Aga private institute for computer science Lecturer: Srwa Mohammad
What is GSM? GSM: Global System for Mobile Communications *Evolution of Cellular Networks 1G 2G 2.5G 3G 4G ---------- ----------------------------------------------- Analog Digital ------------------------ --------------------------------- Circuit-switching Packet-switching *Functional Architecture broadly divided into 4 parts: 1- Mobile Station (MS). 2- Base Station Subsystem (BSS). 3- Network Switching Subsystem (NSS). 4- Operation and Support Subsystem (OSS)
PLMN: The GSM system is made up of sub-networks called: Public Land Mobile Network's (PLMN). GSM network with added elements MS and SIM Mobile Station (MS) enables generic radio and processing functions to access the network through the radio interface. Each MS has a unique IMEI (Identity Mobile Equipment Identity)
Subscriber Identity Module (SIM) is basically a smart card, containing all the related information stored on the user s side of the radio interface. The SIM stores the IMSI What is an IMSI? The International Mobile Subscriber Identity *consists of three parts 1- The MCC identifying a country 2- The MNC identifying a PLMN within this country 3- The MSIN identifying a subscriber within the PLMN
What is an IMEI Identity Mobile Equipment Identity consists of three parts 1-The TAC is given by the GSM body 2-The FAC is given by the Mfg 3-The SNR is the serial no. BTS BTS include or contain radio transmission and reception devices (including antennas). *A BTS is virtually connected to the MS (Air interface) on one side and to the BSC on the other side. *In general a BTS is represented with three cells. Each cell can have more than one TRX (i.e. Antennas). BSC A BSC is in charge of all the radio interface management through the remote command of the BTS and the MS,
BSC is connected on one side to the MSC and on the other side to several BTSs. MSC/VLR A MSC coordinates the setting-up of calls to and from GSM users. A VLR is a database in charge of temporarily storing subscription data The MSC/VLR has interfaces with the BSC on one side and external networks on the other side HLR Overview A HLR is a database holding subscriber information relevant to the provision of telecommunications services as well as some information related to the current location of the subscriber (IMSI, VLR).
Transmission Transmission Direction: Uplink Transmission Transmission from Mobile to Radio Terminal Down Link Transmission Transmission from Radio Terminal to Mobile Uplink and Downlink channels separated by 45 MHz Channel Logical channels On every physical channel, a number of logical channels are mapped. Each logical channel is used for a specific purpose. 11 Logical Channels in the GSM system: 2 are used for Traffic 9 are used for Control Signaling
Logical channels Traffic channels (TCH) i. Full Rate Channel ii. Half Rate Channel B. Control Channels (with horrible abbreviations!) 1. Broadcast Channels (BCH) i. Frequency Correction Channel (FCCH) ii. Synchronization Channel (SCH) iii. Broadcast Control Channel (BCCH) 2. Common Control Channels (CCCH) i. Paging Channel (PCH) ii. Random Access Channel (RACH) iii. Access Grant Channel (AGCH) 3. Dedicated Control Channels (DCCH) i. Stand alone Dedicated Control Channel (SDCCH) ii. Slow Associated Control Channel (SACCH) iii. Fast Associated Control Channel (FACCH)
Broadcast Channels 1. FCCH (FREQUENCY CORRECTION CHANNEL) To able the Mobile to synchronize to the frequency (Downlink only) 2. SCH ( SYNCHRONISATION CHANNEL) Used for sending BSIC (Base station Identity Code) (Downlink only) 3. BCCH ( BROADCAST CONTROL CHANNEL) Used for sending information to the mobile (Downlink only) Common control channels 1. PCH ( PAGING CHANNEL) Used for paging the Mobile. (Downlink only) 2. RACH ( RANDOM ACCESS CHANNEL) Used for responding to the paging (terminating), Location updating or to make call access (originating. (Uplink only) 3. AGCH ( ACCESS GRANT CHANNEL) Used to allocate SDCCH to the mobile. (Downlink only)
Dedicated control channels 1. SDCCH ( STAND ALONE DEDICATED CONTROL CHANNEL) Send Short Text message to Idle Mobile (Uplink & Downlink) 2. SACCH ( SLOW ASSOCIATED CONTROL CHANNEL) Used for sending information to the mobile Send Short Text message to Busy Mobile (Downlink) 3. FACCH ( FAST ASSOCIATED CONTROL CHANNEL) Used for handover. (Uplink & Downlink) Traffic Management Mobility Management A Network can route a call towards a fixed user by simply knowing the network address (e.g., the telephone number). In a cellular system, In order to receive incoming calls, a mobile user must first be located. In practice,three different methods may be used to locate a mobile user:
Systematic Location Updating at Cell Level Paging Message in all cells of the Network when a call arrives Compromise by Introducing the concept of Location Area.