INDEX

1. Telephone Exchange

2. CDOT

3. PCM, Signaling And Multiplexing

4. OFC Communication System

5. GSM

6. CDMA

7. BROAD BAND

8. INTERNET

9. Wi-Fi

10. Wi-Max

11. NGN

12. microwave

1

TELEPHONE EXCHANGE

INTRODUCTION

The main function of an exchange is to process call from a calling subscriber and make the

connection to the called subscriber. This connection can be direct or via another exchange.

This requires all parts of the exchange to work as a unit to ensure the call is properly handled.

CALL PROCESSING ARCHITECTURE

The main function of the exchange is to process subscriber calls. The exchange does this by

connecting an incoming line or trunk to another line or trunk.

However call processing involves much more than simply connecting subscribers. In order to

process the calls the exchange must perform four basic switching function.

Supervision:

Detects and reports service requests, acknowledgements and requests to terminate

service.

Signaling:

Transmits information about lines and trunks and information about other aspects of

call handling to control switching equipment.

Routing:

Converts address information to the location of the corresponding call line or to the

location of a trunk on the way to that line.

Alerting.

Notifies a subscriber of incoming calls.

BASIC CALL TYPES

Subscriber calls are grouped in to categories that distinguish one call from another. These

categories are referred to as call types. The basic call types are

Intra exchange calls: - these are calls between two subscribers served by the same

exchange. These calls are normally line to line calls.

2

Inter exchange calls: - these are calls that involve two or more exchanges. Within a

given exchange there are different types of inter exchange calls.

An outgoing call is a call that goes out of the exchange via a trunk. If the call originated in the

same exchange, it is called an originating outgoing call.

An incoming call is a call that comes into the exchange via a trunk. A tandem call is a call that

comes into the exchange on one trunk and leaves the exchange on another trunk. Thus a

tandem call is both incoming and outgoing.

CALL PROCESSING STAGES

An intra exchange call which is the simplest of the call types mentioned above, progresses

through four basic stages :

FIG.BASIC CALL SAGES INTRA EXCHANGE CALL

Idle

Digit reception and analysis

Ringing talking

3

Inter exchange calls are more complex, and their call processing stages are somewhat

different.

SERVICE CATEGORY

Residence and business subscriber services: - Example of this category are individual,

2-party and multiparty lines, abbreviated dialing, call waiting, 3-way calling all

diversion, call barring and multi line hunting.

Extended business services: - Examples of these services are PBX, indirect inward

dialing and toll diversion.

Public safety services: - Examples of this category are basic emergency service, out

going call trace, and in-progress call trace and in progress call trace.

Miscellaneous local system services: - it like loop-range services, integrated and

universal pair gain interface and line signaling.

Inter exchange services: - Various inter exchange signaling types.

Call processing services: - Generalized screening, digit interpretation timing, routing

and remote switching modules.

4

Toll services: - Toll exchange trunks, auxiliary service trunks, and operator trunks. Of

termination: trunk and line. The trunk termination involves selecting an idle member

in the trunk group and out pulsing the received digits. For a trunk, the particular

selected trunk group, the no. of members in the trunk group and the digits to be out

pulsed and the way the trunk group is selected, are of utmost importance.

The line termination involves checking to find whether the line is busy and applying

rin2ging to the line.

DESCRIPTION OF VARIOUS BLOCKS

(i)DP (Distribution Panel)

Distribution point box commonly know as D.P. box is a terminal arrangement where under

ground cable pairs are connected to overhead wires or drop wires for providing connections at

subscribers premises.

It is a cast iron box with a facility for termination of distribution cable on pins fitted on an

insulating plate. The distribution cable pairs can be connected to these pins by soldering at the

rear. The overhead wires are connected by means of screwing nuts provided on the front side

of insulating plate.

Types of D.Ps.

There are two types of D.Ps. suitable for external/internal use. These are called internal D.P.

and external D.Ps. and are generally available in 10 or 20 pair sizes.

Location of D.Ps.

External D.Ps. are fitted on posts by means of suitable size of U backs. Internal D.Ps. are

fitted in side buildings on the wall at suitable location. In case of multi storied buildings

where the telephone demand is very high, the distribution cables or some times even the

primary cabled are terminated on distribution frames at suitable location, from where the

distribution cables of 20 pairs or 10 pairs sizes are taken to different floors or block and

terminated on 10 or 20 pair subs D.Ps. Individual wire are further provided from the subs

D.Ps. to the location of the telephone.

(ii)Pillar

5

Pillar is fabricated from steel or cast from casings enclosing a frame-work on which cable

terminal boxes are mounted. The term "pillar" is used with reference to a flexibility point

where MDF's cables and DP's cables are interconnected.

(iii)MDF (Main Distribution frame)

The Subscriber's lines enter an exchange through a number of large capacity U/G cables, each

of which serves a different part of the exchange area. The numbers given to the subscriber's

lines do not bear any relationship to the geographical location of the subscriber. Hence, the

exchange numbers included in any one cable are entirely haphazard. Moreover, as subscribers

cease to have telephones and new subscribers are connected, the exchange numbering of the

external cable pairs is constantly changing. On the other hand, all lines within the exchange

are in strict numerical order. It is, therefore, necessary that some means must be provided for

temporary connection between the two. This conversion from the geographical order of the

external pairs to the numerical order within the exchange is carried out on a main distribution

frame. MDF is separately explained in another section

(iv)Exchange

Card is a basic functional unit of the exchange. Various cards are utilized for various purposes

e.g. Subscriber cards are utilized for termination of subscriber's cables coming from MDF.

(v)PCM

Various subscriber's cables coming out from the subscriber's cards (After processing) are

terminated into the DDF (Digital Distribution Frame) located inside PCM in between these

two PCM tag block is there, which provide connectivity between these two. Various DDF's

cables combine together and terminated into the OFC module (which is combination of

electrical to light converter (Multiplexer and Demultiplexer). PCM is separately explained in

another section.

MAIN DISTRIBUTION FRAME

INTRODUCTION

To obtain flexibility in interconnecting, external line plants and the exchange equipment and

between different circuits in the exchange itself, certain arrangements is made by the use of

iron frames. These iron frames are called main distribution frames, intermediate distributions

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frames or combined main and intermediate distribution frames, depending upon their

functions.

MAIN DISTRIBUTION FRAME (M.D.F.)

The subscriber’s line enter an exchange through a number of large capacity cables, each of

which serves a different part of the exchange area. The numbers given to the subscriber’s

lines do not bear any relationship to the geographical location of the subscriber. Hence the

exchange numbers include in any one cable are entirely haphazard. Moreover, as subscribers

cease to have telephones and new subscribers are connected, the exchange numbering of the

external cable pairs is constantly changing. On the other hand, all lines within the exchange

are in strict numerical order. It is, therefore, necessary that some means must be provided for

temporary connection between the two. This conversion from the geographical order of the

external pairs to the numerical order within the exchange is carried out on a main distribution

frame.

FACILITIES PROVIDED BY M.D.F.

The M.D.F. provides for the following requirements:

A means for permanently terminating the external cables.

For mounting the protective devices connected to the incoming circuits.

Providing the connection between the exchange side and the line side by the jumpers.

An interception point for use in connection with fault locating tests.

7

Main distribution frame is mainly divided in two parts.

(1) Vertical Side or Line side

(2) LEN side or Exchange side

VERTICAL SIDE

All the part from vertical side to the subscriber are generally called outdoor section.

1 vertical has 10 tag block.

Each tag block has 10 rows and each row has 10 tags. So each tag block has 100 tags.

Connection between vertical side & subscribers are provided by jelly filled cables.

This wires are first terminated in cabinet box, then according to requirements the

group of the wires (e.g. 200 wires, 100 wires etc.) are terminated in pillar box & from

here connections are given to the subscribers via DP box.

LEN SIDE

All the parts from LEN to the exchange is called indoor section.

The connection of subscriber from exchange is terminated on this side of MDF.

In 1 tag block there are 128 tags. Each tag block is divided in 4 segments. That is 0, 1,

2 & 3 and in each segments. There are sixteen tags.

On the vertical side there is 100 tag in one vertical tag block where as on the LEN side

there is 128 tags on each LEN block. The reason for this difference is that there is

always a reserve of spare capacity in the external cables to cover fluctuations in the

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distribution of the subscribers lines as between the different localities served by the

cables.

DIFFERENT TYPES OF FAULTS

The faults are given below which are established in communication of subscriber with

exchange.

LOOP FAULT:-If two wires are joined together because of improper connection, storming

air etc. then this type of fault occur.

EARTH FAULT:-If two wires get scrape at some places and if this wire comes in contact

with tree, pillar or any metal objects then this type of fault occurs.

CABLE FAULT:-For outdoor connections, jelly filled wires are used which are affected by

natural causes such as rain, earthquake etc. At such time this fault occurs.

DISCONNECT FAULT:-This type of fault occurs due to the breaking of wires between the

vertical side & LEN side.

LOCATION OF FAULTS:-This can be determined by putting pack up. If pack up is put in

one of the tag of LEN side and if dial tone is received only upto the LEN side then fault is in

the outdoor side and if tone is received from the subscriber only upto the vertical side then

fault is in the indoor side. This faults are also identify by either subscriber line tester or by

using the computerized programme.

PROTECTIVE DEVICE USED ON M.D.F.

Fuses

These are the devices used to protect apparatus and wiring from excessive currents. A fuse is

a small length of thin wire which melts if there is an excess of current and disconnect the

9

equipment before possible damage. The rated current of fuse is the maximum current which it

can carry without melting or fusing.

The types of fuses used for connecting line to equipment are:

Glass type

Gate type

GAS DISCHARGE TUBE (GD TUBE)

In case of heavy lighting discharges or induction of high voltages, gas discharge protectors are

used as protective device to protect the communication lines and equipments from damages

due to high voltages. The gas discharge protector essentially consists of two of three tungsten

electrodes sealed in a special glass envelope or ceramic envelop[e containing a mixure of inert

gases , mainly neon. In case of three pin G.D. tube, Two of the electrodes are for connections

to the lines and third is the earth electrode and in case of two pin device, one electrode is

connected to a limb of a line and other electrode is connected to earth. If the potential

difference across the electrodes rises to a certain critical value, the gas is ionized and becomes

conducting. This condition will continue till the potential difference across the electrodes falls

to the extinction voltage value.

For voltages less than striking value, it will not conduct. For normal operating voltages on the

lines, it offers extremely high impedance and thus does not introduce any transmission loss.

APPLICATIONS

a) MDF mainly provide connection between outdoor and indoor.

b) MDF is basically the protection system for exchange.

c) It uses Fuse as a protection device which prevents to reach the high current from

outside to exchange.

d) It uses Gas Discharge Tube (GD Tube) which provide protection against high

excessive voltage.

10

C-DOT MAX-XL

1.1 The C-DOT DSS Family

C-DOT DSS MAX is a universal digital switch which can be configured for different

applications as local, transit, or integrated local and transit switch. High traffic/load handling

capacity up to 8,00,000 BHCA with termination capacity of 40,000 Lines as Local Exchange

or 15,000 trunks as Trunk Automatic Exchange, the C-DOT DSS family is ideally placed to

meet the different requirements of any integrated digital network. The design of C-DOT DSS

MAX has envisaged a family concept. The advantages of family concept are standardized

components, commonality in hardware, documentation, training, installation and field support

for all products and minimization of inventory of spares. In fact this modular design has been

consciously achieved by employing appropriate hardware, software, and equipment practices.

The equipment practices provide modular packaging. Common cards and advanced

components have been used in the system hardware in order to reduce the number and type of

cards. Standard cards, racks, frames, cabinets and distribution frames are used which facilitate

flexible system growth. Interconnection technology has been standardized at all levels of

equipment packaging. All these features, together with ruggedised design, make C-DOT DSS

MAX easy to maintain and highly reliable.

1.2. BASIC GROWTH/BUILDING MODULES

C-DOT DSS MAX exchanges can be configured using four basic modules

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Base Module

Central Module

Administrative Modulei)

BASE MODULE

The Base Module (BM) is the basic growth unit of the system. It interfaces the external world

to the switch. The interfaces may be subscriber lines, analog and digital trunks, CCM and

PBX lines. Each Base Module can interface upto 2024 terminations. The number of Base

Modules directly corresponds to the exchange size. It carries out majority of call processing

functions and, in a small-exchange application, it also carries out operation and maintenance

functions with the help of the Input Output Module.

In Single Base Module (SBM) exchange configuration, the Base Module acts as an

independent switching system and provides connections to 1500 lines and 128 trunks. In such

a configuration, the Base Module directly interfaces with the Input Output Module for bulk

data storage, operations and maintenance functions. Clock and synchronization is provided by

a source within the Base Module. It is a very useful application for small urban and rural

environments. With minimum modifications in hardware through only one type of card, a

Base Module can be remotely located as a Remote Switch Unit (RSU), parented to the main

exchange using PCM links.

CENTRAL MODULE

Central Module (CM) consists of a message switch and a space switch to provide inter-

module communication and perform voice and data switching between Base Modules. It

provides control message communication between any two Base Modules, and between Base

Modules and Administrative Module for operation and maintenance functions. It also

provides clock and synchronization on a centralized basis.

ADMINISTRATIVE MODULE

Administrative Module (AM) performs system-level resource allocation and processing

function on a centralized basis. It performs all the memory and time intensive call processing

support functions and also administration and maintenance functions. It communicates with

the Base Module via the Central Module. It supports the Input Output Module for providing

12

man- machine interface. It also supports the Alarm Display Panel for the audio-visual

indication of faults in the system.

1.3. SYSTEM FEATURES

1.3.1 GENERAL FEATURES

This section includes system features related to the CTOD DSS MAX. They are:

TYPES OF SERVICES

The CDOT DSS of different capacities can be put to use at various switching nodes in the

telecommunication network.

MAX

Main Automatic Exchange MAX is expandable to large capacities of order of 2000 lines or

beyond. The MAX may have Remote Modules (RM) and Remote Line Concentrators (RLC)

connected to it.

RAX

Rural Automatic Exchange (RAX) is a small exchange and is expandable upto 2000 lines

capacity. Single Base Module configuration (i.e. CDOT SBM RAX with or without

concentration) comes under the RAX category.

TYPE OF SYSTEM

The system is Stored Programme Controlled (SPC) which makes it possible to work in

attended/non-attended type of working environment.

TYPE OF NETWORK

The switching network within the system is 4-wire digital.

TYPE OF COMPONENTS

The different type of components used includes integrated circuits, miniature relays, PCB, etc.

The connecting scheme between various modules emphasis connectorised hardware.

NORMAL LINE

13

Line resistance including subscriber’s instrument may go upto 1200 ohms for which

minimum 30 mA loop current is guaranteed. Insulation resistance between (‘a’ wire or ‘b’

wire) and ground or between ‘a’ and ‘b’ wires may be as low as 20K ohms.

1.3.2 LINE SERVICE FEATURES

This section relates to various types of lines that the exchange can cater to, and briefly,

services offered to such lines.

ORDINARY LINE

A subscriber may have an ordinary telephone instrument connected to his/her line.

COIN TELEPHONE (CCB LINE)

The system provides a service by means of a special telephone permitting outgoing calls after

insertion of adequate coin(s) or token(s) and incoming calls without payment. The two classes

of service are:

Local-calls within Unit Fee Zone (UFZ) can be made from coin collection box telephone.

STD – from STD coin box telephones, the STD calls and calls to some special services are

permitted (Not available presently).

14

15

SYSTEM

ARCHITECTURE

2.1 CDOT SYSTEM CAPACITY

2.1.1 INTRODUCTION

The capacity of C-DOT DSS is defined in terms of the following parameters:

• .The termination capacity expressed as the number of lines and trunks

• The amount of traffic (in Erlangs) that can be switched

• The number of Busy Hour Call Attempts (BHCA) that can be processed with a given call-

mix while meeting the overall service quality requirements

This section indicates the maximum capacity of different system elements as well as that of

complete exchange, equipped to its ultimate termination capacity. It has been ensured that the

specified parameters are valid to meet overall reliability objectives for the C-DOT DSS as

specified in ITU-T recommendations.

2.1.2. TERMINATION CAPACITY

A Terminal Card is the basic system element. It interfaces/ terminates the lines and trunks.

The next higher element is a Terminal Unit. The types of terminal cards and terminal units

used in C-DOT DSS along with its functions are explained in H/W description. Termination

capacity of a BM is 488 analog terminals and that of LM is 768 analog terminals. A BM can

be concentrated with 2 LMs to provide maximum termination capacity of 2024 analog lines.

In case of a BM, a maximum of 256 B- channels can be provided for ISDN terminations at the

cost of 128 analog lines. In its maximum configuration of one BM and 2 LMs with

termination capacity of 2024 analog lines, 256 B-channels are provided at the cost of 512

analog lines. One to one replacement of B-channels is planned in immediate future.

Base Module and Line Module are the highest level of system elements Each Base Module

has four Terminal Units whereas a Line Module has six Terminal Units.

A maximum of 16 BMs can be connected in MAX-L and 32 BMs can be connected in MAX-

XL configurations.

Table2.1 summarises the termination capacities of the various system elements of CDOT

DSS MAX.

2.1.3 EXCHANGE CONFIGURATIONS

C-DOT DSS MAX can be configured to support any combination of lines and trunks. For

different applications in the network as Local Exchange, Local cum Tandem Exchange. Trunk

Automatic Exchange (TAX) or Integrated Local cum Transit (ILT) Exchange.

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In its maximum configuration, upto 40,000 lines and 5.500 trunks are supported when

configured as Local/Local cum Tandem. When configured as TAX, 14,500 trunks are

supported.

Table 2.1Termination Capacity of System Elements

Sl System Element Termination Capacity

1 Termination Cards (TC):

A Analog Line CardLCC – 8 Analog Subscribers

CCM – 8 CCB subscribers with last two ports

supporting 16-kHz metering pulsesB Analog Trunk Card TWT/ EMF – 8 Trunks

C A set of DTS/DTC Cards One 2-Mbps E-1 link as CAS/CCS trunks

D #7 PHC Card (SHM) 8 Protocol Handlers/ Signalling Links

E ISDN-BRI Card 8 BRI (2B+D) Interface i.e. 16 B-channels

F ISDN-PRI Card One PRI (30B+D) Interface i.e. 30 B-channels

2 Terminal Unit (TU):

A Analog TU (ATU)16 Analog Terminal Cards (LCC/ CCM/ TWT/

EMF) to support any combination of Lines &

Trunks in multiple of 8 terminationsB Digital TU (DTU) Four 2-Mbps E-1 links as CAS/ CCS7

C #7 Signalling Unit Module

(SUM)

64 Nos., #7 Protocol Handlers/signalling links

D ISDN Terminal Unit (ISTU) 256 Bearer Channels to be configured as BRI,

PRI or any combination3 Base Module (BM):

A Base Module (Line)480 Analog Subscribers. A maximum of 256

B-Channels for ISDN interface can be

provided at the cost of 128 subscriber lines.

B Line Module (LM)768 Analog subscriber lines. A maximum of

two LMs connected with BM supports 2024

lines.C BM (Analog Trunks) 488 Analog Trunks

D BM (Digital Trunks) Fifteen 2-Mbps E-1 links as CAS/ CCS7

E BM (Analog + Digital) Three possible configurations as 360 AT+ 4

PCMs/ 232 AT+ 8 PCMs/ 104 AT+ 12 PCMs

17

Table-2.2

Termination Capacity of Exchange Configurations

Sl Exchange Configuration Termination Capacity

1 Single Base Module (SBM)1,500 Lines & 128 Trunks. The trunks can be

analog and/or digital. The number of trunks can

be increased at the cost of subscribers.

2

Multi-Base Module (MBM) (DSS MAX)

i) MAX-XL

Ideal configuration to support 40,000 lines and

5,500 trunks with 20 Line BMs and 12 Trunk

BMs. The trunk capacity can be increased by 450

at the cost of 2,000 subscribers or vice versa.

ii) MAX-L

Ideal configuration to support 20,000 lines and

2,700 trunks with 10 Line BMs and 6 Trunk BMs.

The trunk capacity can be increased by 450 at the

cost of 2,000 subscribers or vice versa.

3 Remote Switching Unit (RSU) 2,000 subscriber lines. Trunk interface at the cost

of subscriber lines.4 Multi-Base Module TAX 14,500 Trunks

Note: out of the total equipped capacity, a maximum of 30,000 lines may be remote

subscribers through RSUs in MAX-XL whereas 14000 lines may be Remote Subscriber

through RSUs in MAX-L.

2.1.4. TRAFFIC CARRYING CAPACITY

The traffic carrying capacity of C-DOT DSS MAX is ideally 8000 Erlangs in case of MAX-

XL and 4000 Erlangs in case of MAX-L exchanges.

This figure is based on the ideal traffic of one Erlang per switched circuit. But the actual

traffic carrying capacity of one switched path is always less than one in practical application.

Accordingly capacities are reduced to not less than 7,500Erlangs incase of MAX-XL and to

3800 in case of MAX-L exchanges.

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2.1.5. BHCA HANDLING CAPABILITY

The basic processing elements of the exchange are the Base Processor (in the Base Module).

Base processor has the capability of handling 12,500 Busy Hour Call Attempts which can be

increased to 30,000 using upgraded processor card. The C-DOT DSS MAX (MAX-XL)

exchange with 32 Base Modules can handle upto 3,00,000 BHCA. By upgrading the

processor card in BM/CM/AM/SUM and message switch in all the BMs, it is increased to

8,00,000 BHCA. In case of MAX-L exchanges with 16 BMs connectivity, the BHCA

handling capability is 1,50,000.

Various exchange configurations and their traffic capacities are summarised in Table2.3.

Table 2.3 Traffic Capacity of Exchange Configurations

Sl.No. Exchange Configuration Traffic Capacity Description

I. SBM-RAX 250 Erlangs. The BHCA capacity depends on

the type of processor used and it may be 12,500 or

30,000.

2. Remote Switching Unit

(RSU)

250 Erlangs. The BHCA capacity depends on

the type of processor used. It may be 12,600 or

30,000.

3. DSS-MAX/TAX

i) MAX-XL

Not less than 7,500 Erlangs. The BHCA

capacity is more than 3,00,000 and upgradable to

8,00,000 by upgrading only processor cards.

ii) MAX-L Not less than 3800 Erlangs. The BHCA capacityis

1,50,000.

Note: For some of the sites already commissioned with one of the first three configurations,

overall BHCA handling capacity may be lower due to use of old processor cards.

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2.1.6 SYSTEM RELIABILITY

The C-DOT DSS MAX is designed to meet the reliability standards as defined in the

specifications. The system uses fully digital techniques for switching including the subscriber

stage. The system is built using a minimal number of standard units/modules which allow

flexible growth of the exchange and easy upgradation in technology and new features.

A very important feature of C-DOT DSS MAX architecture is the extensive duplication of

units. All controller units are duplicated or have n+1 redundancy. Software design matches

the high degree of redundancy provided by hardware to minimize the system down time.

To minimize failures caused by human and/or software errors the C-DOT DSS MAX has

extensive software maintenance functions. The design of software is such that propagation of

software faults is contained and it provides sufficient checks to monitor the correct

functioning of the system. The facilities are in-built to ensure automatic software recovery on

detection of software faults. Whenever a faulty condition occurs the software provides for the

isolation of the faulty subsystem and automatically initiates diagnostic programs for

diagnostic purposes. The diagnostic programs have a design objective of localizing 95 of the

faults to a single PCB level and the rest to a two PCB level. Provision is also made for safety

of charge-records. The charging information is dumped at regular intervals to non-volatile

duplicated back-up memories automatically. The software maintenance functions include data

audits as well; as system integrity monitors and controls.

Alarm Display Panel is provided for a continuous indication of the system status. Audio-

visual alarms are provided.

3. SUBSCRIBER FEATURES

The C-DOT Digital Switching Systems offer a wide range of telephony features and

supplementary services. Further capabilities can be developed to meet specific customer

needs. Due to mandatory requirement of exchange of messages between the switching

systems and user's equipment, some of the services are exclusively offered to ISDN-

subscribers. In case of few of the services offered to PSTN and ISDN subscribers, the

implementation of services to PSTN subscribers may be partial and invocation procedure may

also differ.

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PSTN (ANALOG) AND ISDN SUBSCRIBER SERVICES

The subscriber services provided by C-DOT DSS MAX exchanges for PSTN (Analog) as

well as ISDN subscribers are-explained as per their logical grouping:

3.1 Number Identification Services

i) Calling Line Identification Presentation (CLIP)

When this service is subscribed by a user as terminating facility, all the incoming calls are

offered to the user along with the details of calling party's identity.

In exceptional cases as the calling party has subscribed CLIR or interworking constraints in

the network, it will not be possible to provide caller's identity.

ii) Calling Line Identification Restriction (CLIR)

This service is offered to the calling party to restrict presentation of it's number to the called

party. When CLIR is subscribed, the originating exchange notifies the destination exchange

that the calling party's number is not allowed to be presented to the called party. The

terminating local exchange may indicate to the called user that the calling user identity is

unavailable due to restriction.

iii) Calling Line Identification Restriction Override (CLIRO)

Subscriber with CLIRO as terminating facility instead of CLIP, receives the call with the

calling line identification even if the calling party has requested that his (the calling party's)

identification should not b« presented to the called user.

The CLIRO facility is offered at the discretion of the administration to special category

subscribers like the police, hospitals, operator positions and other emergency centres.

iv) Malicious Call Identification (MCID)

This facility is used for ascertaining the origin of malicious calls. During conversation the

subscriber has to use suitable procedure to notify the exchange about the malicious call. The

detail of the call is recorded in the exchange which can be retrieved later on. If the caller is

from an exchange which does not support identification of calling line, "junction identity" is

found and an "identification request" may be sent to the originating exchange by tee exchange

personnel.

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3.2 Call Offering Supplementary Services

Call offering services permit the served user to request the network to divert the incoming calls

to a specific number. In call forwarding, the network forwards the call to a pre-registered

number which can be specified by the user or exchange administrator.

(i)Call forwarding unconditional (CFU)

This service permits the served user to request the exchange to forward all incoming calls to

other Number. The served user's originating service remains unaffected. The other number

could be a fixed pre-determined number or a number specified by the subscriber in the

activation request.

(ii)Call Forwarding Busy (CFB)

This service permits the served user to request the exchange to forward all incoming calls to

other number if the served users number is not free. The served user's originating service

remains unaffected.

iii)Call forwarding no reply (CFNR)

This service permits the served user to request the exchange to forward all incoming calls

which are not replied with in ring timeout period. The served user's originating service

remains unaffected.

3.3 Call Completion Services

i) Call Waiting

A subscriber engaged in an existing call, is given an indication (Call Waiting tone or ZIP

tone) that another caller is attempting to connect to his number. The caller will hear ring back

tone. By flashing the hook-switch the called subscriber can talk with either party while

keeping the other on hold (acceptance without clearing). If the called subscriber replaces his

handset in response to the tone (acceptance by clearing), the exchange will automatically

extend ring to the subscriber and re-establish the connection on answer with the party waiting.

ii) Call Hold

This facility is used by the user to put the existing conversation on hold for the time being and

initiate a new call or receive a call in waiting. The call, which has been put on hold, is

retrieved by the user as and when it is required. The procedure of invocation to put the

conversation on hold and its subsequent retrieval is different for ISDN and PSTN subscribers.

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3.4 Multi-Party Services

(i)Three party conference

The three party call service enables the served user to establish, participate in, and control a

simultaneous communication involving the served user and two other parties. The served

user can request to convert two party conversation into a three party conference. During the

three party conversation, the served user can disconnect one party, disconnect the 3-way

conversation or choose to communicate privately with one of the parties, in which case the

call to the other party is held.

(ii)Multi party conference (Add-on conference)

The CONF (Add-on conference) service enables the served user to establish and control a

conference i.e. a simultaneous communication, involving of users (max. up to 6).

When the CONF service is invoked, the serving local exchange allocates conference

resources to the served user and add any existing call indicated by the served user to the

conference. On successful invocation of conference the served user becomes the 'conference

controller'. The conference Controller may then add, drop, isolate, and reattach parties from

the conference. The conference controller can also hold and retrieve the conference (e.g. to

add parties) and finally end the conference.

4. ISDN-SUPPLEMENTARY SERVICES

In addition to the services available for PSTN/Analog as well as ISDN subscribers, a number

of supplementary services are offered only to ISDN-subscribers.

Charging Related Supplementary Services

The Advice Of Charge service provides charging information to the user paying for a call.

The option of providing the information at a predefined stage of the call is based on the type

of AOC facility subscribed.

i) AOC-E, Charging information at the end of the call

The charging information is provided by the serving local exchange at the end of a call. It is

sent in the charge advice information element of the call clearing message.

23

ii) AOC-D, Charging information during a call

In this case the charging information is provided by the serving local exchange every time a

quantum of charge has been added. The charging information is sent in an appropriate

message. When the call is cleared, the remaining number of charge units (incremental case) or

the total charge units (cumulative case) is transferred to the user in the call clearing message.

5.Hardware Architecture

5.1 GENERAL

The hardware architecture of C-DOT DSS MAX is mapped closely on the System Overview

described in the previous chapter. In the following sections, the hardware architecture of each

constituent module is described.

5.2 BASE MODULE (BM)

Base Module (BM) is the basic building block of C-DOT DSS MAX. It interfaces the

subscribers, trunks and special circuits. The subscribers may be individual or grouped PBX

lines, analog or digital lines. The trunks may be Two Wire Physical, E&M Four Wire, E&M

Two Wire, Digital CAS or CCS.

The basic functions of a Base Module:

Analog to digital conversion of all signals on analog lines and trunks

Interface to digital trunks and digital subscribers

Switching the calls between terminals connected to the same Base Module

Communication with the Administrative Module via the Central Module for

administrative and maintenance functions and also for majority of inter-BM switching

(i.e. call processing) functions

Provision of special circuits for call processing support e.g. digital tones,

announcements, MF/DTMF senders/receivers

24

Provision for local switching and metering in stand alone mode of Remote Switch

Unit as well as in case of Single Base Module Exchange (SBM-RAX)

Analog Terminal Unit - to interface analog lines/trunks, and providing special circuits

as conference, announcements and terminal tester.

Digital Terminal Unit - for interfacing digital trunks i.e. 2Mbps E-1/PCM

SS7 Signalling Unit Module - to support SS7 protocol handlers and some call

processing functions for CCS7 calls.

ISDN Terminal Unit - to support termination of BRI/PRI interfaces and

implementation of lower layers of DSS1 signalling protocol.

Time Switch Unit - for voice and message switching and provision of service circuits.

Base Processor Unit - for control message communication and call processing

functions.

6. Cards discription

Analog Subscriber Line Cards:

Two variants of subscriber line cards as LCC or CCM with interfaces upto 8 subscribers,

provide basic BORSCHT functions for each line. Analog to digital conversion is done by per-

channel CODEC according to A-law of Pulse Code Modulation. Each CCM card has the

provision of battery reversal for all the 8 lines with the last two lines having provision to

generate 16 KHz metering pulses to be sent to subscriber's metering equipment.

The 8-bit digital (voice) output of four LCCs is multiplexed to form a 32-channel, 2 Mbps

PCM link - also called a terminal group (TG). Since a Terminal Unit has a maximum of 16

terminal cards, there are four such terminal groups. The signalling information is separated by

a scan/drive logic circuit and is sent to the signalling processor on four different scan/drive

signals. The LCC/CCM also provides test access relay to isolate the exchange side and line

side to test it separately by using the Terminal Test Controller (TTC).

25

Analog Trunk Cards :

Analog trunk cards interface analog inter-exchange trunks which may be of three types as

TWT, EMT and EMF. These interfaces are similar to Subscriber Line Card, with only

difference that the interfaces are designed to can/drive events on the trunks as per predefined

signalling requirement.

Signalling Processor (SP) Card

Signalling Processor (SP) processes the signalling information received from he terminal

cards. This signalling information consists of scan/drive functions like origination detection,

answer detection, digit reception, reversal detection, etc. The validated events are reported to

Terminal Interface Controller for further processing to relieve itself from real-time intensive

functions. Based on the information received from the Terminal Interface Controller, it also

drives the event on the selected terminal through scan/drive signals.

Terminal Interface Controller (TIC) Card

Terminal Interface Controller (TIC) controls the four terminal groups (TG) of 32 channels,

and multiplex them to form a duplicated 128-channel, 8 Mbps link towards the Time Switch

(TS). For signalling information of 128- channels, it communicates with Signalling Processor

(SP) to receive/send the signalling event on analog terminations. It also uses one of the 64

kbps channel out of 128 channels towards Time Switch, to communicate with Base Processor

Unit (BPU). In concentration mode, three other Terminal Units share this 128-channel link

towards the Time Switch to have 4:1 concentration.

Terminal Interface Controller is built around 8-bit microprocessor with associated memory

and interface and it is duplicated for redundancy.

Special Service Cards:

A Terminal Unit has some special service cards such as Conference (CNF) Card to provide

six party conference. Speech samples from five parties are added by inbuilt logic and sent to

the sixth party to achieve conferencing. Terminal Test Controller (TTC) Card is used to test

analog terminal interfaces via the test access relays on the terminal cards.

Announcement Controller (ANN) Card provides 15 announcements on broadcast basis. Only

one service card of each type is equipped in a Base Module with provision of fixed slot for

TTC and variable slots for CNF/ANNC.

26

Announcement and Conference Cards are equipped in Terminal Unit through S/W MMC

command. Two slots are occupied by each card i.e. 16 channels for each card is used out of

128 channels available on a Bus between a TU &TS.

BASE MODULE (BM) CONFIGURATION

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NOTE: 1) TC MAY BE LCC, CCM, TWT or EMF

2) IN CASE OF TU4 AS ATU IN BM, SLOT 24 WILL BE TTC

FIG: ANALOG TERMINAL UNIT (ATU) CONFIGURATION

Digital Terminal Unit (DTU)

Digital Terminal Unit (DTU) is used exclusively to interface digital trunks. One set of Digital

Trunk Synchronization (DTS) card along with the Digital Trunk Controller (DTC) card is

used to provide one E-1 interface.

27

1 2 3 4 5 6 7 8 9 1

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Each interface occupies one TG of 32 channels and four such interfaces share 4 TGs in a

Digital Terminal Unit. The functions performed by TIC and SP in Analog Terminal Unit, are

collectively performed by the Terminal Unit Controller (TUC) in the Digital Terminal Unit.

The scan functions are - HDB3 to NRZ code conversion, frame alignment and reconstitution

of the received frame. The drive functions include insertion of frame alignment pattern and

alignment information. Each interface can be configured as CAS or CCS interface.

FIG: DIGITAL TERMINAL UNIT (DTU) CONFIGURATION

SS7 Signalling Unit Module (SUM)

Any one of the ATU or DTU in a BM can be replaced by SUM frame to support CCS7

signalling. Only one such unit is equipped in the exchange irrespective of its configuration or

capacity. For details of SUM architecture, refer to chapter no.4.

28

FIG: SS7SU CONFIGURATION

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NOTE: 1) SHM IS #7 PROTOCOL HANDLER CARD

2) WITH BPC, ONLY SHM 1-4 CAN BE EQUIPPED

3) HPC IS USED TO SUPPORT SHM1-8 CARDS AND HIGHER MESSAGE

PROCESSING CAPABILITY

ISDN - Terminal Unit (ISTU)

One of the four ATUs/ DTUs in a BM can be replaced by ISTU to provide BRI/PRI interfaces

in C-DOT DSS. The only constraint is that ISTU has to be principal TU i.e. directly

connected to TSU on 8 Mbps PCM link. The ATU/DTU cannot be used in concentration with

ISTU. By equipping one ISTU in the exchange, a max. of 256 B channels are available to the

administrator which can be configured as BRI, PRI or any mix as per site requirement.

Depending on the requirement of number of ISDN-Interfaces, one or more ISTUs can be

integrated in C-DOT DSS, either in one BM or distributed across different BMs.,

29

FIG: 3.2C ISTU CONFIGURATION

NOTE: LC MAY BE BRL or PRL CARDS

Time Switch Unit (TSU)

Time Switch Unit (TSU) implements three basic functions as time switching within the Base

Module, routing of control-messages within the Base Module and across Base Modules and

support services like MF/DTMF circuits, answering circuits, tones, etc. These functions are

performed by three different functional units, integrated as time switch unit in a single frame

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FIG: 3.2F TIME SWITCH UNIT (TSU) CONFIGURATION

NOTE: 1) REPLACE TSS CARDS BY ETS CARDS IN CASE OF REMOTE BASE

MODULES (RSU)

2) MSC AND MSD CARDS ARE REPLACED BY HMS FOR 800K BHCA

Base Processor Unit (BPU)

Base Processor Unit (BPU) is the master controller in the Base Module. It is implemented as a

duplicated controller with memory units. These duplicated sub-units are realised in the form

of the following cards:

Base Processor Controller (BPC) Card

Base Memory Extender (BME) Card

BPC controls time switching within the Base Module via the Base Message Switch and the

Time Switch Controller. It communicates with the Administrative Processor via Base

Message Switch for operations and maintenance functions. In a SBM configuration, BPC

directly interfaces with the Alarm Display Panel and the Input Output Module.

30

To support 8,00,000 BHCA, the BPC card is replaced by High performance Processor Card

(HPC). It is pin to pin compatible for hardware and also for software so that they are

interchangeable at any site to meet specific traffic requirement.

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2

P

S

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FIG: BASE PROCESSOR UNIT (BPU) CONFIGURATION

NOTE: HPC USED TO SUPPORT 800K BHC

31

32

PCM, Signaling And MultiplexingINTRODUCTION

A long distance or local telephone conversation between two persons could be provided by

using a pair of open wire lines or underground cable as early as early as mid of 19th century.

However, due to fast industrial development and increased telephone awareness, demand for

trunk and local traffic went on increasing at a rapid rate.

To cater to the increased demand of traffic between two stations or between two subscribers

at the same station we resorted to the use of an increased number of pairs on either the open

wire alignment, or in underground cable. This could solve the problem for some time only as

there is a limit to the number of open wire pairs that can be installed on one alignment due to

headway consideration and maintenance problems. Similarly increasing the number of open

wire pairs that can be installed on one alignment due to headway consideration and

maintenance problems. Similarly increasing the number of pairs to the underground cable is

uneconomical and leads to maintenance problems.

It, therefore, became imperative to think of new technical innovations which could exploit the

available bandwidth of transmission media such as open wire lines or underground cables to

provide more number of circuits on one pair. The technique used to provide a number of

circuits using a single transmission link is called Multiplexing.

MULTIPLEXING TECHNIQUES

There are basically two types of multiplexing techniques

i. Frequency Division Multiplexing (FDM)

ii Time Division Multiplexing (TDM)

Frequency Division Multiplexing Techniques (FDM)

The FDM techniques is the process of translating individual speech circuits (300-3400 Hz)

into pre- assigned frequency slots within the bandwidth of the transmission medium. The

frequency translation is done by amplitude modulation of the audio frequency with an

appropriate carrier frequency. At the output of the modulator a filter network is connected to

select either a lower or an upper side band. Since the intelligence is carried in either side band,

single side band suppressed carrier mode of AM is used.

33

This results in substantial saving of bandwidth mid also permits the use of low power

amplifiers. Please refer Fig. 2.1. FDM techniques usually find their application in analogue

transmission systems. An analogue transmission system is one which is used for transmitting

continuously varying signals.

Figure : 2.1 FDM Principle

Time Division Multiplexing (TDM)

Basically, time division multiplexing involves nothing more than sharing a transmission

medium by a number of circuits in time domain by establishing a sequence of time slots

during which individual channels (circuits) can be transmitted. Thus the entire bandwidth is

periodically available to each channel. Normally all time slots are equal in length. Each

channel is assigned a time slot with a specific common repetition period called a frame

interval. This is illustrated in Fig.

34

Fig Time Divison Multiplexing

SAMPLING

It is the most basic requirement for TDM. Suppose we have an analogue signal Fig.2. 3 (b),

which is applied across a resistor R through a switch S as shown in Fig. 2.3 (a) . Whenever

switch S is closed, an output appears across R. The rate at which S is closed is called the

sampling frequency because during the make periods of S, the samples of the analogue

modulating signal appear across R. Fig. 2.3(d) is a stream of samples of theinput signal which

appear across R. The amplitude of the sample is depend upon the amplitude of the input signal

at the instant of sampling. The duration of these sampled pulses is equal to the duration for

which the switch S is closed. Minimum number of samples are to be sent for any band limited

signal to get a good approximation of the original analogue signal and the same is defined by

the sampling Theorem.

35

Fig 2.3: Sampling Process

"If a band limited signal is sampled at regular intervals of time and at a rate equal toor more

than twice the highest signal frequency in the band, then the sample contains all the

information of the original signal." Mathematically, if fH is the highest frequency in the signal

to be sampled then the sampling frequency Fs needs to be greater than 2 fH.

i.e. Fs>2fH

Let us say our voice signals are band limited to 4 KHz and let sampling frequency be 8 KHz.

Time period of sampling Ts = 1 sec / 8000

or Ts = 125 micro seconds

If we have just one channel, then this can be sampled every 125 microseconds and the

resultant samples will represent the original signal. But, if we are to sample N.

PULSE CODE MODULATION (PCM) PROCESS

Pulse Code Modulation (PCM) converts analog signals to a digital format (signal). This

process has four major steps.

36

• STEP ONE:- FILTERING

Frequencies below 300Hz and above 3400Hz (Voice Frequency range) are filtered from the

analog signal.. The lower frequencies are filtered out to remove electrical noise induced from

the power lines. The upper frequencies are filtered out because they require additional bits and

add to the cost of a digital transmission system. The actual bandwidth of the filtered signal is

3100Hz (3400- 300). It is often referred to as 4kHz.

• STEP TWO:- SAMPLING

The analog signal is sampled 8000 times per second. The rate at which the analog signal is

sampled is related to the highest frequency present in the signal. This is based on Nyquist

Sampling Theorem. In his calculations, Nyquist used a voice frequency range of 4000Hz

(which represents the voice frequency range that contains “intelligent” speech). Thus, the

standard became a sampling rate of 8000Hz, or twice the bandwidth. The signal that is the

result of the sampling process contains sufficient information to accurately represent the

information contained in the original signal. The output of this sampling procedure is a Pulse

Amplitude Modulated, or, PAM signal.

• STEP THREE:- QUANTIZING

In the third step of the A/D conversion process, we quantize the amplitude of the incoming

samples to one of 225 amplitudes on quantizing scale (figure 3.13). Thus, in this step the

sampled signal is matchrd to the segmented scale. The purpose of step three is to measure the

amplitude (or height) of the PAM signal and assign a decimal value that defines the

amplitude. Based on the quantizing scale, each sampled signal is assigned a number between

0 and +127 to define its amplitude.

• STEP FOUR:- ENCODING

In the fourth step of A/D conversion process, the quantized samples are encoded into a digital

bit stream (series of electrical pulses).

37

A DIGITAL ENCODER-

It recognizes the 255 different voltage levels of the quantized samples. Converts each into a

specific string of 8 bits (1s and 0s) that represent a particular voltage value. Fig. is helpful for

understanding the binary code used in the encoding step. Each bit position in the 8-bit word

(byte) iis given a decimal weight (2 to some power ), except for the first bit position. Using

this coding scheme, we can code any number between +127 and –127 and zero.

For example:- If the PAM signal measures +45 on the quantizing scale, the output of the

encoding step is 10101101 (fig 3.15). This binary number (or 8 bit word) ism transmitted over

the network as a series of electrical or optical pulses. This series of pulses is called a digital

bit stream. The PCM process requires a 64000bps channel to encode a 4kHz audio input

signal because 8000samples/sec.*8 bits/word=64000bps. This is known as the DS0 (Digital

Signal 0) or VF (Voice Frequency) in the digital hierarchy. It is the basic building block of the

digital network.

DIGITAL-TO-ANALOG CONVERSION-

At the receive end of the transmission, the digital signal may need to be converted back into

its analog form. The digital-to-analog (D/A) conversion consists of two steps . Each 8-bit

word (byte) that enters the decoder results in one PAM signal value. The decoder: Reads the

8-bit binary word inputs ,creates a sream of 8000 pulses per second. These pulses have an

amplitude of +127 to –127. The filtering process smoothes out the stream of 8000 pulses per

second into an analog waveform that closely resembles the waveform that was input into the

A/D converter at the originating end. The filter stores a part of each pulse’s energy and slowly

releases it until the next pulse arrives. The filter thus reconstructs the analog signal at a rate of

8000 times per second.

SIGNALING IN PCM SYSTEMS

In a telephone network,-the signaling information is used for proper routing of a call between

two subscribers, for providing certain status information like dial tone, busy tone, ring back.

NU tone, metering pulses, trunk offering signal etc. All these functions are grouped under the

general terms "signaling" in PCM systems. The signaling information can be transmitted in

the form of DC pulses (as in step by step exchange) or multi-frequency pulses (as in cross bar

systems) etc.

38

The signaling pulses retain their amplitude for a much longer period than the pulses carrying

speech information. It means that the signaling information is a slow varying signal in time

compared to the speech signal which is fast changing in the time domain. Therefore, a

signaling channel can be digitized with less number of bits than a voice channel. In a 30 chl

PCM system, time slot Ts 16 in each frame is allocated for carrying signaling information.

The time slot 16 of each frame carries the signaling data corresponding to two VF channels

only. Therefore, to cater for 30 channels, we must transmit 15 frames, each having 125

microseconds duration. For carrying synchronization data for all frames, one additional

frame is used. Thus a group of 16 frames (each of 125 microseconds) is formed to make a

"multi-frame". The duration of a multi-frame is 2 milliseconds. The multi-frame has 16 major

time slots of 125 microseconds duration. Each of these (slots) frames has 32 time slots

carrying, the encoded samples of all channels plus the signaling and synchronization data.

Each sample has eight bits of duration 0.400 microseconds (3.9/8 = 0.488) each. The

relationship between the bit duration frame and multi-frame is illustrated in Fig. 2.4(a) & 2.4

(b)

Fig 2.4(a) Multyframe Concept

39

Fig 2.4(b) 2.048 Mbps PCM Multyframe

We have 32 time slots in a frame; each slot carries an 8 bit word.

The total number of bits per frame = 32 x 8 = 256

The total number of frames per seconds is 8000

The total number of bits per second is 256 x 8000 = 2048 K/bits.

Thus, a 30 channel PCM system has 2048 K bits/sec.

40

OPTICAL FIBER COMMUNICATION

HISTORY

The use of visible optical carrier waves or light for communication has been common for

many years. Simple systems such as signal fires, reflecting mirrors and, more recently

signaling lamps have provided successful, if limited, information transfer. Moreover as early

as 1880 Alexander Graham Bell reported the transmission of speech using a light beam. The

photo phone proposed by Bell just for years after the invention of the telephone modulated

sunlight with a diaphragm giving speech transmission over a distance of 200m.

However, although some investigation of the optical communication continued in the early

part of the 20th century its use was limited to mobile, low capacity communication links. This

was due to both the lack of suitable light sources and the problem that light transmission in

the atmosphere is restricted to line of sight and severely affected by disturbances such as rain,

snow, fog dust and atmospheric turbulence.

A renewed interest in optical communication was stimulated in the early 1960s with the

invention of the laser. This device provided a coherent light source, together with the

possibility of the modulation at high frequency.

The proposals for optical communication via optical fibers fabricated from glass to avoid

degradation of the optical signal by the atmosphere were made almost simultaneously in 1966

by Kao and Hock ham and Werts. Such systems were viewed as a replacement for coaxial

cable system, initially the optical fibers exhibited very high attenuation and were therefore

not comparable with the coaxial cable they were to replace. There were also problems

involved in jointing the fiber cables in a satisfactory manner to achieve low loss and to enable

the process to be performed relatively easily and repeatedly in the field.

In coaxial system the channel capacity is 300 to 10800 and the disadvantages of the coaxial

system are digging, electrical disturbance, in winter cable contracts and breaks mutual

induction. The coaxial cable loss is 0.3db per every km.

(i)In microwave system if we double the distance the loss will be increased by 6db.

(ii)For the shorter distance the loss is higher.

(iii)In ofc system Optical wire is small size, light weight, high strength and flexibility. Its

41

transmission benefits includes wide band width, low loss and low cost.

(iv)They are suitable for both analog and digital transmission.

(v)It is not suffered by digging, electrical interference etc. problems.

Fiber Optic System :

Optical Fibre is new medium, in which information (voice, Data or Video) is transmitted

through a glass or plastic fibre, in the form of light, following the transmission sequence give

below

(1)Information is Encoded into Electrical Signals.

(2)Electrical Signals are Coverted into light Signals.

(3)Light Travels Down the Fiber.

(4)A Detector Changes the Light Signals into Electrical Signals.

(5)Electrical Signals are Decoded into Information.

- Inexpensive light sources available.

- Repeater spacing increases along with operating speeds because low loss fiber are used at

high datarates.

Fig: 4.1 Fiber optic system

42

OFC types

The refractive Index profile describes the relation between the indices of the core and

cladding. Two main relationship exists :

(I) Step Index

(II) Graded Index

The step index fibre has a core with uniform index throughout. The profile shows a sharp step

at the junction of the core and cladding. In contrast, the graded index has a non-uniform core.

The Index is highest at the center and gradually decreases until it matches with that of the

cladding. There is no sharp break in indices between the core and the cladding. By this

classification there are three types of fibres :

(I) Multimode Step Index fibre (Step Index fibre)

(II) Multimode graded Index fibre (Graded Index fibre)

(III) Single- Mode Step Index fibre (Single Mode Fibre)

1 .STEP-INDEX MULTIMODE FIBER has a large core, up to 100 microns in diameter. As

a result, some of the light rays that make up the digital pulse may travel a direct route,

whereas others zigzag as they bounce off the cladding. These alternative pathways cause the

different groupings of light rays, referred to as modes, to arrive separately at a receiving point.

The pulse, an aggregate of different modes, begins to spread out, losing its well-defined

shape. The need to leave spacing between pulses to prevent overlapping limits bandwidth that

is, the amount of information that can be sent. Consequently, this type of fiber is best suited

for transmission over short distances, in an endoscope, for instance.

Fig :- STEP-INDEX MULTIMODE FIBER

2. GRADED-INDEX MULTIMODE FIBER contains a core in which the refractive index

diminishes gradually from the center axis out toward the cladding. The higher refractive index

at the center makes the light rays moving down the axis advance more slowly than those near

the cladding.

43

Fig:- GRADED-INDEX MULTIMODE FIBER

3. SINGLE-MODE FIBER has a narrow core (eight microns or less), and the index of

refraction between the core and the cladding changes less than it does for multimode fibers.

Light thus travels parallel to the axis, creating little pulse dispersion. Telephone and cable

television networks install millions of kilometers of this fiber every year.

Fig:- . SINGLE-MODE FIBER

OPTICAL FIBRE PARAMETERS

Optical fiber systems have the following parameters.

(I) Wavelength

(II) Frequency

(III) Window

1 WAVELENGTH

It is a characteristic of light that is emitted from the light source and is measures in

nanometers (nm). In the visible spectrum, wavelength can be described as the colour of the

light.

For example, Red Light has longer wavelength than Blue Light, Typical wavelength for fibre

use are 850nm, 1300nm and 1550nm all of which are invisible.

2 FREQUENCIES

It is number of pulse per second emitted from a light source. Frequency is measured in units

of hertz (Hz). In terms of optical pulse 1Hz = 1 pulse/ sec.

3 WINDOWS

A narrow window is defined as the range of wavelengths at which a fibre best operates.

Typical windows are given below :

44

FEATURES

The fiber optics has become a preferred medium due to its some important features like:

(1) The bandwidth of the fiber and light beam is extremely wide. It is possible to handle

signals which turn on and off at gigabit per second rates (1 gigabit, gbit =1000 Mbitts).

(2)The fiber itself is very thin and not expensive. The thinness means that it is easy to handle,

and many fibers can be put in the trenches or narrow conduits.

(3)The light signal is absolutely immune to electrical noise from any sources. Even if there

are sources of electrical noise directly touching the cable, the electric fields of the noise

source cannot affect the light beam in the fiber.

(4)The signal in the cable is secure from unauthorized listeners. It is relatively hard to tap into

the cable without being noticed, and the entire light signal is confined within the fiber. No

light escapes to the outside where someone else could see it.

(5)Since there is no electricity or electrical energy in the fiber, it can be run in hazardous

atmospheres where the danger of explosion from spark may exist. Also, the fiber itself is

immune to many types of poisonous gases, chemicals, and water.

OFC SPLICING

Splices are permanent connection between two fibres. The splicing involves cutting of the

edges of the two fibres to be spliced.

Splicing Methods

The following three types are widely used :

45

1. Adhesive bonding or Glue splicing.

2. Mechanical splicing.

3. Fusion splicing.

Adhesive Bonding or Glue Splicing

This is the oldest splicing technique used in fibre splicing. After fibre end preparation, it is

axially aligned in a precision V–groove. Cylindrical rods or another kind of reference surfaces

are used for alignment. During the alignment of fibre end, a small amount of adhesive or glue

of same refractive index as the core material is set between and around the fibre ends. A two

component epoxy or an UV curable adhesive is used as the bonding agent. The splice loss of

this type of joint is same or less than fusion splices. But fusion splicing technique is more

reliable, so at present this technique is very rarely used.

Mechanical Splicing

This technique is mainly used for temporary splicing in case of emergency repairing. This

method is also convenient to connect measuring instruments to bare fibres for taking various

measurements. The mechanical splices consist of 4 basic components :

(i) An alignment surface for mating fibre ends.

(ii) A retainer

(iii) An index matching material.

(iv) A protective housing

A very good mechanical splice for M.M. fibres can have an optical performance as good as

fusion spliced fibre or glue spliced. But in case of single mode fibre, this type of splice cannot

have stability of loss.

Fusion Splicing

The fusion splicing technique is the most popular technique used for achieving very low

splice losses. The fusion can be achieved either through electrical arc or through gas

flame.The process involves cutting of the fibres and fixing them in micro–positioners on the

fusion splicing machine. The fibres are then aligned either manually or automatically core

aligning (in case of S.M. fibre) process. Afterwards the operation that takes place involve

withdrawal of the fibres to a specified distance, preheating of the fibre ends through electric

46

arc and bringing together of the fibre ends in a position and splicing through high temperature

fusion.

EQUIPMENT REQUIRE FOR OFC JOINT

1) Optical fiber fusion splicer specification ( spicer machine )

• AC input – 100 to 240v, frequency – 50/60Hz

•DC input 12v/aA

2) Fiber cutter

•It converts irregular shaped fiber end into smooth & flat end.

3) Chemicals used in OFC joint

• HAXENE : To remove jelly from the fiber

• ACETONE : For cleaning the OFC

• ISO PROPENOT: For smoothness of optical glass.

4) Sleeve: - To enclose fiber joint.

5) Tool Kit

6) Joint kit.

• Joint encloser

• Buffer

• Adhesive tap.

7) Generator /12V Battery

8) Cotton clothes for fiber cleaning.

ADVANTAGES OF OPTICAL FIBER COMMUNICATION

• Enormous Potential Bandwidth: - The optical carrier frequency in the range 1013 to 1016

Hz (generally in the near infrared around 1014 Hz or 105 GHz) yields a far grater potential

transmission bandwidth than metallic cable systems. (i.e. coaxial cable bandwidth up to

around 500 MHz) or even millimetre wave radio systems (i.e. systems currently operating

with modulation bandwidths of 700 MHz ). At present, the bandwidth available to fiber

systems is not fully utilized but modulation at several gigahertz over a hundred kilometers and

hundreds of megahertz over three hundred kilometers without intervening electronics

(repeaters) is possible. Therefore, the information – carrying capacity of optical fiber systems

has proved far superior to the best copper cable systems. By comparison the losses in

47

wideband coaxial cable systems restrict the transmission distance to only a few kilometers at

bandwidths over one hundred megahertz.

Although the usable fiber bandwidth will be extended further towards the optical carrier

frequency, it is clear that this parameter is limited by the use of a signal optical carrier signal.

Hence a much enhanced bandwidth utilization for an optical fiber can be achieved by

transmitting several optical signals, each at different centre wavelengths, in parallel on the

same fiber. This wavelength division multiplexed operation, particularly with dense packing

of the optical wavelengths ( or, essentially, fine frequency spacing ), offers the potential for a

fiber information carrying capacity which is many orders of magnitude in excess of that

obtained using copper cables or a wideband radio system.

• Small Size and Weight: - Optical fibers have very small diameters which are often no

grater than the diameter of a human hair. Hence, even when such fibers are covered with

protective coatings they are far smaller and much lighter than corresponding copper cables.

This is a tremendous boon towards the alleviation of duct congestion in cities, as well as

allowing for an expansion of signal transmission within mobiles such as aircraft, satellites and

even ships.

• Electrical Isolation: - Optical fibers which are fabricated from glass, or sometimes a plastic

polymer, are electrical insulators and therefore, unlike their metallic counterparts, they do not

exhibit earth loop and interface problems. Furthermore, this property makes optical fiber

transmission ideally suited for communication in electrically hazardous environments as the

fibers create no arching or spark hazard at abrasions or short circuits.

• Immunity To Interference And Crosstalk :- Optical fibers form a dielectric waveguide

and are therefore free from electromagnetic interference (EMI), radiofrequency interference

(RFI), or switching transients giving electromagnetic pulses (EMP). Hence the operation of an

optical fiber communication system is unaffected by transmission through an electrically

noisy environment and the fiber cable requires no shielding from EMI. The fiber cable is also

not susceptible to lightning strikes if used overhead rather than underground. Moreover, it is

fairly easy to ensure that there is no optical interference between fibers and hence, unlike

communication using electrical conductors, crosstalk is negligible, even when many fibers are

cabled together.

• Signal Security: - The light from optical fibers does not radiate significantly and therefore

they provide a high degree of signal security. Unlike the situation with copper cables, a

48

transmitted optical signal cannot be obtained from a fiber in a noninvasive manner (i.e.

without drawing optical power from the fiber). Therefore, in theory, any attempt to acquire a

message signal transmitted optically may be detected. This feature is obviously attractive for

military, banking and general data transmission (i.e. computer network) application.

• Low Transmission Loss :- The development of optical fibers over the last twenty years has

resulted in the production of optical fiber cables which exhibit very low attenuation or

transmission loss in comparison with the best copper conductors. Fibers have been fabricated

with losses as low as 0.2 dB km-1 (see Section 3.3.2) and this feature has become a major

advantage of optical fiber communications. It facilitates the implementation of

communication links with extremely wide repeater spacing ( long transmission distances

without intermediate electronics), thus reducing both system cost and complexity. Together

with the already proven modulation bandwidth capability of fiber cable this property provides

a totally compelling case for the adoption of optical fiber communication in the majority of

long-haul telecommunication applications.

• Ruggedness and Flexibility :- Although protective coatings are essential, optical fibers may

be manufactured with very high tensile strengths. Perhaps surprisingly for a glassy substance,

the fibers may also be bent to quite small radii or twisted without damage. Furthermore cable

structures have been developed which have proved flexible, compact and extremely rugged.

Taking the size and weight advantage into account, these optical fiber cables are generally

superior in terms of storage, transportation, handling and installation to corresponding copper

cables, whilst exhibiting at least comparable strength and durability.

• System Reliability And Ease Of Maintenance :- These features primarily stem from the

low loss property of optical fiber cables which reduces the requirement for intermediate

repeaters or line amplifiers to boost the transmitted signal strength. Hence with fewer

repeaters, system furthermore, the reliability of the optical components is no longer a problem

with predicted lifetimes of 20 to 30 years now quite common. Both these factors also tend to

reduce maintenance time and costs.

• Potential Low Cost :- The glass which generally provides the optical fiber transmission

medium is made from sand – not a scarce resource. So, in comparison with copper

conductors, optical fibers offer the potential for low cost line communication. Although over

recent years this potential has largely been realized in the costs of the optical fiber

transmission medium which for bulk purchases is now becoming competitive with copper

49

wires (i.e. twisted pairs), it has not yet been achieved in all the other component areas

associated with optical fiber communication. For example, the costs of high performance

semiconductor lasers and detector photodiodes are still relatively high, as well as some of

those concerned with the connection technology ( demountable connectors, couplers, etc. ).

DRAWBACKS OF OPTICAL FIBER COMMUNICATION

The use of fibers for optical communication does have some drawbacks in practice. Hence to

provide a balance picture these disadvantages must be considered. They are

• The fragility of the bare fibers;

• The small size of fibers and cables which creates some difficulties with splicing and forming

connectors;

• Some problems involved with forming low loss T- couplers;

• Some doubts in relations to the long term reliability of optical fibers in the presence of

moisture;

• An independent electrical power feed is required for any electronic repeaters;

• New equipment and field practice are required;

• Testing procedures tend to be more complex.

APPLICATION OF THE OPTICAL FIBER COMMUNICATION

TRUNK NETWORK

The trunk or toll network is used for carrying telephone traffic between major conurbations.

Hence there is generally a requirement for the use of transmission systems which have a high

capacity in order to minimize costs per circuit. The transmission distance for trunk systems

can very enormously from under 20 km to over 300 km, and occasionally to as much as 1000

km. Therefore transmission systems which exhibit low attenuation and hence give a

maximum distance of unrepeatered operation are the most economically viable. In this context

optical fiber systems with their increased bandwidth and repeater spacing offer a distinct

advantage.

JUNCTION NETWORK

The junction or interoffice network usually consists of routes within major conurbations over

distances of typically 5 to 20 km. However, the distribution of distances between switching

50

centers (telephone exchanges ) or offices in the junction network of large urban areas varies

considerably for various countries.

MILITARY APPLICATION

In these applications, although economics are important, there are usually other, possibly

overriding, considerations such as size, weight, deployability, survivability (in both

conventional and nuclear attack and security. The special attributes of optical fiber

communication system therefore often lend themselves to military use.

•MOBILES

One of the most promising areas of milita5ry application for optical fiber communication

is within military mobiles such as aircraft, ships and tanks. The small size and weight of

optical fibers provide and attractive solution to space problems in these mobiles which are

increasingly equipped with sophisticated electronics. Also the wideband nature of optical

fiber transmission will allow the multiplexing of a number of signals on to a common bus.

Furthermore, the immunity of optical transmission to electromagnetic interference (EMI) in

the often noisy environment of military mobiles is a tremendous advantage. This also applies

to the immunity of optical fiber to lighting and electromagnetic pulses (EMP) especially

within avionics. The electrical isolation, and therefore safety, aspect of optical fiber

communication also proves invaluable in these applications, allowing routing through both

fuel tanks and magazines.

•COMMUNICATION LINKS

The other major area for the application of optical fiber communication in the military sphere

includes both short and long distance communication links. Short distance optical fiber

systems may be utilized to connect closely spaced items of electronics equipment in such

areas as operations rooms and computer installations. A large number of this system have

already been installed in military installations in the united kingdom. These operate over

distances from several centimeters to a few hundred meters at transmission rates between 50

bauds and 4.8 kbits-1. In addition a small number of 7 MHz video links operating over

distances of up to 10 m are in operation. There is also a requirement for long distance

communication between military installations which could benefit from the use of optical

fibers. In both these advantages may be gained in terms of bandwidth, security and immunity

to electrical interference and earth loop problems over conventional copper systems.

51

CIVIL APPLICATION

The introduction of optical fiber communication systems into the public network has

stimulated investigation and application of these transmission techniques by public utility

organizations which provide their own communication facilities over moderately long

distances. For example these transmission techniques may be utilized on the railways and

along pipe and electrical power lines. In these applications, although high capacity

transmission is not usually required, optical fibers may provide a relatively low cost solution,

also giving enhanced protection in harsh environment, especially in relation to EMI and EMP.

Experimental optical fiber communication systems have been investigated within a number of

organizations in Europe, North America and Japan. For instance, British Rail has successfully

demonstrated a 2 Mbits-1 system suspended between the electrical power line gantries over a

6 km route in Cheshire. Also, the major electric power companies have shown a great deal of

interest with regard to the incorporation of optical fibers within the metallic earth of overhead

electric power lines.

52

GSM

INTRODUCTION

A GSM system is basically designed as a combination of three major subsystems: the network

subsystem, the radio subsystem, and the operation support subsystem. In order to ensure that

network operators will have several sources of cellular infrastructure equipment, GSM

decided to specify not only the air interface, but also the main interfaces that identify different

parts. There are three dominant interfaces, namely, an interface between MSC and the base

Transceiver Station (BTS), and an Um interface between the BTS and MS.

GSM NETWORK STRUCTURE

Every telephone network needs a well-designed structure in order to route incoming called to

the correct exchange and finally to the called subscriber. In a mobile network, this structure is

of great importance because of the mobility of all its subscribers [1-4]. In the GSM system,

the network is divided into the following partitioned areas.

• GSM service area;

• PLMN service area;

• MSC service area;

• Location area;

• Cells.;

Fig:- GSM Architechture

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MS(Mobile Station)

The MS includes radio equipment and the man machine interface (MMI) that a subscribe

needs in order to access the services provided by the GSM PLMN. MS can be installed in

Vehicles or can be portable or handheld stations. The MS may include provisions for data

communication as well as voice. A mobile transmits and receives message to and from the

GSM system over the air interface to establish and continue connections through the system.

BASE STATION SYSTEM(BSS)

The BSS is a set of BS equipment (such as transceivers and controllers) that is in view by the

MSC through a single A interface as being the entity responsible for communicating with

MSs in a certain area. The radio equipment of a BSS may be composed of one or more cells.

A BSS may consist of one or more BS. The interface between BSC and BTS is designed as an

A-bis interface. The BSS includes two types of machines: the BTS in contact with the MSs

through the radio interface and the BSC, the latter being in contact with the MSC. The

function split is basically between transmission equipment, the BTS, and managing equipment

at the BSC. A BTS compares radio transmission and reception devices, up to and including

the antennas, and also all the signal processing specific to the radio interface. A single

transceiver within BTS supports eight basic radio channels of the same TDM frame. A BSC is

a network component in the PLMN that function for control of one or more BTS. It is a

functional entity that handles common control functions within a BTS.

BTS(Base Transreceive System)

As stated, the primary responsibility of the BTS is to transmit and receive radio signals from a

mobile unit over an air interface. To perform this function completely, the signals are

encoded, encrypted, multiplexed, modulated, and then fed to the antenna system at the cell

site. Trans-coding to bring 13- kbps speech to a standard data rate of 16 kbps and then

combining four of these signals to 64 kbps is essentially a part of BTS, though, it can be done

at BSC or at MSC. The voice communication can be either at a full or half rate over logical

speech channel. In order to keep the mobile synchronized, BTS transmits frequency and time

synchronization signals over frequency correction channel (FCCH and BCCH logical

channels. The received signal from the mobile is decoded, decrypted, and equalized for

channel impairments. Random access detection is made by BTS, which then sends the

54

message to BSC. The channel subsequent assignment is made by BSC. Timing advance is

determined by BTS. BTS signals the mobile for proper timing adjustment. Uplink radio

channel measurement corresponding to the downlink measurements made by MS has to be

made by BTS.

BTS-BSC Configurations

There are several BTS-BSC configurations: single site; single cell; single site; multicell; and

multisite, multicell. These configurations are chosen based on the rular or urban application.

These configurations make the GSM system economical since the operation has options to

adapt the best layout based on the traffic requirement. Thus, in some sense, system

optimization is possible by the proper choice of the configuration. These include Omni

directional rural configuration where the BSC and BTS are on the same site; chain and

multidrop loop configuration in which several BTSs are controlled by a single remote BSC

with a chain or ring connection topology; rural star configuration in which several BTSs are

connected by individual lines to the same BSC; and sectorized urban configuration in which

three BTSs share the same site amd are controlled by either a collocated or remote BSC.

BSC(Base Switching Controller)

The BSC, as discussed, is connected to the MSC on one side and to the BTS on the other. The

BSC performs the Radio Resource (RR) management for the cells under its control. It assigns

and release frequencies and timeslots for all MSs in its own area. The BSC performs the

intercell handover for MSs moving between BTS in its control. It also reallocates frequencies

to the BTSs in its area to meet locally heavy demands during peak hours or on special events.

The BSC controls the power transmission of both BSSs and MSs in its area. The minimum

power level for a mobile unit is broadcast over the BCCH. The BSC provides the time and

frequency synchronization reference signals broadcast by its BTSs. The BSC also measures

the time delay of received MS signals relative to the BTS clock. If the received MS signal is

not centered in its assigned timeslot at the BTS, The BSC can direct the BTS to notify the MS

to advance the timing such that proper synchronization takes place.

55

MSC(Mobile Switching Controler)

As stated, the main function of the MSC is to coordinate the set up of calls between GSM

mobile and PSTN users. Specifically, it performs functions such as paging, resource

allocation, location registration, and encryption. Specifically, the call-handling function of

paging is controlled by MSC. MSC coordinates the set up of call to and from all GSM

subscribers operating in its areas. The dynamics allocation of access resources is done in

coordination with the BSS. More specifically, the MSC decides when and which types of

channels should be assigned to which MS. The channel identity and related radio parameters

are the responsibility of the BSS, The MSC provides the control of interworking with

different networks. It is transparent for the subscriber authentication procedure. The MSC

supervises the connection transfer between different BSSs for MSs, with an active call,

moving from one call to another. This is ensured if the two BSSs are connected to the same

MSC but also when they are not . In this latter case the procedure is more complex, since

more then one MSC in involved. The MSC performs billing on calls for all subscribers based

in its areas. When the subscriber is roaming elsewhere, the MSC obtains data for the call

billing from the visited MSC. Encryption parameters transfers from VLR to BSS to facilitate

ciphering on the radio interface are done by MSC. The exchange of signaling information on

the various interface toward the other network elements and the management of the interface

themselves are all controlled by the MSC. Finally, the MSC serves as a SMS gateway to

forward SMS messages from Short Message Service Centers (SMSC) to the subscribers and

from the subscribers to the SMSCs. It thus acts as a message mailbox and delivery system.

VLR(Visitor Lacation Register)

The VLR is collocated with an MSC. A MS roaming in an MSC area is controlled by the

VLR responsible for that area. When a MS appears in a LA, it starts a registration procedure.

The MSC for that area notices this registration and transfers to the VLR the identify of the LA

where the MS is situated. A VLR may be in charge of one or several MSC LA’s. The VLR

constitutes the databases that support the MSC in the storage and retrieval of the data of

subscribers present in its area. When an MS enters the MSC area borders, it signals its arrival

to the MSC that stores its identify in the VLR. The information necessary to manage the MS

is contained in the HLR and is transferred to the VLR so that they can be easily retrieved if so

required.

56

HLR(Home Location Register)

The HLR is a database that permanently stores data related to a given set of subscribers. The

HLR is the reference database for subscriber parameters. Various identification numbers and

addresses as well as authentication parameters, services subscribed, and special routing

information are stored. Current subscriber status including a subscriber’s temporary roaming

number and associated VLR if the mobile is roaming, are maintained.

The HLR provides data needed to route calls to all MS-SIMs home based in its MSC area,

even when they are roaming out of area or in other GSM networks. The HLR provides the

current location data needed to support searching for and paging the MS-SIM for incoming

calls, wherever the MS- SIM may be. The HLR is responsible for storage and provision of

SIM authentication and encryption parameters needed by the MSC where the MS-SIM is

operating. It obtains these parameters from the AUC. The HLR maintains record of which

supplementary service each user has subscribed to and provides permission control in

granting services. The HLR stores the identification of SMS gateways that have messages for

the subscriber under the SMS until they can be transmitted to the subscriber and receipt is

knowledge. Some data are mandatory, other data are optional. Both the HLR and the VLR can

be implemented in the same equipment in an MSC (collocated). A PLMN may contain one or

several HLRs.

AUC(Authentic Unit Controller)

The AUC stores information that is necessary to protect communication through the air

interface against intrusions, to which the mobile is vulnerable. The legitimacy of the

subscriber is established through authentication and ciphering, which protects the user

information against unwanted disclosure. Authentication information and ciphering keys are

stored in a database within the AUC, which protects the user information against unwanted

disclosure and access. In the authentication procedure, the key Ki is never transmitted to the

mobile over the air path, only a random number is sent. In order to gain access to the system,

the mobile must provide the correct Signed Response (SRES) in answer to a random number

(RAND) generated by AUC. Also, Ki and the cipher key Kc are never transmitted across the

air interface between the BTS and the MS. Only the random challenge and the calculated

response are transmitted. Thus, the value of Ki and Kc are kept secure. The cipher key, on the

other hand, is transmitted on the SS7 link between the home HLR/AUC and the visited MSC,

57

which is a point of potential vulnerability. On the other hand, the random number and cipher

key is supposed to change with each phone call, so finding them on one call will not benefit

using them on the next call. The HLR is also responsible for the “authentication” of the

subscriber each time he makes or receives a call. The AUC, which actually performs this

function, is a separate GSM entity that will often be physically included with the HLR. Being

separate, it will use separate processing equipment for the AUC database functions.

EIR (EQUIPMENT IDENTIFY REGISTER)

EIR is a database that stores the IMEI numbers for all registered ME units. The IMEI

uniquely identifies all registered ME. There is generally one EIR per PLMN. It interfaces to

the various HLR in the PLMN. The EIR keeps track of all ME units in the PLMN. It

maintains various lists of message. The database stores the ME identification and has nothing

do with subscriber who is receiving or originating call. There are three classes of ME that are

stored in the database, and each group has different characteristics.

• White List: contains those IMEIs that are known to have been assigned to valid MS’s. This

is the

category of genuine equipment.

• Black List: contains IMEIs of mobiles that have been reported stolen.

• Gray List: contains IMEIs of mobiles that have problems (for example, faulty software,

wrong make

of the equipment). This list contains all MEs with faults not important enough for barring.

58

CDMA

INTRODUCTION

Access network, the network between local exchange and subscriber, in the Telecom Network

accounts for a major portion of resources both in terms of capital and manpower. So far, the

subscriber loop has remained in the domain of the copper cable providing cost effective

solution in past. Quick deployments of subscriber loop, coverage of inaccessible and remote

locations coupled with modern technology have led to the emergence of new Access

Technologies. The various technological options available are as follows :

1. Multi Access Radio Relay

2. Wireless In Local Loop

3. Fibre In the Local Loop

Different Codes

Walsh Code :

In CDMA the traffic channels are separated by unique “Walsh” code. All such codes are

orthogonal to each other. The individual subscriber can start communication using one of

these codes. These codes are traffic channel codes and are used for orthogonal spreading of

the information in the entire bandwidth. Orthogonality provides nearly perfect isolation

between the multiple signals transmitted by the base station. The basic concept behind

creation of the code is as follows:

(a) Repeat the function right

(b) Repeat the function below

(c) Invert function (diagonally)

Long code :

the long pseudo random noise (PN) sequence is based on 242 characteristic polynomial. With

this long code the data in the forward direction (Base to Mobile) is scrabled. The PN codes

59

are generated using linear shift registers. The long code is unique for the subscribers and is

known as users address mask.

Short Code :

The short pseudo random noise (PN) sequence is based on 215 characteristic polynomial. This

short code differentiates the cells & the sectors in a cell. It also consists of codes for I & Q

channel feeding the modulator.

Advantages

CDMA wireless access provides the following unique advantages:

1. Larger Capacity :

let us discuss this issue with the help of Shannon’s Theorem. It states that the channel

capacity is related to product of available band width and S/N ratio.

C = W log 2 (1+S/N)

Where C = channel capacity

W = Band width available

S/N = Signal to noise ratio.

It is clear that even if we improve S/N to a great extent the advantage that we are expected to

get in terms of channel capacity will not be proportionally increased. But instead if we

increase the bandwidth (W), we can achieve more channel capacity even at a lower S/N. That

forms the basis of CDMA approach, wherein increased channel capacity is obtained by

increasing both W & S/N. The S/N can be increased by devising proper power control

methods.

2.Vocoder and variable data rates:

As the telephone quality speech is band limited to 4 Khz when it is digitized with PCM its bit

rate rises to 64Kb/s Vocoding compress it to a lower bit rate to reduce bandwidth. The

transmitting vocoder takes voice samples and generates an encoded speech/packet for

transmission to the receiving vocoder. The receiving Vocoder decodes the received speech

packet into voice samples. One of the important feature of the variable rate vocoder is the use

of adaptive threshold to determine the required data rate. Vocoders are variable rate vocodes.

By operating the vocoder at half rate on some of the frames the capacity of the system can be

60

enhanced without noticeable degradation in the quality of the speech. This phenomenon helps

to absorb the occasional heavy requirement of traffic apart from suppression of background

noise. Thus the capacity advantage makes spread spectrum an ideal choice for use in areas

where the frequency spectrum is congested.

3.Seamless Hand-off :

CDMA provides soft hand-off feature for the mobile crossing from one cell to another cell by

combining the signals from both the cells in the transition areas. This improves the

performance of the network at the boundaries of the cells, virtually eliminating the dropped

calls.

4.No Frequency Planning :

A CDMA system requires no frequency planning as the adjacent cells use the same common

frequency. A typical cellular system (with a repetition rate of 7) and a CDMA system is

shown in the following figures which clearly indicates that in a CDMA network no frequency

planning is required.

Fig: CDMA 38frequency

Fig: GSM Frequency

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5. High Tolerance to Interference :

The primary advantage of spread spectrum is its ability to tolerate a fair amount of interfering

signals as compared to other conventional systems. This factor provides a considerable

advantage from a system point of view.

BROAD BAND

INTRODUCTION

With the evolution of computer networking and packet switching concept a new era of

integrated communication has emerged in the telecom world. Rapid growth of data

communication market and popularity of Internet, reflect the needs of enhanced infrastructure

to optimize the demand of traffic. Integration of telecom and computer networking technology

trend has further amplified the importance of telecommunications in the field of information

communication. It becomes a tool for the conveyance of information, and thus can be critical

to the development process.Telecommunications has become one of the most important

infrastructures that are very essential to the socio-economic well being of any nation. As the

Internet market continues to explode, demand for greater bandwidth and faster connection

speeds have led to several technological approaches developed to provide broadband access to

all consumers. The demand for high-speed bandwidth is growing at a fast pace, driven mostly

by growth in data volumes as the Internet and related networks become more central to

business operations. The rapid growth of distributed business applications, e-commerce, and

bandwidth-intensive applications (such as multimedia, videoconferencing, and video on

demand) generate the demand for bandwidth and access network.

IMPLEMENTATION OF BROADBAND

To Strengthen Broadband Penetration, the Government of India has formulated a Broadband

Policy whose main objectives are to:-

• Establish a regulatory framework for the carriage and the content of information in the

scenario of convergence.

• Facilitate development of national infrastructure for an information based society.

• Make available broadband interactive multimedia services to users in the public network.

62

• Provide high speed data and multimedia capability using new technologies to all towns with

a population greater than 2 lakhs.

• Make available Internet services at panchayat (village) level for access to information to

provide product consultancy and marketing advice.

TECHNOLOGY OPTIONS FOR BROADBAND SERVICES

• Narrow Band :2.4 kbps – 128kbps

• Broadband: 256kbps – 8000kbps

• LAN: 1000kbps – 100Mbps / Giga Ethernet Various Access Technologies are used for the

delivery of broadband services. Broadband communications technology can be divided

broadly in to Following categories: -

• Wireline Technology

• Wireless Technologies Service providers according to available technology and access

provide the broadband services to customers. The access technologies that are adopted by the

services providers are mainly Optical Fiber Technologies, DSL on copper loop, Cable TV

Network, Satellite Media, cellular and fixed wireless, Terrestrial Wireless etc. Technology

options for broadband services may be classified according to the mode of access. Wire line

Technologies include

• Digital Subscriber Lines (DSL) on copper loop

• Optical Fiber Technologies

• Cable TV Network

• PLC (Power Line Communication) Wireless Technologies include

• Satellite Media

• Terrestrial Wireless

• 3G Mobile

• Wi-Fi (Wireless Fidelity)

• WiMax

• LMDS and MMDS

• FSO (Free Space Optics)

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BROADBAND NETWORK

The broadband services reached to customer from the three providers. Basically these are

Service Provider, Network Provider and Access Provider. The role of Network Provider is to

provide the services offered to customer through the access extended by Access Provider.

There are various types of networks which are capable of transmitting and managing the

broadband traffic to desired nodes or locations.

Wire line access technology through DSL, Fiber, Cable etc are generally adopts:

• IP based Network

• ATM Network

Wireless access technology through Wi-Fi, Wi-Max. 3G mobile etc provides wireless access

to ingress point of any core network any migrates to Internet world.

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INTERNET

INTRODUCTION

• Smaller private version of Internet. It uses Internet protocols to create enterprise-wide

network which may consists of interconnected LANs.

• It may or may not include connection to Internet.

• Intranet is an internal information system based on Internet technology and web protocols

for implementation within a corporate organization.

• This implementation is performed in such a way as to transparently deliver the immense

informational resources of an organization to each individual’s desktop with minimal cost,

time and effort.

• The Intranet defines your organization and display it for everyone to see.

WHO NEEDS AN INTRANET:

In an Intranet environment is used to communicate over two or more networks across

different locations.

1. Users having multi-locations with multi-networks.

2. Users having single locations with multi-networks.

3. Users having single locations with single networks.

WHAT’S REALLY COOL ABOUT INTRANET:

From a technology point of view, an Intranet is simply beautiful Because:

1. It is saleable.

2. It is Interchangeable.

3. It is platform independent

4. It is Hardware independent.

5. It is vendor independent.

WHY INTRANET FOR AN ORGANIZATION:

• Quick access to voice, video, data and other resources needed by users.

• Variety of valuable applications of Intranet applications improve communication and

productivity across all areas of an enterprise. An Intranet can give immediate access to

products specifications, pricing charts and new collateral’s, sales lead, competitive

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information and list of customer wins Including profit/loss analysis, thus boosting the success

of the business.

APPLICATIONS OF INTRANET

1. Publishing Corporate documents Corporate documents such as newsletters, annual reports,

maps, company facilities, price lists, product’s information literature can be easily published

and propagated across an organization. Intranet technology facilitates efficient, timely and

accurate communication across the entire corporate organization and cuts down on the cost of

publishing the information on paper every now and then.

2. Access into searchable directories Intranet provides rapid access to corporate phone books

and the like. By using this technology, information can be made more widely available.

Excellent Mailing Facilities .With Intranet mail products mailing attachment of documents,

sound, vision And other multimedia is facilitated. With the evolution of this web technology

one-to-many communication has become more effective.

3. Proper Sharing of Information Using Intranet technology, applications such as Bulletin

Board Services can help every individual in an organization to put forth his views on various

topics and discuss it with others in the organization.

4. Developing Groupware Applications The flow of documents can be automated by

incorporating intranet in an organization. Thus the overall efficiency of an organization

increases as less manual and paper involvement will be required. Typical examples are

sanctioning of expense reports/travel reports, Conference room booking, etc.

FIG: TYPICAL INTERANET SETUP

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TECHNICAL OVERVIEW OF THE INTRANET TECHNOLOGY

Intranet runs on open TCP/IP network, enable companies to employ the same type of servers

and browser used for World Wide Web for internal applications distributed over the corporate

LAN . A typical Intranet implementation involves a high end machine called a server which

can be accessed by individual PCs commonly referred to as clients, through the network.

The Intranet site setup can be quite inexpensive, especially if your users are already connected

by LAN. Most popular Intranet web servers can run on a platform widely found in most

organizations. Basic requirements for setting up an intranet site are:

REQUIREMENTS :

Software :

• Server : OS can be Windows server, Unix, LINUX .Web Server s/w should be installed

• Client : OS can be Windows workstation, LINUX .Web Browser software

HARDWARE:

• Server: 4 GB RAM, 360 GB secondary storage, Pentium processor with CD ROM .

• Client: 1GB RAM, 180 GB Secondary storage, Pentium processor .

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Wi-Fi

INTRODUCTION

Scope:Wi-Fi is a registered trademark by the Wi-Fi Alliance. The products tested and

approved as "Wi-Fi Certified" are interoperable with each other, even if they are from

different manufacturer. It is Short form for “Wireless-Fidelity” and is meant to generically

refer to any type of ‘802.11’ network, whether ‘802.11’b, ‘802.11’a, dual-band, etc. Initially

the term "Wi-Fi" was used in place of the 2.4GHz ‘802.11’b standard, in the same way that

"Ethernet" is used in place of IEEE 802.3 but Alliance has expanded the generic use of the

term to cover ‘802.11’a, dual-band etc.

GENERAL DESCRIPTION OF WI-FI NETWORK:

A Wi-Fi network provides the features and benefits of traditional LAN technologies such as

Ethernet and Token Ring without the limitations of wires or cables. It provides the final few

metres of connectivity between a wired network and the mobile user thereby providing

mobility, scalability of networks and the speed of installation. WIFI is a wireless LAN

Technology to deliver wireless broad band speeds up to 54 Mbps to Laptops, PCs, PDAs ,

dual mode wifi enabled phones etc. In a typical Wi-Fi configuration, a transmitter/receiver

(transceiver) device, called the Access Point (AP), connects to the wired network from a fixed

location using standard cabling. A wireless Access Point combines router and bridging

functions, it bridges network traffic, usually from Ethernet to the airwaves, where it routes to

computers with wireless adapters. The AP can reside at any node of the wired network and

acts as a gateway for wireless data to be routed onto the wired network as shown in Figure-It

supports only 10 to 30 mobile devices per Access Point (AP) depending on the network

traffic. Like a cellular system, the Wi-Fi is capable of roaming from the AP and re-

connecting to the network through another AP. The Access Point (or the antenna attached to

the Access Point) is usually mounted high but may be mounted essentially anywhere that is

practical as long as the desired radio coverage is obtained.

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Fig: A typical Wi-Fi network

Fig: Extending Wi-Fi coverage with multiple AP

Wi-Fi Network Configuration:

(1.) A Wireless Peer-To-Peer Network: This mode is also known as ADHOC mode. Wi-Fi

networks can be simple or complex. At its most basic, two PCs equipped with wireless

adapter cards can set up an independent network whenever they are within range of one

another. This is called a peer-to-peer network. It requires no administration or pre-

configuration. In this case, each client would only have access to the resources of the other

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client and not to a central server as shown in Figure-

Fig: Peer to Peer network

(2.)Client and Access Point: This is known as INFRASTUCTURE mode and is normally

employed. However, wireless gateway can be configured to enable peer to peer

communication in this mode as well. In this mode, one Access Point is connected to the wired

network and each client would have access to server resources as well as to other clients. The

specific number client depends on the number and nature of the transmissions involved. Many

real-world applications exist where a single Access Point services from 15 to 50 client devices

as shown in Figure-

Fig: Server and Client network in Wi-Fi

(3.) Multiple Access Points and Roaming: Access points can be connected to each other

through UTP cable or they can be connected to each other over radio through wireless

bridging. There is an option to connect access points in a mesh architecture where in event of

a fault in an access point the network heals itself and connectivity is ensured through other

access point. This changeover takes place dynamically.

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Fig:- Multiple Access Points and Roaming in Wi-Fi

BENEFITS OF WI-FI:

In a Wi-Fi users can access shared information without looking for a place to plug in, and

network managers can set up or augment networks without installing or moving wires. Wi-Fi

offers the following productivity, conveniences, and cost advantages over traditional wired

networks:

• Mobility: Wi-Fi systems can provide LAN users with access to real-time information

anywhere in their organization. This mobility supports productivity and service opportunities

not possible with wired networks.

• Installation Speed and Simplicity: Installing a Wi-Fi system can be fast and easy and can

eliminate the need to pull cable through walls and ceilings.

• Installation Flexibility: Wireless technology allows the network to go where wire cannot go.

• Reduced Cost-of-Ownership: While the initial investment required for Wi-Fi hardware can

be higher than the cost of wired LAN hardware, overall installation expenses and life-cycle

costs can be significantly lower. Long-term cost benefits are greatest in dynamic

environments requiring frequent moves, adds, and changes.

LIMITATION OF WI-FI NETWORKS:

• Coverage: A single Access Point can cover, at best, a radius of only about 60 metres.

Hundreds of Access Points are necessary to provide seamless coverage in small area. For 10

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square kms area roughly 650 Access Points are required, where as CDMA 2000 1xEV-DO

requires just 09 sites.

• Roaming: It lacks roaming between different networks hence wide spread coverage by one

service provider is not possible, which is the key to success of wireless technology.

• Backhaul: Backhaul directly affects data rate service provider used Cable or DSL for

backhaul. Wi- Fi real world data rates are at least half of the their theoretical peak rates due to

factors such as signal strength, interference and radio overhead .Backhaul reduces the

remaining throughput further.

• Interference: Wi-Fi uses unlicensed spectrum, which mean no regulator recourse against

interference. The most popular type of Wi-Fi, ‘802.11’b uses the crowded 2.4 GHz band

which is already used in Bluetooth, cordless phones and microwave ovens.

• Security: Wi-Fi Access Points and modems use the Wired Equivalent Privacy (WEP)

Standards, which is very susceptible to hacking and eavesdropping.

• Security: WEP (Wired Equivalent Privacy) is not very secure. WPA (WIFI Protected

Access) offers much better security with the help of dynamic key encryption and mutual

authentication.

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Wi-Max

SCOPE:

The Wi-MAX certification mark is given to product that pass conformity and Interoperability

test for the IEEE 802-16 standard which caters for the Air interface standard for point-to-

multipoint broad- band Internet access over a wireless connection.

GENERAL DETAILS OF WI-MAX:

Wi-MAX is an acronym that stands for World-wide Interoperability for Microwave Access. It

is an ideal method for ISP to deliver high speed broadband to locations where wired

connections would be difficult or costly. Wi-MAX delivers a point-to-multipoint architecture.

It doesn't require a direct line of sight between the source and endpoint and it has a service

range of 50 Kms. It provides a shared data rate of up to 70 Mbps, which is enough to service

up to a thousand homes with high-speed access.

THE MAIN ADVANTAGES OF WI-MAX ARE:

• High speed of broadband service upto 70 Mbps.

• Wireless rather than wired access, so that it would be a lot less expensive than cable or

Digital Subscriber Line (DSL) and much easier to extend to suburban and rural areas.

• Broad coverage like the cell phone network instead of small Wi-Fi hotspots , 50 Kms.

There are following, two corresponding Wi-MAX standards:

1. IEEE 802.16-2004 is for fixed point-to-point and point-to-multipoint wireless access. It is

akin to a faster, airborne version of Digital Subscriber Line (DSL) or cable-modem services,

It is also called first Non Line of Sight (NLOS), Broad-Band Wireless access (BWA)

standard.

2. IEEE 802.16e is for mobile wireless access from laptops and hand held. It is analogous to a

faster version of third-generation (3G) telecommunications technology. (Wi-Max proponent

Intel Corp. has promised 802.16e-enabled laptops by early 2007)

WORKING OF WI-MAX:

Wi-MAX operates similar to Wi-Fi but at higher speeds, over greater distances and for a

greater number of users. It consists of following two parts:

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a) A Wi-MAX tower, similar in concept to a cell-phone tower, and which can provide

coverage to a very large area as big as 3,000 square miles (~8,000 square km).

b) A Wi-MAX receiver, and antenna could be like a PCMCIA (Personal Computer Memory

Card International Association) card, or they could be built into a laptop similar to Wi-Fi

access.

It can provide two forms of wireless service:

a) The non-line-of-sight, Wi-Fi sort of service, where a small antenna on your computer

connects to the tower. In this mode, Wi-MAX uses a lower frequency range - 2 GHz to 11

GHz (similar to Wi- Fi). As lower-wavelength transmissions are not as easily disrupted by

physical obstructions they provided non line of sight coverage.

b) The line-of-sight service, where a fixed dish antenna points straight at the Wi-MAX tower

from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it is able

to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies,

with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and

lots more bandwidth as shown in Figure

Fig Working of Wi-Max

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WI-MAX (IEEE 802.16) SPECIFICATIONS:

• Range: 30 miles (50-kms) radius from base station.

• Speed: 70 Mbps.

• Line-of-sight not needed between user and base station.

• Frequency bands: 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed Bands)

NGN

INTRODUCTION

Telecommunication industry is changing at a rapid pace. This change in the industry is

basically driven by demand of new services from subscriber's side and urge to reduce CAPEX

(Capital Expenditure) and OPEX (Operational Expenditure) from carrier side. Today All most

all telecommunication giants are maintaining at least three kinds of basic Network.

PSTN: Public Switch Telephone Network was basically developed and engineered for giving

voice connectivity to the wire line subscribers. The network consists of Local exchange/RSU

as a part of Access Network and TAXs as a part of core Network. Already huge amount of

money has been invested in PSTN setup. Because of tough competition from Mobile & Voice

over IP, it is becoming white elephant day by day for the operators. Another fact about PSTN

is that most of its equipment are going to exhaust their lives in coming years.

PLMN: (Public Land Mobile Network): PLMN has been developed to provide voice services

for wireless subscribers, though in recent times SMS has emerged as killer application for

mobile. PLMN includes BTS/BSC as access network and MSC as a core Network.

NGN Definition

A Next Generation Network (NGN) is a packet-based network able to provide

Telecommunication Services to users and able to make use of multiple broadband, QoS-

enabled transport technologies and in which service-related functions are independent of the

underlying transport-related technologies. It enables unfettered access for users to networks

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and to competing service providers and services of their choice. It supports generalized

mobility which will allow consistent and ubiquitous provision of services to users.

Fig: NGN Architecture

1. Access Layer:

Access Layers is responsible for direct subscriber attachment function. NGN can support all

kind of existing access as well as upcoming access. In fact NGN does not matter about type of

access. NGN is capable of processing traffic originated from PSTN, GSM, CDMA, xDSL,

WiMAX or any other access system. Depending upon the type of access, protocol conversion

and/or media conversion may be required at the NGN Gateways. Access Layer consists of

Gateways. Examples of gateways are media Gateway, Access gateway and Signaling gateway

Media gateway terminates media, coming from PSTN/PLMN in E1 / STM. Here it is

responsible for packetisation of media under the instruction of control layer. After

packetisation of information it throws packets to the transport Network. Subscriber can

directly be terminated in Access Gateway. All the required configuration of such subscribers

should be done at control layer. Access Gateway and Media Gateways are responsible for

carriage of Media whereas Signaling gateway is carrying signaling generated by PSTN and

informs Control Layer about the signaling in required format.

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Media Gateway :

The media gateway (MG) supports packetized voice and the interface to whatever medium the

voice is to be transported on. The MG performs the task of packetizing voice and providing

connections from switched circuits (TDM) to packetized circuits (IP, Frame Relay, or ATM).

Following functions are performed by Media Gateway:

• Media Conversion

The MC must be able to provide conversion from TDM circuit-switched connections to ATM,

IP, or Frame Relay connections. This includes the packetization of the voice itself. Media

processing includes transcoding, conferencing, interactive voice recognition, and other audio

resource functions.

• Resource Allocation

Resource allocation includes the reservation and release of all resources. It is important to

understand that although the MG is responsible for resource allocation and management, it

does so under the direction of the MGC. The MGC holds the ultimate responsibility of

defining what resources are to be allocated for a call. The MG is capable of providing either

point-to-point connections or point-to-multipoint connections (such as in a conference call).

The MC must also support voice, data, video, and facsimile.

• Event Notification

The MG must also maintain the state of all resources and report the state to the MGC. If a

particular resource fails, the MG reports the failure to the MGC. The MGC maintains a state

table for all resources within the MGs in its zone.

Signaling gateway :

The IETF defines the signaling gateway (SG) as being the bridge to the PSTN. It supports

STP functions to the network. The SG should be capable of providing conversions between

SS7 addresses (point codes) and IP addresses. The addressing in IP signaling networks

provides far more flexibility than in conventional SS7 networks. All entities in the SS7

environment are addressed through the use of point codes. The point code administrator in

each country issues point codes. When a carrier uses an IP network, the entities in the IP

network are addressed by IP addresses rather than point codes. This requires the use of an SG

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to resolve the addresses from the SS7 network to the addresses in the IP network. For

transporting CCS7 signaling information within NGN SIGTRAN architecture is used between

SGW and MGC.

Access Gateway :

Performs the functions of Media conversion , Codec Negotiation and termination of line side

interfaces like phones, devices and PBXs.

2. Transport Layer

Transport Layer of NGN is based on IP. It can utilize the advantage of MPLS. Transport

Layer forms the core of the Network. It basically consists of Routers, which are responsible

for carrying traffic originated by access layer. As the same core network is going to be used

for all kinds of subscribers enjoying different kind of real time and non real time services, it

should be able to make use of band width policies and Qos policies. Operator has to think of

managed Network for its subscribers. It is basically an assembly of routers connected with

optical network. Traffic coming from gat ways is properly routed by those routers.

3. Control Layer

It is responsible of call setup, routing and charging policies and other controls in NGN

environment. It consists of call servers where all information of the network resides. These

call servers are responsible for setting up, modifying, charging and tear down of the calls.

NGN may work on soft switch principle. It consists of MGC (Media Gateway Controller) as

an overall controller and MGs(Media Gateway) for termination of traffic MGC is basically a

server and it is having all the necessary information of network MGC instructs MGs for

establishing the call. SIP (Session Initiation Protocol) is used for communication between

two MGCs and between a SIP enabled user terminal and MGC. Under the control of MGC,

MG performs different call related tasks such as connection modification and termination of

media streams, packetisation of media etc.

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PSTN versus NGN:

• As shown in above figure PSTN Switch consists of interface, Switching and call control. All

the functional entities are shown in one box that means they are interacting with each other

using proprietary protocol. Where as in NGN model entities are interacting using standard

protocols.

• In PSTN each node should have call control separately whereas NGN may have centralized

call control .

• PSTN is dedicated network for providing voice services to the subscribers whereas NGN is

developing with the idea of carrying all kind of traffic over it.

• PSTN is working on circuit switched principle whereas NGN is working on Packet

switching.

• PSTN provides excellent quality of voice and it is tested in all conditions whereas NGN will

provide good quality of voice and it is to be tested in adverse network conditions.

• In PSTN service integration is very difficult and because of vendor dependent technologies

it is difficult to introduce services easily. Whereas NGN shall be able to provide separate

service platform for introduction of services without depending upon underlying network

related technologies.

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CONCLUSION:

It is understood that in near future operators will migrate to complete IP communication. But

it is to be ensured that during this migration should be smooth. At present there should not be

any hurry to implement NGN immediately. Operator’s first work out for building reliable IP

backbone and then process of migration can be started.

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