Gsm Architecture

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INDEX

1. GSM Architecture……………………………………………… 2 2. The Cellular System ....…………………………………………. 7 3. Air Interface ...………………………………………………….. 10 4. Signaling Concepts…..…………………………………………. 17 5. Functions And Services of GSM ………….…………………… 30 6. Frequency Hopping……..…………………………………….. 39 7. GSM Identities……..………………………………………….. . 45 8. Traffic Cases……………………………………………………. 50 9. The GSM Transmission Process………………………………. 65 10. E1……………………………………………………………… 70 11. Transmission...…………………………………………………. 80

CHAPTER-1
GSM ARCHITECTURE
1.1 INTRODUCTION
Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. The standardized system met certain favorable criterion:

* Spectrum efficiency
* International roaming
* Low mobile and base stations costs
* Good subjective voice quality
* Compatibility with other systems such as ISDN (Integrated Services Digital Network) * Ability to support new services
* Distinction between user and device identification
* Extensive security features
1.2 GSM NETWORK ELEMENTS
* THE SWITCHING SYSTEM
The switching system (SS) is responsible for performing call processing subscriber related functions. The switching system includes the following functional units. * HOME LOCATION REGISTER (HLR)

The HLR is a centralized network database that stores and manages all mobile subscriptions belonging to a specific operator. It acts as a permanent store for a person’s subscription information until that subscription is cancelled. The information stored includes: * Subscriber identity

* Subscriber supplementary services
* Subscriber location information
* Subscriber authentication information
The HLR can be implemented in the same network node as the MSC or as a stand-alone database. If the capacity of a HLR is exceeded by the number of subscribers, additional HLRs may be added. * MOBILE SERVICES SWITCHING CENTRE (MSC)

The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signalling and others.

* VISITOR LOCATION REGISTER (VLR)
The VLR database contains information about all the mobile subscribers currently located in an MSC service area. Thus, there is one VLR for each MSC in a network. The VLR temporarily stores subscription information so that the MSC can service all the subscribers currently visiting that MSC service area. The VLR can be regarded as a distributed HLR as it holds a copy of the HLR information stored about the subscriber. When a subscriber roams into a new MSC service area, the VLR connected to that MSC requests information about the subscriber from the subscriber’s HLR. The HLR sends a copy of the information to the VLR and updates its own location information. When the subscriber makes a call, the VLR will already have the information required for call set-up.

* AUTHENTICATION CENTRE (AUC)
A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world. The AUC is a database connected to the HLR which provides it with the authentication parameters and ciphering keys used to ensure network security.

* EQUIPMENT IDENTITY REGISTER (EIR)
The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR...
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