course material for module 5

8/3/2019 Course Material for Module 5

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T 703 Modern Communication Systems

MODULE 5

Wireless LAN Concepts

Wireless LAN technology is becoming increasingly popular for a wide variety of applications. After evaluating the technology, most users are convinced of its reliability,satisfied with its performance and are ready to use it for large-scale and complex wirelessnetworks. Originally designed for indoor office applications, todays Wireless LANs can

be used for both indoor peer-to-peer networks as well as for outdoor point-to-point and point-to-multipoint remote bridging applications.Wireless LANs can be designed to be modular and very flexible. They can also beoptimized for different environments. For example, point-to-point outdoor links are lesssusceptible to interference and can have higher performance if designers increase thedwell time and disable the collision avoidance and fragmentation mechanismsdescribed later in this section.Topology

Wired LAN Topology

Traditional LANs (Local Area Networks) link PCs and other computers to one another and to file servers, printers and other network equipment using cables or optic fibers as

the transmission medium.Figure 1: Wired LAN Topology

Prepared By Ms.Sreenu.G, Department Of Computer Science, RASET


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Wireless LAN Topology

Wireless LANs allow workstations to communicate and to access the network using radioPropagation as the transmission medium. The wireless LAN can be connected to anexisting wired LAN as an extension, or can form the basis of a new network. Whileadaptable to both indoor and outdoor environments, wireless LANs are especially suitedto indoor locations such as office buildings, manufacturing floors, hospitals anduniversities.The basic building block of the wireless LAN is the Cell . This is the area in which thewireless communication takes place. The coverage area of a cell depends on the strengthof the propagated radio signal and the type and construction of walls, partitions and other

physical characteristics of the indoor environment. PC-based workstations, notebook and pen-based computers can move freely in the cell.



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Each Wireless LAN cell requires some communications and traffic management. This iscoordinated by an Access Point (AP) which communicates with each wireless station inits coverage area.

Stations also communicate with each other via the AP, so communicating stations can behidden from one another. In this way, the AP functions as a relay, extending the range of the system. The AP also functions as a bridge between the wireless stations and the wirednetwork and the other wireless cells. Connecting the AP to the backbone or other wirelesscells can be done by wire or by a separate wireless link, using wireless bridges. The rangeof the system can be extended by cascading several wireless links, one after the other.



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Figure 3: Wireless LAN ConnectivityRoaming

When any area in the building is within reception range of more than one Access Point,the cells coverage is said to overlap. Each wireless station automatically establishes the

best possible connection with one of the Access Points. Overlapping coverage areas arean important attribute of the wireless LAN setup, because it enables seamless roaming

between overlapping cells.



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Roaming allows mobile users with portable stations to move freely between overlappingcells, constantly maintaining their network connection. Roaming is seamless; a work session can be maintained while moving from one cell to another. Multiple access pointscan provide wireless coverage for an entire building or campus. When the coverage areaof two or more APs overlap, the stations in the overlapping area can establish the best

possible connection with one of the APs, continuously searching for the best AP. In order to minimize packet loss during switchover, the old and new APs communicate tocoordinate the process.Load BalancingCongested areas with many users and heavy traffic load per unit may require a multi-cell

structure. In a multi-cell structure, several co-located APs illuminate the same areacreating a common coverage area which increases aggregate throughput. Stations insidethe common coverage area automatically associate with the AP that is less loaded and

provides the best signal quality. The stations are equally divided between the APs inorder to equally share the load between all APs. Efficiency is maximized because all APsare working at the same low level load. Load balancing is also known as load sharing.



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Dynamic Rate SwitchingThe data rate of each station is automatically adjusted according to the received signalquality. Performance (throughput) is maximized by increasing the data rate anddecreasing re-transmissions. This is very important for mobile applications where thesignal quality fluctuates rapidly, but less important for fixed outdoor installations wheresignal quality is stable.Media Access

When many users are located in the same area, performance becomes an issue. Toaddress this issue, Wireless LANs use the Carrier Sense Multiple Access (CSMA)algorithm with a Collision Avoidance (CA) mechanism in which each unit senses themedia before it starts to transmit. If the media is free for several microseconds, the unitcan transmit for a limited time. If the media is busy, the unit will back off for a randomtime before it senses again. Since transmitting units compete for air time, theProtocol should ensure equal fairness between the stations.

FragmentationFragmentation of packets into shorter fragments adds protocol overhead and reduces

protocol efficiency when no errors are expected, but reduce the time spent on re-transmissions if errors are likely to occur. No fragmentation or longer fragment lengthadd overhead and reduce efficiency in case of errors and re-transmissions (multi-path).Collision AvoidanceTo avoid collisions with other incoming calls, each station transmits a short RTS(Request to Send) frame before the data frame. The Access Point sends back a CTS(Clear to Send) frame with permission to start the data transmission. This frame includesthe time that this station is going to transmit. This frame is received by all the stations in



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the cell, notifying them that another unit will transmit during the following X msec, sothey can not transmit even if the media seems to be free (the transmitting unit is out of range).Channelization

Using Frequency Hopping Spread Spectrum (FHSS), different hopping sequences areassigned to different co-located cells. Hopping sequences are designed so different cellscan work simultaneously using different channels. Since hopping sequences and hoppingtiming of different cells cannot be synchronized (according to FCC regulations), differentcells might try to use the same channel occasionally. Then, one cell uses the channelwhile the other cell backs off and waits for the next hop. In the case of a very noisyenvironment (multiples and interference), the system must hop quickly. If the link is quietand clean, it is better to hop slowly, reducing overhead and increasing efficiency.

WLAN: Wireless LAN by IEEE 802.11, 802.11a, 802.11b, 802.11g, 802.11n

The Wireless Local Area Network (WLAN) technology is defined by the IEEE 802.11family of specifications. There are currently four specifications in the family: 802.11,802.11a, 802.11b, and 802.11g. All four use the Ethernet protocol and CSMA/CA(carrier sense multiple access with collision avoidance instead of CSMA/CD) for pathsharing.

802.11 -- applies to wireless LANs and provides 1 or 2 Mbps transmission in

the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) ordirect sequence spread spectrum (DSSS). 802.11a -- an extension to 802.11 that applies to wireless LANs and provides

up to 54 Mbps in the 5GHz band. 802.11a uses an orthogonal frequencydivision multiplexing (OFDM) encoding scheme rather than FHSS or DSSS.The 802.11a specification applies to wireless ATM systems and is used inaccess hubs.

802.11b (also referred to as 802.11 High Rate or Wi-Fi) -- an extension to802.11 that applies to wireless LANS and provides 11 Mbps transmission (witha fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. 802.11b uses onlyDSSS. 802.11b was ratification to the original 802.11 standard, allowingwireless functionality comparable to Ethernet.

802.11g -- offers wireless transmission over relatively short distances at 20 -54 Mbps in the 2.4 GHz band. The 802.11g also uses the OFDM encodingscheme.

802.11n - builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). IEEE 802.11n offers high throughput wirelesstransmission at 100Mbps 200 Mbps.

The modulation used in 802.11 has historically been phase-shift keying (PSK). Themodulation method selected for 802.11b is known as complementary code keying



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(CCK), which allows higher data speeds and is less susceptible to multipath-propagationinterference. 802.11a uses a modulation scheme known as orthogonal frequency-divisionmultiplexing (OFDM) that makes possible data speeds as high as 54 Mbps, but mostcommonly, communications takes place at 6 Mbps, 12 Mbps, or 24 Mbps.

For short range and low power wireless (less than 10 meters) communications among personal devices such as PDA, Bluetooth and subsequent IEEE standards (802.15) aretaking effects. For long range wireless communications in the metropolitan areas, WiMaxas defined in the IEEE 802.16 is the standard.

The 802.11 stack structure is as follows:

Protocol Structure - WLAN: Wireless LAN by IEEE 802.11, 802.11a,802.11b,802.11g, 802.11n

801.11 protocol family MAC frame structure:

2 2 6 6 6 2 6 0-2312 4

FrameControl Duration

Address1

Address2

Address3 Seq

Address4 Data

Checksum

Frame Control Structure:

2 2 4 1 1 1 1 1 1 1 1

Version Type Subtype To DS From DS MF Retry Pwr More W O



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Protocol Version - indicates the version of IEEE 802.11 standard. Type - Frame type: Management, Control and Data. Subtype - Frame subtype: Authentication frame, Deauthentication frame;

Association request frame; Association response frame; Reassociation requestframe; Reassociation response frame; Disassociation frame; Beacon frame;Probe frame; Probe request frame and Probe response frame.

To DS - is set to 1 when the frame is sent to Distribution System (DS) From DS - is set to 1 when the frame is received from the Distribution System

(DS) MF- More Fragment is set to 1 when there are more fragments belonging to

the same frame following the current fragment Retry indicates that this fragment is a retransmission of a previously

transmitted fragment. (For receiver to recognize duplicate transmissions of frames)

Pwr - Power Management indicates the power management mode that thestation will be in after the transmission of the frame.

More - More Data indicates that there are more frames buffered to thisstation.

W - WEP indicates that the frame body is encrypted according to the WEP(wired equivalent privacy) algorithm.

O - Order indicates that the frame is being sent using the Strictly-Orderedservice class.

Duration/ID (ID) -o Station ID is used for Power-Save poll message frame type.o The duration value is used for the Network Allocation Vector (NAV)

calculation. Address fields (1-4) - contain up to 4 addresses (source, destination,

transmission and receiver addresses) depending on the frame control field(the To DS and From DS bits).

Sequence Control - consists of fragment number and sequence number. It isused to represent the order of different fragments belonging to the sameframe and to recognize packet duplications.

Data - is information that is transmitted or received. CRC - contains a 32-bit Cyclic Redundancy Check (CRC).

Related ProtocolsIEEE 802.2 , 802.3, Bluetooth 802.15 , WiMax 802.16 , 802.11, 802.11a, 802.11b,802.11g, 802.11n

http://www.javvin.com/protocolLLC.htmlhttp://www.javvin.com/protocolEthernet.htmlhttp://www.javvin.com/protocolBluetooth.htmlhttp://www.javvin.com/protocolWiMAX.htmlhttp://www.javvin.com/protocolLLC.htmlhttp://www.javvin.com/protocolEthernet.htmlhttp://www.javvin.com/protocolBluetooth.htmlhttp://www.javvin.com/protocolWiMAX.html


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ISDN

ISDN (Integrated Services Digital Network) is an all digital communications line thatallows for the transmission of voice, data, video and graphics, at very high speeds, over standard communication lines. ISDN provides a single, common interface with which toaccess digital communications services that are required by varying devices, whileremaining transparent to the user. Due to the large amounts of information that ISDNlines can carry, ISDN applications are revolutionizing the way businessescommunicate.ISDN is not restricted to public telephone networks alone; it may betransmitted via packet switched networks, telex, CATV networks, etc.

The ISDN is illustrated here in relation to the OSI model:

ISDN applications

LAPD



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The LAPD (Link Access Protocol - Channel D) is a layer 2 protocol which is defined inCCITT Q.920/921. LAPD works in the Asynchronous Balanced Mode (ABM). Thismode is totally balanced (i.e., no master/slave relationship). Each station may initialize,supervise, recover from errors, and send frames at any time. The protocol treats the DTEand DCE as equals.

The format of a standard LAPD frame is as follows:

Flag Address field Control field Information FCS Flag

LAPD frame structure

FlagThe value of the flag is always (0x7E). In order to ensure that the bit pattern of the framedelimiter flag does not appear in the data field of the frame (and therefore cause framemisalignment), a technique known as Bit Stuffing is used by both the transmitter and the

receiver.

Address fieldThe first two bytes of the frame after the header flag is known as the address field. Theformat of the address field is as follows:

8 7 6 5 4 3 2 1

SAPI C/R EA1

TEI EA2

LAPD address field

EA1 First Address Extension bit which is always set to 0.C/R Command/Response bit. Frames from the user with this bit set to 0 are

command frames, as are frames from the network with this bit set to 1.Other values indicate a response frame.

EA2 Second Address Extension bit which is always set to 1.TEI Terminal Endpoint Identifier. Valid values are as follows:

0-63 Used by non-automatic TEI assignment user equipment.64-126 Used by automatic TEI assignment equipment.

127 Used for a broadcast connection meant for all TerminalEndpoints.

Control fieldThe field following the Address Field is called the Control Field and serves to identifythe type of the frame. In addition, it includes sequence numbers, control features anderror tracking according to the frame type.

FCSThe Frame Check Sequence (FCS) enables a high level of physical error control byallowing the integrity of the transmitted frame data to be checked. The sequence is first



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calculated by the transmitter using an algorithm based on the values of all the bits in theframe. The receiver then performs the same calculation on the received frame andcompares its value to the CRC.

Windowsize

LAPD supports an extended window size (modulo 128) where the number of possibleoutstanding frames for acknowledgement is raised from 8 to 128. This extension isgenerally used for satellite transmissions where the acknowledgement delay issignificantly greater than the frame transmission times. The type of the link initializationframe determines the modulo of the session and an "E" is added to the basic frame typename (e.g., SABM becomes SABME).

FrametypesThe following are the Supervisory Frame Types in LAPD:

RR Information frame acknowledgement and indication to receive more.

REJ Request for retransmission of all frames after a given sequencenumber.RNR Indicates a state of temporary occupation of station (e.g., window

full).

The following are the Unnumbered Frame Types in LAPD:

DISC Request disconnectionUA Acknowledgement frame.DM Response to DISC indicating disconnected mode.FRMR Frame reject.

SABM Initiator for asynchronous balanced mode. No master/slaverelationship.SABME SABM in extended mode.UI Unnumbered Information.XID Exchange Information.

ISDN Devices

ISDN devices include terminals, terminal adapters (TAs), network-termination devices,line-termination equipment, and exchange-termination equipment. ISDN terminals come

in two types. Specialized ISDN terminals are referred to as terminal equipment type 1(TE1). Non-ISDN terminals, such as DTE, that predate the ISDN standards are referredto as terminal equipment type 2 (TE2). TE1s connect to the ISDN network through afour-wire, twisted-pair digital link. TE2s connect to the ISDN network through a TA. TheISDN TA can be either a standalone device or a board inside the TE2. If the TE2 isimplemented as a standalone device, it connects to the TA via a standard physical-layer interface. Examples include EIA/TIA-232-C (formerly RS-232-C), V.24, and V.35.



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Beyond the TE1 and TE2 devices, the next connection point in the ISDN network is thenetwork termination type 1 (NT1) or network termination type 2 (NT2) device. Theseare network-termination devices that connect the four-wire subscriber wiring to theconventional two-wire local loop. In North America, the NT1 is a customer premisesequipment (CPE) device. In most other parts of the world, the NT1 is part of the network

provided by the carrier. The NT2 is a more complicated device that typically is found indigital private branch exchanges (PBXs) and that performs Layer 2 and 3 protocolfunctions and concentration services. An NT1/2 device also exists as a single device thatcombines the functions of an NT1 and an NT2.

ISDN specifies a number of reference points that define logical interfaces betweenfunctional groups, such as TAs and NT1s. ISDN reference points include the following:

R The reference point between non-ISDN equipment and a TA.

S The reference point between user terminals and the NT2.

T The reference point between NT1 and NT2 devices.

U The reference point between NT1 devices and line-termination equipment in thecarrier network. The U reference point is relevant only in North America, where the NT1function is not provided by the carrier network.

Figure 12-1 illustrates a sample ISDN configuration and shows three devices attached toan ISDN switch at the central office. Two of these devices are ISDN-compatible, so theycan be attached through an S reference point to NT2 devices. The third device (astandard, non-ISDN telephone) attaches through the reference point to a TA. Any of

these devices also could attach to an NT1/2 device, which would replace both the NT1and the NT2. In addition, although they are not shown, similar user stations are attachedto the far-right ISDN switch.

Figure 12-1 Sample ISDN Configuration Illustrates Relationships Between Devices andReference Points



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Services

There are two types of services associated with ISDN:

BRI

PRI

ISDN BRI Service

The ISDN Basic Rate Interface (BRI) service offers two B channels and one D channel(2B+D). BRI B-channel service operates at 64 kbps and is meant to carry user data; BRID-channel service operates at 16 kbps and is meant to carry control and signalinginformation, although it can support user data transmission under certain circumstances.The D channel signaling protocol comprises Layers 1 through 3 of the OSI referencemodel. BRI also provides for framing control and other overhead, bringing its total bitrate to 192 kbps.The BRI physical layer specification is International Telecommunication Union-Telecommunications Standards Section (ITU-T) (formerly the Consultative Committeefor International Telegraph and Telephone [CCITT]) I.430.

ISDN PRI Service

ISDN Primary Rate Interface (PRI) service offers 23 B channels and 1 D channel in North America and Japan, yielding a total bit rate of 1.544 Mbps (the PRI D channel runs



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at 64 kbps). ISDN PRI in Europe, Australia, and other parts of the world provides 30 Bchannels plus one 64-kbps D channel and a total interface rate of 2.048 Mbps. The PRI

physical layer specification is ITU-T I.431.

ISDN Specifications

This section describes the various ISDN specifications for Layer 1, Layer 2, and Layer 3.

Layer 1

ISDN physical layer (Layer 1) frame formats differ depending on whether the frame isoutbound (from terminal to network) or inbound (from network to terminal). Both

physical layer interfaces are shown in Figure 12-2.

The frames are 48 bits long, of which 36 bits represent data. The bits of an ISDN physicallayer frame are used as follows:

F Provides synchronization

L Adjusts the average bit value

E Ensures contention resolution when several terminals on a passive bus contendfor a channel

A Activates devices

S Is unassigned

B1 , B2 , and D Handle user data

Figure 12-2 ISDN Physical Layer Frame Formats Differ Depending on Their Direction



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Multiple ISDN user devices can be physically attached to one circuit. In thisconfiguration, collisions can result if two terminals transmit simultaneously. Therefore,ISDN provides features to determine link contention. When an NT receives a D bit fromthe TE, it echoes back the bit in the next E-bit position. The TE expects the next E bit to

be the same as its last transmitted D bit.

Terminals cannot transmit into the D channel unless they first detect a specific number of ones (indicating "no signal") corresponding to a pre-established priority. If the TE detectsa bit in the echo (E) channel that is different from its D bits, it must stop transmittingimmediately. This simple technique ensures that only one terminal can transmit its Dmessage at one time. After successful D-message transmission, the terminal has its

priority reduced by requiring it to detect more continuous ones before transmitting.Terminals cannot raise their priority until all other devices on the same line have had anopportunity to send a D message. Telephone connections have higher priority than allother services, and signaling information has a higher priority than no signalinginformation.

Layer 2

Layer 2 of the ISDN signaling protocol is Link Access Procedure, D channel (LAPD).LAPD is similar to High-Level Data Link Control (HDLC) and Link Access Procedure,Balanced (LAPB) (see Chapter 16, "Synchronous Data Link Control and Derivatives,"and Chapter 17, "X.25," for more information on these protocols). As the expansion of the LAPD acronym indicates, this layer is used across the D channel to ensure that



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control and signaling information flows and is received properly. The LAPD frameformat (see Figure 12-3) is very similar to that of HDLC; like HDLC, LAPD usessupervisory, information, and unnumbered frames. The LAPD protocol is formallyspecified in ITU-T Q.920 and ITU-T Q.921.

Figure 12-3 LAPD Frame Format Is Similar to That of HDLC and LAPB

The LAPD Flag and Control fields are identical to those of HDLC. The LAPD Addressfield can be either 1 or 2 bytes long. If the extended address bit of the first byte is set, theaddress is 1 byte; if it is not set, the address is 2 bytes. The first Address-field bytecontains the service access point identifier (SAPI), which identifies the portal at whichLAPD services are provided to Layer 3. The C/R bit indicates whether the frame containsa command or a response. The Terminal Endpoint Identifier (TEI) field identifies either asingle terminal or multiple terminals. A TEI of all ones indicates a broadcast.

Layer 3

Two Layer 3 specifications are used for ISDN signaling: ITU-T (formerly CCITT) I.450(also known as ITU-T Q.930) and ITU-T I.451 (also known as ITU-T Q.931). Together,these protocols support user-to-user, circuit-switched, and packet-switched connections.A variety of call-establishment, call-termination, information, and miscellaneousmessages are specified, including SETUP, CONNECT, RELEASE, USER INFORMATION, CANCEL, STATUS, and DISCONNECT. These messages arefunctionally similar to those provided by the X.25 protocol (see Chapter 17 for moreinformation). Figure 12-4, from ITU-T I.451, shows the typical stages of an ISDNcircuit-switched call.

Figure 12-4 An ISDN Circuit-Switched Call Moves Through Various Stages to ItsDestination



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Summary

ISDN is comprised of digital telephony and data-transport services offered by regionaltelephone carriers. ISDN involves the digitization of the telephone network to transmitvoice, data, text, graphics, music, video, and other source material over existingtelephone wires.

ISDN devices include the following:

Terminals



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Terminal adapters (TAs)

Network-termination devices

Line-termination equipment

Exchange-termination equipment

The ISDN specification references specific connection points that define logicalinterfaces between devices.

ISDN uses the following two types of services:

Basic Rate Interface (BRI, which offers two B channels and one D channel (2B+D)

Primary Rate Interface (PRI), which offers 23 B channels and 1 D channel in North

America and Japan, and 30 B channels and 1 D channel in Europe and Australia

ISDN runs on the bottom three layers of the OSI reference model, and each layer uses adifferent specification to transmit data.

Broadband ISDN

The original specifications for the integrated services digital network (ISDN) , were based around voice and non-voice telephone-type services: telephony, data, telex,facsimile, as it was hoped that the ISDN would evolve from the (then) emerging digitaltelephone networks. Indeed, this is one of the reasons that the fundamental element of anISDN link is the 64 Kb/s B-Channels. However, the planning for ISDN was startedaround 1976, and as technology evolved, so did the requirements of the users that wantedto use this technology. In 1988, the CCITT released a document that described a new setof Broadband ISDN (B-ISDN) services. To distinguish this new concept from theoriginal ISDN service, we now refer to the latter as Narrowband ISDN (N-ISDN) .

Broadband ISDN services

The need for a Broadband ISDN service sprung from the growing needs of the customers.The planned Broadband ISDN services can broadly be categorized as follows:



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Interactive services. These are services allowing information flow between twoend users of the network, or between the user and the service provider. Suchservices can be subdivided:

o Conversational services. These are basically end-to-end, real-timecommunications, between users or between a user and a service provider,

e.g. telephone-like services. Indeed, B-ISDN will support N-ISDN typeservices. (Note also that the user-to-user signaling, user-to-network signaling, and inter-echange signaling are also provided but outside our scope.) Also the additional bandwidth offered will allow such services asvideo telephony, video conferencing and high volume, high speed datatransfer.

o Messaging services. This differs from conversational services in that it ismainly a store-and-forward type of service. Applications could includevoice and video mail, as well as multi-media mail and traditionalelectronic mail.

o Retrieval services. This service provides access to (public) information

stores, and information is sent to the user on demand only. This includesthings like tele-shopping, videotex services, still and moving pictures,telesoftware and entertainment.

Distribution services. These are mainly broadcast services, are intended for mainly one way interaction from a service provider to a user:

o No user control of presentation. This would be for instance, a TV broadcast, where the user can choose simply either to view or not. It isexpected that cable TV companies will become interested in BroadbandISDN as a carrier for the high definition TV (HDTV) services that areforseen for the future.

o User controlled presentation. This would apply to broadcast information

that the user can partially control, in that the user can decide which part of it he/she accesses, e.g. teletext and news retrieval services.

Protocol Reference Model

The network is described in terms of a protocol reference model (PRM) (Figure ). Not all of the PRM is fully defined. The main aspects of the model are that it can beviewed in terms of the three planes -- user plane, control plane and management plane --and in terms of the 3 layers -- ATM adaptation layer, ATM layer and the Physical layer.

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Figure: Broadband ISDN protocol reference model

The functions of the layers are as follows:

ATM adaptation layer (AAL). This layer is responsible for mapping the serviceoffered by ATM to the service expected by the higher layers. It has two sublayers.

o Convergence sub layer (CS). Responsible for presenting the ATMservice to the higher layers. The functionality of this sub layer is verymuch dependent on the higher layer service.

o Segmentation and reassembly (SAR). This layer is responsible for, at thetransmitter, splitting the higher level PDU into 48 octet chunks, and at thereceiving side, to reassemble the 48 octet chunks back into the originalPDU.

ATM Layer. This layer is independent of the physical medium over whichtransmission is to take place. It has four functions:

o Generic flow control (GFC) function. This can be used to alleviate shortterm overload conditions above the ATM layer, as it is accessible by theuser.

o Cell header generation and extraction. At the transmitter, adds header information to a cell and at the receiver removes it.

o Cell multiplex and demultiplex. At the transmitter, multiplex cells intoone continuous stream and at the header demultiplex the cells according toVPI and VCI values.

Physical layer. This consists of two sublayers:o Transport Convergence (TC). This sub layer has five functions:

Cell rate decoupling. Insertion and extraction of idle cells.Header error control (HEC) generation and verification. In thetransmitter, generation of the HEC, and in the receiver checking of the HEC. The HEC that is used can detect and correct a 1 bit error and can further detect certain multiple bit errors.Cell delineation. In the receiver, detection of cell boundaries.



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Transmission frame adaptation. Adapts cell flow according tothe payload of the Physical level frame being used, e.g. for SDH.Transmission frame generation and recovery. At thetransmitter, generates Physical level frames, and at the receiver,extracts the ATM cells from the Physical level frame.

o

Physical medium (PM). This contains two sublayers:Bit timing. Insertion and extraction of bit timing information andgeneration and reception of waveforms.Physical medium. Bit transmission, bit alignment and opticalelectrical conversion, if required. (The physical medium need not

be optical, at least for transmission rates of 155Mb/s and lower.)

This (sub-) layering of the PRM is depicted in Figure .

Figure: Broadband ISDN layer functionality

The management plane consists of two functions to perform layer management andplane management . The plane management is not layered as the other layers are. This is

because it relies needs information on all aspects of the the system to providemanagement facilities for the systems as a whole. The layer management providesinformation and control facilities for the protocol entities that exists in each individuallayer. This includes operation and maintenance (OAM) functions for each layer.

The control plane is responsible for the supervision of connections, including call set-up,call release and maintenance.

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The user plane provides for the transfer of user information. It also includes mechanismsto perform error recovery, flow control etc.

Broadband ISDN intends to offer many Mb/s to the user, but intends to remain backwards compatible with Narrowband ISDN. Indeed, the Narrowband services will

eventually need to be offered over the global Broadband network to come. To this extentthe user interface to Broadband ISDN is very similar to that for Narrowband ISDN.Figure shows the position of the user to network interface (UNI) , as well as theinternal network to network interface (NNI) for BISDN.

Figure: Broadband ISDN user and network interfaces

Figure: Broadband ISDN UNI configuration reference points

Note that in Figure , it is expected that Narrowband ISDN (or even other PSTN)equipment will be able to connect to the Broadband network via a suitable terminaladaptor. The various functional groups are now described:

B-NT1. This group contains functions that are considered to be part of OSI layer 1. It represents the physical connection point to the network, i.e. the socket on thewall. It includes functions such as:

o Line transmission termination. Provision of the physical connection.o Transmission interface handling. The interface to the transmission

channel, be it electrical or optical.

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o Operation and Maintenance (OAM). This is not normally associatedwith the socket in the wall. However, it is expected that for B-ISDN, moresophisticated management capabilities will be required than at present.

B-NT2. This group contains OSI layer 1 and higher OSI layer functions:o Adaptation functions. For different physical media and network

topologies.o Multiplexing and demultiplexing. The user data may be sent and

received on several VCCs and VPCs.o Buffering. User data may be sent and/or received at varying rates with

respect to the B-ISDN user and the network.o Signaling. VCCs/VPCs must be established, controlled and released.o Interface. Interaction with the B-ISDN user.

B-TE1. Equipment requiring B-ISDN access. B-TA. Equipment allowing connection of other B-ISDN, N-ISDN and non-ISDN

equipment. B-TE2. B-ISDN with special interface needs or N-ISDN equipment.

TE2. Non-ISDN equipment.

Note that these are logical units. The physical implementation may be quite different. For instance, it may be common to find the following in the same physical unit, depending onneed: B-NT1 and B-NT2; B-TE1 and B-NT2; B-TA and B-TE2 etc.

Further, the way in which the terminal equipment is connected to the user-to-network interface via B-NT1/B-NT2 is not restricted with respect to local topologies (Figure).



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Figure: Broadband ISDN multiple interface configurations

The B-NT2 equipment is considered to be the customer premisis equipment (CPN)(Figure). This could in real terms be an private branch exchange (PBX) or other localswitch.



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Figure: B-ISDN customer premisis network configuration

The discussion above has mentioned the OSI reference model. This was developed incollaboration between the ISO and the (then) CCITT. It seems surprising therefore thatthere is no defined relationship between the B-ISDN PRM and the OSI reference model.Figure is the author's view of the relationship between the two.

Figure: Broadband ISDN PRM compared with OSI model

As there is unlikely to be a user interface directly to the AAL, included in this figure arethe interfaces to the service classes defined by the ATM Forum for the UNI:

Constant bit rate (CBR). The CBR service offers a very simple, reliableguaranteed channel that effectively acts as circuit emulation. The QoS of thisservice must be maintained throughout the lifetime of a CBR connection, as thedata rate is expected to be constant. It is intended for use by applications withstringent real-time constraints on delay and jitter, e.g.\ real-time video.

Variable bit rate (VBR). This service is also intended for use by by real-timeapplications. However, it differs from CBR in that it does not expect the data rateto be constant, i.e. the sources may use variable bit rate coding for efficiency andalso be statistically multiplexed.

Available bit rate (ABR). This service class offers the B-ISDN user some degreeof fairness, and also control of loss or delay with respect to QoS, but is intendedfor non real-time applications. It is likely that ABR QoS statements will specifythat there are minimum acceptable parameters, but that if better QoS should



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become available then it will be used. ABR is intended for use by unit-orientedapplications such as database access and electronic mail.

Unspecified bit rate (UBR). UBR is intended for applications that send data verysporadically and the use of CBR, VBR or ABR would be wasteful of resources. Infact, this service class is effectively a best-effort approach which is similar to

today's IP. Applications that use this service would have non-real timerequirements and not be too sensitive to loss, e.g. file transfers.

Asynchronous Transfer Mode (ATM)

Is a cell relay, packet switching network and data link layer protocol which encodes datatraffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ATM provides data link layer services that run over Layer 1 links. This

differs from other technologies based on packet-switched networks (such as the InternetProtocol or Ethernet), in which variable sized packets (known as frames whenreferencing layer 2) are used. ATM is a connection-oriented technology, in which alogical connection is established between the two endpoints before the actual dataexchange begins.

The Asynchronous Transfer Mode (ATM) composes a protocol suite which establishes amechanism to carry all traffic on a stream of fixed 53-byte packets (cells). A fixed-size

packet can ensure that the switching and multiplexing function could be carried outquickly and easily. ATM is a connection-oriented technology, i.e.; two systems on thenetwork should inform all intermediate switches about their service requirements and

traffic parameters in order to establish communication.

The ATM reference model, which has two forms - one for the user-to-network interface(UNI) and the other for the network-to-node interface (NNI), is divided into three layers:the ATM adaptation layer (AAL), the ATM layer, and the physical layer. The AALinterfaces the higher layer protocols to the ATM Layer, which relays ATM cells bothfrom the upper layers to the ATM Layer and vice versa. When relaying informationreceived from the higher layers, the AAL segments the data into ATM cells. Whenrelaying information received from the ATM Layer, the AAL must reassemble the

payloads into a format the higher layers can understand. This is called Segmentation andReassembly (SAR). Different AALs are defined in supporting different types of traffic or

service expected to be used on ATM networks.

The ATM layer is responsible for relaying cells from the AAL to the physical layer for transmission and from the physical layer to the AAL for use at the end systems, itdetermines where the incoming cells should be forwarded to, resets the correspondingconnection identifiers and forwards the cells to the next link, as well as buffers cells, andhandles various traffic management functions such as cell loss priority marking,



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congestion indication, and generic flow control access. It also monitors the transmissionrate and conformance to the service contract (traffic policing).

The physical layer of ATM defines the bit timing and other characteristics for encodingand decoding the data into suitable electrical/optical waveforms for transmission and

reception on the specific physical media used. In addition, it also provides frameadaptation function, which includes cell delineation, header error check (HEC) generationand processing, performance monitoring, and payload rate matching of the differenttransport formats used at this layer. SONET , DS3, Fiber, twisted-pair are few mediaoften used at the physical layer.

ATM Model

The ATM model's primary layers are the physical layer, the ATM layer, and the ATM

Adaptation layer. Each layer and sublayer is described in more detail in the followingsections.

Physical Layer

The physical layer provides for the transmission and reception of ATM cells across a physical medium between two ATM devices; this can be a transmission between an ATMendpoint and an ATM switch, or it can be between two ATM switches. The physicallayer is subdivided into a Physical Medium Dependent sublayer and TransmissionConvergence sublayer.

Top of page

PMD Sublayer

The Physical Medium Dependent (PMD) sublayer is responsible for the transmission andreception of individual bits on a physical medium. These responsibilities encompass bittiming, signal encoding, interacting with the physical medium, and the cable or wireitself.

ATM does not rely on any specific bit rate, encoding scheme or medium and variousspecifications for ATM exist for coaxial cable, shielded and unshielded twisted pair wire,

and optical fiber at speeds ranging from 64 kilobits per second to 9.6 gigabits per second.In addition, the ATM physical medium can extend up to 60 kilometers or more usingsingle-mode fiber and long-reach lasers, so it can readily support campus-wideconnectivity and even private metropolitan area networks (MANs). The independence of ATM from a particular set of hardware constraints has allowed it to be implemented over radio and satellite links.

http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/intwork/indc_atm_fvsb.mspx#tophttp://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/intwork/indc_atm_fvsb.mspx#tophttp://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/intwork/indc_atm_fvsb.mspx#top


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Transmission Convergence Sublayer

The Transmission Convergence (TC) sublayer functions as a converter between the bitstream of ATM cells and the Physical Medium Dependent sublayer. When transmitting,the TC sublayer maps ATM cells onto the format of the Physical Medium Dependent

sublayer (such as DS-3 or SONET frames). Because a continuous stream of bytes isrequired, unused portions of the ATM cell stream are "filled" by idle cells. These idlecells are identified in the ATM header and are silently discarded by the receiver. They arenever passed to the ATM layer for processing.

The TC sublayer also generates and verifies the Header Error Control (HEC) field for each cell. On the transmitting side, it calculates the HEC and places it in the header. Onthe receiving side, the TC sublayer checks the HEC for verification. If a single bit error can be corrected, the bit is corrected and the results are passed to the ATM layer. If theerror cannot be corrected (as in the case of a multi-bit error) the cell is silently discarded.

Finally, the TC sublayer delineates the ATM cells, marking where ATM cells begin andwhere they end. The boundaries of the ATM cells can be determined from the PhysicalMedium Dependent layer formatting or from the incoming byte stream using the HECfield. The PMD performs the HEC validation per byte on the preceding 4 bytes. If it findsa match, the next ATM cell boundary is 48 bytes away (corresponding to the ATM

payload). The PMD performs this verification several times to ensure that the cell boundaries have been determined correctly.

The ATM Layer

The ATM layer provides cell multiplexing, demultiplexing, and VPI/VCI routing

functions. The ATM layer also supervises the cell flow to ensure that all connectionsremain within their negotiated cell throughput limits. If connections operate outside their negotiated parameters, the ATM layer can take corrective action so the misbehavingconnections do not affect connections that are obeying their negotiated connectioncontract. The ATM layer also maintains the cell sequence from any source.

The ATM layer multiplexes and demultiplexes and routes ATM cells, and ensures their sequence from end to end. However, if a cell is dropped by a switch due to congestion or corruption, it is not the ATM layer's responsibility to correct the dropped cell throughretransmission or to notify other layers of the dropped cell. Layers above the ATM layer must sense the lost cell and decide whether to correct it or disregard it.

In the case of interactive voice or video, a lost cell is typically disregarded because itwould take too long to resend the cell and place it in the proper sequence to reconstructthe audio or video signal. A significant number of dropped cells in time-dependentservices, such as voice or video, results in a choppy audio or video playback, but theATM layer cannot correct the problem unless a higher Quality of Service is specified for the connection.



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In the case of data (such as a file transfer), the upper layer application must sense theabsence of the cell and retransmit it. A file with missing 48-bytes chunks here and thereis a corrupted file that is unacceptable to the receiver. Because operations such as filetransfers are not time dependent, the contents of the cell can be recovered by incurring adelay in the transmission of the file corresponding to the recovery of the lost cell.

ATM Layer Multiplexing and Demultiplexing

ATM layer multiplexing blends all the different input types so that the connection parameters of each input are preserved. This process is known as traffic shaping.

ATM layer demultiplexing takes each cell from the ATM cell stream and, based on theVPI/VCI, either routes it (for an ATM switch) or passes the cell to the ATM AdaptationLayer (AAL) process that corresponds to the cell (for an ATM endpoint).

ATM Adaptation Layers

The ATM Adaptation Layers (AAL) are responsible for the creation and reception of 48- byte payloads through the lower layers of ATM on behalf of different types of applications. Though there are five different types of AALs, Windows 2000 supportsonly AAL5. ATM Adaptation is necessary to link the cell-based technology at the ATMLayer to the bit-stream technology of digital devices (such as telephones and videocameras) and the packet-stream technology of modern data networks (such as FrameRelay, X.25 or LAN protocols such as TCP/IP or Ethernet).

The five different AALs each provide a distinct class of service:

AAL0 AAL0 is user-defined, or No AAL, meaning that no AAL layer is used. In allother AAL types, some delineation of the data segment is included at the AAL level

before the segment is made into cells. This affects how the data is passed up to the ATMlayer. With AAL5, the data is not passed up until a complete AAL segment is received.With AAL0, for example, there is no delineation or synchronization, so individual cellsare passed up as they are received, or the adapter might optimize and accrue a certainamount before indicating that a cell can be passed along.

AAL1 AAL1 provides circuit emulation over an ATM network. This requires constant

bit rate, time-dependent service. To provide this, AAL1 adds timestamps, error checkingand sequencing to the data payload. Additional functionality is provided in AAL1 to loadthe 48-byte cell payload with multiple smaller-than-48-byte samples, as is usuallyrequired with voice streams. Due to its high overhead, AAL1 is used only when thesefeatures are required. This format is most commonly used with voice or videoapplications.



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AAL2 AAL2 is a mechanism that allows the transfer of high-speed, variable bit rateinformation in an isochronous, connection-oriented manner. Unlike AAL1, AAL2 isdesigned to use bandwidth only when data is sent. AAL2 has never been fully defined bythe standards committee and did not gained wide acceptance. It has largely beensupplanted by AAL5.

AAL3/4 AAL3/4 combines two once-separate AAL specifications. AAL3 was intendedfor the framing of connection-oriented protocols, while AAL4 was intended for theframing of connectionless protocols. While pursuing these two standards, the ATMstandards bodies learned that there was no difference in the framing between the twotypes of protocols; therefore, they combined the two separate framing methods to createAAL3/4. This AAL adds information to the payload regarding segment size, sequencing,and ordering control. However, AAL 3/4 is rarely used because of the high overheadrequired; AAL5 provides the same services with minimal overhead.

AAL5 AAL5 provides a way for non-isochronous, variable bit rate, connectionless

applications to send and receive data. AAL5 was developed as a way to provide a moreefficient transfer of network traffic than AAL3/4. AAL5 merely adds a trailer to the payload to indicate size and provide error detection. AAL5 is the AAL of choice whensending connection-oriented or connectionless LAN protocol traffic over an ATMnetwork. Windows 2000 supports AAL5.

Bluetooth Technology



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In an attempt to standardize data transfer and synchronization between disparate mobiledevices in the short-distance range , Intel and Microsoft established in 1998 a major industry consortium that included IBM, Toshiba, Ericsson, Nokia, and PumaTechnology.

Code-named Blue Tooth for the 10th century Danish king who unified Denmark, thecompanies have created a single synchronization protocol to address end-user problemsarising from the proliferation of various mobile devices -- including smart phones, smart

pagers, PDAs, handheld PCs, copiers, printers, notebooks, and many future digitalappliances at home -- that need to keep data consistent from one device to another.

The proposed Bluetooth solutions (hardware and software-based) would automaticallysynchronize mobile devices when end-users enter their offices or home. Intel and othersare designing the sending and receiving radio frequency chip sets. Price point for hardware is in $5-20 range eventually.

Since the start of this initiative in 1998, interest in Bluetooth has grown tremendously -signified by 1800 members of Bluetooth consortium by mid 2000.

While Bluetooth consortium demonstrated prototype products in the 1999-2000, there areno production-quality end-user products using blue tooth technology as of now, as far aswe know. Component products (radios and chips) that can be integrated into finished

products have started becoming available from Ericsson and others. However, here is anopportunity for more start-up companies. irDA is a competing technology and has beenimplemented in many products for over 6-7 years now but Bluetooth has a few distinctadvantages - with Ericsson/Microsoft/Intel team behind it. In our opinion, there arerelative benefits with several competing technologies - there is some overlap too. Let

competitive products thrive so that we the users get the best solutions.How does Blue Tooth compare to irDA - a competitive (or complimentary) technology?Click here for a vendor viewpoint by Counterpoint division of Extended Systems.

Bluetooth is actually a standard for wireless communications between devices in a personal area network (PAN) using radio frequency for a short range (around 10 meters).So any two devices that follow the standard can communicate and exchange data betweeneach other without the need of any connection to be made between them. A group of Bluetooth devices like a mobile phone, a digital camera, a hand held device etc. caninstantly form a network with each other as soon as they are switched on. You could havea mobile phone in your pocket and you could be sending e-mails using your laptopwithout making any connection between your laptop and the mobile. Your refrigerator could be placing an order with the supermarket if your milk supply has been exhaustedusing your mobile phone.

Briefly, Bluetooth technology

uses radio waves in 2.4 GHz band - therefore, no line of sight is required



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supports multipoint, not just point to point works in a small confined area - 10 to 15 meters apart is able to support speeds of 1-2 Mbps today but will offer higher speeds in future chip sets are relatively inexpensive (though more expensive than IrDA)- $10 to

$20 today in large quantities - will go down in future

has significant industry support with over 1800 members in the industryconsortium

Bluetooth is a high-speed, low-power microwave wireless link technology, designed toconnect phones, laptops, PDAs and other portable equipment together with little or nowork by the user. Unlike infra-red, Bluetooth does not require line-of-sight positioning of connected units. The technology uses modifications of existing wireless LAN techniques

but is most notable for its small size and low cost. The current prototype circuits arecontained on a circuit board 0.9cm square, with a much smaller single chip version indevelopment. The cost of the device is expected to fall very fast, from $20 initially to $5in a year or two. It is envisioned that Bluetooth will be included within equipment rather

than being an optional extra. When one Bluetooth product comes within range of another,(this can be set to between 10cm and 100m) they automatically exchange address andcapability details. They can then establish a 1 megabit/s link (up to 2 Mbps in the secondgeneration of the technology) with security and error correction, to use as required. The

protocols will handle both voice and data, with a very flexible network topography.

This technology achieves its goal by embedding tiny, inexpensive, short-rangetransceivers into the electronic devices that are available today. The radio operates on theglobally-available unlicensed radio band, 2.45 GHz (meaning there will be no hindrancefor international travelers using Bluetooth-enabled equipment.), and supports data speedsof up to 721 Kbps, as well as three voice channels. The Bluetooth modules can be either

built into electronic devices or used as an adaptor. For instance in a PC they can be builtin as a PC card or externally attached via the USB port.

Each device has a unique 48-bit address from the IEEE 802 standard. Connections can be point-to-point or multipoint. The maximum range is 10 meters but can be extended to 100meters by increasing the power. Bluetooth devices are protected from radio interference

by changing their frequencies arbitrarily up to a maximum of 1600 times a second, atechnique known as frequency hopping. They also use three different but complimentaryerror correction schemes. Built-in encryption and verification is provided.



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Moreover, Bluetooth devices won't drain precious battery life. The Bluetoothspecification targets power consumption of the device from a "hold" mode consuming 30micro amps to the active transmitting range of 8-30 milliamps (or less than 1/10th of awatt). The radio chip consumers only 0.3mA in standby mode, which is less than 3 % of the power used by a standard mobile phone. The chips also have excellent power-saving

features, as they will automatically shift to a low-power mode as soon as traffic volumelessens or stops.

Bluetooth devices are classified according to three different power classes, as shown inthe following table.

Power Class Maximum Output Power

1 100 mW (20 dBm)

2 2.5 mW (4 dBm)

3 1 mW (0 dBm)

But beyond untethering devices by replacing the cables, Bluetooth radio technology provides a universal bridge to existing data networks, a peripheral interface, and amechanism to form small private ad hoc groupings of connected devices away from fixednetwork infrastructures. Designed to operate in a noisy radio frequency environment, theBluetooth radio uses a fast acknowledgment and frequency hopping scheme to make thelink robust. Bluetooth radio modules avoid interference from other signals by hopping toa new frequency after transmitting or receiving a packet. Compared with other systemsoperating in the same frequency band, the Bluetooth radio typically hops faster and usesshorter packets. This makes the Bluetooth radio more robust than other systems. Short

packages and fast hopping also limit the impact of domestic and professional microwave

ovens. Use of Forward Error Correction (FEC) limits the impact of random noise onlong-distance links. The encoding is optimized for an uncoordinated environment.

Bluetooth guarantees security at the bit level. Authentication is controlled by the user byusing a 128 bit key. Radio signals can be coded with 8 bits or anything up to 128 bits.The Bluetooth radio transmissions will conform to the safety standards required by thecountries where the technology will be used with respect to the affects of radiotransmissions on the human body. Emissions from Bluetooth enabled devices will be nogreater than emissions from industry-standard cordless phones. The Bluetooth modulewill not interfere or cause harm to public or private telecommunications network.

The Bluetooth base band protocol is a combination of circuit and packet switching. Slotscan be reserved for synchronous packets. Each packet is transmitted in a different hopfrequency. A packet nominally covers a single slot, but can be extended to cover up tofive slots. Bluetooth can support an asynchronous data channel, up to three simultaneoussynchronous voice channels, or a channel, which simultaneously supports asynchronousdata and synchronous voice. It is thus possible to transfer the date asynchronously whilstat the same time talking synchronously at the same time. Each voice channel supports 64kb/s synchronous (voice) link. The asynchronous channel can support an asymmetric link



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of maximally 721 kb/s in either direction while permitting 57.6 kb/s in the returndirection, or a 432.6 kb/s symmetric link.

ModesofoperationAn interesting aspect of the technology is the instant formation of networks once the

Bluetooth devices come in range to each other. A piconet is a collection of devicesconnected via Bluetooth technology in an ad hoc fashion. A Piconet can be a simpleconnection between two devices or more than two devices. Multiple independent andnon-synchronized piconets can form a scatternet. Any of the devices in a piconet can also

be a member of another by means of time multiplexing. i.e a device can be a part of morethan one piconet by suitably sharing the time. The Bluetooth system supports both point-to-point and point-to-multi-point connections. When a device is connected to another device it is a point to point connection. If it is connected to more that one (up to 7 ) it is a

point to multipoint connection. Several piconets can be established and linked together adhoc, where each piconet is identified by a different frequency hopping sequence. Allusers participating on the same piconet are synchronized to this hopping sequence. If a

device is connected to more than one piconet it communicates in each piconet using adifferent hopping sequence. A piconet starts with two connected devices, such as a portable PC and cellular phone, and may grow to eight connected devices. All Bluetoothdevices are peer units and have identical implementations. However, when establishing a

piconet, one unit will act as a master and the other(s) as slave(s) for the duration of the piconet connection. In a piconet there is a master unit whose clock and hopping sequenceare used to synchronize all other devices in the piconet. All the other devices in a piconetthat are not the master are slave units. A 3-bit MAC address is used to distinguish

between units participating in the piconet. Devices synchronized to a piconet can enter power-saving modes called sniff and hold mode, in which device activity is lowered.Also there can be parked units which are synchronized but do not have a MAC addresses.

These parked units have a 8 bit address, therefore there can be a maximum of 256 parkeddevices.



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Voice channels use either a 64 kbps log PCM or the Continuous Variable Slope DeltaModulation (CVSD) voice coding scheme, and never retransmit voice packets. The voicequality on the line interface should be better than or equal to the 64 kbps log PCM. TheCVSD method was chosen for its robustness in handling dropped and damaged voicesamples. Rising interference levels are experienced as increased background noise: evenat bit error rates up 4%, the CVSD coded voice is quite audible.

What are the Applications?(Major Portion of Content Provided by Puneet Gupta - a MobileInfo.Com TechnologyWriter)

Bluetooth has a tremendous potential in moving and synchronizing information in alocalized setting. Potential for Bluetooth applications is huge, because we transact

business and communicate more with people who are close by than with those who arefar away - a natural phenomenon of human interaction. The following list represents onlya small set of potential applications - in future many more imaginative applications willcome along:

By installing a Bluetooth network in your office you can do away with thecomplex and tedious task of networking between the computing devices, yet havethe power of connected devices. No longer would you be bound to fixed locationswhere you can connect to the network. Each Bluetooth device could be connectedto 200 other devices making the connection of every device with every other

possible. Since it supports both point to point and point to multipoint it willvirtually make the maximum number of simultaneously linked devices unlimited.



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The Bluetooth technology connects all your office peripherals wirelessly. Connectyour PC or notebook to printers, scanners and faxes without the ugly and troublesome cable attachments. You can increase your freedom by connecting your mouse or the keyboard wirelessly to your computer.

If your digital cameras in Bluetooth enabled, you can send still or video imagesfrom any location to any location without the hassle of connecting your camera tothe mobile phone on the wire line phone.

Bluetooth allows us to have three way phones. At home, your phone functions asa portable phone (fixed line charge). When you're on the move, it functions as amobile phone (cellular charge). And when your phone comes within range of another mobile phone with built-in Bluetooth wireless technology it functions as awalkie-talkie (no telephony charge).

In meetings and conferences you can transfer selected documents instantly with

selected participants, and exchange electronic business cards automatically,without any wired connections.

Connect your wireless headset to your mobile phone, mobile computer or anywired connection to keep your hands free for more important tasks when you're atthe office or in your car.

Have automatic synchronization of your desktop, mobile computer, notebook (PC-PDA and PC-HPC) and your mobile phone. For instance, as soon as youenter your office the address list and calendar in your notebook will automatically

be updated to agree with the one in your desktop, or vice versa.

Automatic Message Delivery: Compose e-mails on your portable PC while you'reon an airplane. As soon as you've landed and switched on your mobile phone, allmessages are immediately sent.

Upon arriving at your home, the door automatically unlocks for you, the entryway lights come on, and the heat is adjusted to your pre-set preferences.

IBM researchers are working on a number of personal devices like a Watch Padthat could be connected with other devices through Bluetooth. The Watch Pad isvery thin and contains 8MB of RAM. They are also working on a version of

CyberPhone called CyberPhone - that can project data onto a small mirror. TheCyberPhone can show as much information as a small PDA because of highresolution VGA screen.

You enter the airport-waiting lounge, equipped with Bluetooth-enabled Internet ports.Via the ports, you and other guests use Bluetooth-enabled laptops, PDAs, and other devices to access your office or home-based servers via the airline server. Using voice-over IP, you also make "free" Internet voice calls courtesy of your airline.



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The WAP Model

The WAP programming model (Figure 2) is the WWW programming model with a fewenhancements. Adopting the WWW programming model provides several benefits to theapplication developer community, including a familiar programming model, a provenarchitecture, and the ability to leverage existing tools (e.g., Web servers, XML tools,etc.). Optimizations and extensions have been made in order to match the characteristicsof the wireless environment. Wherever possible, existing standards have been adopted or have been used as the starting point for the WAP technology. The most significantenhancements WAP has added to the programming model are: Push

Telephony Support (WTA)

Figure 2. WAP Programming Model

The classical request-response mechanism is commonly referred to as pull to contrast itwith the push mechanism.WAP content and applications are specified in a set of well-known content formats based on the familiar WWW content formats. Content istransported using a set of standard communication protocols based on the WWWcommunication protocols. The WAP microbrowser in the wireless terminal co-ordinatesthe user-interface and is analogous to a standard web browser.

WAP defines a set of standard components that enable communication between mobileterminals and network servers, including: Standard naming model WWW-standard URLs are used to identify WAP content onorigin servers. WWWstandard URIs are used to identify local resources in a device, e.g.call control functions. Content typing All WAP content is given a specific type consistent with WWWtyping. This allows WAP user agents to correctly process the content based on its type.



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Standard content formats WAP content formats are based on WWW technology andinclude display markup, calendar information, electronic business card objects, imagesand scripting language. Standard communication protocols WAP communication protocols enable thecommunication of browser requests from the mobile terminal to the network web server.

The WAP content types and protocols have been optimised for mass market, hand-heldwireless devices.

Feature/Performance-Enhancing Proxies

WAP utilizes proxy technology to optimise and enhance the connection between thewireless domain and the WWW. The WAP proxy may provide a variety of functions,including:

Protocol Gateway The protocol gateway translates requests from a wireless protocolstack (e.g., the WAP 1.x stackWSP, WTP, WTLS, and WDP) to the WWW protocols(HTTP and TCP/IP). The gateway also performs DNS lookups of the servers named bythe client in the request URLs.

Content Encoders and Decoders The content encoders can be used to translate WAPcontent into a compact format that allows for better utilisation of the underlying link dueto its reduced size.

User Agent Profile Management User agent profiles describing client capabilities and

personal preferences [UAProf] are composed and presented to the applications.

Caching Proxy A caching proxy can improve perceived performance and network utilisation by maintaining a cache of frequently accessed resources.

This infrastructure ensures that mobile terminal users can access a wide variety of Internet content and applications, and that application authors are able to build contentservices and applications that run on a large base of mobile terminals.



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The WAP proxy allows content and applications to be hosted on standard WWW serversand to be developed using proven WWW technologies such as CGI scripting.While the nominal use of WAP will include a web server, WAP proxy and WAP client,the WAP architecture can quite easily support other configurations.

Supporting Servers

Figure 4. Supporting Services

The WAP Architecture also includes supporting servers, which provide services todevices, proxies, and applications as needed. These services are often specific in function,

but are of general use to a wide variety of applications.The supporting servers defined by the WAP Forum include, but are not limited to:

PKI PortalThe PKI Portal (shown in Figure 4) [WPKI] allows devices to initiate thecreation of new public key certificates.

UAProf ServerThe UAProf Server [UAProf] allows applications to retrieve the clientcapabilities and personal profiles of user agents and individual users.

Provisioning ServerThe Provisioning Server [ProvArch] is trusted by the WAPdevice to provide its provisioning information.



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WAP Network Elements

A typical WAP network is shown in Figure 5.

Figure 5. Example WAP Network

WAP clients communicate with application servers through a number of different proxiesor directly. WAP clients support the proxy selection mechanism that allows them to

utilise the most appropriate proxy for a given service or to connect directly to that serviceas necessary. Proxies can be used to augment a request. They translate between WAPand WWW protocols (HTTP, TCP), thereby allowing the WAP client to submit requeststo the origin server.Proxies may be located in a number of places, including wireless carriers or independentservice providers in order to provide feature enhancements coupled to the wirelessnetwork (e.g., telephony, location and provisioning) or to optimise the communication

between device and application server (e.g., protocol translation and cookie caching).Proxies may be located in a secure network to provide a secure channel between wirelessdevice and the secure network.In some instances, the device might make direct connections to application servers, for

example to provide a secure connection directly between the device and applicationserver.The supporting servers provide support functions required by or generally useful todevices, proxies, and application servers. These functions include Provisioning, PKI, user agent profiles, etc.

Device Architecture



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Figure 6. WAP Client Architecture

The architecture for WAP devices is shown in Figure 6. The Application Framework provides the device execution environment for WAP applications. WAP applications arecomprised of markup, script, style sheets and multimedia content, all of which arerendered on the device. The WAP Application Environment (WAE) processing model

defines the structure in which these various forms of executable and non-executablecontent interact. The network protocols on the WAP client are shared between client andserver. They are described in further detail below. Content renderers interpret specificforms of content and present them to the end user for perusal or interaction.Common functions are defined to be utilised by the application framework, including

persistence and data synchronisation.The Wireless Identity Module (WIM), as specified in [WIM], contains the identity of thedevice and the cryptographic means to mutually authenticate WAP devices and servers.The architecture also provides a mechanism to access external functions that areembedded or attached to the devices via the External Functionality Interface (EFI).

Security Model

WAP enables a flexible security infrastructure that focuses on providing connectionsecurity between a WAP client and server.WAP can provide end-to-end security between protocol endpoints. If a browser andorigin server desire end-to-end security, they can communicate directly using the security

protocols. Moreover, the WAP specifications include support for application-levelsecurity, such as signed text.

Components of the WAP Architecture



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Figure 7. WAP Stack Architecture

The WAP architecture provides a scaleable and extensible application development

environment for mobile communication devices. This is achieved through a layereddesign of the protocol stack (Figure 7). Each layer provides a set of functions and/or services to other services and applications through a set of well-defined interfaces. Eachof the layers of the architecture is accessible by the layers above, as well as by other services and applications.The WAP architecture separates service interfaces from the protocols that provide thoseservices to allow for evolution of the specifications and selection of the most appropriate

protocol for a given context. Many of the services in the stack may be provided by morethan one protocol. For example, either HTTP [RFC2616] or WSP [WSP] may providethe Hypermedia Transfer service.

Bearer Networks

Protocols have either been designed or selected to operate over a variety of different bearer services, including short message, circuit-switched data, and packet data. The bearers offer differing levels of quality of service with respect to throughput, error rate,and delays. The protocols are designed to compensate for or tolerate these varying levelsof service.



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Since the Transport Services layer provides the interface between the bearer service andthe rest of the WAP stack, the transport specifications (e.g., [WDP]) may list the bearersthat are supported and the techniques used to allow the protocols to run over each bearer.The list of supported bearers will change over time with new bearers being added asthe wireless market evolves.

Transport Services

The Transport Services layer offers a set of consistent services to the upper layer protocols and maps those services to the available bearer services. The TransportServices transport unstructured data across the underlying bearer networks.These transport services create a common abstraction that is consistent across all the

bearers. The Transport Services include, but are not limited to:

Datagrams The datagram service provides data transport in which self-contained,independent entities of data carry sufficient information to be routed from the source to

the destination computer without reliance on earlier exchanges between this source anddestination computer and the transporting network. UDP (User Datagram Protocol)[STD0006] and WDP (Wireless Datagram Protocol) [WDP] are two protocols used to

provide the datagram transport service in the WAP architecture.

Connections The connection service provides data transport service in whichcommunication proceeds in three well-defined phases: connection establishment, two-way reliable data transfer and connection release. TCP (Transmission Control Protocol)[STD0007] is a protocol used to provide the connection transport service of IP1 bearersfor the WAP architecture. In order to cope with the wireless network characteristics, theTCP protocol can be profiled for its use, see [WP-TCP].

Transfer Services

The Transfer Services provide for the structured transfer of information between network elements. The Transfer Services include, but are not limited to: Hypermedia Transfer The hypermedia transfer services provides for the transfer of self-describing hypermedia resources. The combination of WSP (Wireless SessionProtocol) [WSP] and WTP (Wireless Transaction Protocol) [WTP] provide thehypermedia transfer service over secure and non-secure datagram transports. The HTTP(Hypertext Transfer Protocol) [RFC2616] provides the hypermedia transfer service over secure and non-secure connection-oriented transports.

Streaming The streaming services provide a means for transferring isochronous datasuch as audio and video.

Message Transfer The message transfer services provide the means to transfer asynchronous multimedia messages such as email or instant messages. MMSEncapsulation [MMSEncapsulation] is a protocol used to transfer messages betweenWAP devices and MMS servers.



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Session Services

The session services provide for the establishment of shared state between network elements that span multiple network requests or data transfers. For example, the Push

session establishes that the WAP Device is ready and able to receive pushes from thePush Proxy.The Session Services include, but are not limited to:

Capability Negotiation The WAP architecture includes specifications for describing,transmitting, and managing capabilities and preference information about the client, user,and network elements. See [UAProf] for more information. This allows for customisationof information and content returned by the origin server or pushed by the application.

Push-OTA The Push-OTA (Over The Air) session service provides for network-initiated transactions to be delivered to wireless devices that are intermittently able to

receive data (e.g., modal devices and devices with dynamically assigned addresses). ThePush-OTA service operates over the connection-oriented transport service and datagramtransport [PushOTA].

Sync The Sync service provides for the synchronisation of replicated data.1 Utilisation of TCP connections over IP may require additional components of theTCP/IP protocol suite. One example for such a component is ICMP.

Cookies The Cookies service allows applications to establish state on the client or proxy that survives multiple hypermedia transfer transactions. See [HTTP State] for moreinformation.

Application Framework

The Application Framework provides a general-purpose application environment basedon a combination of World Wide Web (WWW), Internet and Mobile Telephonytechnologies. The primary objective of the Application Framework is to establish aninteroperable environment that will allow operators and service providers to buildapplications and services that can reach a wide variety of different wireless platforms inan efficient and useful manner. The Application Frame work includes, but is not limitedto: WAE/WTA User-Agent WAE is a micro-browser environment containing or allowingfor markup (including WML and XHTML), scripting, style-sheet languages, andtelephony services and programming interfaces, all optimised for use in hand-held mobileterminals. See [WAE] for more information. Push The Push service provides a general mechanism for the network to initiate thetransmission of data to applications resident on WAP devices. See [PushArchOverview]for more information.



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Multimedia Messaging The Multimedia Message Service (MMS) provides for thetransfer and processing of multimedia messages such as email and instant messages toWAP devices. Content Formats The application framework includes support for a set of well-defineddata formats, such as color images, audio, video, animation, phone book records, and

calendar information.

Security Services

Security forms a fundamental part of the WAP Architecture, and its services can be foundin many of its layers. In general the following security facilities offered are:

Privacy facilities to ensure that communication is private and cannot be understood by any intermediate parties that may have intercepted it.

Authentication facilities to establish the authenticity of parties to the communication.

Integrity facilities to ensure that communication is unchanged and uncorrupted.

Non-Repudiation facilities to ensure parties to a communication cannot deny thecommunication took place.

The Security Services span all the various layers of the WAP Architecture. Some specificexamples of the security services include:

Cryptographic Libraries This application framework level library provides services for signing of data for integrity and non-repudiation purposes. See [WMLScriptCrypto] for more information.

Authentication The Security Services provide various mechanisms for client andserver authentication. At the Session Services layer HTTP Client Authentication[RFC2617] may be used to authenticate clients to proxies and application servers. At theTransport Services layer, WTLS and TLS handshakes may be used to authenticateClients and servers.

Identity WIM provides the functions that store and process information needed for user identification and authentication [WIM]

PKI The set of security services that enable the use and management of public-keycryptography and certificates [WPKI], [WAPCert].

Secure Transport The Transport Services layer protocols are defined for securetransport over datagrams and connections. WTLS is defined for secure transport over datagrams and TLS is defined for secure transport over connections (i.e. TCP). See[WTLS] and [WAPTLS] for more information.


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course material for module 5

Documents