GSM -‐ Some facts • GSM stands for Global System for Mobile Communications• It is estimated that 80% of the global mobile market uses this standard.• GSM evolved because of the need for a standard mobile telephone system that could be deployed across Europe• It uses the Gaussian Minimum Shift Keying [ GMSK ] technique for modulation• GSM networks operate in the 900 MHz or 1800 MHz bands
Why GSM? • Dominant global market share• Large number of infrastructure and handset vendor’s giving advantage in terms of price and other commercial terms• Wide choice of handsets• Seamless interoperability between networks and handsets• Global footprint for international roaming including SMS, data and other value added services
GSM Architecture PSTN GMSC VLR HLR MSC AUC Network Switching EIR System BSC BTS Mobile Station BTS BTS BSS
Mobile Station (MS) Mobile Sta+on Subscriber IdenAty Mobile Equipment Module [ SIM ] Mobile staAon provides user access to GSM network for Voice & Data Subscriber data is read from a SIM card that plugs into MS Each MS has a unique number called as IMEI number, Mobile Transmit and Receive voice at 13 KB/s over air interface
Base Transceiver Station (BTS) Air interface signalling Ciphering Speech processing (channel coding, interleaving, and burst formaTng) GeneraAon of alarms and staAsAcs Baseband/Radio frequency transformaAon
BSC -‐ Base Station Controller • ConnecAon establishment between the MS and the NSS • Mobility management • StaAsAcal raw data collecAon • Several BTSs are connected to the BSC • BSC Manages channel allocaAon, handovers and release of channels at connected BTSs
MSC – Mobile Switching Centre • Exchange where calls are established, maintained and released • Database for all subscribers and their associated features. • Communicates with the BSCs • MSC is weighted on the number of subscribers it can support.
HLR -‐ Home Location Register • MSC has all subscriber database stored in HLR • HLR has all permanent subscriber database • MSC communicates with HLR to get data for subscribers on call MSC HLR • HLR will have the series of all subscriber numbers, which may not be activated or issued .
VLR – Visiting Location Register• A subscripAon when acAvated is registered in VLR • VLR has all the subscriber numbers which are acAve. • VLR has a temporary database of all acAve subscribers (on/ oﬀ, locaAon informaAon) HLR MSC VLR
VLR – Visiting Location Register HLR MSC VLR VLR MSC • MSC communicates with HLR for subscribers coming from diﬀerent MSCs. If the subscriber is found valid, then it registers the subscriber in the VLR
AUC – Authentication Centre• AuthenAcaAon is a process by which a SIM is veriﬁed • Secret data and the veriﬁcaAon process algorithm are stored in AUC • AUC is the element which carries out the veriﬁcaAon of the SIM • AUC is associated with the HLR MS MSC HLR AUC
EIR (Equipment Identity Register) • EIR is the Mobile Equipment Database which has a series of IMEIs • MSC asks the Mobile to send its IMEI • MSC then checks the validity of IMEI with the EIR • All IMEIs are stored in EIR with relevant classiﬁcaAons EIR MSC