GSM Network Structure Lance Westberg

GSM Standard Architecture

GSM Up Close

GSM Phones Mobile Station (MS) MS station provide user access to the GSM network All GSM mobiles comply with the international Standard GSM Phones use a SIM card that holds subscriber data GSM Phones are far more secure then CDMA phones. Each MS has a unique number called a International Mobile Equipment Identity (IMEI) number, which is stored in the “Equipment Identity Register (EIR) station” used for authentication of the MS user Mobile Station Identities CC - Country Code NDC - National Destination Code SN - Serial Number MSISDN - Mobile Station ISDN Number

SIM Card Security Two Levels of Protection When you turn on your mobile phone, it will ask user for a PIN(Personal ID Number) User gets 3 tries to enter PIN, after that its locked You need a PUK (Pin Unblock Key) You get 10 attempts to enter the PUK After that the SIM card is BLOCKED Each SIM Card has a secret identity number called a International Mobile Subscriber Identity (IMSI) Each SIM card contains: • Subscriber telephone number (MSISDN) • International subscriber number (IMSI) • State of the SIM card • Service code (operator) • Authentication key • PIN (Personal Identification Code) • PUK (Personal Unlock Code)

International Mobile Subscriber Identity (IMSI) The SIM Cards secret identity number is made up of these parts. MCC - Mobile Country Code MNC - Mobile network Code MSIN - Mobile Subscriber Identity

Base Transceiver Station (BTS) BTS has a set of transceivers (TRXs) to communicate with mobiles in the area One BTS covers one or more cell regions But depends on the number of transceivers in the cell BTS is connect to the Base Station Controller (BSC) through an Interface BTS transmits and receives voice at 13kbps over air interface to the mobiles device

Base Station Controller (BSC) BSC manages channel allocation, handover of channels connected the BTS's BSC connects to the BTS via the Abis interface and to the mobile switching center (MSC) Interface. Transcoder Rate Adaptation Unit (TRAU) TRAU converts the data rates between 13kbps GSM rate to 64kbps Standard ISDN rate

Mobile Switching Center (MSC) This is where calls are established maintained and released Holds database subscribers information Communicates with BSCs and PSTN on fixed line MSC is weighted on the number of subscribers means one MSC is enought till subscriber base increase up to 1 lac, beyond which another MSC is required Very complicated to connect each MSC to each other and each MSC to the PSTN

Other Databases and Servers Home Location Register (written HLR): a database containing information (geographic position, administrative information, etc.) on the subscribers registered in the area. Visitor Location Register (VLR): a database containing information on users other than the local subscribers. The VLR retrieves the data on a new user from the HLR of the user's subscriber zone. The data are maintained as long as the user is in the zone and are deleted when the user leaves. Equipment Identify Register (EIR): a database listing the mobile terminals. Authentication Centre (AUC): responsible for verifying user identities. Short message service center (SMSC) Its purpose is to store, forward, convert and deliver SMS messages.

GSM and the World The End