5”Typical” Mobile operator One to ten MSC per 1 M subscribersTen to one hundred BSC per MSCThousands of BTS per 1 M subscribers
6Base Transceiver Station Controls the radio linkencryptionerror controlsignal strength1 - 6 duplex carriers, for example:two layers120o sectors(6+8)*3 = 42 voice callsCost ~ 100 – 200 k$
7Base Station Controller communication with the mobile terminallocal hand-overvoice codecscarrier allocationpaging to terminalstalks to the MSCserves up to 40 BTSscould be co-located with MSC
8Mobile Swicthing Center Mobility managementidentifies and authenticateslocatesswitches between BSCsHandover to other MSCs64 kbps regular voice channels
9Radio Access network A carrier is divided into logical channels control channels CCHtraffic channels TCHThe first carrier holds 2 controll channels and 6 traffic channels. Additional carriers holds only traffic channels.
10Control Channels Broadcast Common control Dedicated control Frequency correction: to synchronize (FCCH)Broadcast control: this is me, these are my neighbours (BCCH)Common controlPaging: to notify a mobile station (PCH)Random access: for the mobile to request service (RACH)Access grant: reply with assigned dedicated control channel (AGCH)Dedicated controlStandalone dedicated control: used during call set-up, SMS etc (SDCCH)Slow associated control: power, time etc (SACCH)Fast associated control: handover etc, uses the TCH (FACCH)Cell broadcast: cell broadcast
11Traffic Channels Duplex Error control Full rate (TCH/F) Forward Error Correction (FEC)retransmission (ARQ)Full rate (TCH/F)13 Kbps speech9,6 or 14,4 Kpbs dataHalf rate (TCH/H)6,5 Kbps speech7,2 or 4,8 Kbps data
12Logical channels Hyperframe: 2048 superframes 3h28m Superframe: 26 or 51 multiframes 6.12 sCCHCCHMultiframe: 26 or 51 TDMA framesCCHTCH8 time-slot TDMA frame ms
13One TDMA frame Normal burst Frequency correction burst 148 b mstailguard8.25tailtrainingNormal burst357 b26 b57 b3user datauser datastealing flagsFrequency correction burstSynchronization burstDummy burstAccess burst
14Keeping track of a mobile station VLR visiting location registerLocation areaLocation areaupdate the VLR with new location area
15Moving to a new MSC VLR which LA which MSC ? Location area update the VLR with new location area and new MSC
16but also…. HLR home location register VLR update the home location register!
17Home Location Register incomming callPSTNwhere is the mobile?GMSCHLRMSCHow do we reach him?VLR
18Mobile station numbers mobile subscriber ISDN number (MSISDN) i.e. the phone numberPSTNGMSCHLRMobile Station Roaming Number (MSRN).MSCVLRTemporary Mobile Subscriber IdentityInternational Mobile Subscriber Identity
19GPRS Access Network BTS BSC BTS MS BTS Internet Gateway GPRS Support Node GGSNAccess NetworkPacket Control UnitBTSBSCUDP/TCP tunnelServing GPRS Support Node SGSNBTSMSBTS