department of: technical programs

Department of: Technical programs

Transmission Junction network

Part 1

Transmission junction network

Sub - Sections

1 Telephone Network Pages (1-10)

Transmission

Junction Systems

2 Transmission Media Pages (1-17)

3 Transmission Systems Pages (1-27)

This document consists of pages 54

Chapter 1: Telephone Network

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Chapter 1 Telephone Network

Aim of study

This Chapter introduces an introduction to telecommunication networks and telephone

layer model.

Contents

1-1 Introduction to Telecommunication Networks 2

1-2 Telephone Layer Model 7


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Chapter 1

Telephone Network

The History of the Telephone

In the 1870s, two inventors Elisha Gray and Alexander Graham Bell both

independently designed devices that could transmit speech electrically (the

telephone). Both men rushed their respective designs to the patent office

within hours of each other; Alexander Graham Bell patented his telephone

first. Elisha Gray and Alexander Graham Bell entered into a famous legal

battle over the invention of the telephone, which Bell won.

The telegraph and telephone are both wire-based electrical systems, and

Alexander Graham Bell's success with the telephone came as a direct result of

his attempts to improve the telegraph.

1.1 Introduction to Telecommunication Networks

Telecommunications today is perhaps the fastest evolving field of study. It is

continuously offering new challenges and opportunities to

telecommunications network planners. The subscriber part of the

telecommunications network or the network connecting the subscribers to the

central office or the access network that has been traditionally simple twisted

copper pair based, point-to-point, and passive network is now becoming

increasingly complex. In the present scenario, it becomes imperative for the

access network planner to be familiar with both traditional and new

technologies, structures and methods as their plans would have a profound

long-term impact on how the network shapes up and meets the desired

objectives... The basic idea of telecommunication is the exchange of

information. The information may include voice, text, data, image and video.

A telecommunications network is therefore a system, which can provide these


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services to a number of end users. From the end users' perspective. The

network has some main tasks:

Make interconnection of end users possible.

Facilitate exchange of information in a form desired and suitable for their

terminals.

Send and receive signals to/from the end users to facilitate the

establishment, maintenance and dismantling of connections.

It is very important for network planners to pay attention to the technical

evolution of telecommunication systems. This would to enable proven new

technologies to provide high quality telephone service and meet demands of

new telecommunication services.

Demand and traffic patterns will change faster in the future than they do

today. To cope with this, one important property a network should have is

flexibility. Flexibility in simple term implies being able to provide bandwidth

on demand. If bandwidth can be provided on demand then the network

becomes capable of deploying and supporting a wide variety of services and

with greater ease and speed.

1.1.1 Local Exchange

Subscribers of a local area are connected to their respective telephone

exchange called local-exchange or local switch or terminal exchange. The

local area could be a single exchange local area in which case all the

subscribers are terminated on the same switch or a multi-exchange area when

the number of subscribers is large and one exchange cannot effectively and

economically serve the entire subscriber. In the case of multiexchange area,

each local exchange has its own area called exchange area and the envelope

of all exchange areas would be the local area.


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Calls among subscriber of the same exchange can be switched through

without the need of any other kind of links except the pairs linking

subscribers to this exchange.

Fig (1.1) Subscribers in a single exchange area

In a multi-exchange area, however, the subscribers connected to different

local exchanges can only communicate if the exchanges themselves are

linked. These links between the local exchanges are called junctions.

Fig (1.2) Subscribers in a multi-exchange area

Whereas each subscriber normally has one dedicated pair up to the exchange,

the junctions are dimensioned based on the traffic between exchanges and the

Local

Exchange


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grade-of-service required. Variations on this classical theme are coming and

we will see them as we proceed.

A multi-exchange local area may have another type of exchange called transit

or local transit. Transits, unlike a local exchange, does not have subscribers

connected to it and therefore does not act as a source or sink for traffic in the

network. It only collects and redirects the traffic among the local exchanges in

the local area. An example of such a network is shown below.

1.1.2 Transit Exchange (TR)

Here the diagram depicting the junction network also shows a new element

viz. a local transit exchange (TR). A transit would normally be used in bigger

sized network to ease traffic routing and cost optimizing the junction network.

In this example, the local area of the city is geographically divided into two

by a physical obstruction i.e. the river and the transit would make it easier and

less expensive to interconnect the local exchanges on both the sides to each

other as also the local exchanges on the other side to the national switch.

Fig (1.3) the Junction Network

NS

TR

TR NS

Local

Switch

National

Switch

Local Transit

Switch

Junctions

River


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1.1.3 National Exchange

What other links would be required if the subscribers of two different local

areas need to communicate? As we linked all the local exchanges of one local

area to each other, we could also directly link all the local exchanges of one

local area to all the exchanges of other local areas in the country. This, though

technically feasible, would be economically a disaster. Telecommunications

network therefore have another type of exchange called national switch or

trunk automatic exchange. All the local exchanges of one local area are

connected to at least one such switch. All the national switches of a country

are then connected to each other based on the switching plan. A national

switch is also a type of transit exchange as it collects and redistributes traffic.

Fig (1.4) Local Network

All the international calls are routed through international gateways to which

the national exchanges would be connected. International gateways of

different countries would be linked through terrestrial, submarine or satellite

links.

The links among national switches, among international switches and between

national and international switches are called trunks.


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Fig (1.5) Trunk Network

1.2 Telephone Layer Model

The telecommunication network can be described by a layered model

consisting of the following layers:

1. The Switching and Services layer consists of all the switching nodes,

local as well as transit. It also consists of any other equipment and like

computers and software used to provide services to the customers.

2. The Transport Layer represents the links among the nodes and

provides the medium and systems to carry the information from one node to

the other. These are junctions and trunks. Junctions are links between the

local switches and local and national switches. Trunks are the links between

the national switches, the national and international switches and between the

international switches i.e. the long distance network. The long distance or

trunk network is composed of multiplexed channels of varying capacity

connecting the National Switches and the International Switches. The trend

has been to move from point-to-point links using Plesiochronous Digital

Hierarchy (PDH) towards advanced networks with built in controllability

based on Synchronous Digital Hierarchy (SDH) technique. The two most

important trends in the long distance networks are digitization and

introduction of fiber-optic technologies. These developments have reduced

the transmission cost per channel-kilometer and improved the quality.

NS

NS

NS

NS

NS International

Switch

National

Switch

Trunks


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3. The Access Layer represents the access network that links the

customers to the local switch.

Fig (1.6)

Where:

MDF Main Distribution Frame

CCC Cross Connect Cabinet

DP Distribution Point.

1.2.1 Main Distribution Frame (MDF)

Though located in the exchange building, MDF is as much a part of the

external network as it is of internal plant. It is the meeting point of internal

and external plant. It provides terminating space for the primary cable and the

cables from the exchange line terminating units. MDF provides the flexibility

of connecting any of the exchange side circuit to any of the external pairs by

jumper wires. The MDF has traditionally consisted of iron framework of

verticals and horizontals. The number verticals will depend on the size of the

exchange. The verticals are numbered' A, B, C... 'And are also known as bars.

There are ten horizontals resulting in ten cross points per vertical. On the line

side where the primary cables are terminated, each cross-point will have a

terminating block with a terminating capacity of 100 pairs.


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The exchange side (or the equipment side) of the MDF is not only reserved

for line circuit termination but it is also used as a termination point for

transmission circuits and other miscellaneous systems. The number of these

terminations per vertical will vary depending on the type of exchange and the

block used.

The MDF also gives a convenient place to put devices for over voltage and

over current protection. It also provides an isolation point for testing the line-

side and exchange side separately.

Fig (1.7)

1.2.2 Copper Conductor Cables

The primary cables are normally air-spaced, as they have to be pressurized.

The distribution cables are jelly filled.

The common conductor diameters are 0.4 mm, 0.5 mm, 0.63 mm and 0.9 mm.

The commonly used sizes are 5, 10, 20, 50, 100, 200, 600, 800, 1000, 1200,

1600 and 2000 pairs.

1.2.3 Cross Connect Cabinet

A cabinet has an arrayed arrangement of termination block. Cabinets are

available with varying termination capacity. An example could be a cabinet

with a total termination capacity of 1600 pairs including 800 for primary


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cable and 800 for distribution cable. A cabinet is provided in the network to

provide flexibility, separate primary side from distribution side, provide test

point for maintenance; cross connect primary pairs to distribution pairs.

1.2.4 Distribution Point DP

Secondary cable are distributed to DP each has a capacity 10 pair or 20 pair or

30 pair.

Chapter 2: Transmission Media

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Chapter 2 Transmission Media

Aim of study

This Chapter discusses the different types of transmission media.

Contents

2-1 Open Wire 2

2-2 Twisted Pair 2

2.3 Coaxial Cable 3

2.4 Microwave 5

2.5 Fiber Optics 6


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Chapter 2

Transmission Media

2.1 Open Wire

Open wire is traditionally used to describe the electrical wire strung along

power poles. There is a single wire strung between poles. No shielding or

protection from noise interference is used. We are going to extend the

traditional definition of open wire to include any data signal path without

shielding or protection from noise interference. This can include multi

conductor cables or single wires. This medium is susceptible to a large degree

of noise and interference and consequently is not acceptable for data

transmission except for short distances under 20 ft.

Fig (2.1)

2.2 Twisted Pair

Twisted pair is most widely used media for local data distribution.

They can carry digital or analog signals.

Bandwidth - 250 KHz

Data rate is several M bps.

They are used as local media, such as in a building, or a few rooms.

Open Wire


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Low cost.

Fig (2.2)

To connect between exchanges we prefer to use twisted pair with diameter 0.9

mm because it has low impedance and this enable to reach long distance.

2.3 Coaxial Cable

Coaxial cable consists of two conductors. The inner conductor is held inside

an insulator with the other conductor woven around it providing a shield. An

insulating protective coating called a jacket covers the outer conductor.

Bandwidth - 500 MHz

Fig (2.3)

Coaxial cable is a cable type used to carry radio signals, video signals,

measurement signals and data signals. Coaxial cable exists because we cannot

run open-wire line near metallic objects (such as ducting) or bury it. We trade

signal loss for convenience and flexibility. Coaxial cable consists of an

insulated center conductor that is covered with a shield. The signal is carried

between the cable shield and the center conductor. This arrangement give

Jacket Twisted Pair Bare wire

Jacket Shield Insulator Center

conductor


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quite good shielding against noise from outside cable, keeps the signal well

inside the cable and keeps cable characteristics stable.

Coaxial cables and systems connected to them are not ideal. There is always

some signal radiating from coaxial cable. Hence, the outer conductor also

functions as a shield to reduce coupling of the signal into adjacent wiring.

More shield coverage means less radiation of energy (but it does not

necessarily mean less signal attenuation).

Coaxial cables are typically characterized with the impedance and cable loss.

The length has nothing to do with coaxial cable impedance. Characteristic

impedance is determined by the size and spacing of the conductors and the

type of dielectric used between them. For ordinary coaxial cable used at

reasonable frequency.

2.3.1 Coaxial Cable Characteristic Impedance

The characteristic impedance depends on the dimensions of the inner and

outer conductors. The characteristic impedance of a cable (Zo) is determined

by the formula:

Zo = 138 log b/a

Where:

b the inside diameter of the outer conductor .

a the outside diameter of the inner conductor.

Here is a quick overview of common coaxial cable impedances and their main

uses:

1)50 ohms: 50 ohms coaxial cable is very widely used with radio transmitter

applications. It is used here because it matches nicely to many common

transmitter antenna types, can quite easily handle high transmitter power and


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is traditionally used in this type of applications (transmitters are generally

matched to 50 ohms impedance).

2)75 ohms: The characteristic impedance 75 ohms is an international

standard, based on optimizing the design of long distance coaxial cables. is

the coaxial cable type widely used in video and telecommunications

applications.

2.4 Microwave

- Requires no obstacles between transmitter and receiver

(Line Of Sight Link)

– Data rate - up to 300 Mbps

– Uses a parabolic dish antenna

Fig (2.4)

Direct line of sight transmission

between two ground stations

Microwave transmission


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2.5 Fiber Optics System

Low-loss glass fiber optic cable offers almost unlimited bandwidth and

unique advantages over all previously developed transmission media. The

basic point-to-point fiber optic transmission system consists of three basic

elements: the optical transmitter, the fiber optic cable and the optical receiver.

Fig (2.5)

The Optical Transmitter

The transmitter converts an electrical analog or digital signal into a

corresponding optical signal. The source of the optical signal can be either a

light emitting diode, or a solid-state laser diode. The most popular

wavelengths of operation for optical transmitters are 850, 1300, or 1550 nm .

The Fiber Optic Cable

The cable consists of one or more glass fibers, which act as waveguides for

the optical signal. Fiber optic cable is similar to electrical cable in its

construction, but provides special protection for the optical fiber within. For

systems requiring transmission over distances of many kilometers, or where

two or more fiber optic cables must be joined together, an optical splice is

commonly used .

Signal Input Signal Output

Fiber Optic Cable Optical

Transmitter

Optical

Receiver


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The Optical Receiver

The receiver converts the optical signal back into a replica of the original

electrical signal. The detector of the optical signal is either a PIN-type

photodiode or avalanche-type photodiode .

2.5.1 Advantages of Fiber Optic Systems and Application

Fiber optic transmission systems – a fiber optic transmitter and receiver,

connected by fiber optic cable – offer a wide range of benefits not offered by

traditional copper wire or coaxial cable. These include :

1- The ability to carry much more information and deliver it with greater

fidelity than either copper wire or coaxial cable .

2- Fiber optic cable can support much higher data rates, and at greater

distances, than coaxial cable, making it ideal for transmission of serial digital

data .

3- The fiber is immune to virtually all kinds of interference, including

lighting, and will not conduct electricity. It can therefore come in direct

contact with high voltage electrical equipment and power lines. It will also

not create ground loops of any kind .

4- As the basic fiber is made of glass, it will not corrode and is unaffected by

most chemicals. It can be buried directly in most kinds of soil or exposed to

most corrosive atmospheres in chemical plants without significant concern .

5- Since the only carrier in the fiber is light, there is no possibility of a Spark

from a broken fiber.

6- Fiber optic cables are virtually unaffected by outdoor atmospheric

conditions, allowing them to be lashed directly to telephone poles or existing

electrical cables without concern for extraneous signal pickup .

7- A fiber optic cable, even one that contains many fibers, is usually much

smaller and lighter in weight than a wire or coaxial cable with similar


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information carrying capacity. It is easier to handle and install, and uses less

duct space (It can frequently be installed without ducts).

8- Fiber optic cable is ideal for secure communications systems because it is

very difficult to tap but very easy to monitor. In addition, there is no electrical

radiation from a fiber .

Applications of Optical Fiber:

1- Computer Networks.

2- Trunks and Telephone Lines.

3- Medical Applications.

4- Submerged Communication.

5- Power Station.

6- Military Applications.

2.5.2 Light Basics

* Light rays propagate in different media with different velocities according

to the refractive index (n) of each medium.

* The refractive index is the ratio between the speed of light in both free

space and the medium respectively (n =c / ν)

* The speed of light in free space and air is (3x10 8 m / sec ) .

* When the light crosses the surface between two media, it is splitted into two

components one is reflected back in the first medium and the other is

refracted in the second medium according to the refractive indecies N1 & N2

obeying Snell's laws.


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Θ1 θ2

N1

N2

Θ2

Fig (2.6)

Note that:

The incidence angle (θ1): the angle between the incident ray and the plan

normal to the interface.

The incidence angle (θ2): the angle between the refracted ray and the plan

normal to the interface.

Snell's Law :

1- N1 Sin θ1 = N2 Sin θ2

2- The angle of incidence = the angle of reflection

Total Internal Reflection ( TIR ):

This occurs when: 1- (N1 > N2)

2- (θ1 > θc)

Critical Angle (θc) :

the incidence angle at which the refracted ray make refracted angle of 90

N1 Sin θc = N2 Sin θ1 = (N2/N1)


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When the (θ1 > θc) the refracted ray undergo total internal reflection in

the first medium.

In fiber optics the light is transmitted through the core of refractive index

N1 & the cladding has a refractive index N2 such that ( N1 >N2)

Fig (2.7)

Maximum Acceptance Angle( Φc ):

The maximum angle between the input ray & the axis of the fiber so that the

input ray can propagate along the fiber

By applying Snell's law of refraction at the (air-core) interface

Sin Φ1 =N1 Sin Φ2

At θ1 = θc Sin θ1 = Cos Φ2 = (N2/N1)

NA = Sin Φc =2

2

2

1 NN

This value is called numerical aperture (NA), is used to determine the

directions of accepted rays inside the optical fiber, and is considered a

characteristic property of the optical fiber.

CLADDING

CLADDING

CORE

θ1

Φ2

Φ1


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2.5.3 Fiber Structure

The basic structure of an optical fiber consists of three parts; the core, the

cladding, and the coating or buffer.

Fig (2.8)

CORE

1- The core is a cylindrical rod of dielectric material.

2- Dielectric material conducts no electricity.

3- Light propagates mainly along the core of the fiber.

4- The core is generally made of glass.

5- The core is described as having a radius of (a) and an index of

refraction n1.

CLADDING

1- The core is surrounded by a layer of material called the cladding.

2- Even though light will propagate along the fiber core without the layer

of cladding material, the cladding does perform some necessary

functions.

3- The cladding layer is made of a dielectric material with an index of

refraction n2.


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4- The index of refraction of the cladding material is less than that of the

core material.

5- The cladding is generally made of glass or plastic.

The cladding performs the following functions:

Reduces loss of light from the core into the surrounding air.

Reduces scattering loss at the surface of the core.

Protects the fiber from absorbing surface contaminants.

Adds mechanical strength.

COATING

1- Extra protection, the cladding is enclosed in an additional layer called

the coating or buffer.

2- The coating or buffer is a layer of material used to protect an optical

fiber from physical damage.

3- The material used for a buffer is a type of plastic.

4- The buffer is elastic in nature and prevents abrasions.

5- The buffer also prevents the optical fiber from scattering losses caused

by micro bends.

6- Micro bends occur when an optical fiber is placed on a rough and

distorted surface.

2.5.4 Optical Fiber Types

Fibers are classified according to the number of modes that they can

propagate.

* The first type is single mode fibers.

* The second type is multimode fibers.

The structure of the fiber can permit or restrict modes from propagating in a

fiber.


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2.5.4.1 Single Mode Fibers

The core size of single mode fibers is small.

The core size (diameter) is typically around 8 to 10 micrometers.

A fiber core of this size allows only the fundamental or lowest order mode

to propagate around a 1300 nanometer (nm) wavelength. Single mode fibers

propagate only one mode.

2.5.4.2 Multimode Fibers

As their name implies, multimode fibers propagate more than one mode.

Multimode fibers can propagate over 100 modes.

The number of modes propagated depends on the core size.

As the core, size the number of modes increases.

Another advantage is that multimode fibers permit the use of light-emitting

diodes (LEDs).

Multimode fibers also have some disadvantages.

As the number of modes increases, the effect of modal dispersion increases.

Modal dispersion (inter modal dispersion) means that modes arrive at the

fiber end at slightly different times. This time difference causes the light pulse

to spread. Modal dispersion affects system bandwidth.

Fiber refractive index profiles classify single mode and multimode fibers as

follows:


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Fig (2.9)

Comparison between Single mode and Multimode fiber

Single mode fiber. Multimode fiber.

Only one mode propagates

Along the fiber.

Multimode propagates

Along the fiber.

Used in long distances,

High-speed communication.

Used in short distances, low Speed

communication.

Uses LD as an Optical Source. LED used as an optical source.

Table 1


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2.5.5 Optical Source Properties

Optical source converts electrical signal to optical signal

Comparison between optical sources

Light Emitting Diode

LED

Laser Diode

LD

More simple circuit More complex circuit.

More cheap Very expensive

Low output power High output power

Low temperature sensitivity High temperature sensitivity

Higher Radiance (wider output Beam

angle)

Lower Radiance (narrow output Beam

angle)

Used with multimode fiber Used with single mode fiber

In general LED is used in Short distance

and low Bandwidth Systems

In general LD is used in Long distance

and wide Bandwidth System

Table 2

2.5.6 Optical Detectors

Optical detectors coverts light signal to electrical signal.

Fig (2.10)

Photo diodes

P-I-N junction

Avalanche


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2.5.7 Fiber Optic Loses Curve

Wave length (nm)

Fig (2.11)

According to the previous curve, the most used wavelengths are 850 nm,

1310 nm and 1550 nm.

Att

enu

ati

on

(db

/km

)

0.1

0.2

0.5

1.0

2.0

5.0

10

20

100

200 400 600 800 1000 1200 1400 1600 1800

Visible light 850 nm

Window

Early 1970s Fiber

Modern Fiber

1310 nm

window 1550 nm

window


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2.5.8 Optical Fiber Connectors

Fig (2.12)

DEUTSH 1000 AMP OPIMATE SMA

D4 FC BICONIC

ST SC FDDI

ESCON SODC

3M Voition

LC MT-RJ OptUack

Duplex SC (for

corrpaision)

ST FDDI SC

Chapter 3: Transmission Systems

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Chapter 3 Transmission Systems

Aim of study

This Chapter discusses the analog, digital transmission and different multiplexing

techniques.

Contents

3-1 Analog and digital transmission in telecommunication 2

3-2 Pulse Code Modulation (PCM) 3

3.3 Plesiochronous Digital Hierarchy (PDH) 13

3.4 Synchronous Digital Hierarchy (SDH) 15

3.5 Concatenation 21

3.6 Ethernet Over SDH (EOS) 23

3.7 WDM (Wavelength Division Multiplexing) 25

3.8 Acronym 26


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Chapter 3

Transmission Systems

3.1 Analog and digital transmission in telecommunication

3.1.1 Analog Signal (AS)

That has a continuous nature rather than a pulsed or discrete nature.

Fig (3.1)

Disadvantages of analog signal:

1- Error cannot be detected and corrected.

2- Signal takes any values at any interval of time.

3- More exposed to noise.

4- Hard to separate noise.

5- High cost circuits.

3.1.2 Digital Signal (DS)

A digital signal is a discrete signal. It is depicted as discontinuous.

Fig (3.2)

(A) MODULATION

Digital signal


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Each pulse (on/off) is known as a bit. Bit is a contraction of the words binary

and digit a binary (two-level) signal (1 or 0) is the most common digit signal

in the telecommunication. The number of bits transmitted per second is the bit

rate of the signal.

Advantages of digital signal

1- Error often can be corrected.

2- Holds a fixed value for a specific length of time.

3- Has a sharp, abrupt change.

4- Present number of values allowed.

Applications of digital signal

Typical applications of digital signal processing are, for example, speech

compression and transmission in (digital) mobile phones, weather forecasting

and economic forecasting, analysis and control of industrial processes,

computer-generated animations in movies and image manipulation

3.2 Pulse Code Modulation (PCM)

When telephone communication began individual connecting paths were

used, i.e. a separate pair of wires was used for every telephone connection.

This was known as space-division multiplex (SDM) because of the fact that a

multitude of lines were arranged physically next to each other. Since a

particularly large proportion of capital is invested in the line plant, efforts

were made at an early stage to make multiple uses of at least those lines used

for long-range communications. This led to the introduction of frequency-

division multiplex (FDM). FDM is used in analog systems.

It is not the only way of making multiple uses of lines however, another

possibility is offered by time-division multiplex (TDM). Here, the transmitted

telephone signals are separated in time.

http://www.fact-index.com/w/we/weather_forecasting.html


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Sampling Theorem

The sampling theorem is used to determine the minimum rate at which an

analog signal can be sampled without information being lost when the

original signal is recovered.

The sampling frequency (f S) must be more than twice the highest frequency

contained in the analog signal (f A):

f S >= 2 f A

3.2.1 Analog-to-Digital Conversion

1) Sampling

A sampling frequency (f A) of 8000 Hz has been specified internationally for

the frequency band (300 Hz to 3400 Hz) used in telephone systems, i.e. the

telephone signal is sampled 8000 times per second. The interval between two

consecutive samples from the same telephone signal (sampling interval = TA)

is calculated as follows:

TA = = = 125μs

Figure (3.3) shows how the telephone signal is fed via a low-pass filter to an

electronic switch. The low-pass filter limits the frequency band to be

transmitted; it suppresses frequencies higher than half the sampling

frequency. The electronic switch - driven at the sampling frequency of 8000

Hz - takes samples from the telephone signal once every 125 μs. A pulse

amplitude modulated signal is thus obtained at the output of the electronic

switch: PAM signal.

1

F A

1

8000 Hz


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Fig (3.3)

2) Quantizing

The pulse amplitude modulated signals (PAM signal) still represents the

telephone signal in analog form. The samples can be transmitted and further

processed much more easily in digital form. The first stage in the conversion

to a digital signal - in this case a pulse code modulated signal (PCM signal) –

is quantizing. The whole range of possible amplitude values is divided into

quantizing intervals.

The quantizing principle is shown in Figure (3.4) .In order to simplify the

explanation only 16 equal quantizing intervals are numbered from +1 to +8 in

the positive range of the telephone signal and from -1 to -8 in the negative

range.

The appropriate quantizing interval is determined for each sample. Decision

values form the boundaries between adjacent quantizing intervals. On the

transmit side, therefore, several different analog values fall within the same

quantizing interval. On the receive side one signal value, corresponding to the

midpoint of the quantizing interval, is recovered for each quantizing interval.


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This causes small discrepancies to occur between the original telephone signal

samples on the transmit side and the recovered values. The discrepancy for

each sample can be up to half a quantizing interval. The quantizing distortion

which may arise on the receive side as a result of this manifests itself as noise

superimposed on the useful signal. Quantizing distortion decreases as the

number of quantizing intervals are increased. If the quantizing intervals are

made sufficiently small the distortion will be minimal and the noise

imperceptible.

Fig (3.4)

If equally large quantizing intervals are used over the whole amplitude range,

relatively large discrepancies will occur in the case of small signal amplitudes

(uniform quantizing). These discrepancies might be of the same order of

magnitude as the input signals themselves and the signal-to-quantizing noise

ratio would not be large enough. For this reason, 256 unequal quantizing

intervals are used in the practice (non-uniform quantizing):

- Small quantizing intervals for lower signal values

+8

+7

+6

+5

+4

+3 +2

+1

-1

-2

-3

-4

-5

-6

-7

-8

Decision

Values

PAM signal Quantizing intervals

Sampling instants


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- Larger quantizing intervals for higher signal values

a) The "13 segment characteristic"

(A-law, e.g. for the PCM30 transmission system in Europe)

b) The "15 segment characteristic"

(μ-law, e.g. for the PCM24 transmission system in the USA)

We will focus on A-law

Fig (3.5)

3) Encoding

In this case, each sample is represented in 8 bit so we have 28

= 256 level and

the 8 bit is formatted as follow:

8-bit word

1- Bit (8) used for sign.

1 2 3 4 5 6 7 8


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1 Positive Side 0 Negative Side

2- Bits (5), (6) and (7) used for segment number.

3- Bits (1), (2), (3) and (4) used to determine the level number inside the

segment.

We have 8000 sample each second and each sample is encoded in 8 bit so we

have:

Bit rate = 8000 × 8 = 64 Kbps

3.2.2 Structure of the 2 Mbit/s Frame (Europe)

In the direction of transmission, the primary multiplexer PCM30 transforms

up to 30 signals with different features into 64-kbit/s-digital signals and then

combines them by the time division multiplexing procedure to a 2048-kbit/s

(2-Mbit/s)-signal. The individual signals can be either speech signals

converted by pulse code modulation, or digital signals (e.g. data).

In the receive direction a demultiplexer isolates the individual signals out of

the 2 Mbit/s signal. The 64-kbit/s-digital signals are then converted again into

analog signals.

The 2-Mbit/s pulse frame accord. To CCITT-recommendation G.704 consists

of 32 time intervals with 8 bits each. In the intervals, 1 to 15 and 17 to 31

speech or digital signals are transmitted. Interval 16 contains the channel-

associated signaling information (CAS) combined in one multi-frame,

optionally, an additional device specific data channel. In the Interval 0


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Fig (3.6) The Multi-frame in case of using CAS

There is an alternate transmission of a frame alignment signal (FAS) or a

service word (SW).


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Fig (3.7)


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PCM30 bit rate calculation:

Bit rate = 32 × 8 × 8000 = 2.048 Mbps

This is called E1.

PCM24 (American)

There is American standard PCM24 for digital transmission

Fig (3.8)

PCM24 bit rate calculation:

Bit rate = [1+ (24×8)] × 8000 = 1.544 Mbps

This is called T1.


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Comparison between PCM30 and PCM 24

Common characteristics

8 KHz Sampling frequency 1

8000 /s No. of samples per telephone

signal 2

Pulse frame period 3

8 bits No. of bits in a PCM word 4

b.d = 8000 /s ×8 bits =64 kbit /s Bit rate of a telephone channel 5

PCM 24 PCM 30 System– specific characteristics

Law- µ

15

A-law

13

Encoding / Decoding

No. of segments in characteristic 1

24 32 Number of channel time slots per

pulse frame 2

d.g+1*=(8bit×24) +1*

= 193 bits.

d.g = 8bit × 32 =

256 bits

Number of bits per pulse frame

(* = additional bit) 3

Period of an 8-bit channel time

slot 4

b.h =

8000/s×193bits= 1544

kbit /s

b.h =

8000/s×256bits=

2048 kbit /s

Bit rate of time division multiplex

signal 5

Table 1


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3.3 Plesiochronous Digital Hierarchies (PDH)

Digital multiplexers are applied wherever a high transmission capacity with

effective use of transmission paths to be realized.

The basic idea of multiplexing is the time interleaving of digital signals of

different sources in order to form a common signal with a bit rate, which is

correspondingly higher (multiplex process). On the system's receiving side

the appropriate separate signals are reobtained from the sum signal (de-

multiplex process). This means that the original digital signals of the

multiplexed signal sources are available again at the output of such a system.

The European plesiochronous digital hierarchy (CEPT-standard) is based on a

2048 kbit/s digital signal (stage 1) which may come for example from a

PCM30 system, a digital exchange or from any other device.

Starting from this signal, the next higher hierarchies are formed, each having

a transmission capacity, which is four times the previous one.

Bit-by-bit interleaving

This method is used for all systems beyond the 2 Mbit/s hierarchy. Here a

cyclic transmission sequence is applied, where only one bit of each separate

signal is transmitted. This means that the signal of a certain multiplexer input

appears only in every fourth bit of the sum signal.


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Fig (3.9)

For Europe system PDH Hierarchy is:

E2 = 4 X E1 = 8448 Kbps

E3 = 4 x E2 = 34368 Kbps

E4 = 4 x E3 = 139264 Kbps

E5 = 4 x E4 = 564992 Kbps

The Signals 2 Mbps, 34 Mbps, 140 Mbps are called PDH signals.

Primary rate

2. Order

Japanese standard

North American

Standard

European

Standard


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3.4 Synchronous Digital Hierarchy (SDH)

SDH (Synchronous Digital Hierarchy) is an international standard for high-

speed telecommunication over optical/electrical networks, which can

transport digital signals in variable capacities. It is a synchronous system,

which intends to provide a more flexible, yet simple network infrastructure.

Why using SDH?

Although PDH was a breakthrough in the digital transmission systems, it has

many weaknesses:

No world standard for optical interfaces. Networking is impossible at the

optical level.

Rigid asynchronous multiplexing structure.

Limited management capability.

Because of PDH disadvantages, it was obvious that a new multiplexing

method is needed. The new method was called SDH.

3.4.1 SDH Advantages

First world standard in digital format.

First optical Interfaces.

Transversal compatibility reduces networking cost. Multivendor

environment drives price down

Flexible synchronous multiplexing structure.

Easy and cost-efficient traffic add-and-drop and cross connect capability.

Reduced number of back-to-back interfaces improves network reliability

and serviceability.

Powerful management capability.

New network architecture. Highly flexible and survivable self-healing

rings available.


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Backward and forward compatibility: Backward compatibility to existing PDH.

Byte-by-Byte interleaving

SDH uses byte-by-byte interleaving to generate multiplex sum signal.

3.4.2 SDH Hierarchy

The following diagram shows these multiplexing paths:

Fig (3.10)

Container ( Cn )

To transmit PDH signal along SDH network it putted first in frame called

container.

Each PDH signal has a specific container, for example:

C12 2 Mbps

C3 34 Mbps

C4 140 Mbps

STM-1 AUG AU-4 VC-4 C-4 139264

Kb/s

HO

P

44736 Kb/s

(DS3)

34388 Kb/s

C-3

VC-3 TU-3 TUG-3

VC-3 AU-3

TUG-2 TU-2

TU-12

TU-11

VC-2

VC-12

VC-11

C-2

C-12

C-11

6312 Kb/s

(DS2)

2048 Kb/s

1544 Kb/s

(DS1)

LOP

xN

x1

x3

x3

x1

x3

x1

x4

x7

x7


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Virtual Containers ( VCn )

Once a container has been created, path overhead byte is added to create a

virtual container. Path overheads contain alarm, performance and other

management information.

Vcn = Cn + POH

Ex:

VC12 = C12 + POH

Tributary Unit ( TUn )

Tun = VCn + Pointer

We put pointer to define the beginning of VCn signal so overcome the change

in the clock difference in the network.

Ex:

TU12 = VC12 + Pointer

Tributary unit group ( TUGn )

It is multiplexing between homogenous signals.

Administrative Unit ( AU4 )

AU4 = VC4 + Section overhead (SOH)

3.4.3 SDH basic frame

A frame with a bit rate of 155.52 Mbit/s is defined in ITU-T Recommendation

G.707. This frame is called the synchronous transport module (STM). Since

the frame is the first level of the synchronous digital hierarchy, it is known as

STM-1. It is made up from a byte matrix of 9 rows and 270 columns.

Transmission is row by row, starting with the byte in the upper left corner and

ending with the byte in the lower right corner. The frame repetition rate is 125

ms. each byte in the payload represents a 64 kbit/s channel.


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Fig (3.11)

Section overhead (SOH)

The first 9 bytes in each of the 9 rows are called the overhead. G.707 makes a

distinction between the regenerator section overhead (RSOH) and the

multiplex section overhead (MSOH). The reason for this is to be able to

couple the functions of certain overhead bytes to the network architecture.

The table below describes the individual functions of the bytes.

AU Pointer

It is first 9 bytes, which located in the fourth row and it is used mainly to

define the beginning of VC4 frame.

Payload

It is used to carry the traffic. It can carry 63 E1 or 3 E3 or 1 E4 or mixing

of E1s and E3s

STM-1 bit rate calculation :

Bit rate = 270 x 9 x 8 x 8000 = 155.52 Mbps

270 columns (Bytes)

270

9

1

1

3

4

5

9

RSOH

AU pointer

MSOH

Payload

(Transport capacity)


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SDH Rates

SDH is a transport hierarchy based on multiples of 155.52 Mbit/s

The basic unit of SDH is STM-1:

STM-1 = 155.52 Mbit/s STM-4 = 622.08 Mbit/s

STM-16 = 2588.32 Mbit/s STM-64 = 9953.28 Mbit/s

Fig (3.12)

3.4.4 SDH Network Topology

Traditional networks make use of Point-to-Point, Mesh and Hub (i.e. star)

arrangements.

Fig (3.13)

STM-N = N x STM-1

Section

Overhead

Section

Overhead

Section

Overhead

STM-1

STM-4

STM-16

Each Frame is sent in 125µs!

9/ Rows

9/ Rows

9/ Rows

9 Col

36 Col

144 Col 4.176 Col

261 Col

1.044 Col

2488.32 Mbps

622.08 Mbps

155.52 Mbps


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However, SDH allows these to be used in a much more comprehensive way:

Fig (3.14)

3.4.5 SDH Network Protection

1) 1+1 Protection

Fig (3.15)

2) 1+N Protection

Fig (3.16)


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3) Ring Protection

Fig (3.17)

3.5 Concatenation

This mechanism is provided to allow bit rates in excess of the excess of the

capacity of C-4 container to be transmitted; the AU-4-4c is intended for

Ethernet. The advantage of this method is that the payload must not be split

up, since a virtually container is formed within STM-4. The payloads of

several consecutive AU-4s are linked by setting all pointers to a fixed value,

the concatenation indicator (CI), with the exception of the pointer for the first

AU-4.

ADM

ADM

ADM

ADM


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The first pointer indicates J1

All other pointers are set to concatenation indication (CI)

Fig (3.18)

Fig (3.19)

Fig (3.20)


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3.6 Ethernet Over SDH (EOS)

Refers to a set of protocols, which allow Ethernet traffic to be carried over

synchronous digital hierarchy networks in an efficient and flexible way.

Ethernet frames which are to be sent on the SDH link are sent through an

"encapsulation" block (typically Generic Framing Procedure or GFP) to

create a synchronous stream of data from the asynchronous Ethernet packets.

The synchronous stream of encapsulated data is then passed through a

mapping block, which typically uses virtual concatenation (VCAT) to route

the stream of bits over one or more SDH paths. As this is byte interleaved this

provides better level of security compared to other mechanism for Ethernet

transport.

After traversing SDH paths, the traffic is processed in the reverse fashion:

virtual concatenation path processing to recreate the original synchronous

byte stream, followed by decapsulation to converting the synchronous data

stream to an asynchronous stream of Ethernet frames.

The SDH paths may be VC-4, VC-3, and VC-12 paths. Up to 64 VC-12 paths

can be concatenated together to form a single larger virtually concatenated

group. Up to 256 VC-3 or VC-4 paths can be concatenated together to form a

single larger virtually concatenated group. The paths within a group are

referred to as "members". A virtually concatenated group is typically referred

to by the notation:

<Path Type>-<X>v

Where:

<Path Type> VC-4, VC-3, VC-12 or VC-11

X the number of members in the group.


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A 10-Mbit/s Ethernet link is often transported over a VC-12-5v, which

allows the full bandwidth to be carried for all packet sizes.

A 100-Mbit/s Ethernet link is often transported over a VC-3-2v, which

allows the full bandwidth to be carried when smaller packets are used (< 250

bytes) and Ethernet flow control restricts the rate of traffic for larger packets.

A 1000-Mbit/s (or 1G) Ethernet link is often transported over a VC-3-21v

or a VC-4-7v which allows the full bandwidth to be carried for all packets.

Link Capacity Adjustment Scheme (LCAS), which dynamically changes the

amount a bandwidth used for a virtual concatenated channel. Using Link

Capacity Adjustment Scheme (LCAS), signaling messages are exchanged

within the SDH overhead in order to change the number of tributaries being

used by a Virtually Concatenated Group (VCG). The number of tributaries

may be either reduced or increased, and the resulting bandwidth change may

be applied without loss of data in the absence of network errors.

Fig (3.21)


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3.7 WDM (Wavelength Division Multiplexing)

Until the late 1980s, optical fiber communications was mainly confined to

transmitting a single optical channel. Because fiber attenuation was involved,

this channel required periodic regeneration, which included detection,

electronic processing, and optical retransmission. Such regeneration causes a

high-speed optoelectronic bottleneck and can handle only a single

wavelength. After the new generation amplifiers were developed, it enabled

us to accomplish high-speed repeater less single-channel transmission. We

can think of single ~ Gbps channel as a single high-speed lane in a highway in

which the cars are packets of optical data and the highway is the optical fiber.

However, the ~25 THz optical fiber can accommodate much more bandwidth

than the traffic from a single lane. To increase the system capacity we can

transmit several different independent wavelengths simultaneously down a

fiber to fully utilize this enormous fiber bandwidth. Therefore, the intent was

to develop a multiple-lane highway, with each lane representing data traveling

on a different wavelength. Thus, a WDM system enables the fiber to carry

more throughputs. By using wavelength-selective devices, independent signal

routing also can be accomplished.

WDM (wavelength division multiplexing), in which several baseband-

modulated channels are transmitted along a single fiber but with each channel

located at a different wavelength. Each of N different wavelength lasers is

operating at the slower Gbps speeds, but the aggregate system is transmitting

at N times the individual laser speed, providing a significant capacity

enhancement. The WDM channels are separated in wavelength to avoid cross

talk when they are (de)multiplexed by a non-ideal optical fiber. The

wavelengths can be individually routed through a network or individually

recovered by wavelength-selective components. WDM allows us to use much

of the fiber bandwidth, although various device, system, and network issues


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will limit the utilization of the full fiber bandwidth. Note that each WDM

channel may contain a set of even slower time-multiplexed channels.

Fig (3.22)

3.8 Acronym

Add Drop Multiplexer ADM

Analog Signal AS

Administrative Unit AU4

Cross Connect Cabinet CCC

Channel-associated signaling CAS

Concatenation Indicator CI

Container Cn


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Distribution Point. DP

Digital signal DS

Ethernet Over SDH EOS

Frame Alignment Signal FAS

Frequency-Division Multiplex FDM

Generic Framing Procedure GFP

Link Capacity Adjustment Scheme LCAS

Light Emitting Diode LED

Laser Diode LD

Main Distribution Frame MDF

Pulse Amplitude Modulated PAM

Pulse Code Modulation PCM

Plesiochronous Digital Hierarchy PDH

Path Overhead POH

Space-Division Multiplex SDM

Synchronous Digital Hierarchy SDH

Section Overhead SOH

Synchronous Transport Module STM

Service Word SVW

Time-Division Multiplex TDM

Total Internal Reflection TIR

Tributary Unit TUn

Virtual Container VCn

Virtually Concatenated Group VCG

Wavelength Division Multiplexing WDM

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Part 2

SS7

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SS7 Overview

Training SectorChapter2 : SS7 Overview

٢

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1 Introduction

2 Signaling Network

2.1 Components of a Signaling Network

2.2 Modes of Signaling

2. Signaling Network Structure

Introduction of Signaling

Contents

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1 Introduction

Why do we need signaling?

Communication networks connect terminal equipments by using nodes (exchanges) to

communicate speech, data, text, images etc.

The nodes have to exchange some information in order to control the setup and clear

down of these connections and also to maintain the network itself, this information is

called signaling.

Basically we have two kinds of signaling information:

Signaling between the terminal equipment and the nodes.

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Signaling between two nodes.

Signaling between two nodes is divided into Two different types.

Type 1: Channel-associated signaling (CAS)

In such a system the 32 channels are divided as follows:

30 channels available for up to 30 voice calls and also can carry Register signals.

Channel (0) dedicated to carrying frame synchronization information.

Channel (16)dedicated to carrying signaling information (Line signals).

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All 30-speech channels have to share the capacity of this one signaling channel.

Time slot 16 of any one frame is always assigned to two different speech channels

simultaneously, with each speech channel being allocated 4 bits respectively.

Channel-associated signaling systems re used mainly in networks employing

preferably analog exchanges.

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Exchange A Exchange B

Speech channel

Common channel

Figure 1.Channel-Associated signaling

٧


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E xc h a n ge

A

E xc h an g e

B

C h .1C h .0 C h .2 C h.1 6 C h .3 1C h .3 0

P C M 1

S yn c h ro n iza t io n

U s e rIn fo .+R e gi s te r

S i gn a ls

L i ne S i gn a ls

C h .1C h .0 C h .2 C h.1 6 C h .3 1C h .3 0

P C M n

S yn c h ro n iza t io n

U s e rIn fo .+R e gi s te r

S i gn a ls

L i ne S i gn a ls

Figure 2.Connection between two exchanges using CAS signaling

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٥

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FAS TS 1 TS 2 TS 30TS 16Fram e 0

FA S SW

SW TS 1 TS 2 TS 31TS 30F ram e 1

T S 1 T S 17

TS 16 TS 17

TS 31

TS 31

TS 17

Figure 3.a Frames of one of the PCMs in case of using CAS signaling

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F AS TS 1 TS 2 T S 3 1T S 3 0F ra m e 2

T S 2 T S 1 8

TS 1 6 T S 3 1TS 1 8T S 1 7

SW TS 1 T S 3 1F ra m e 1 5

T S 1 5 T S 3 1

TS 1 6 T S 3 1TS 1 8T S 1 7T S 1 5

Figure 3.b Frames of one of the PCMs in case of using CAS signaling

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Type 2: Common channel signaling (CCS)

In such a system one common signaling channel is provided for a number of speech

channels.

Thus, the capacity of the signaling channel is available as a common pool and is

used by the speech channels according to the dynamic demand, i.e. there is no

permanent assignment of signaling channel to speech channel.

The common signaling channel (often referred to as signaling link) carries out the

signaling information transport for a number of speech channels.

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The signaling link can be viewed as a tunnel, which connects two exchanges,

possesses a typical transmission rate of 64 kbit/s and accepts and conveys all

signaling information.

Signaling information transfer is made possible by sending messages. A message is

an information block whose structure and meaning of the single elements in the block

are defined by specifications.

The control of signaling information transfer is separated from the control of speech-

channel through-connection.

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Speech channel

Common channel

Figure 4.Common channel signaling

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E x c h a n g e

A

E x c h a n g e

B

C h . 1C h . 0 C h . 2 C h . 3 1C h . 3 0

P C M 1

S y n c h ro n i z a t i o n U s e r I n f o .

S i g n a l i n gC h a n e l

C h . 1C h . 0 C h . 2 C h . 3 1C h . 3 0

P C M n

S y n c h ro n i z a t i o n U s e r I n f o .

C h . n

Figure 5.Connection between two exchanges using CCS signaling

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What are the advantages of common channel signaling

systems?

• The separation between speech channel network and signaling network is the key to

the more flexible communications networks of the future (ISDN).

•The creation of common signaling channels allows unrestricted communication and

flexible data transfer between two exchanges and/or their processors. This

data transfer can also be used for network

management, operating and administration functions.

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• The common signaling channels can also be used

to exchange non-circuit-related control information between exchanges (e.g.

CCBS, CCNR, IN applications, etc.).

• Signaling information can be exchanged without

regard to the speech channel or circuit status, and

without disturbing the calling or called party.

• Reduced call setup times thanks to the high

transmission capacity (normally 64 kbit/s) and the

usage of message structures (one message can

include all called party digits).

• Processor-friendly message structure (multiples of 8 bits).

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• Common channel signaling also supports services

such as

User-to-user signaling

Messages are exchanged directly between

two terminals and pass through the network

in transparent mode.

End-to-end signaling

Messages are exchanged between the

originating and destination exchange without

being evaluated in the transit exchanges.

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• Reliability is high because error detection and

correction measures provide for error-free message

transmission. If one signaling link fails, Rerouting

guarantees that the signaling information will still be

transferred.

• Like most modern protocols, the SS7 protocol is layered. The layered structure of the

system gives us the ability to change a level without affecting the other levels. This

means future services and applications can be implemented fast and cost-effectively.

The first two common channel signaling systems

specified internationally by ITU-T were

ITU-T signaling system No. 6 (CCS6) and

ITU-T signaling system No. 7 (SS7)

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Speech channels

Com m on channel signaling links

Exchange C

Figure 6.Alternative paths through the signaling network

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2 Signaling Network

2.1 Components of a SS7 Signaling Network

Basic concepts

A telecommunications network served by common channel signalling is composed of a

number of switching and processing nodes interconnected by transmission links. To

communicate using SS7, each of these nodes requires to implement the necessary

“within node” features of SS7 making that node a signalling point within the SS7

network. In addition, there will be a need to interconnect these signalling points such

that SS7 signalling information (data) may be conveyed between them. These data

links are the signalling links of SS7 signalling network.

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The combination of signalling points and their interconnecting signalling links form the

SS No. 7 signalling network.

Signaling network components

Signaling points

A distinction is made between:

• Signaling points (SP) and

• Signaling transfer points (STP).

The signaling points are the sources (origination points) and sinks (destination points) of the

signaling traffic. In a communications network both these points are usually exchanges.

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The signaling transfer points forward received signaling messages to another signaling

points.

No call processing of the message takes place in a signaling transfer point. A signaling

transfer point may be integrated in a signaling point (e.g. an exchange) or may be a

separate node in the signaling network.

All signaling points in a SS No. 7 network are identified by a unique code known as a point

code (Signaling Point Code (SPC)) defined by a corresponding numbering scheme and can

therefore be addressed specifically in a signaling message.

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Signaling link

The common channel signalling system uses signalling links (time slots belonging to an

existing transmission route [e.g. a PCM30 link] ) to convey the signalling messages

between two signalling points.

For redundancy purposes, more than one signaling link generally exists between two

signaling points. If one signaling link fails the SS7 functions cause the signaling traffic to be

diverted to functioning alternative links.

A number of signalling links that directly interconnect two signalling points forms what is

called a signalling link-set.

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Two signaling points that are directly interconnected by a signaling link are, from a signaling

network structure point of view, referred to as adjacent signaling points.

Switching

network

Control

Signaling linkterminal

Signaling linkterminal

Switching

network

Control

Signaling link

Circuits

Figure 7.Signaling and circuit network

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2.2 Modes of signaling

Two different signaling modes can be used in the signaling network.

If the associated mode of signaling is used, the signaling link is routed together with the

associated circuit group.

That is to say, the signaling link is connected with those signaling points, which are also

the end points of the circuit group. This signaling mode is recommended in cases

where the traffic relation between the signaling points A and B carries high traffic loads.

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In the quasi-associated mode of signaling the signaling links and the circuit group

follow different routes. Although the circuit group connects the signaling points A and B

directly, one or more signaling transfer points handle the signaling for the circuit group.

This mode is advantageous for less busy traffic relations as it allows one signaling link

to be used for several destinations simultaneously.

Signaling point A S ignaling point B

C ircu it group

S ignaling link

Figure 8.Associated mode of signaling

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Signaling point A Signaling point B

Circuit group

Signaling links

Signaling point C/

signaling transfer point

Figure 9.Quasi-associated mode of signaling

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Signaling point modes

A signaling point, at which a message is generated, is the originating point of that

message.

A signaling point to which a message is destined, is the destination point of that

message.

A signalling point at which a message is received on one signalling link and is

transferred

to another link, is a Signal Transfer Point (STP).

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Signaling routes

The path determined for the signaling between an origination point and a destination

point is termed the signaling route.

Between these two signaling points the signaling traffic can be distributed over several

different signaling routes.

All the signalling routes that may be used between an originating point and a

destination point by a message traversing the signalling network is the signalling route

set for that signalling relation.

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O r i g in a t in g

p o in t AD e s t in a t io n

p o in t BL S E T 2T 2 T 4

T 1 T 5

T 3

L S E T 3

L S E T 1

T x : S ig n a l in g t r a n s fe r p o in t

Figure 10.Signaling route set

٣٠

In Figure 10 the signaling routes from A to B are LSET1, LSET2 and LSET3.

These routes comprise the signaling route set for B.


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2.3 Signaling Network structure

The definition of two different modes of signaling allows various signaling network designs.

A network can be structured with a uniform mode of signaling (associated or quasi-

associated) or else with a mixed mode (associated and quasi-associated).

The worldwide signaling network is categorized by two functionally independent levels, the

first one is the international level and the second one is the national level. Each network has

a separate numbering scheme for its own signaling points.

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The circuits between two adjacent signaling points are combined to form a circuit

group.

Figure 11. Network Structure

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