling process can be frozen, but parts of the scrolled information cannot be selected. Only a limited amount of data can be sent with each television screen update, so displaying the selected “page” can take a little while, whilst all the transmission goes through all the other “pages”. However only the selected “page” will be displayed, the screen remaining blank or showing the previous “page”, until the selected “page” is reached.

The information is generated by specialised systems run by the Broadcaster, and they are provided with the traffic and travel information through manual input. This is done so that the Broadcaster can exercise editorial control over what is displayed, and can ensure that the information is edited to fit within the “page” format. The “pages” display text and character based graphics, using a low resolution – about 20 lines with 30 characters per line. This makes the graphics rather “crude”, but good enough to show an identifiable map of the UK.

Both Ceefax and Oracle provide comprehensive traffic and travel information. This can be selected by mode, and by UK region. It may also include severe weather warnings when appropriate. Because of the limitations of the “page” format, the information can be very concise which may leave the viewer with not much idea about the real situation. For example there are no maps to show the location of incidents within the road network. There is also no information about such things as parking.

As noted in the introduction, this system is not interactive because the viewer cannot select particular information through input. However the information is organised by mode (for the whole UK) and by UK region (covers road, ferry and train). It can also be time consuming



because of the low refresh rate, which means that it may take several minutes to view the required “page(s)”.

Digital Video Broadcasting (DVB)

Background

Until late 1990, digital television broadcasting to the home was thought to be impractical and costly to implement. During 1991, broadcasters and consumer equipment manufacturers discussed how to form a concerted pan-European platform to develop digital terrestrial TV. Towards the end of that year, broadcasters, consumer electronics manufacturers and regulatory bodies came together to discuss the formation of a group that would oversee the development of digital television in Europe - the European Launching Group (ELG).

The ELG expanded to include the major European media interest groups, both public and private, the consumer electronics manufacturers, common carriers and regulators. It drafted a Memorandum of Understanding (MoU) establishing the rules by which this new and challenging game of collective action would be played.

Memorandum of Understanding

The concept of the MoU was a departure into unexplored territory and meant that commercial competitors needed to appreciate their common requirements and agendas. Trust and mutual respect had to be established. The MoU was signed by all ELG participants in September 1993, and the Launching Group became DVB (Digital Video Broadcasting). Work to develop digital television, already underway in Europe, moved into top gear. Around this time, the Working Group on Digital Television prepared a study of the prospects and possibilities for digital terrestrial television in Europe. The highly respected report introduced important new concepts, such as proposals to allow several different consumer markets to be served at the same time (e.g. portable television and HDTV). In conjunction with all this activity, change was coming to the European satellite broadcasting industry, and it was becoming clear that the once state-of-the-art MAC systems would have to give way to all-digital technology. DVB provided the forum for gathering all the major European television interests into one group. It promised to develop a complete digital television system based on a unified approach. It became clear that satellite and cable would deliver the first broadcast digital television services. Fewer technical problems and a simpler regulatory climate meant that they could develop more rapidly than terrestrial systems. Market priorities meant that digital satellite and cable broadcasting systems would have to be developed rapidly. Terrestrial broadcasting would follow.

DVB Standards

By 1997 the development of the DVB Project had successfully followed the initial plans. The project had also entered its next phase, promoting its open standards globally, and making digital television a reality.

Open, Interoperable, Flexible, Market-led



DVB systems are developed through consensus in the working groups of the Technical Module. Members of the groups are drawn from the general assembly of the project. Once standards have been published, through ETSI, they are available at a nominal cost for anyone, worldwide. Open standards free manufacturers to implement innovative and value added services. It doesn’t matter where DVB technology is developed. It is available worldwide.

Interoperable

Because the standards are open, all the manufacturers making compliant systems are able to guarantee that their DVB equipment will work with other manufacturers’ DVB equipment. Not only this, but because the standards are designed with a maximum amount of commonality, and based on the common MPEG-2 coding system, they may be effortlessly carried from one medium to another, which is frequently needed in today’s complex signal distribution environment. DVB signals move easily and inexpensively from satellite to cable, from cable to terrestrial.

Flexible

Owing to the use of MPEG-2 packets as “data containers”, and the critical DVB Service Information surrounding and identifying those packets, DVB can deliver to the home almost anything that can be digitised. It does not matter whether this is High Definition TV, multiple channel Standard definition TV (PAL / NTSC or SECAM) or even exciting new broadband multimedia data and interactive services.

Market-led

In contrast to earlier initiatives in Europe and the United States, the DVB Project works to strict commercial requirements established by organisations that work every day to meet its needs. It is not a regulator or government-driven (top-down) initiative. Working to tight timescales and strict market requirements means achieving a considerable economy of scale, which ensures that, in the transformation of the industry to digital, broadcasters, manufacturers and, finally, the viewing public will benefit.

DVB Standards Adoption

For each specification, a set of User Requirements is compiled by the Commercial Module. These are used as constraints on the specification. User requirements outline market parameters for a DVB system (price-band, user functions, etc.).

The Technical Module then develops the specification, following these user requirements. The approval process within DVB requires that the Commercial Module supports the specification before it is finally approved by the Steering Board.

Following approval by the Steering Board, DVB specifications are offered for standardisation to the relevant international standards body (ETSI or CENELEC), through the EBU/ETSI/CENELEC JTC (Joint Technical Committee), the ITU-R, ITU-T and DAVIC.



DVB – The Future

At the moment DVB carries digital versions of the analogue channels, plus other specialised digital only channels. Unlike analogue television, it is only available through subscription, although some hotels may provide access to some channels as part of “room service”. Also there is no dedicated traffic and travel information channel at the moment. It would probably have to be provided as part of another channel, or “bundled in” with the price of another channel. There should also be scope for viewer interaction via the “set top” boxes that DVB uses for channel selection, etc. This means that DVB is becoming more like an Internet service, which may appeal to those who do not want to have a home PC with an Internet connection and opens up the possibility of other services such as personalised trip planning being provided.

2.5 Positioning

Introduction

For many ITS services it is quite important that a most accurate positioning of the user can take place. The best examples for this are emergency and breakdown services where an exact position is needed. This can be provided specialised positioning systems.

Global Positioning Systems (GPS) are space-based radio positioning systems that provide 24-hour three-dimensional position, velocity and time information to suitably equipped users anywhere on or near the surface of the Earth (and sometimes off the earth). Global Navigation Satellite Systems (GNSS) are extended GPS systems, providing users with sufficient accuracy and integrity information to be useable for critical navigation applications. The NAVSTAR system, operated by the U.S. Department of Defence, is the first GPS system widely available to civilian users. The Russian GPS system, GLONASS, is similar in operation and may prove complimentary to the NAVSTAR system.

Satellite Navigation

Satellite navigation (also positioning) is a tool to determine position, velocity and precise time world-wide. Signals transmitted from several satellites are picked up by a receiver and used to calculate position, velocity and time.

User navigation receivers measure the distance of the receiver to the satellite using a technique called 'Cooperative ranging'. The satellites send a signal with their position and a timestamp. The distance to each satellite is derived from the measurement of the time taken for the navigation signal to travel from the satellite to the receiver, which is the timestamp from the receiver at the moment of reception minus the timestamp of the signal.

The signals of 4 satellites are necessary to determine the position of an object an earth, as there are 4 unknown factors that have to be calculated by the receiver. These are longitude, latitude, altitude of the object and the exact distance between receiver and satellites, or the error in the distance (derr) respectively that can be considered constant for all signals sent at the same time. The time in the receiver’s clock and the satellite clock are not exactly the same. Furthermore on its way from the satellite to the receiver the signal is bend in the



ionosphere33, and so the way of the signal is longer than the real distance between satellite and receiver, also due to other effects.

To correct this error, the data of the fourth satellite is needed. The result is four equations with four unknowns:

(x0 - x1)2 + (y0 - y1)2 + (z0 - z1)2 = d12

(x0 - x2)2 + (y0 - y2)2 + (z0 - z2)2 = d22

(x0 - x3)2 + (y0 - y3)2 + (z0 - z3)2 = d32

(x0 - x4)2 + (y0 - y4)2 + (z0 - z4)2 = d42

With the coordinates of the object, x1,2,3,4, y1,2,3,4, z1,2,3,4 the coordinates of the 4 satellites and d1,2,3,4 the distances between the satellites and the object, while d = dreal + derr.

2.5.1 Global Positioning Systems

Introduction

GPS stands for Global Positioning System. Users of a global positioning system can determine their location anywhere on the earth. There are two "public" GPS systems - the NAVSTAR system (USA) and the GLONASS system (Russia). The NAVSTAR system is often referred to as ‘the GPS’ because it was the first public available system. Nevertheless, both systems are GPS systems.

Both systems provide two sets of positioning signals. The higher accuracy signal is reserved for each country's military use. The lower accuracy signal is available to civilian users free of charge.

A global positioning system uses the characteristics of radio transmissions for localisation. Satellite based transmitters are used to cover earth with signals needed for a high accuracy localisation. The information the satellites transmit are actual system time, satellite location and satellite status. A special radio receiver - a GPS receiver - to receive the transmissions from the satellite is needed. The GPS receiver contains a special computer that calculates the location of the receiver based on the information from the satellites.

NAVSTAR

The NAVSTAR system consists of 24 active satellites. Four satellites are located in each of six orbits. The orbits are distributed evenly around the earth, and are inclined 55 degrees from the equator. Each satellite transmits two different signals: L1 (1575.42 MHz) and L2 (1227.60 MHz). L1 is modulated with two pseudo-random noise signals - the protected (P) code, and the coarse/acquisition (C/A) code. L2 carries only the P code. Each satellite transmits a unique code for identifying the signals. When a feature called "Anti-Spoofing" is active, the P code is encrypted. Civilian receivers only use the C/A code on the L1 frequency.

The receiver measures the time required for the signal to travel from the satellite to the receiver. This is calculated by the time that the signal left the satellite and the time it is

33 The characteristics of the ionosphere are not constant, depending on the influence of the sun



received. If the receiver had a perfect clock, synchronised with those on the satellites, three measurements from three different satellites would be sufficient to calculate the location in 3 dimensions. As you can't get a perfect clock that will fit in a low cost GPS receiver a fourth satellite is needed to correct the error caused by the receiver clock. If more than these four satellites can be received the calculation can be done with a higher accuracy.

Each measurement ("pseudo range") gives a position on the surface of a sphere centred on the corresponding satellite. Due to the receiver clock error, the four spheres will not intersect at an exact point. Thus the receiver must adjust its clock until the correct intersection point is found.

The Standard Positioning Service (SPS), which is available to civilian users, should give 20 metre horizontal accuracy. However this accuracy is normally reduced to 100 metres (95 % of the time) by Selective Availability (SA). The vertical accuracy is about 1.5 times worse than horizontal.

Selective Availability is an intentional degradation of accuracy. It is intended to prevent "the enemy" from making tactical use of the full accuracy of GPS. SA is normally switched on. Military receivers can use the encrypted P code to get 20 metre accuracy, or better, regardless of the state of SA.

Since the receiver must adjust its clock to be precisely synchronised with GPS time, a GPS receiver can be used as an exact time reference. The GPS system time (as used by the system itself) does not include leap seconds. Thus the difference between GPS time and UTC is included in the information sent by the satellites, so receivers can display current UTC or zonetime, rather than the GPS system time. Currently there is an 11 second difference.

GLONASS34

GLONASS (GLObal NAvigation Satellite System) is a satellite based radio navigation system, which enables unlimited number of users to make all-weather 3D positioning, velocity measuring and timing anywhere in the world or near-Earth space.

GLONASS serves for: • Air and naval traffic management, safety increasing;

• Geodesy and cartography;

• Ground transport monitoring;

• Time scale synchronisation of the remote from each other objects;

• Ecological monitoring, search and riscue operation organisation

The GLONASS system is managed for the Russian Federation Government by the Russian Space Forces, system operator, providing significant benefits to the civil users community through a variety of applications. The GLONASS system has two types of navigation signal: standard precision navigation signal (SP) and high precision navigation signal (HP). SP

34 Source: http://www.glonass-center.ru



positioning and timing services are available to all GLONASS civil users on a continuous, worldwide basis and provide the capability to obtain horizontal positioning accuracy within 57-70 meters (99.7 % probability), vertical positioning accuracy within 70 meters (99.7 % probability), velocity vector components measuring accuracy within 15 cm/s (99.7 % probability) and timing accuracy within 1 mks (99.7 % probability). These characteristics may be significantly increased using differential mode of navigation and special methods of measurements (e.g. carrier phase etc.).

To make 3D positioning, velocity measuring and timing user of the GLONASS use navigation radio signals, continuously transmitted by satellites. Each GLONASS satellite transmits two types of signal: standard precision (SP) and high precision (HP). SP signal L1 have a frequency division multiple access in L-band: L1= 1602 MHz + n0.5625 MHz, where "n" is frequency channel number (n=0,1.2...). It means that each satellite transmit signal on its own frequency which differ from the one of other satellites. However, some satellites have the same frequencies but those satellites are placed in antipodal slots of orbit planes and they do not appear at the same time in user's view. A GLONASS receiver automatically receives navigational signals from at least 4 satellites and measures their pseudo-ranges and velocities. Simultaneously it selects and processes the navigation message from the satellite signals. The computer of the GLONASS receiver processes all the input data and calculates three coordinates, three components of velocity vector, and the precise time.

GLONASS constellation

Fully deployed the GLONASS Constellation is composed of 24 satellites in three orbital planes whose ascending nodes are 120 degrees apart. 8 satellites are equally spaced in each plane with argument of latitude displacement of 45 degrees. Besides the planes themselves have 15 degrees argument of latitude displacement. Each GLONASS satellite operates in circular 19100 km orbits at an inclination angle of 64.8 degrees and each satellite completes an orbit in approximately 11 hours 15 minutes. The spacing of satellites in orbits is arranged so that a minimum of 5 satellites are in view to users world-wide, with adequate geometry, i.e. GLONASS Constellation allows to provide continuous and global navigation coverage for performing of successful navigation observations. Each GLONASS satellite transmits radiofrequency navigation signals containing navigation messages for users.

Ground-based control complex

The GLONASS Constellation is operated by the Ground-based Control Complex (GCS). It consists of the System Control Center (SCC, Krasnoznamensk, Moscow region), and several Command Tracking Stations (CTS) are placed over a wide area of Russia. The CTSs track the GLONASS satellites in view and accumulate ranging data and telemetry from the satellite signals. The information from CTSs is processed at the SCC to determine satellite clock and orbit states, and to update the navigation message of each satellite. This updated information is transmitted to the satellites via the CTSs, which also are used for transmitting of control information. The CTSs ranging data is periodically calibrated using a laser ranging devices at the Quantum Optical Tracking Stations, which are within GCS. Each GLONASS satellite specially carries laser reflectors for this purpose. The synchronisation of all the processes in the GLONASS system is very important for its proper operability. There is the Central Synchroniser within GCS to meet this requirement. The Central Synchroniser is a high-



precise hydrogen atomic clock, which forms the GLONASS system time scale. The onboard time scales (on a basis of satellite caesium atomic clocks) of all the GLONASS satellites are synchronised with the State Etalon UTC (CIS) in Mendeleevo, Moscow region, through the GLONASS System Time scale.

GLONASS System Time

The GLONASS satellites are equipped with caesium clocks, daily frequency instabilities of which are no more than 5x10E(-13). This provides an accuracy of satellite time synchronisation relative to GLONASS System Time of about 15 nanoseconds (one sigma), with clocks corrections uploaded to the satellite twice a day. GLONASS System Time (GLONASST) is generated on the basis of Central Synchroniser time. Daily instabilities of Central Synchronizer hydrogen clocks are no more than 5x10E(-14). GLONASST shift relative to UTC (CIS) should be less than 1 millisecond. The accuracy of the shift should be less than 1 microsecond. It is well known that the fundamental time scale for all the earth time keeping is the International Atomic Time (TAI). It results from analyses by the Bureau International de l'Heure (BIH) in Paris of data from atomic standards of many countries. The fundamental unit of TAI is the SI second, defined as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium 133 atom". Because TAI is a continuous time scale, it has one fundamental problem in practical use: the earth's rotation with respect to the sun is slowing down by a variable amount which averages, at present about 1 second per year. Thus TAI would eventually become inconveniently out of synchronisation with the solar day. This problem has been overcome by introducing UTC, which runs at the same rate as TAI but is incremented by 1 second jumps ("leap seconds") when necessary, normally at the end of June or December of each year. It is also well-known that each of the world's time centres keeps a local realisation of UTC, the epoch and rate of which relative to UTC (BIH) are monitored and corrected periodically. UTC (CIS) is maintained by the Main Metrological Centre of Russian Time and Frequency Service (VNIIFTRI) at Mendeleevo, Moscow region. When UTC is incremented by leap seconds, GLONASST is incremented too. Therefore, there is no integer-second difference between GLONASST and UTC. However there is a constant offset of three hours between GLONASST and UTC (CIS) due to GLONASS monitoring specific features. GLONASST = UTC+03h.00min. As for GPS, GPS System Time (GPST) is not incremented by leap seconds, and there is the integer-second difference between GPST and UTC. GPST-UTC = +10 s and TAI-UTC = + 29 s (at the time of writing). And at any instant: GPST + 19 s = TAI.

For more and actual information about GLONASS and its constellation status please see the GLONASS website at www.glonass-center.ru .

Differential GPS

Differential GPS (DGPS) is a method of correcting some system errors by using the errors seen at a known location to correct the readings of a moving receiver.

First the exact position of the reference station must be determined. As this reference station does not move its position can be compared with the calculated GPS position. The result is an error measurement, which must be repeated because its value changes permanently. These



error measurements are passed to the moving receiver, which can adjust its GPS calculated position to compensate.

In addition to the permanent change of the error the measurement depends on the particular satellites used to compute the position. So the reference station must compute the errors in the pseudo range measurements for each single satellite, which can be received. Thus the error in the pseudo range measurements, and other system status information to identify the satellites, must be broadcasted by some means (e.g. sub-carriers on FM). A differential GPS receiver receives and decodes this differential information. Then this information is combined with the pseudo range measurements from the GPS system before the receiver calculates the position.

DGPS will eliminate the error introduced by Selective Availability, and errors caused by variations in the ionosphere, resulting in reported positions within about 10 metres of the true position 95 % of the time.

2.5.2 European Systems

Introduction

The evolution of GNSS is expected to occur in two phases. The first (GNSS-1) is a transitional step that builds upon the existing GPS and GLONASS satellite navigation systems. This phase will augment the current GPS and GLONASS navigation signals available to the public to provide improved availability, accuracy and integrity.

The European contribution to the second phase of the GNSS evolution (GNSS-2) will overcome many of the concerns regarding dependency upon third country systems. Examples of these are GPS and GLONASS.

EGNOS - GNSS-135

The European Geostationary Navigation Overlay Service (EGNOS) is Europe's first foray into satellite navigation. It is being developed by ESA under a tripartite agreement between the European Commission (EC), the European Organisation for the Safety of Air Navigation (Eurocontrol) and European Space Agency (ESA). Several air traffic service providers are supporting the development programme with their own investments.

EGNOS will complement the GPS and GLONASS systems. It will disseminate, on the GPS L1 frequency, integrity signals giving real-time information on the health of the constellation. Correction data will improve the accuracy of the current services from about 20 m to better than 5 m. The EGNOS coverage area includes all European states and could be readily extended to include other regions, such as South America, Africa, and parts of Asia and Australia, within the coverage of three geostationary satellites being used.

EGNOS offers all users of satellite radio navigation a high-performance navigation and positioning service, superior to that currently available in Europe. The system is composed of

35 Source: http://europa.eu.int/comm/dgs/energy_transport/galileo/intro/steps_en.htm



three transponders installed in geostationary satellites and a ground network of 34 positioning stations and four control centres, all interconnected. EGNOS will be used foremost for safety-critical transport applications, e.g. in the aviation and maritime sectors and should be operational in 2004.

More information about EGNOS can be obtained at the website of the European Commission, http://europa.eu.int/comm/dgs/energy_transport, in the “Galileo” section of the Directorate-Generale Energy and Transport.

GALILEO - GNSS-2

During 1999, the European Commission recommended that Europe should develop a new satellite navigation constellation known as Galileo. Galileo will be based on 21 or more medium Earth orbit satellites, being fully compatible with GPS, yet independent from it. The Galileo ground infrastructure will comprise a global network of monitoring stations and the associated system control and Earth stations. Galileo will provide to all users an accuracy of a few metres, which is beyond the current GPS standard positioning service.

Furthermore, Galileo will fulfil the requirements of safety critical applications by providing service guarantees, thereby enabling certifications and international standardisation. In addition to the basic service, which will be available to everybody free of charge, a second service level or 'controlled access service' (CAS) will be offered to specific users, with associated availability and liability guarantees. Galileo will be fully operable in 2008, with signal transmission commencing in 2005.

36GALILEO is based on a constellation of 30 satellites and ground stations providing information concerning the positioning of users in many sectors such as transport (vehicle location, route searching, speed control, guidance systems, etc.), social services (e.g. aid for the disabled or elderly), the justice system and customs services (location of suspects, border controls), public works (geographical information systems), search and rescue systems, or leisure (direction-finding at sea or in the mountains, etc.).

For more and actual information please see the Galileo pages at the website of the European Commission at http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm .

36 Source: http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm



3 WIRED TECHNOLOGIES

3.1 Introduction

Wired technologies cover those that use some form of fixed link. Typically this may be copper or fibre, but other media may also be used, or be developed in the future.

3.2 Telephone

3.2.1 Introduction

The main task of Telephony is to give the customer the possibility to carry on a speech conversation with someone far away. For this electrical signals are transmitted by wires between the locations of these customers. By the time several data services evolved.

The early phone network consisted of a pure analogue system that connected telephone users directly by an interconnection of wires. This system was very inefficient, was very prone to breakdown and noise, and did not lend itself easily to long-distance connections. Beginning in the 1960s, the telephone system gradually began converting its internal connections to a digital switching system. Today, nearly all voice switching is digital within the telephone network. Still, the final connection from the local central office to the customer equipment is an analogue Plain-Old Telephone Service (POTS) line. But more and more of these connections are replaced by digital (e.g. ISDN) lines.

3.2.2 POTS (analogue)

POTS (Plain Old Telephony Service) stands for the commonly known analogue wireline telephone service. It has provided the main form of communication link between the “central” and “roadside” parts of ITS applications for over thirty years. Many applications still use it because there is a large infrastructure available that (for the moment) reaches many geographic locations that digital networks do not reach. The technology required to transmit the data is relatively simple (modems), cheap to purchase and widely available from many suppliers. However there are several factors that are forcing ITS applications to move to other forms of wired links. These can be summarised as follows:

• high line costs compared with the amount of data that can be transferred;

• low capacity in terms of the amount of data that can be transmitted in a given time, particularly if services providing travel information such as graphics are required;

• increasing availability of relatively cheap digital based links due to other pressures, e.g. the drive for more widely available high speed access to the Internet.

Therefore although POTS is currently widely used, it is expected that in the future the trend will be to other forms of communication. Thus there may be little or no future development of new equipment that uses POTS. However the existing equipment will continue to be



available from suppliers and used for some time (years) to come. One reason for this will be its wide spread availability in less developed countries and its ability to use low quality physical links.

3.2.3 Integrated Services Digital Network (ISDN)

ISDN, which stands for Integrated Services Digital Network, is a system of digital phone connections that has been available for some time. This system allows data to be transmitted using end-to-end digital connectivity.

With ISDN, voice and data are carried by bearer channels (B channels) occupying a bandwidth of 64 Kbps. A data channel (D channel) handles signalling at 16 Kbps or 64 Kbps, depending on the service type.

There are two basic types of ISDN service: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI consists of two 64 Kbps B channels and one 16 Kbps D channel for a total of 144 Kbps. This basic service is intended to meet the needs of most individual users or the SOHO market.

PRI is intended for users with greater capacity requirements. In Europe, PRI consists of 30 B channels plus one 64 Kbps D channel for a total of 1984 Kbps. It is also possible to support multiple PRI lines with one 64 Kbps D channel using Non-Facility Associated Signalling (NFAS).

To access BRI service, it is necessary to subscribe to an ISDN phone line. Customer must be within 5,5 km of the telephone company central office for BRI service; beyond that, expensive repeater devices are required, or ISDN service may not be available at all. Customers will also need special equipment to communicate with the network switch and with other ISDN devices. These devices include ISDN Terminal Adapters and ISDN Routers.

Speed

ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring used for analogue lines. The change comes about when the telephone company's switches can support digital connections. Therefore, the same physical wiring can be used, but a digital signal, instead of an analogue signal, is transmitted across the line. This scheme permits a much higher data transfer rate than analogue lines. BRI ISDN supports an uncompressed data transfer speed of 128 Kbps. In addition, the latency, or the amount of time it takes for a communication to begin, on an ISDN line is typically about half that of an analogue line. This improves response for interactive applications.

Multiple Devices

With POTS (see chapter above), it was necessary to have a phone line for each device you wished to use simultaneously. For example, one line each was required for a telephone, fax, computer, bridge/router, and live videoconference system. Transferring a file to someone while talking on the phone or seeing their live picture on a video screen would require several phone lines.



It is possible to combine many different digital data sources and have the information routed to the proper destination. Since the line is digital, it is easier to keep the noise and interference out while combining these signals. ISDN technically refers to a specific set of digital services provided through a single, standard interface. Without ISDN, distinct interfaces are required instead.

Signalling

Instead of the phone company sending a ring voltage signal to ring the bell in the phone ("In-Band signal"), it sends a digital packet on a separate channel ("Out-of-Band signal"). The Out-of-Band signal does not disturb established connections, and call set up time is very fast.

A multitude of supplementary services is defined by ISDN, too. Some of these services are the indication who is calling, what type of call it is (data/voice/fax), and what number was dialled. These supplementary services are for example used by intelligent ISDN phone for making decisions on how to direct the call.

A special packet switched data service (called X.31) is defined within ISDN. This service uses the D-channel to transmit packet data to the X.25 network. Thus this service will be described in that chapter.

3.3 Digital Subscriber Line (DSL)

3.3.1 Introduction

The Digital Subscriber Line was developed to bring high-bandwidth information to homes and small businesses over ordinary copper telephone lines. Hence, it allows to use the existing infrastructure to add data transmission on wires which were only transporting voice up to now. The purpose of these technologies is mainly to provide permanent connections to a data network at high rates, with limited costs. In other words, They are mainly high data rates local loop technologies. Commercial offers are just beginning to appear in Europe.

3.3.2 Types of DSL

The term xDSL refers to different variations of DSL, such as ADSL, HDSL, and RADSL. The speed of an xDSL line can go up to 6,1 Mbps (of a theoretical 8,448 Mbps). More typically, individual connections will provide from 1.544 Mbps to 512 Kbps downstream (from the network to the user) and about 128 Kbps upstream (from the user to the network). A DSL line can carry both data and voice signals. The part of the line dedicated to data is continuously connected. Compaq, Intel, and Microsoft working with telephone companies have developed a standard and easier-to-install form of ADSL called G.Lite that is expected to accelerate deployment. Within a few years, DSL is expected to replace ISDN in many areas and to compete with the cable modem in bringing high-speed access to homes and small businesses.



3.3.3 Overview and Description

DSL is very different from traditional use of a modem on a telephone line. With a traditional modem the ability of a home PC to receive information has to go through a bottle neck: the telephone company filters information that arrives as digital data, puts it into analogue form into telephone line, using the same narrow channel as that used for voice. In other words, the analogue transmission between your home or business and the phone company is a bandwidth bottleneck.

DSL assumes digital data does not require conversion to analogue voice transmission. Digital data is transmitted to your computer as-is and this allows the phone company to use a much wider bandwidth for transmitting it to you. By the way, the signal can be separated so that some of the bandwidth is used to transmit an analogue voice signal. This makes it possible to use the telephone and computer on the same line and at the same time. Different DSL modem makers are using either Discrete Multitone Technology (DMT) or Carrierless Amplitude Modulation (CAP). A third technology, known as Multiple Virtual Line (MVL), is another possibility that may be used.

To interconnect multiple DSL users to a high-speed backbone network, the telephone company uses a Digital Subscriber Line Access Multiplexer (DSLAM). Typically, the DSLAM connects to an ATM network that can handle data transmission at gigabit data rates. At the other end of each transmission circuit, the reverse operation is made: a DSLAM de-multiplexes the different signals and forwards them to appropriate individual DSL end user.

Another issue is linked to the splitter. In order to separate data from voice, most DSL technologies require that a signal splitter is installed at the user end, causing the expense of an installation by a professional. However, it is possible to avoid this using a specific standard. This is known as splitterless DSL, DSL Lite, G.Lite, or Universal ADSL and has recently been made a standard.

3.3.4 Asymmetric Digital Subscriber Line (ADSL)

This variation is the form of DSL that will become most familiar to home and small business users (SOHO – Small Office/Home Office). ADSL is called "asymmetric" because most of its two-way or duplex bandwidth is devoted to the downstream direction, sending data to the user. Only a smaller portion of the bandwidth is available for upstream, form the user. This is was designed to fit the Internet model. Most Internet and especially graphics- or multi-media intensive Web data need lots of downstream bandwidth, but user requests and responses are small and require little upstream bandwidth. Using ADSL, up to 6.1 megabits per second of data can be sent downstream and up to 640 Kbps upstream. The high downstream bandwidth means that your telephone line will be able to bring motion video, audio, and 3-D images to your computer or hooked-in TV set. In addition, a small portion of the downstream bandwidth can be devoted to voice rather data, and you can hold phone conversations without requiring a separate line.



3.3.5 Consumer DSL (CDSL)

Consumer DSL is a trademarked version of DSL that is somewhat slower than ADSL (1 Kbps downstream, probably less upstream) but has the advantage that a "splitter" does not need to be installed at the user's end. CDSL uses its own carrier technology rather than DMT or CAP ADSL technology.

3.3.6 G.Lite or DSL Lite

This is also known as DSL Lite, splitterless ADSL, and Universal ADSL. It is essentially a slower ADSL that doesn't require splitting of the line at the user end but manages to split it for the user remotely at the telephone company. This saves the cost of installing a splitter at home. G.Lite provides a data rate from 1.544 Mbps to 6 Mbps downstream and from 128 Kbps to 384 Kbps upstream. G.Lite is expected to become the most widely installed form of DSL.

3.3.7 High bit-rate DSL (HDSL)

The earliest variation of DSL to be widely used has been HDSL (High bit-rate DSL), which is used for wide band digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. For this reason, the maximum data rate is lower than for ADSL. HDSL can carry as much on two wires of twisted-pair as can be carried on a T1 line in North America or an E1 line in Europe (2,320 Kbps). This technology has several drawbacks, in particular two wires are needed, and it is quite “noisy”.

Public TelephoneSwitch

Customer TelephoneWired Lines

Splitter Splitter

DSLAMADSL

Modem

POTS

Network

Data Network

Network



37HDSL2: (2nd generation HDSL) delivers 1.5 Kbps service each way, supporting voice, data, and video using either ATM (asynchronous transfer mode), private-line service or frame relay over a single copper pair. This ANSI (American National Standards Institute) standard for this symmetric service gives a fixed 1.5 Kbps rate both up and downstream. HDSL2 does not provide standard voice telephone service on the same wire pair. HSDL2 differs from HDSL in that HDSL2 uses one pair of wires to convey 1.5 Kbps whereas ANSI HDSL uses two wire pairs.

3.3.8 Single pair HDSL (S-HDSL)

Single pair HDSL operates on a single copper pair, as opposed to HDSL requiring two and allows operators to implement high symmetrical bit rates on a single local loop while maintaining the existing telephone service on the same line. The typical bit rate is 768 Kbps.

3.3.9 ISDN Digital Subscriber Line (IDSL)

This is a hybrid combination of ISDN and ADSL, essentially being a form of ISDN where the data signal is separated before the switch. Currently, IDSL supports speeds of 128 Kbps. Newer IDSL modems will take advantage of the unused D-channel bandwidth and support 144 Kbps connections. In the European market, ISDN seems to have taken over and IDSL is unlikely to make a substantial impact.

3.3.10 Rate-Adaptive DSL (RADSL)

Rate-Adaptive DSL is an ADSL technology designed to operate at a variety of data rates. Software is able to determine the rate at which signals can be transmitted on a given customer phone line and adjust the delivery rate accordingly. Westell's FlexCap2 system uses RADSL to deliver from 640 Kbps to 2.2 Kbps downstream and from 272 Kbps to 1.088 Kbps upstream over an existing line.

3.3.11 Single-line DSL (SDSL)

Single-line DSL is apparently the same thing as HDSL with a single line, carrying 1.544 Kbps (U.S. and Canada) or 2.048 Kbps (Europe) each direction on a duplex line.

3.3.12 Unidirectional DSL (UDSL)

Unidirectional DSL is a proposal from a European company. It's a unidirectional version of HDSL.

37 Source: http://www.dslforum.org



3.3.13 Very high data rate DSL (VDSL)

Very high data rate DSL is a developing technology that promises much higher data rates over relatively short distances (between 51 and 55 Kbps over lines up to 1,000 feet or 300 meters in length). It's envisioned that VDSL may emerge somewhat after ADSL is widely deployed and co-exist with it. The transmission technology (CAP, DMT, or other) and its effectiveness in some environments is not yet determined. A number of standards organisations are working on it.

The actual data rate of connections with the various xDSL depends on several factors. In particular, surrounding electric “noise”, physical quality of the wires, bridge taps, and especially distance. In fact, each technology can only be used on a limited distance as shown on the following chart.

Figure 6 xDSL speed vs copper pair length

3.4 X.25 (Packed Switched Data)

In the 70s, the need for interconnecting international networks has arisen. In response, telecommunication operators have developed the X.25 protocol.

X.25 is a low level network protocol based on packet switching. Packet-switched networks enable end stations to dynamically share the network medium and the available bandwidth. Variable-length packets are used for more efficient and flexible transfers. These packets then are switched between the various network segments until the destination is reached. Statistical multiplexing techniques control network access in a packet-switched network. The advantage of this technique is that it accommodates more flexibility and more efficient use of bandwidth.

X.25 implements the 3 lowest layers of the OSI model. It is based on Data Terminal Equipment (DTE) at end users premises or at the edge of the network and a meshed network

Dat

a R

ate

(Mbp

s)

VDSL

ADSL

ISDN/IDSL

HDSL

25

2.5

0.25

2 4 6Wire Distance (km)



of nodes equipment (called Data Circuit Terminating). A DTE user on an X.25 network may communicate with a number of remote DTEs simultaneously.

It allows international secure transmission of data, with error correction and flow control at each node. The transmission delay depends on the number of nodes between DTE. On most single networks the turn-around delay is about 0.6 seconds. This makes it unsuitable for voice telecommunication, and may be a serious drawback for transaction based on heavy interactions.

Prior to a transmission, a virtual circuit (VC) must established between the communicating DTE. Permanent virtual circuit (PVC) can also be set up. The integrity of the delivered data is guarantied. Packets are received in the same order they were sent.

It is also possible to send datagramms, which contain the address of the receiver DTE. In that case there is no need to establish a virtual circuit, but the delivery is not guarantied and they are received in any order.

In most parts of the world, X.25 is paid for by a monthly connect fee plus packet charges. There is usually no holding charge, making X.25 adequate for permanent connections. Another useful feature is speed matching: because of the store-and-forward nature of Packet Switching, plus excellent flow control, DTEs do not have to use the same line speed. So it is possible to have, for instance, a host connected at 56 Kbps communicating with numerous remote sites connected with cheaper 19.2 Kbps lines.

3.5 Frame Relay

Frame Relay is a high-performance WAN protocol that operates at the physical and data link layers of the OSI reference model (the two lowest layers). Like X.25, Frame Relay is an example of a packet-switched technology (see above). Frame Relay transports variable size frames (e.g. IP packets) through established virtual circuits (VCs) making use of statistical multiplexing.

Compared to X.25, Frame Relay reduces the packet processing at the internal network node, since the error control/retransmission and flow control is performed on an end-to-end basis at the network edge nodes. On the other hand, it does not provide guaranty on data integrity. The network delivers frames, whether the CRC38 matches or not. It does not even necessarily deliver all frames, discarding frames whenever there is network congestion. Thus it is imperative to run an upper layer protocol above Frame Relay that is capable of recovering from errors, such as IPX or TCP/IP. In practice, however, the network delivers data quite reliably. Unlike the analogue communication lines that were originally used for X.25, modern digital lines have very low error rates. Very few frames are discarded by the network, particularly at this time when the networks are operating at well below design capacity.

Frame Relay offers a VPN service through the use of permanent VCs. Although switched virtual circuit specifications are available from the Frame Relay Forum, existent Frame relay

38 CRC (Cyclic Redundancy Check): for each frame a CRC is calculated based on all of its bits. If the frame has been altered during transmission, the receiver will calculate a different CRC which enables him to notice the alteration, and, under certain conditions, to correct it.



networks provide only permanent virtual circuits. Upon establishment of a virtual circuit, the user specifies a CIR (Committed Information Rate) that must bee guaranteed by the network provider. Current CIR values range from 64 Kbps up to 2 Mbps and limited (in specific cases) to 45 Kbps. It was proposed by the Frame Relay Forum. Commercial offers allow aggregating of several circuits to obtain higher throughput (typically up to 8 Mbps).

Frame Relay is used mostly to route Local Area Network protocols such as IPX or TCP/IP. It can also be used to carry asynchronous traffic, SNA or even voice data. With respect to voice data, voice is digitised and compressed; silent periods (and echo) are omitted. Every frame can transport several voice packets. Voice is compressed at 6,3 Kbps, 8 Kbps or 16 Kbps. For example, a 64 Kbps link can simultaneously transport up to six 8 Kbps (+ overhead) compressed communications. Voice over frame relay is seen as an attractive solution for companies requiring voice and data integration. Typical European Frame Relay networks have an ATM core network with Frame relay links (from 64 Kbps up to 2 Kbps).

3.6 Asynchronous Transfer Mode (ATM)

ATM is a high speed switching technology that allows the integration of different traffic media over a single physical network.

ATM was adopted by the ITU-T as the standard for the B-ISDN. Nevertheless, there are few similarities with ISDN, and standards are now mostly provided by the ATM Forum. With ATM all data (digital voice, video, files, etc.) are transferred in small fixed length cells (53 bytes, 5 bytes of overhead) over virtual connections. Connections are established prior to any data transfer.

This technology has been defined for use over wired lines, and enables high data rates. Instead of direct use over wires, it may also be installed over high speed SDH networks39, or even WDM networks40. It may provide network services in direct connection with applications (e.g. to transport voice or video), in particular for large Local Area Networks, but the most common place of implementation is the backbone of operators’ networks, in particular it is adapted to the transport X.25, Frame Relay or IP data.

At connection establishment phase, the user selects the type of the required connection. According to the Quality of service needed to transfer his information several kinds of services are available, in particular the amount of bandwidth needed and the shape of the traffic is negotiated prior to any connection.

Since all kinds of data flows may be sent on the same wires through switched cell flows, ATM statistical multiplexing improves resource utilisation. The granularity of transmission link speeds and the support of QoS make it suitable for high-speed applications having different characteristics.

39 SDH (Synchronous Data Hierarchy): protocol of high-speed low-level network that enables high-speed transport of other protocols. 40 WDM (Wavelength Digital Multiplexing): protocol for very high speed low level networks that make use of several wavelengths over fibber optical networks instead of a traditional single wavelength. It enables very high-speed transport of other protocols.



Standardisation bodies (ITU-T, IETF, ATM Forum) propose solutions for scalable signalling and routing solutions such as PNNI, or IP over ATM support such as MPLS, Classical IP over ATM (CLIP, RFC 1577), LANE, or MPOA.

ATM is currently widely used in backbone networks while other high-speed technologies (e.g. switched Ethernet, Gigabit Ethernet) appear as an alternative option at the LAN level. Industries with stringent QoS and bandwidth requirements see ATM as an attractive (and sometimes unavoidable) solution.

3.7 Internet

3.7.1 Overview

The use if the Internet is widespread, both in terms of take-up by users and in terms of the information that is available. In the Internet there is much information available, but sometimes it is difficult to find the required information, if the provider or the right website address (URL, Unified Resource Locator) is not known. Via the Internet various public and commercial services are offered, such as timetables and purchase of tickets for public transport or registration services at communes.

There is an increasing move towards the development of Internet access through “wireless” based technology, the mobile Internet, e.g. via GSM, GPRS or UMTS that has its own custom-made protocol (WAP) and websites, e.g. with less or without graphics to reduce the data to be transferred.

3.7.2 Technology41

Technical specifications or protocols describe how to exchange data over the network. These protocols are formed by discussion within the Internet Engineering Task Force (IETF) and its working groups, which are open to public participation and review. These committees produce documents that are known as Requests For Comments (RFCs). Some RFCs are raised to the status of Internet Standard by the Internet Architecture Board (IAB).

Some of the most used protocols in the Internet protocol suite are IP (Internet Protocol), TCP (Transmission Control Protocol), UDP (User Datagram Protocol), DNS (Domain Name System), PPP (Point to Point Protocol), SLIP (Serial Line Internet Protocol), ICMP (Internet Control Message Protocol), POP3 (Post Office Protocol version 3), IMAP (Internet Message Access Protocol), SMTP (Simple Mail Transfer Protocol), HTTP (Hypertext Transport Protocol), HTTPS (Secure HTTP), SSH (Secure Shell), Telnet, FTP (File Transfer Protocol), LDAP (Lightweight Directory Access Protocol), and SSL (Secure Sockets Layer).

Some of the popular services on the Internet that make use of these protocols are e-mail, Usenet newsgroups, file sharing, the World Wide Web, Gopher, session access, WAIS (Wide area information server), finger, IRC (Internet Relay Chat), MUDs (multi-user dungeon), and MUSHs (multi-player shared hallucination). Of these, e-mail and the World Wide Web are

41 http://en.wikipedia.org



clearly the most used, and many other services are built upon them, such as mailing lists and web logs. The internet makes it possible to provide real-time services such as web radio and webcasts that can be accessed from anywhere in the world.

3.7.3 Use in Telematics

Internet Services are provided through Service Providers. These enable those with home or office PC’s (including Laptops) to have access to Web Sites. These Web Sites are used to display a wide variety of information in varying amounts of detail. It is also possible to provide interactive Web Sites so that the user can select exactly the information that is required. The content can include text and graphics, and can be of very high resolution. It is also possible to include video images, such as those provided by CCTV systems. For traffic purposed, this can include “real time” views of the actual traffic situation where ever there is a camera.

It would be impossible to describe the wide range of traffic and travel related Web Sites that are currently available. They also cover most modes of transport, particularly road, rail and Public Transport. For road information, many of the larger Cities and Towns throughout Europe are beginning to set up their own Web Sites to display the traffic and travel information. Generally they will show the information in various ways, that may include, graphical maps, and/or textual data, and/or video images. The maps vary from the rough schematic, to data overlaid on top of digital maps provided by specialist companies. Some sites also include trip planning, which may go outside the immediate area served by the operator of the Web Site.

Most users will access Web Sites from home or office based PC’s. Therefore their use is to gain an indication of the current traffic and travel situation. Unless access can be gained from a Laptop PC via a mobile telephone, the information that is provided will become increasing less useful to the Traveller once they have left their home or office (and the PC). This is because a great deal of traffic and travel information is usually time dependent and therefore becomes out of date. But not only for transport issues the wired access is still very important, e.g. for trip planning, because (at the moment) it is much cheaper than the wireless access via e.g. GPRS.



4 OPTICAL NETWORKING

4.1 Introduction

Below are described the two main techniques for a more efficient backbone through utilisation of optical fibres which may be more expensive to lay out but undoubtedly the fastest means available. SONET and WDM are discussed. There was a proposition by key companies in European backbone technology to move from ATM based to SONET based backbone since for the former, nearly 10% of traffic is overhead (5 bytes of header every 53 bytes of information). Encapsulating IP packets over ATM grows the overhead to 30 % of the traffic whereas for SONET this falls down to less than 1 %.

Currently, many ATM proponents argue that the lack of QoS in SONET cancel out this gain but the fact is that carrying IP over a SONET backbone has advantages that will grow as technology changes, like IP v6 for example.

Figure 7 Evolaution of Infrastructure

IP based optical core(SONET/SDH, WDM, DWDM)

Internet

Web Server

PSTN

Long-term evolution of Infrastructure

Laptop

Businesses

SOHO

Wireless

IP Phone

HFC

xDSL

Fibre



4.2 SDH/SONET

The Synchronous Digital Hierarchy/Synchronous Optical NETwork provides an advanced physical layer multiplexing transmission technology over fibre optic support. SDH/SONET provides flexible insertion/extraction of virtual circuits in a frame based hierarchical structure allowing transmission at high-speed rates.

Normalised speeds for SDH are 155,52 Kbps for STM-1 and up to 2488,32 Kbps for STM-16. SONET (US ANSI equivalent), provides an additional lower rate, OC-1 at 52,840 Kbps. User information is copied asynchronously into the user field of an SDH frame. A set of pointers (described in the header of the frame) allow to locate the user information within the frame allowing to directly extract, for example, a STM-1 circuit from a higher hierarchical multiplex such as a STM-16. SDH in ring configuration has the self-healing characteristic, restoring link failures in around 50 ms. SDH/SONET currently appears as the most widely physical layer backbone technology deployed for transporting different types of upper layer traffic such as ATM, or even IP packets as described hereafter.

Figure 8 Comaprison of different types of SDH/SONET

IP

ATM

SONET/SDH

WDM

IP

SONET/SDH

WDM

IP

WDM

Increasing efficiency, lower

Increasing QoS control, management capabilities,

Infrastructure Development

4.3 Packet over SONET (POS)

This consists of encapsulating IP packets over PPP over SDH/SONET providing a gain in the order of 25 % to 30 % compared to the IP/AAL5/ATM/SDH approach. Network switches and routers are also less expensive than ATM equipment. Nevertheless, POS does not have support for QoS and as IP traffic increase, IP routers may become traffic bottlenecks. POS



equipment in the market can provide 155 Kbps (STM-1), 622 Kbps (STM-4) and 2,5 Gbps (STM-16) speeds. In POS networks, IP addresses are assigned to each interface and protocols such as RIP or OSPF are defined just as with any other IP network (in contrast, ATM requires address translation and higher management capabilities).

This technology is more oriented to operate over backbones dedicated to data transfer over the Internet while ATM is more adapted to multimedia developments (ATM will likely continue to appeal big telecom operators). The emergence of new protocols such as IPv6, RSVP, DiffServ, providing a certain degree of QoS, will probably favour this technology.

In order to increase capacity even more there are three distinct options for an optical network:

• Installation of new fibre equipment and transmission (expensive and time consuming)

• Transmission speed increase. Usual is 2.5 Gbps (OC-48) and to extend beyond that, a higher grade of fibre is needed. Transmission at 10 Gbps (OC-192) is starting to become an option and there is research for 40 Gbps (OC-768).

• Use of Wavelength Division Multiplexing with the existing fibre structure.

The last mentioned of these seems appealing at the moment.

4.4 Wavelength Division Multiplexing (WDM)

Wavelength Division Multiplexing and Dense-WDM (DWDM) technologies allow the multiplexing of several different wavelengths over a single fibre optic increasing the available bandwidth capacity of the fibre. The WDM technologies allow multiple lasers carrying independent signals to be transmitted in the same fibre with appropriate spacing of wavelengths (frequencies) between laser carriers.

Because of the broad bandwidths of lasers, the carried signals can be format-independent and be routed in networks independently. The lasers can carry digital or analogue signals. The digital signals can be any speeds (155 MB/s OC-3, 625 MB/s OC-12, 2.5 GB/s OC-48 or 10 GB/s OC-192) or format (security-coding, compressed data and etc). The analogue signals can be any formats or co-exist with digital signals. The analogue signals can also be Frequency-Division-Multiplexed (FDM) in one laser because of the broad bandwidth of the laser beam.

For digital signals, WDM systems increase network capacities. For example, the maximum network capacity for a eight-wavelength WDM system increases to 20GB/s when each laser carries a 2.5 GB/s (SONET OC-48) signal. Furthermore, the broadband feature of optical communications allows transparent networks where the lasers can carry independent signal formats. For example, wavelength_1 can carry analogue signals; wavelength_2 can carry a 2.5-GB/s digital signal while wavelength_3 carries a 155-MB/s digital signal. The transparent feature provides securities and flexibility to the networks. To achieve the transparency, the devices used in the networks have to be all optical.



Figure 9 Graph of network capacity for different WDM sppeds

Currently, ITU-T has defined around a hundred different wavelengths, each of these wavelengths having a bandwidth of 2,5 Gbps (up to 10 Gbps in some cases, or more). WDM systems are universal and transparent to the type of flow they transport (e.g. digital signals, SDH, analogue signals such as video).

Backbone Speed

OC-192

WDM (300 wavelengths)

OC-3 OC-12OC-48

0

5

10

15

20

25

30

35

40

45

Gbp

s



5 Synthesis Table

5.1 Introduction

The table in the next section shows the main characteristics of the Telecommunication Technologies linked with ITS. The meanings of the columns are summarised in the table below:

Table 3 Values of the Synthesis Table

Item Sub-Item Values Description

Technology Name of the Technology (Communication System)

Name Name of a special Supplementary Service of that technology.

Configuration Type x-y x and y are chosen among p, m, and b. p = point; m = multi-point; b = broadcast. Hence p-m = point to multi-point configuration. This means that the same message is send from one point and received simultaneously at several points.

Connectivity (Con)

Wl, Wd Wl = wireless wd = wired technology.

Range Short, medium long

(this may be only applicable for wireless)

Directions (Dir)

d, sd, u d = duplex, sd = semi duplex and u = unidirectional

Quantification Frequency (Freq)

s, min, h, d, w, mth, y

Typical frequency of communication per single link (order of magnitude, e.g. s = several times per second). ( s = second, min = minute, h = hour, d = day, w = week, mth = month, y = year)

Latency (Lat)

s, min, h, d The order of magnitude of the acceptable latency of the communication (s = second, min = minute, h = hour, d = day).

Bandwidth (Bwth)

B/s, KB/s, MB/s Order of typical Bandwidth per second. Bit/s, Kbps, Kbps,

Security (Sec) A(x), I, C A(x) = Authentication required where x is/are the party which authenticates it’s identity (possible values for x: Sr; Sk; Sr,Sk). E.g. A(Sr,Sk), source and sink needs to authenticate their identity before transmission.



Item Sub-Item Values Description

I = Data integrity. The integrity of data cannot be altered (by chance or on purpose) without the system noticing it. ‘I’ indicate that special algorithms such as signed message digests must be available. C = Confidentiality. Prevents a third party to overhear the communication. Encryption means must be available to protect data against disclosure. Symbols may be combined. E.g. A(Sr)/C: confidentiality must be insured and Source authenticated with strong mechanisms.

Availability (Avail)

Comments on the availability of this technology should be stated here, e.g. GSM can be used World-wide (roaming), TETRA and TETRAPOL are only regional / in some nations

Data Type Text, Audio, Video, Photo,

Graphic, Animation, Multimedia,

Raw data

Text: simple formatted text; Audio: simple audio record; Video: video record – no sound; Graphic: image which can be reconstructed out of a couple of data. Photo: still image; Animation: the image is not completely still some parts may be animated (moving icon for instance). Multimedia: the choice of the actual type is up to the application design. Raw data : formatted messages, queries, security data, etc.

For physical transfer, a ‘p’ is put in front of the type (e.g. pText: physical transfer of Text).

A combination of several type is possible (e.g. Audio/Video).

Comments Definition of the session when needed,Comparable physical data flows, remarks on the way values were chosen, hypothesis, reason for not giving a value, etc.

5.2 Synthetic Table

The table comparing the characteristics of the different types of communications links is shown in the following pages.

TR1048 - KAREN Communication Architecture - D 3.3 Annex 2

May 2000 Page 72 of 84 Version 3

Table 4 Synthetic table on telecommunication technologies linked with ITS

Configuration Quantification Technology Name

Type Con Range

Dir. Freq Lat Bwth

Sec Avail. Data-Type

Comments

Land based wireless telephony systems

GSM WL Long A

Voice p-p d 10 s for call set

up

ms World The supplementary service "multi-party" enables the user to set up a conference call

with several others

Data (connection

oriented)

p-p d 10 s for call set

up

ms World

SMS p-p, p-m

d World p-m only if direct connection to SMSC42, roaming complicated (mainly caused by

network providers)

CB p-b u Some countries

GPRS p-p, p-m, p-b

d Coming

HSCSD p-p d Some countries

42 SMSC: Short Message Service Centre




Type Con Range

Dir. Freq Lat Bwth


Comments

UMTS p-p WL Long d Some countries

DECT p-p WL Med d Local

TETRA p-p, p-m

WL Long d, sd Few countries

TETRAPOL p-p, p-m

WL Long d, sd Few countries

Satellite Systems

GPS p-b WL very long

u World system for exact positioning, exact time can be determined, main problem: American

military system

IRIDIUM World financial problems.

Globalstar World chances to survive

Mass Broadcast Systems

Radio WL Long none

FM p-b u Europe

DAB p-b u Few countries

DRM p-b u Some countries

TV WL Long none




Type Con Range

Dir. Freq Lat Bwth


Comments

analogue p-b u World

DVB p-b u

Satellite p-b u World

Special Wireless Systems

WLL-Technologies WL Short

Beacon Systems p-b WL Short u none only special applications

Bluetooth WL very short World

DSRC WL short d World

Fixed line systems

Telephone Wr

POTS p-p d ms

ISDN p-p d ms

ADSL p-p Wr d

X.25 / X.31 p-p Wr d

Frame Relay

Wr

ATM Wr d

Internet p-p, p-m

Wr d




Type Con Range

Dir. Freq Lat Bwth


Comments

Ethernet Wr d



6 Short introduction to the OSI model

The OSI (Open System Interconnection) Reference Model of network architecture and a suite of protocols (protocol stack) to implement it were developed by ISO in 1978 as a framework for international standards in heterogeneous computer network architecture. This standard is described in the ITU X.200 suite.

The architecture is split between seven layers, from lowest to highest: 1 physical layer, 2 datalink layer, 3 network layer, 4 transport layer, 5 session layer, 6 presentation layer, 7 application layer. For each layer it is possible to specify protocols and functions required for two nodes to communicate using the underlying network infrastructure (physical medium, switches, routers, bridges, multiplexers, intermediate nodes). Each layer uses the layer immediately below it and provides a service to the layer above.

Figure 10 OSI Model Layer Structure

Application Layer 7

Programmes and applications

Mailer, Web Browser, etc.

Presentation Layer 6

Conversion system ASN.1 ASCII translation ...

Session Layer 5

Network Operating

System

Netware IP/IPX - NetBios - DEC - TCP/IP

Transport Layer 4

NWIP, PCLAN, LanManager, DECNET, PC/TCP

Network Layer 3

ISO 8802.1 (IEEE 802.1)

ISO 8802.2 (IEEE 802.2)

Access Layer 2

Logical Link Control

Medium Access Control

ISO 8802.3

IEEE 802.3

CSMA/CD

ISO 8802.4

IEEE 802.4

TOKEN BUS

ISO 8802.5

IEEE80

2.5 TOKEN RING

-

IEEE 802.6

DQDB

ISO 9314

ANSI

X3T9.5FDDI

SDH

Physical Layer 1

WDM

Detailed comments on each of the seven layers that make up the OSI Model are provided on the following page.

• Physical Layer. This is concerned with the transmission of signals. Choosing a solution at this level means choosing, for instance, fibber optics, copper wires, air and the equipment which actually create the signal.



• Data Link Layer. This is concerned with making the transmission reliable. Choosing a solution at this level means choosing algorithms to trigger the signal.

• Network Layer. This is concerned with routing data to the appropriate destination. Choosing a solution at this level means choosing a protocol which enable different sources and sinks to exchange the expected data and that only.

• Transport Layer. This is concerned with making the best use of the network on behalf of the entity which receives or sends the data. It is normally present only at both end of a communication channel. Choosing a protocol at this level means choosing a protocol which enables or not to multiplex data, to prioritise data, to control the flow, to detect/correct errors, to open or close a communication.

• Session Layer. This is concerned with providing means to establish a dialogue: open or close a conversation, synchronise exchanges etc. Choosing a protocol at this level means choosing how dialogues will be managed.

• Presentation Layer. This is concerned with formatting the information that applications are exchanging. Choosing a protocol at this level means choosing which common dictionary or message format will be used by both end. It may also mean to choose a protocol which describes in real time the exchanged data. (This is more or less the language issue described below).

• Application Layer. This is the highest layer were the information is processed before being handed over to lower layers for transmission, when not stored or handed to users.

In practice, this theoretical model is not followed by industrial telecommunication companies. De facto, protocols often cover several layers. For instance the ATM protocol covers part of the second, the third, and of the fourth layer. In its own manner GSM covers all layers. Additionally, they are not fully independent. Most of the time it is not possible to use any physical layer with a given protocol. For instance ATM was first designed for fibber optic networks.



7 References

(a) European ITS User Needs Deliverable Document, Issue 1, May 2000.

(b) European ITS Framework Architecture Functional Architecture Deliverable Document (D 3.1), Issue 1, August 2000.

(c) European ITS Framework Architecture Physical Architecture Deliverable Document (D 3.2), Issue 1, August 2000.

A copy of any of the above Documents can be found on the European ITS Framework Architecture CD-ROM, or at “http://www.trentel.org/transport/frame1.htm” by selecting “Deployment Information” and then “System Architecture”.

frame comunication arhitecture

Documents

architecture documentation

satellite communication

long range communication

mobile communication

european commission

european systems

public deliverable number

public report authors