OCB-283 EXCHANGE

INTRODUCTION

The telephone network is an interconnection of telephone exchange through transmission

links serving the connected subscribers. OCB-283 stations are normally designed on the

principle of multiprocessing multitasking computer structured on design of M-68020 and

68030 microprocessors. All the stations have almost bus structure and many of the PCBs

are repeated in stations, so no. of types of PCBs is very errorless. Only 35 types of PCBs

are in use in whole exchange except CSN. Including CSN's special PCBs, total types of

PCBs are only 55.

The full abbreviation of OCB is "Organ Control Bersion" retrieved from French

exchange, which introduced the technology of OCB-283. In exchange, switch room is

named as OCB-283 based on an advanced technology recently introduced in H.P. Only 4

districts in H.P. namely Mandi, Solan, Shimla and Dharamshala have OCB-283

exchanges.

SWITCH ROOM

OCB-283 is digital switching system supporting a variety of communication needs like

basic telephone, ISDN, interface to mobile/data communication etc. which has been

developed by CTT AICATEL of France so has many similarities to its predecessor E-

10B (also known as OCB 181 in France).

The first OCB-283 exchange of RII version was commissioned in Brest (France) and

Beijing (China) in 1991.The first OCB-283 exchange came to India in 1993.The system

has been upgraded and current version R-20 was fully validated in Jan. 1994,which are

being supplied to India.

SALIENT FEATURES

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It is digital switching systemwith single 'T' stage switch and a maximum number of

2048 PCMs can be connected.

It supports both analog and digital subscribers.

The system supports all the existing signaling system like decadic, MF (R2), CAS

and also CCIII # 7 signaling system.

It provides telephone, ISDN, data communication, cellular radio and other value

added service.

The system has automatic recover feature. When a serious fault occurs in a control

unit, it gives a message to SMM (O&M unit) which puts this unit out of service, loads

software of this unit in a back up unit and brings it into service.

It has a double remoting facility subscribers access unit CSND can be placed at a

remote place and connected to main exchange through PCM links. Line connectors

can also be placed at a remote location and connected to CSNL or CSND through

PCMs meating urban, rural and tribal necessities.

Various units are connected across token rings (IEE 802.5 standard) enabling fast

exchange of information, avoiding complicated links and wring between various

units.

The subscribers charge accounts are saved in the disc automatically, once in a day

avoiding loss of revenue due to total power supply/battery failure.

It can handle 8,00,000 BHCA and 25,000 erlangs of traffic depending on which

maximum of 20,000 subscribers or 60,000 circuits can be connected, so it has huge

traffic handling capacity.

The exchange can be managed locally or from NMC through 64 Kbps link.

All control units are controlled on same type of hardware called station.

It is made of 35 types of cards excluding cards required for CSN, due to this no. of

spare cards for maintenance of cards are drastically reduced.

It has modular structure. The expansion can be easily carried out by adding hardware

and software.

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The SMMs are duplicated with one active and other hot standby. Switch takes over

automatically in case of faults. Discs are connected to both SMMs avoiding cables

from one system to another.

The hard disc is very small in size, compact and maintenance free. It has huge

memory capacity of 1.2Gb.

EXCHANGE HAS THREE BASIC SUB SYSTEMS

Subscriber Access Sub System

Connection And Control Sub System

Operation And Maintenance Sub System

FUNCTIONAL ARCHITECTURE

It comprises of following components.

CONNECTION UNITS

These provide facility to connect a subscribers loop or circuit from an external PCM and

transfer these speech signals on selected time slots called voice channels on LR link

towards switching matrix. These units are:

NO. NAME FUNCTIONAL NAME

1. Subscriber Connection Units CSNL, CSND, CSEN

2. Circuit Connection Units SMT (URM)

3. Frequency Generator, Sender and receiver

and CCS protocol handlers

SMA (ETA), SMA (PUPE)

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CONTROL UNITS

These provide control of calls on basis of stored programmes. They process calls on

reception of dialed digits from calling Subs.circuit and take part in call set of handling

and release by processing, monitoring, measuring charging of calls and other important

functions nedded for working of automatic common control exchange.

NAME OF FUNCTION NATURE OF JOB

Mr. MULTIREGISTER Call handler set up and release of call.

Tr. TRANSLATOR

Translation of digit Data bank of subs.

& chtsin files.

TX CHARGER

Computing charge of a cell, keeping

meter.

MQ MARKER

Message Distribution between common

control and connection units.

GX MATRIX SYSTEM HANDLER

Process and makes connections in

switching matrix on orders from MR

and Or MQ.

PC CCS NETWORK

CONTROLLERS

Manage the CCst network for signaling.

SWITCHING NETWORK

These provide facility for connecting LRs (internal PCMs) coming from connection units

and performs switching operations for calling subscribers TS on to called subscribers TS

and vice versa for a two way connection per call of telephony.

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O & M UNITS AND MAINTENANCE PERIPHERALS:

All the operational and maintenance activities are performed by O & M unit providing

assess for man machine dialogues for human operations to interact and command the

working of exchange equipments.

SYSTEM ARCHITECTURE

The following hardware units are:

1. SUBSCRIBER ACCESS UNITS

i) CSNL-(MSU) Subs. Unit.

ii) CSND-(RSU) Subs. Unit.

iii) CSED-Remote Access Unit.

2. TRUNKS AND JUNCTION CONNECTION UNITS.

i) SMT-Trunk Control Station

3. SWITCHING MATRIX

i) SMX-Matrix Control Station

4. AUXILLARY EQUIPMENT

i) SMA-Auxillary Equipment Rack

5. CONTROL UNITS

i) SMC-Main Control System

6. COMMUNICATION MULTIPLEXES

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i) MTS-Interstation Multiplex

ii) MAS-Station Access Multiplex

iii) MAL-Alarm Multiplex

7. TIME BASE GENERATOR

i) STS-Time Switch Control

8. OPERATION AND MAINTENANCE UNIT

i) SMM-Maintenance Station

The subscriber connection units CSN, SMPs and SMAs are connected to

switching network through PCM links. The interchange of messages between

SMT, SMX, SMA and control units SMCs takes place on 'MAS' token rings. The

control units interchange messages with one another and with SMM on 'MIS'

token rings. The SMM is the O & M function unit and is duplicated as SMMA

and SMMB. These work is pilot/standby mode. The SMCs are the units holding

the control functions MR, TR, TX, MQ, PC, GX these functional units are in

software form and are duplicated except MR which can be more than two.

The duplicated functions work in load sharing mode(except PC) hence SMCs can

be minimum 2 And maximum 32 as per design. The SMA stations hold the ETA

and PUPE functions and these are also minimum 2 to maximum 32.SMT station

which is the interface for the external PCMs is made of duplicated hardware and

can handle either 32 PCMs if SMTIG or 128 PCMs if 2G. The SMTs hardware is

fully duplicated and functions P/R mode.

The brief description of these units is as follows:

SWITCHING NETWORK

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The switching network in OCB-283 is single 'T' stage system. It is made up:

a) Host switching matrix

b) Branch selection and amplification(SAB) function

HOST SWITCHING MATRIX

The host switching matrix consists of two identical branches A and B.The host switching

matrix is implemented on the hardware units known Matrix control station(SMX). Each

having upto 2048 incoming PCM links (LRE) and 256 outgoing links. Out of 2048

incoming links are coming from the other seven SMXs. In full configuration, the host

switching matrix is 2048 X 2048 matrix.

A matrix control station canm establish between any TS on 2048 LRE and my TS on 256

LRS. Similarly a host switching matrix can establish connections between any TS on

2048 LRE and TS on 2048 LRS.

The matrix control station is built around a processor implementing switching machine

MLCOM functions, to establish and break connections between time slots caring out two

way communications with other units in the system over MAS rings.

THE SWITCHING CONCEPT

This time switch comprises of a speech buffer memory, a control memory, an incoming

highway of digital speech in parallel bits and an outgoing highway. This is an INPUT

ASSOCIATED CONTROLLED TIME SWITCH

In this switch the BUFFER MEMORY AND CONTROL MEMORY are controlled type

i.e the writing in it is controlled. The control function writes in the Control memory at the

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location corresponding to the INCOMING TIME SLOT NUMBER the location where it

should be written in the buffer memory. Both these memories are sequential read type.

Reading of control memory gives the address in BUFFER MEMORY for writing the

INCOMING TS BYTE. And thus reading of buffer memory sequentially the TS will be

read from the location given by the control memory. Thus a one way TIME switching has

taken place.

DUPLICATED SWITCHING

The switching is done in OCB-283 in two fully duplicated branches simultaneously. For

this purpose from each connection units the LR links originate in two parallel branches

towards two parallel sets of switching matrices called the SMX and SMXB and these

branches of such network are called A & B and are terminated on the respective

connection units. The duplicated branches of switching have been designed to prove

highly reliable switching path for DATA SWITCHING, VIDEO CONFERENCING,

ISDN ETC.

SAB FUNCTION

The connection units have their internal duplicated hardware called control logic,

working in pilot/reverse arrangement. The duplicate LRs originate from a function in

connection units called SAB-Selection and Amplification of Branches. Its role is to

generate two sets of LRs in trans direction with calculation of parity etc. In reverse

direction it gets data from both the branches which it checks for parity etc and compares

to detect any error in the two branches. In case of error the samples from only the good

branch are taken after automatic testing of the quality of transmission of both the

branches by the common control and the faulty branch is withdrawn from service.

The connection unit's LR links are performed into group of 8 LRs at the factory into

cables with both ends terminated with plugs for the convenience of installation. Such

groups of LRs are called GLR.

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SUBSCRIBER ACCESS UNITS (CSN)

Subscriber connection units (CSN) are so designed that they can be equipped with either

analogue of digital subscriber or both having different cards for each.

CSN can either placed in the exchange switch room or at a remote location. Depending

on their location, CSN is known as CSNL or CSND and the subscriber shelf is known as

local or remote concentrator, CNL or CNE.

The CSNL is connected to switching matrix(SMX) through a minimum of IGLR or a

maximum of 2 GLRs(group of 8 LR is called as a GLR and each LR is a PCM link

having 32 times slots). The CSND is connected to SMT rack through a minimum of 2

PCM and a maximum of 16 PCMs.CSED of E-10B System can also be connected to an

SMT.The message interchanges between CSN and control units take on a common

signaling channel using local version of CCS#7 signaling.

ARCHITECTURE OF CSN

The CSN can have one BASIC RACK and three EXTENSION RACKS and its

architecture can be broadly divided into 2 parts:

i) DIGITAL CONTROL UNIT (UCN)

ii) CONCENTRATOR (CNL OR CNE)

1. DIGITAL CONTROL UNIT (DCU)

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The digital control unit (UCN) is the interface between concentrators and the exchange. It

is in Basic Rack and placed in switch room for CSNL and at a remote location for

CSND.It can be further broken down into:

a) CONTROL AND CONNECTION UNIT (UCX)

There are two such units which are the controlling logics of the CSN and operate in the

pilot standby mode. The active UCX controls the working of CSN and also updates

standby UCX.

b) AUXILLARY EQUIPMENT PROCESSING GROUP (GTA)

This component performs the following functions in case of stand alone operation (i.e.

when CSND is isolated from main exchange):

i) Generates tones and recorded announcements for local communication.

ii) Decodes DTMF dialing

2. CONCENTRATORS

The shelf which accommodates subscriber line cards is known as concentrator. The

concentrators can either be co-located with the digital unit in which case they are known

as local concentrators. CNL or at a remote location in which case they are known as

remote concentrators CNE.When a remote concentrator is used than to connect its PCMs

to digital control unit an interface shelf ICNE is required. The maximum capacity of a

concentrator is 256 subscribers.

The following type of subscribers can be connected to a concentrator, by equipping

suitable kind of card.

i) ANALOGUE SUBSCRIBER (TABAS CARD)

ii) 2B+D DIGITAL SUBSCRIBER (TAVAE CARD)

iii) 30B-D DIGITAL ACCESS (TADP CARD)

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When all the concentrators are local, a maximum of 19 concentrators can be equipped in

one CSN having 4 rack shelves, which as if all are remote or if atleast 2 are remote, a

maximum of 20 concentrators can be equipped in one CSN.

SIGNALING BETWEEN CN & UCN AND WITH PUPE

The interchange of message between concentrators (local and remote) and digital control

unit of CSN takes place through HDLC protocol whereas the signaling between CSN and

the exchange is through local version of CITT#7.

TRUNK AND JUNCTION CONNECTION UNIT (SMLT)

This is also known as PCM trunk control station and is an interface between PCM

junction coming from other exchanges (or CSND, CSEDs) and the switch. The current

version of SMT being supplied to India is SMT 2G. In each SMT 2G, there are 8

modules and in module there are 16 PCMs. Thus there are 128 PCMs, in a single SMT 2

G is built around microprocessor 68030.

GENERAL ARCHITECTURE

SMT 2G consists of duplicated processing subsystems. SMTA and SMTB which are

connected through internal links LISM. Both of them to PCM interfaces as well as to

MAS token tings. PCMs are connected to PCM interfaces, which are not duplicated.

SMT 2G is connected to SMX A and SMX B through 128 PCMs which are connected to

SAB branch A and SAB branch B. Speech samples are sent on both the branches from

SMX, but one which is better is selected and connected to the concerned PCMTS by

SMT. Out of the two processing logics SMT A and SMT B one remains active and other

standby. In case of fault in active logic, automatic switch takes over place providing an

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uninterrupted service and locavar is activated on the faulty logic and the diagnostic is

printed on a terminal.

FUNCTIONS:

The software MLURM is loaded on SMT to perform functions of a PCM controller

The functions performed on receive side

i) Converts HDB3 code to binary.

ii) Extracts channel associated signaling.

iii) Manages CCS 7 messages carried on TS 16.

iv) Cross connects a channel on PCM to a TS on LR.

The Functions performed on transmit side

i) Converts binary code to HDB-3 (line) code.

ii) Injects channel associated signaling.

iii) Manages CCS 7 messages on TS 16.

iv) Cross connects a TS on LR to a channel on PCM.

AUXILLARY EQUIPMENTS CONTROL STATION (SMA)

The SMA contains the following two functional units.

i) ETA

ii) PUPE

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ETA

The ETA contains following subcomponents.

a) Frequency receiver/generators.

b) Conference call circuits.

c) Tone generators.

The frequency receivers/generators recognizes the digits dialed through DTMF

instrument and also the MF(R2) signals received on junctions. They also generate the

various frequencies required for MF(R2) signaling and testing etc.

The conference circuits are used to set up connection between a maximum of 4

subscribers. These 4 subscribers can hold conference on the telephone i.e. they can talk to

each other.

Tone generators generate various tones required to be connected during call processing.

These tones are dial tone, Busy tone, Ring back tone, processing tone etc.

PUPE

The PUPE performs level 2 part of level 3 functions for CCITT No.7 signaling. The rest

of the level 3 functions performed by PC. The various functions performed by PUPE are

as below.

TRANSMIT SIDE:

i) It sends 'flag' and 'check bit' in the HDLC frame while transmitting CCS7

messages. It also inserts zeros. When there are more than 5 consecutive

AOnes (Is) in the message.

ii) PUPE sends 'fill in signal units' (FISU) automatically, when there are no

messages to be sent.

iii) PUPE also sends 'link status signal units' (LISU) when commanded.

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iv) It re-transmits a signal unit on receipt of negative acknowledgement.

RECEIVE SIDE:

i) On receipt of CCS 7 signaling messages, it eliminates zeros which were

inserted after five consecutive ones(Ls)

ii) It detects the flag and also computes the checksum and compares them

with bits. If these two match it sends positive acknowledgement otherwise

it sends a negative acknowledgement.

iii) It eliminates fill in signal units as they do not carry any information.

IMPLEMENTATION OF ETA AND PUPE ON SMA

Either ETA or PUPE or both can be implemented on the same SMA. When both are

implemented on the same SMA MLPUPE (logic machine PUPE i.e. (PUPE software) is

loaded on the principal processor (PUP) and MLETA is loaded on secondary processor

(PUS).

When only PUPE is implemented on SMA, it is loaded on PUP and when only ETA is

implemented, it is loaded on PUS. Only first two ETAs have tone generators CCFs and

RGFs are provided as per requirements.

The PCB used is common for RGF, CCF and tone generators, only the

Software is different when no CCF or tone generator is required an ETA can have a

maximum of 96 RGFs.

An SMA is connected to SMX by 8 LR links. The following table illustrated the capacity

and modularity of SMA.

SMA UNITS

EQUIPPED WITH

CAPACITY MIN. MAX &

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ETA alone 96 RGF 2 to 32

PUPE alone 64 CCS-7 Channels 2 to 15

ETA and PUPE both 64 RGFs/32 CCS-7

Channels

2 to 15

CONTROL UNITS

All control units like MR, MQ, TX, TR, ETC and SMA are implemented on common

type of hardware architecture, called station which is built around a microprocessor

station bus 'BSM'. One or more processors and 1 or more intelligent couplers can be

connected to this bus. They exchange data through common memory.

The main processor is connected to common memory through a 32 bit private bur, apart

from through BSM. All the processors are Motorola 68020 processors and operate at 15.6

MHZ.clock. Multiprocessor station bus BSM is a 16 bit bus operating at 44.8 Mbps.

There can be 1 principal processor (PUP) and 4 secondary processor (PUS) in a station.

Also, there can be 1 main coupler (CMP) and upto 4 secondary couplers (CMS).

A station can function as MR, TR or any unit when a particular software is loaded in the

station depending on traffic. A functional unit can be implemented on the principal or

secondary processor and on main or secondary coupler.

A software called 'SUPERVISOR' is provided in station for communication and loading

facilities; 'HYPERVISOR' to permit co-habitation of many software machines on same

station. The station is generally called SMC.

CONTROL STATION

There are 6 common control functions in an OCB-283 which are alloted max. and min.

nos.

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SR. NO. NAME OF UNIT MINIMUM MAXIMUM

1. MR 2 7

2. TR 2 2

3. TX 2 2

4. MQ 2 2

5. PC 2 2

6. GX 2 2

They are called 'LOGICAL MACHINES' in software form. 'ML' is implemented on

hardware of SMC (station) by loading suitable software on it. An SMC can support any 1

or many MLs in defined combinations.

SMCs can be min. 2 and max. 32 bit nos. depending upon exchange configurations and

traffic requirement. The required no. of SMCs is decided

by planners & manufacturers. There is also a 'BACKUP SMC STATION' not loaded with

any software.

When any SMC becomes faulty, it sends message to SMM which blocks this unit and

informs all control units regarding non-availability of this unit. SMM then loads software

of all functional units on back up station and brings it into service. So, there is automatic

recovery.

FUNCTIONS OF VARIOUS COMMON CONTROL SOFTWARE MLs

MULTIREGISTER (MLMR)

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It establishes and releases calls and takes real time decisions for call processing. It

consults TR to find out subs. Entitlements and orders for connections and disconnections

of various tones and subs. It also carries out observation functions.

TRANSLATOR (MLTR)

The TR stores exchange data base in its memory and tells MR the characteristic and

entitlements of subs. and circuits on request. It stores routing and analysis data and

converts received digits into equipment no. of the called subs.

MARKER (MLMQ)

It carries out messages between control functions MLs and connection units for

subs./circuits. It also acts as 'gate' for messages while passing from one communication to

other. The MQ also supervises semi permanent connections in the network.

CHARGING UNIT (MLTX)

The TX carries out charging for each communication set up. It keeps charge account of

all subs. and prepares and sends detail billing messages to SMM. It also carries out subs.

and circuit observation functions.

MATRIX SYSTEM HANDLER (MLGX)

The GX monitors the connections in the switching network and in case of fault carries

out appropriate defence functions. It also monitores internal links in the switching

network.

CCS 7 CONTROLLER (MLPC)

The PC carries out 'routing and traffic' management functions for CCITT No.7 signaling.

It also carries out observation functions and defence of PUPE, if a PUPE developes fault,

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it is automatically blocked, the semi-permanent link is reconfigured and 'standby PUPE,

is brought in service.

EXCHANGE CONFIGURATION

OCB-283 can have 4 configurations depending upon its size and traffic. One or more

MLs can be implemented on one SMC station. Taking advantage of this flexibility the

following 4 configurations are designed.

a) COMPACT 'C' CONFIGURATION.

b) SMALL 'P' CONFIGURATION.

c) MEDIUM 'M' CONFIGURATION.

d) LARGE 'G' CONFIGURATION.

SR.NO. COMPACT (C) SMALL (P) MEDIUM (M) LARGE (G)

1. SMC 2 2+1 BACK UP 2 or 3 MR + 2

= 5

4 to 7 MR + 2

+ 2 SMC for

others.

2. SMA 2 2 2 or MORE = 3 2 or MORE

3. SMT 1 1 1 or MORE = 2 1 or MORE

4. SMX 1 (48 LR) 1 1 or MORE =2 1 or MORE

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5.(1or 2)

SMCs can

be loaded

with

(1) MR, TR,

TX, MQ, GX &

PC Software.

(1) MR, TR,

TX, MC, GX &

PC Software.

(2) TR, TX,

MQ, GX & PC

Software.

(2) TR, MQ,

GX & PC

Software.

6.SMA can

be loaded

with

ETA, PUPE

Software.

ETA/PUPE

Software.

ETA, PUPE

Software.

ETA, PUPE

Software.

7.Performa-

nce Data

5 CA/S or

BHCA.

36 CA/S or

1,30,000

BHCA

100 CA/S or

3,60,000

BHCA.

220 CA/S or

8,00,000

BHCA.

INTERNATIONAL INTELLIGENT NETWORK (IN)

DEFINITION

In an intelligent network (IN), the logic for controlling telecommunications services

migrates from traditional switching points to computer based, service independent

platforms. This provides network operators an open platform provisioned with generic

service components that can incorporate with elements from different vendors, based on

published, open-interface standards. This platform can be used to develop new and

different services.

OVERVIEW

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The evolution and direction of the IN is based on International Telecommunications

Union-Telecommunications Standardization Sector (ITU-T) and European

Telecommunications Standards Institute (ETSI) standards development.

DRIVING FORCES BEHIND THE INTELLIGENT NETWORK

Within the traditional telecommunications environment, telecommunications companies

acted both as network operators and service providers. The network operator is the entity

that owns and operates the network infrastructure. A service provider is an entity that

offers services to the subscribers. The service provider uses the network infrastructure of

a network operator to deliver the service to the subscriber but is responsible for the

management and development of the service.

Service offerings were more likely driven by technological availability rather than

customer need, as much of the network infrastructure has been based on proprietary

interfaces with bounded capabilities. This type of environment resulted in long

development times and large investments to deploy services. New technological

capabilities, privatization and deregulation, and changes in market and customer demand

have driven the emergence of INs. The result is an increase in competition that has forced

operators and service providers to add new features rapidly to attract and retain

customers.

The IN can play an important role in providing such new features and services. In an

intelligent network, control of call processing is moved out of the switch and into the

network. The idea is to give service providers the ability to develop new services quickly,

independently and inexpensively; a capability they do not have when new services are

implemented on the network switches. With the IN, service providers or their IN vendors

develop the intelligence or service logic to provide new services using service creation

environments. Then they deploy this intelligence on network control points within the IN.

so, service providers can use the facilities of IN to deploy new services to their

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subscribers without any change in the programming in the network switches. By

separating services from switching equipment, the IN opens markets for

telecommunications-service creation and switching-equipment providers.

OVERVIEW OF THE INTELLIGENT NETWORK

Within traditional public switched telephone networks, the hierarchy of switching

equipment and software must be upgraded each time a new service is added to the

network. This is a complex and costly process. Further, network switches could not

provide new number translation, routing and charging capabilities. As

telecommunications services have evolved, the need to reduce the maintenance and

service upgrades or additions.

The IN essentially separates these services from switching equipment and organizes a

centralized system so that providers need not perform major modifications on multiple

switches when they introduce new services. The first step in IN development was to

create separate service data in a centralized database outside the switching nodes. The

second step was to separate the service programs, or service logic, and to define a

protocol that would permit interaction between switching systems and intelligent nodes

containing the service logic and data.

For service switching points and service control points (intelligent nodes) to work,

common channel signaling, or out-of-band was required as opposed to the traditional

inband signaling. Relaying on out-of-band signaling, or signaling system 7 (SS7)

protocols, provides the mechanism to place various logic and service data into dedicated

network elements that can remotely handle call control and connection. SS 7 also enables

intelligent applications to communicate with other applications and to access databases

located in various parts of the network.

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Certain network elements can be distinguished in every IN, as shown in the figure

below:

IN FUNCTIONS AND FUNCTIONAL RELATIONSHIPS FOR CS-1

CCAF Call control agent function

CCF Call control function

SCEF Service function

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SCF Service control function

SDF Service data function

SMAF Service management access function

SMF Service management function

SRF Service resource function

SSF Service switching function

Service switching points (SSPs) are stored program control switches that interface to the

SS7 signaling network. The SSP embodies the call control function (CCF) and service

switching function (SSF) entities. The SSF recognizes IN service calls and routes the

appropriate queries to the service control function (SCF) that resides in a service control

point (SCP) via the SS7 network through signaling transfer points (STPs). STPs are high-

capacity, high-reliability packet switches that transport signaling messages, using large

routing databases, between the IN nodes.

SCP commands are used by the SSP to process calls. The SCP is a fault-tolerant, high-

capacity, transaction processing entity that provides call-handling information in response

to SSP queries. The service management point (SMP) provides operation, administration

and maintenance function for the IN. the intelligent peripheral (IP) provides enhanced

services or function under the control of an SCP, possibly relayed by an SSP, such as

play announcements and speech recognition.

The IN architecture is fundamentally based on SS7 and its protocol architecture. A

common signaling transport capability known as the message transfer part (MTP) handles

the corresponding open systems interconnections (OSI) physical, data link and network

layers. The next level, signaling connection control part (SCCP), augments the MTP by

providing both connection-less and connection oriented message transport, as well as

enabling addressing capabilities application part (TCAP) provides procedure for real-time

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transaction control. The final layer, IN application protocol (INAP) defines the operations

required between IN network elements, such as SSPs and SCPs.

The figure shows the IN protocol architecture:

IN PROTOCOL STACK

An important concept in IN has been the notion of service independence. Here, the

primary goal is to identify and create generic sets of reusable service components that

could be used to build new services and loaded in SCPs to generate new services rapidly.

These service components are also called as service independent building blocks (SIBs).

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To provide a framework that would lead toward IN engineering standardization, the IN

conceptual model (INCM) was developed.

The INCM is a tool for describing IN capabilities and characteristics, is composed of four

‘planes’ that represent different aspects of implementing IN services. This model depicts

the relationship among services and service features, global service logic, distributed

service logic and the physical network entities such as SCP and SSP.

These planes include the service plane, the global functional plane, the distributed

functional plane and the physical plane as shown in the figure shown:

The service plane describes services from a user perspective, where a service consists of

generic blocks or service features that make up part or all of a service (e.g., free phone).

The global functional plane deals with service creation and is comprised of the SIBs that

will be used to create service features. Global service logic defines how SIBs are linked

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together to form features and how these SIBs interact with another basic SIB known as

the basic call process (BCP). The BCP is the process that optimally supports services that

do not require special features and is basic to the processing of all services. The

distributed functional plane defines a set of functional entities that perform specific

actions. SIBs are implemented through a specific sequence of functional-entity actions

performed by those functional entities. Table 1 describes functional-entity components as

well as their relationship to IN physical entities.

Table 1. IN Physical and Functional Entities

Physical

component

Distributed functional

components

Description

Service Switching

Point(SSP)

Call Control Function(CCF)

Connects call processing and provides

network connection services.

Service Switching Function

(SSF)

Supports IN triggering during call

processing and access to IN

functionality

Specialized Resource Function

(SRF)

Supports the interaction between the

call processing software on the switch

and the service control function.

Call Control Agent Function

(CCAF)

Supports specialized network

resources generally associated with

caller interaction: provides user access

to the network.

26

Service Control Point

(SCP)

Service Control Function

(SCF)

Executes IN service logic and

influences call processing on the

switch via its interface to the SSF.

Service Data Function (SDF)

Manages customer and network data

for real-time access by the SCF in the

execution of an IN service.

Intelligent Peripheral

(IP)

Specialized Resource Function

(SRF)

Supports specialized network

resources generally associated with

caller interaction.

Service Management

Point (SMP)

Service Management Function

(SMF)

Alloys deployment and provision of

IN services and allows the support of

ongoing operation.

Service Management Access

Function (SMAF)

Provides an interface between service

managers and SMF (could be

implemented in a separate physical

element, the SMAP)

Service Creation

Environment Point

SCEP)

Service Creation Environment

Function (SCEF)

Allows services provided in the IN to

be defined, developed, tested and

input to the SMF.

Service Data Point

(SDP)

Service Data Function (SDF)

Manages customer and network data

for real-time access by the SCF in the

execution of an IN service.

CAPABILITY SETS: STANDARDS FOR INTELLIGENT NETWORKS

International standards work for IN began in 1989 within the ITU and ETSI. These

standards embodies have been developing IN capability sets that will be upwardly

compatible in parallel. The ITU builds its”Q.1200 Recommendation Series for IN

27

architecture”, and ETSI takes these recommendations and modifies them for use by

European operators.

Capability sets refers to a set of services and service features that can be built using SIBs.

All capability sets use the IN conceptual model. Each capability set is associated with a

planned phase in the standards process. The first capability set CS-1 was defined by the

ITU in 1992 but was found to be too extensive and incomplete by ETSI. ETSI defined

the Core INAP standard in 1994 as a subset of the original CS-1. The ITU adopts this

work and reissued the standard in 1995.

Examples of basic CS-1 information flow include the following:

Connect

Prompt and collect user information

Analyze information

Play announcement

Release call

Using a common IN service, the premium rate service, the interrelationship of services,

service features and the SIBs is provided below. The premium rate service provides a

business owner with a special premium-rate number. Customers that call this special

number are charged at a special rate for the call as well as the information and/or services

obtained through the call. The network operator collects the revenue associated with the

call and distributes a share to the business owner of the premium-rate number. Examples

of premium rate include weather, stock, sports, and other information services.

A premium rate service has two core service features:

1. The one number service feature permits the business owner (subscriber) to have

two or more terminating line sin a number of locations, using a single premium-

rate number.

2. The premium charging service feature permits the subscriber to receive some of

the revenue associated with each premium-rate call.

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There are other optional service features associated with the premium-rate service,

such as call distribution, time and origin-dependent routing, recorded announcements

and many others.

Within the premium charging service feature there are three associated SIBs: the

charging SIB, the call log information SIB and the service data management SIB.

Within the charge SIB, there are a number of information flows/operations at work.

For example, the SCF can issue a Furnish Charging Information flow that carries

charging characteristics for particular call to the SSF. Once the SSF receives these

characteristics, the SSF generates a billing record. Within the same SIB, the SCF may

also issue the Send Charging Information flow that send charging characteristics to an

SSF that controls the way that the SSF charges for a call. Other information flows are

associated with this SIB, such as Event Notification Charging and Apply Charging

that perform related charging function.

INTERNET

INTRODUCTION

1. (Lower case "i"nternet) A large network made up of a number of smaller networks.

2. (Upper case "I"nternet) The largest network in the world. It is made up of more than

100 million computers in more than 100 countries covering commercial, academic and

government endeavors. Originally developed for the U.S. military, the Internet became

widely used for academic and commercial research. Users had access to unpublished data

and journals on a variety of subjects. Today, the "Net" has become commercialized into a

worldwide information highway, providing data and commentary on every subject and

product on earth.

29

Internet, the, international computer network linking together thousands of individual

networks at military and government agencies, educational institutions, nonprofit

organizations, industrial and financial corporations of all sizes, and commercial

enterprises (called gateways or service providers) that enable individuals to access the

network. The most popular features of the Internet include electronic mail (e-mail),

discussion groups (called newsgroups or bulletin boards, where users can post messages

and look for responses on a system called Usenet), on-line conversations (called chats),

adventure and role-playing games, information retrieval, and electronic commerce (e-

commerce).

The public information stored in the multitude of computer networks connected to the

Internet forms a huge electronic library, but the enormous quantity of data and number of

linked computer networks also make it difficult to find where the desired information

resides and then to retrieve it. A number of progressively easier-to-use interfaces and

tools have been developed to facilitate searching. Among these are search engines, such

as Archie, Gopher, and WAIS (Wide Area Information Server), and a number of

commercial indexes, which are programs that use a proprietary algorithm to search a

large collection of documents for keywords and return a list of documents containing one

or more of the keywords. Telnet is a program that allows users of one computer to

connect with another, distant computer in a different network. The File Transfer Protocol

(FTP) is used to transfer information between computers in different networks. The

greatest impetus to the popularization of the Internet came wit

E-Mail Was the Beginning

The Internet's surge in growth in the mid 1990s was dramatic, increasing a

hundredfold in 1995 and 1996 alone. There were two reasons. Up until then, the

major online services (AOL, CompuServe, etc.) provided e-mail, but only to

customers of the same service. As they began to connect to the Internet for e-mail

exchange, the Internet took on the role of a global switching center. An AOL

member could finally send mail to a CompuServe member, and so on. The

30

Internet glued the world together for electronic mail, and today, SMTP, the

Internet mail protocol, is the global e-mail standard.

The Web Was the Explosion

Secondly, with the advent of graphics-based Web browsers such as Mosaic and

Netscape Navigator, and soon after, Microsoft's Internet Explorer, the World

Wide Web took off. The Web became easily available to users with PCs and

Macs rather than only scientists and hackers at Unix workstations. Delphi was the

first proprietary online service to offer Web access, and all the rest followed. At

the same time, new Internet service providers (ISPs) rose out of the woodwork to

offer access to individuals and companies. As a result, the Web grew

exponentially, providing an information exchange of unprecedented proportion.

The Web has also become "the" storehouse for drivers, updates and demos that

are downloaded via the browser as well as a global transport for delivering

information by subscription, both free and paid.

Newsgroups

Although daily news and information is now available on countless Web sites,

long before the Web, information on a myriad of subjects was exchanged via

Usenet (User Network) newsgroups.

Chat Rooms

Chat rooms provide another popular Internet service. Internet Relay Chat (IRC)

offers multiuser text conferencing on diverse topics. Dozens of IRC servers

provide hundreds of channels that anyone can log onto and participate in via the

keyboard.

The Original Internet

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The Internet started in 1969 as the ARPAnet. Funded by the U.S. government, the

ARPAnet became a series of high-speed links between major supercomputer sites and

educational and research institutions worldwide, although mostly in the U.S. A major part

of its backbone was the National Science Foundation's NFSNet. Along the way, it

became known as the "Internet" or simply "the Net." By the 1990s, so many networks

had become part of it and so much traffic was not educational or pure research that it

became obvious that the Internet was on its way to becoming a commercial venture. It

Went Commercial in 1995 when, the Internet was turned over to large commercial

Internet providers (ISPs), such as MCI, Sprint and UUNET, which took responsibility for

the backbones and have increasingly enhanced their capacities ever since. Regional ISPs

link into these backbones to provide lines for their subscribers, and smaller ISPs hook

either directly into the national backbones or into the regional ISPs.

The TCP/IP Protocol

Internet computers use the TCP/IP communications protocol. There are more than

100 million hosts on the Internet, a host being a mainframe or medium to high-

end server that is always online via TCP/IP. The Internet is also connected to non-

TCP/IP networks worldwide through gateways that convert TCP/IP into other

protocols.

History of the Internet

The story of the Internet begins in 1969 with the implementation of

ARPANET by academic researchers under the sponsorship of the United States

Department of Defense Advanced Research Projects Agency (ARPA). Some early

research which contributed to the ARPANET included work on decentralized networks,

queueing theory, and packet switching. However, ARPANET itself did not interact easily

with other computer networks that did not share its own native protocol.

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Today's Internet

Some of the most used protocols in the Internet protocol suite are IP, TCP, UDP, DNS,

PPP, SLIP, ICMP, POP3, IMAP, SMTP, HTTP, HTTPS, SSH, Telnet, FTP, LDAP, SSL,

and TLS.

Some of the popular services on the Internet that make use of these protocols are e-mail,

Usenet newsgroups, file sharing, Instant Messenger, the World Wide Web, Gopher,

session access, WAIS, finger, IRC, MUDs, and MUSHs. Of these, e-mail and the World

Wide Web are clearly the most used, and many other services are built upon them, such

as mailing lists and web logs. The Internet makes it possible to provide real-time services

such as web radio and webcasts that can be accessed from anywhere in the world.

The World Wide Web

Through keyword-driven Internet research using search engines like Google, millions

worldwide have easy, instant access to a vast and diverse amount of online information.

Compared to encyclopedias and traditional libraries, the Internet has enabled a sudden

and extreme decentralization of information and data.

33

OSI MODEL

INTRODUCTION

The Open Systems Interconnection Reference Model (OSI Model or OSI Reference

Model for short) is a layered abstract description for communications and computer

network protocol design, developed as part of the Open Systems Interconnect initiative. It

is also called the OSI seven layer model.

Purpose

The OSI model divides the functions of a protocol into a series of layers. Each layer has

the property that it only uses the functions of the layer below, and only exports

functionality to the layer above. A system that implements protocol behavior consisting

of a series of these layers is known as a 'protocol stack' or 'stack'. Protocol stacks can be

implemented either in hardware or software, or a mixture of both. Typically, only the

lower layers are implemented in hardware, with the higher layers being implemented in

software.

This OSI model is roughly adhered to in the computing and networking industry. Its main

feature is in the junction between layers which dictates the specifications on how one

layer interacts with another. This means that a layer written by one manufacturer can

operate with a layer from another (assuming that the specification is interpreted

correctly.) These specifications are typically known as Request for Comments or "RFC"s

in the TCP/IP community. They are ISO standards in the OSI community.

Usually, the implementation of a protocol is layered in a similar way to the protocol

design, with the possible exception of a 'fast path' where the most common transaction

allowed by the system may be implemented as a single component encompassing aspects

of several layers.

34

This logical separation of layers makes reasoning about the behaviour of protocol stacks

much easier, allowing the design of elaborate but highly reliable protocol stacks. Each

layer performs services for the next higher layer, and makes requests of the next lower

layer. An implementation of several OSI layers is often referred to as a stack

The OSI reference model is a hierarchical structure of seven layers that defines the

requirements for communications between two computers. The model was defined by the

International Standards Organisation. It was conceived to allow interoperability across

the various platforms offered by vendors. The model allows all network elements to

operate together, regardless of who built them. By the late 1970's, ISO was

recommending the implementation of the OSI model as a networking standard,

unfortunately, TCP/IP had been in use for years. TCP/IP was fundamental to ARPANET

and the other networks that evolved into the Internet. Only a subset of the whole OSI

model is used today. It is widely believed that much of the specification is too

complicated and its full functionality has taken too long to implement, although there are

many people that strongly support the OSI model.

35

36

.

Description of layers

Physical layer Layer 1: The physical layer defines all electrical and physical

specifications for devices. This includes the layout of pins, voltages, and cable

specifications. Hubs and repeaters are physical-layer devices. The major functions

and services performed by the physical layer are:

o establishment and termination of a connection to a communications

medium.

o participation in the process whereby the communication resources are

effectively shared among multiple users. For example, contention

resolution and flow control.

o modulation, or conversion between the representation of digital data in

user equipment and the corresponding signals transmitted over a

37

communications channel. These are signals operating over the physical

cabling -- copper and fibre optic, for example. SCSI operates at this level.

Data link layer Layer 2: The Data link layer provides the functional and

procedural means to transfer data between network entities and to detect and

possibly correct errors that may occur in the Physical layer. The addressing

scheme is physical which means that the addresses are hard-coded into the

network cards at the time of manufacture. The addressing scheme is flat. Note:

The best known example of this is Ethernet. Other examples of data link protocols

are HDLC and ADCCP for point-to-point or packet-switched networks and LLC

and Aloha for local area networks. This is the layer at which bridges and switches

operate. Connectivity is provided only among locally attached network nodes.

Network layer Layer 3: The Network layer provides the functional and

procedural means of transferring variable length data sequences from a source to a

destination via one or more networks while maintaining the quality of service

requested by the Transport layer. The Network layer performs network routing,

flow control, segmentation/desegmentation, and error control functions. The

router operates at this layer -- sending data throughout the extended network and

making the Internet possible, although there are layer 3 (or IP) switches. This is a

logical addressing scheme - values are chosen by the network engineer. The

addressing scheme is hierarchical.

Transport layer Layer 4: The purpose of the Transport layer is to provide

transparent transfer of data between end users, thus relieving the upper layers

from any concern with providing reliable and cost-effective data transfer. The

transport layer controls the reliability of a given link. Some protocols are stateful

and connection oriented. This means that the transport layer can keep track of the

packets and retransmit those that fail. The best known example of a layer 4

protocol is TCP.

38

Session layer Layer 5: The Session layer provides the mechanism for managing

the dialogue between end-user application processes. It provides for either duplex

or half-duplex operation and establishes checkpointing, adjournment, termination,

and restart procedures. This layer is responsible for setting up and tearing down

TCP/IP sessions.

Presentation layer Layer 6: The Presentation layer relieves the Application

layer of concern regarding syntactical differences in data representation within the

end-user systems. MIME encoding, encryption and similar manipulation of the

presentation of data is done at this layer. An example of a presentation service

would be the conversion of an EBCDIC-coded text file to an ASCII-coded file.

Application layer Layer 7, the highest layer: This layer interfaces directly to

and performs common application services for the application processes. The

common application services provide semantic conversion between associated

application processes. Examples of common application services include the

virtual file, virtual terminal (for example, Telnet), and "Job transfer and

Manipulation protocol" (JTM, standard ISO/IEC 8832).

TYPES OF INTERNET CONNECTIONS

Dial-up

Refers to analog modem service for connecting to the Internet or to the company LAN.

For home users, dial-up was the first Internet access service available. It was followed by

ISDN, cable and DSL.

MODEM

39

Modem [modulator/demodulator], an external device or internal electronic circuitry used

to transmit and receive digital data over a communications line normally used for analog

signals. A modem attached to a computer converts digital data to an analog signal that it

uses to modulate a carrier frequency. This frequency is transmitted over a line, frequently

as an audio signal over a telecommunications line, to another modem that converts it

back into a copy of the original data.

Synchronous data transmission uses timing signals in the data stream along with

transmitted bits of uniform duration and interval. This permits the receiving modem to

ignore spurious signals that do not conform to the anticipated signal. Although most

modems are either of the synchronous or asynchronous variety, some employ both

methods of communication. Wireless modems send or receive data as a radio signal.

Broadband

1. High-speed transmission. The term is commonly used to refer to Internet access

via cable modems or DSL, which is faster than dial-up. For years, "broadband"

has referred to a higher-speed connection, but the actual speed threshold has

varied. While T1 (1.5 Mbps) has been widely used as the threshold, others have

used T3 (45 Mbps) for broadband. For example, after the turn of the century,

South Korea leapfrogged the U.S. in Internet access, offering DSL up to 50 Mbps

and calling their 1.5 Mbps service "light." In every case, however, it implies

transmitting at higher speeds

2. A method of transmitting data, voice and video using frequency division

multiplexing (FDM), such as used with cable TV. Modems are required to

modulate digital data streams onto the line. Broadband in this context is used in

contrast with "base band," which is all digital transmission and uses time division

multiplexing (TDM).

Leased line

40

A leased line is a (usually) symmetric telecommunications line connecting two locations

together. Unlike traditional PSTN lines they do not have a telephone number, each side of

the line being permanently connected to the other. They can be used for telephone, data

or Internet services.

INTERNET PROTOCOLS

Refers to all the standards that keep the Internet running. The foundation protocol is

TCP/IP, which provides the basic communications mechanism as well as ways to copy

files (FTP) and send e-mail (SMTP). The Web added the HTTP protocol for downloading

Web pages and HTML, XML and XHTML for formatting them. There are many others

and many more are expected, as the Internet has become "the" arena for global standards.

Internet protocol suite  

Application layerHTTP, HTTPS, SMTP, FTP, UUCP, NNTP,

SSH, IRC, SNMP, SIP, RTP, Telnet ,...

Transport layer TCP, UDP, SCTP, DCCP, ...

Network layer IPv4, IPv6, ICMP, ARP, IGMP, ...

Data link layer Ethernet, Wi-Fi, Token ring, FDDI, PPP, ...

Physical layer RS-232, EIA-422, RS-449, EIA-485...

The Internet Protocol (IP) is a data-oriented protocol used by source and destination

hosts for communicating data across a packet-switched internet work.

IP addressing and routing

Perhaps the most complex aspects of IP are addressing and routing. Addressing refers to

how end hosts are assigned IP addresses and how subnetworks of IP host addresses are

divided and grouped together. IP routing is performed by all hosts, but most importantly

by internetwork routers, which typically use either interior gateway protocols (IGPs) or

41

external gateway protocols (EGPs) to help make IP datagram forwarding decisions across

IP connected networks.

GSM

(GLOBAL SYSTEM FOR MOBILE COMMUNICATION)

INTRODUCTION

(Global System for Mobile Communications) A digital cellular phone technology based

on TDMA that is the predominant system in Europe, but is also used around the world.

Developed in the 1980s, GSM was first deployed in seven European countries in 1992.

Operating in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz PCS band in the

U.S., GSM defines the entire cellular system, not just the air interface (TDMA, CDMA,

etc.). As of 2000, there were more than 250 million GSM users, which is more than half

of the world's mobile phone population.

GSM phones use a Subscriber Identity Module (SIM) smart card that contains user

account information. Any GSM phone becomes immediately programmed after plugging

in the SIM card, thus allowing GSM phones to be easily rented or borrowed. SIM cards

can be programmed to display custom menus for personalized services.

GSM provides a short messaging service (SMS) that enables text messages up to 160

characters in length to be sent to and from a GSM phone. It also supports data transfer at

9.6 Kbps to packet networks, ISDN and POTS users. GSM is a circuit-switched system

that divides each 200 kHz channel into eight 25 kHz time slots.

Home Location Register (HLR)

A Home Location Register (HLR) is a database that contains semi-permanent mobile

subscriber information for a wireless carriers' entire subscriber base. HLR subscriber

information includes the International Mobile Subscriber Identity (IMSI), service

subscription information, location information (the identity of the currently serving

42

Visitor Location Register (VLR) to enable the routing of mobile-terminated calls),

service restrictions and supplementary services information.

The HLR handles SS7 transactions with both Mobile Switching Centers (MSCs) and

VLR nodes, which either request information from the HLR or update the information

contained within the HLR. The HLR also initiates transactions with VLRs to complete

incoming calls and to update subscriber data.

Traditional wireless network design is based on the utilization of a single Home Location

Register (HLR) for each wireless network, but growth considerations are prompting

carriers to consider multiple HLR topologies.

Visitor Location Register (VLR)

A Visitor Location Register (VLR) is a database which contains temporary information

concerning the mobile subscribers that are currently located in a given MSC serving area,

but whose Home Location Register (HLR) is elsewhere.

When a mobile subscriber roams away from his home location and into a remote

location, SS7 messages are used to obtain information about the subscriber from the

HLR, and to create a temporary record for the subscriber in the VLR. There is usually

one VLR per MSC.

International Mobile Subscriber Identity (IMSI) Number

The IMSI is a unique non-dial able number allocated to each mobile subscriber in the

GSM system that identifies the subscriber and his or her subscription within the GSM

network. The IMSI resides in the Subscriber Identity Module (SIM), which is

transportable across Mobile Station Equipment (MSE). The IMSI is made up of three

parts (1) the mobile country code (MCC) consisting of three digits, (2) the Mobile

Network Code (MNC) consisting of two digits, and (3) the Mobile Subscriber Identity

Number (MSIN) with up to 10 digits.

43

Mobile Subscriber ISDN (MSISDN) Number

The MSISDN is the dial able number that callers use to reach a mobile subscriber. Some

phones can support multiple MSISDNs - for example, a U.S.-based MSISDN and a

Canadian-based MSISDN. Callers dialing either number will reach the subscriber.

Mobile Station Equipment (MSE) Subscription Services

GSM carriers typically order Mobile Station Equipment (MSE) (or GSM phones) from

their suppliers (Nokia, Motorola, Sony, etc.) in large quantities (e.g. 1000 Units). After

receiving an order, the equipment supplier will program the ordered MSE SIMs with a

range of IMSI numbers.

Example: ABC Communications Inc. orders 1000 MSE Units with the following range

of IMSIs.

  MCC MNC MSIN

Unit #1 310 68 4451000

Unit #1000 310 68 4451999

Once the range of IMSI numbers has been determined, the HLR can be populated with

the new IMSI records that will be configured and activated at a future date by authorized

sales or service subscription representatives. The fact that the HLR can be populated with

ranges or blocks of IMSI numbers creates efficiencies in the storage and retrieval of

routing information.

The wireless carrier distributes the Mobile Station Equipment to Sales Outlets that sell

GSM subscription services. When a new subscriber orders a GSM phone at one of the

outlets, the service representative will create a Service Order (SO) to enter the new

subscriber's service subscription information, including the MSISDN number. The key to

the Service Order is the IMSI that is programmed in the SIM. The SO is sent to the HLR,

44

where the IMSI record is created. It can either be set to an active state immediately,

allowing the new subscriber to send and receive telephone calls or it can be activated at a

future date.

Note that the MSISDN numbers are assigned one at a time as each new customer

subscribes. The MSISDN numbers are therefore provisioned individually, rather than in

blocks, which complicates the MSISDN based routing of messages.

GPRS

(General Packet Radio Service) An enhancement to the GSM mobile communications

system that supports data packets. GPRS enables continuous flows of IP data packets over

the system for such applications as Web browsing and file transfer. GPRS differs from

GSM's short messaging service (GSM-SMS) which is limited to messages of 160 bytes in

length.

Customized Applications for Mobile networks Enhanced Logic

Customised Applications for Mobile networks Enhanced Logic, or CAMEL for short, is a

set of GSM standards designed to work on a GSM core network. They allow an operator to

define services over and above standard GSM services. The CAMEL architecture is based

on the Intelligent Network (IN) standards.

Many services can be created using CAMEL, and it is particularly effective in allowing

these services to be offered when a subscriber is roaming.

GSM Call Routing

Mobile Subscriber Roaming

45

When a mobile subscriber roams into a new location area (new VLR), the VLR

automatically determines that it must update the HLR with the new location information,

which it does using an SS7 Location Update Request Message. The Location Update

Message is routed to the HLR through the SS7 network, based on the global title

translation of the IMSI that is stored within the SCCP Called Party Address portion of the

message. The HLR responds with a message that informs the VLR whether the subscriber

should be provided service in the new location.

Mobile Subscriber ISDN Number (MSISDN) Call Routing

When a user dials a GSM mobile subscriber's MSISDN, the PSTN routes the call to the

Home MSC based on the dialed telephone number. The MSC must then query the HLR

based on the MSISDN, to attain routing information required to route the call to the

subscribers' current location.

The MSC stores global title translation tables that are used to determine the HLR

associated with the MSISDN. When only one HLR exists, the translation tables are

trivial. When more than one HLR is used however, the translations become extremely

challenging, with one translation record per subscriber (see the example below). Having

determined the appropriate HLR address, the MSC sends a Routing Information Request

to it.

When the HLR receives the Routing Information Request, it maps the MSISDN to the

IMSI, and ascertains the subscribers' profile including the current VLR at which the

subscriber is registered. The HLR then queries the VLR for a Mobile Station Roaming

Number (MSRN). The MSRN is essentially an ISDN telephone number at which the

mobile subscriber can currently be reached. The MSRN is a temporary number that is

valid only for the duration of a single call.

The HLR generates a response message, which includes the MSRN, and sends it back

across the SS7 network to the MSC. Finally, the MSC attempts to complete the call using

the MSRN provided.

46

Adding a Second HLR to the GSM Network

As a GSM wireless carrier's subscriber base grows, it will eventually become necessary

to add a second HLR to their network. This requirement might be prompted by a service

subscription record storage capacity issue, or perhaps an SS7 message processing

performance issue. It might possibly be prompted by a need to increase the overall

network reliability.

The new HLR can be populated with service subscription records as new subscribers are

brought into service or existing service subscription records can be ported from the old

HLR to the new HLR to more evenly distribute the SS7 traffic load.

Typically, when new subscribers are brought into service, the second HLR will be

populated with blocks of IMSI numbers that are allocated when new MSE equipment is

ordered. As the following example shows, this grouping of IMSI numbers within a single

HLR simplifies the routing translations that are required within the SS7 network for VLR

to HLR Location Update Request transactions. Global Title Translation(GTT) tables will

contain single translation records that translate an entire range of IMSIs numbers into an

HLR address. Even if some individual records are moved between the HLRs, as shown in

the example, the treatment of IMSIs as blocks results in a significant simplification of the

Global Translation tables.

Much more complicated SS7 message routing Global Title Translations are required for

Routing Information Request transactions between the MSCs distributed over the entire

wireless carrier serving area and the two or more HLRs. MSC Routing Information

Requests are routed to the appropriate HLR based on the dialed MSISDN and not the

IMSI. Unlike the IMSI numbers, the MSISDN numbers can not easily be arranged in

groups to reside within a single HLR and therefore, the MSC must contain an MSISDN

to HLR address association record for every mobile subscriber homed on each of the

MSCs. As the example illustrates, the MSC routing tables quickly grow much more

47

extensive than the STP tables. The network administration becomes increasingly complex

and prone to error.

Example: Simple Network with two MSCs and two HLRs

The following example illustrates the issues relating to GSM network routing table

administration with multiple HLRs. A simple GSM network is shown, with the various

routing tables following:

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49