Group Special Mobile(GSM) - Seminar Paper

Group Special Mobile(GSM)
INTRODUCTION OF GSM                                
At the beginning of the 1980s it was realized that the European Countries were using many different, incompatible mobile phones Systems. At the same time, the needs for telecommunication services were remarkably increased.
Due to this, CEPT (Conference Europeans Pastes Telecommunications) founded a group to specify a common mobile system for Western Europe. This group was named “Group Special Mobile” and the system name GSM arose. But after that it is known as Global System for Mobile. Communications.


  • GSM specifications define two truly open interfaces, which limiting certain parts of the GSM system.
  • GSM network is made up of three subsystems:-
  • Network Switching Subsystem (NSS)
  • Base Station Subsystem (BSS)
  • Network Management Subsystem (NMS)
The interfaces defined between each of these sub systems include:-
‘Um’ air interfaces between MS and BSS
‘Abis’ interface within the  BSS
‘A’ interface between the BSS and NSS

It is a combination of terminal equipment and subscriber data. The terminal equipment as such is called ME (Mobile Equipment) and the subscriber's data is stored in a separate mudule called SIM (Subscriber Identity Module).
Therefore, ME + SIM = MS

A BSS itself may cover a considerably large geographical area consisting of many
Cells. Each cell is identified by an identification number called Cell Global Identity
(CGI) which comprises the following elements:
MCC: - Mobile Country Code
MNC: - Mobile Network Code
LAC:- Location Area Code
CI: -        Cell Identity
The Base Station Subsystem consists of the following elements:
BSC: - Base Station Controller
BTS:- Base Transceiver Station

The Base Station Controller (BSC)
It is the central network element of the BSS and it controls the radio network. This means, that the main responsibilities of the BSC are make Connection Establishment between MS and NSS, Mobility management, Statistical Raw data collection Air and An interface signaling support.

The Base Transceiver Station (BTS)
It is a network element maintaining the Air interface. It takes care of Air interface signaling, Air interface Ciphering and speech processing. Speech processing refers to all the functions; the BTS performs in order to guarantee an error-free Connection between the MS and the BTS.

The Transcoder (TC):-
It is a BSS element taking care of speech transcoding, I.e. it is capable of converting speech from one digital Coding format to another and vice versa.

The key elements of Network Switching Subsystem:

  • Mobile Services Switching Centre (MSC)
  • Visitor Location Register (VLR)
  • Home Location Register (HLR)
  • Equipment Identity Register (EIR)
  • Authentication center (AUC)
  • Gateway MSC (GMSC)

The MSC is responsible for controlling calls in the mobile network.  It identifies the origin and destination of a call (either a mobile station or a fixed telephone in both cases), as well as the type of a call. An MSC acting as a bridge between a mobile network and a fixed network is Called a Gateway MSC. An MSC is normally integrated with a VLR, which maintains information related to the subscribers who are? Currently in the service area of the MSC or not.

 The following are typical MSC functions in a cellular system:-
Provide switched connection with PSTN
Provide  switched connections between mobile subscribers
Provide coordinate over signaling with mobiles
Coordinate the location and handover process
Provide custom services to mobile users
Collect billing data

The VLR carries out location registrations and updates.  A VLR database is always temporary, in the VLR; the subscriber data is stored temporarily. When the subscriber moves to another VLR area, its data is erased from the old VLR and stored in the new VLR.

Fundamentals of VLR
Updating the mobile subscriber data
Receiving and delivering the short messages
Continuity of speech (Handover)


The HLR stores the basic data of the subscriber on a permanent basis. The only variable data in the HLR is the current location (VLR address) of the subscriber. The HLR also maintains a temporary database which contains the current location of its customers. This data is required for routing call. The HLR is informed every time the subscriber moves from one VLR area to another, i.e.  The HLR knows in which VLR area the subscriber is currently register red.

The Fundamentals of HLR
Providing Roaming Number
Alert service center
Hold the address like MSISDN, IMSI,
Send routing information for SMS

Authentication is a procedure used in checking the validity and Integrity of subscriber data. With the help of the authentication procedure, the operator prevents the use of false SIM modules in the network. The authentication procedure is based on an identity key, Ki that is issued to each subscriber when his data are established in the HLR.
The authentication procedure verifies that the Ki is exactly the same on the subscriber side as on the network side. Authentication is performed by the VLR at the beginning of every Call establishment, location update and call termination


An option exists in GSM where the network may check the validity of the mobile station hardware. The mobile station is requested to provide the International Mobile Equipment Identity (IMEI) number. This number consists of type approval code, final assembly code and serial number of the mobile station. The network stores the IMEI numbers in the Equipment Identity Register (EIR).

IMEI-International Mobile Equipment Identifier:-
The IMEI is an internationally unique serial number allocated to the MS hardware at the time of manufacture. It is registered by the network operator and stored in the AUC for validation purposes.

IMSI-International Mobile Subscriber Identifier:-
When a subscriber register with a network operator, a unique subscriber IMSI identifier is issued and stored in the SIM of the MS as well as in the HLR. An MS can function fully if it is operated with a valid SIM inserted into am MS with a valid IMEI. IMSI consists of three parts:
MCC- Mobile Country Code: - It contains three digits number.
MNC- Mobile National Code: - It contains two digits number.
MSIN- Mobile Subscriber Identification Number: It contains ten digits of number.

MSRN-Mobile Station Roaming Number:-
The MSRN is a temporary, location dependent ISDN number issued by the parent VLR to all MSs within its area of responsibility. It is stored in the VLR an associated. HLR but not in the MS. The MSRN is used by the VLR associate MSC for call routing within the MSC/VLR service area.

MSISDN-   Mobile Station ISDN Number:-
The MSISDN represents the true or dialed number associated with the subscriber. It is assigned to the subscriber by the network operator at registration and is stored in the SIM.


CC     =     Country Code
NDC =     National destination Code
SN     =     Subscriber Number

Call Control: -   this identifies the subscriber, establishes a call and clears the connection after the conversation is over.
Charging: -   This collects the charging information about a call such as the numbers of the caller and the called subscriber, the time and type of the transaction etc, and transfers it to the Billing Centre.
Subscriber data handling: -   This is the permanent data storage in the HLR and temporary storage of relevant data in the VLR.
Locating the subscriber: -    This locates a subscriber before establishing a call.

The Network Management Subsystem (NMS):- The purpose of the NMS is to monitor various functions and elements of the network. These tasks are carried out by the NMS/2000
This consists of a number of Work Stations, Servers and a Router. This connects to a Data Communications Network (DCN).
The operator workstations are connected to the database and communication servers via a Local Area Network (LAN). The database server stores the management information about the network. The communications server takes care of the data communications between the NMS
and the equipment in the GSM network known as “Network Elements”. These communications are carried over a Data Communications Network (DCN), which connects to the NMS via a router. The DCN is normally implemented using an X.25 Packet Switching Network. BSC the functions of the NMS can be divided into three categories:
Fault Management
Performance Management
These functions cover the whole of the GSM network elements from the level of individual BTSs, up to MSCs and HLRs.

Fault Management
The purpose of Fault Management is to ensure the smooth operation of the network and rapid correction of any kind of problems that are detected. Fault management provides the network operator with information about the current status of alarm events and maintains a history database of alarms.

Configuration Management
The purpose of Configuration Management is to maintain up to date information about the operation and configuration status of network elements. Specific configuration functions include the management of the radio network, software and hardware management of the network elements, time synchronizations and security operations.

Performance Management
In performance management, the NMS collects measurement data from individual network elements and stores it in a database. On the basis of these data, the network operator is able to compare the actual performance of the network with the planned performance and detect
Both good and bad performance areas within the network.


  • Process of planning:-
  • Costs of building the network
  • Capacity of the network
  • Coverage of the area
  • Maximum congestion allowed (grade of service)
  • Quality of calls
  • Further development of the network.

The main steps of a Network Planning process are as follows:-
Collection of all relevant information such as topographical maps and statistical books
Network Dimensioning based on coverage and capacity requirements
Selection of Base Station sites
Survey of intended sites
Use of computer aided design system for coverage prediction,
Interference analysis and frequency planning

Omni directional BTS:-
The type and location of the BTS depends on the characteristics of the surroundings. In sparsely populated areas, we use powerful BTS’s which are usually mounted on high ground to provide maximum unobstructed coverage to all directions. This type of BTS is called Omni directional BTS  35 kilometers and the number of available frequencies depends on the traffic volume.

2-Sectorised BTS:-
In urban areas, where traffic volume is higher, the size of a cell is much smaller and the distance between BTS’s is shorter. The standard type of BTS is also different: the cell is divided into three sectors that have a few frequencies each. A string of two-sector BTS’s is installed along the road. This is called Sectorised BTS.

3-sectorised BTS:-
These types of Sectorised BTS are used to provide coverage for highways. Instead of three-sector BTS’s, a string of two-sector BTS’s is installed along the road.

Full coverage and mobility for 144Kbits/s, preferably 384Kbits/s.
Limited coverage and mobility for 2Mbit/s
Efficient use of radio spectrum compared with existing systems.
Flexible architecture to allow introduction of new services.
Compromises must be made on the speed of data transmission compared with the distance
And mobility.

Network operators will offer video and to her multimedia applications.
Advanced mobile handsets will be required to handle large amounts of
High-speed data in what is known as the 3rd Generation Mobile systems.
the radio frequencies between  1885MHz and 2200MHz to be reserved for the
IMT-2000, on a global basis.

GSM is evolving to provide much higher data rates:
High Speed Circuit Switched Data (HSCSD)
General Packet Radio Services (GPRS)
Enhanced Data rates for GSM Evolution (EDGE)

EDGE will provide a bridge from GSM into the 3rd Generation mobile networks. EDGE provides data speeds of 384Kbits/s but still using the existing 200 KHz GSM channel. The extra capacity is achieved by increasing the data capacity of a single GSM timeslot from 9.6Kbits/s to 48Kbits/s and possibly up to nearly 70Kbits/s under good radio conditions.

EDGE will provide GSM network with the ability to handle wireless multimedia Services.
EDGE Will also provide Internet/intranet, videoconferencing, and fast electronic mail transfer.
EDGE uses the same TDMA frame structure and channel bandwidth of 200 KHz as current GSM networks high-capacity areas such as dense city areas, air ports, etc.

GPRS gives a direct link between the worlds of the Internet and mobile communications users to have the same experience as if they were connected to their office LAN.GPRS allows users to be charged for the actual amount of data they transfer. The higher transmission speeds provided by GPRS. The file downloads are faster. GPRS brings cost efficient use of existing resources to the operators. By allowing faster or slower data speeds dynamically according to the amount of radio resources will help to increase the average usage level of radio resources.

Code Division Multiple Access is a technique that allows many different mobile telephones to use the same frequency at the same time but with each phone assigned a unique code sequence known as a "spreading code". CDMA is a form of "spread spectrum" where the information is spread across the available bandwidth of the radio channel. The spreading code is used to encode information bearing digital signal. The receiver uses the same code to decode the

For the 3rd generation mobile systems, a high bit rate is required for multi-media data. The W-CDMA systems has a bandwidth of approximately 5MHz.In the W-CDMA system the spreading codes are used to spread out the data signal to cover the whole wideband spectrum which is allocated for the data transfer. The ETSI proposals for W-CDMA uses direct spread with a chip rate of 4.096Mchips/s.

3G networks consists of Radio Access Network (RAN), Core Network and NMS
RAN represents BSS and
Core Network represents NSS of a GSM network.
A mobile station can have possibility of handover between a GSM and WCDMA networks.

After undergoing a practical training we concluded that on the basis of our theoretical knowledge we can develop any complex utility. In GSM Architecture I studied high functionality of seamless global roaming. In call processing I was taught about call origination and call termination. Also various new feature and services provided by the third generation.

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