Subject Name: GSM Subject Code: 10EC843 Prepared By: Gopika D K, Shruthi N Department: ECE Date

GSM LOGICAL CHANNELS & FRAME STRUCTURES UNIT 3 GSM LOGICAL CHANNELS & FRAME STRUCTURES 11/9/2018

GSM LOGICAL CHANNEL Physical Channel Logical Channel 11/9/2018

Physical Channel Each timeslot in TDMA frame is called a physical channel. There are 8 physical channels per carrier in GSM. Physical channels may be used to carry speech data or signaling information. Logical Channel The Information carried by physical channels is known as logical channel. There are a several type of logical channels available in GSM. 11/9/2018

USER INFORMATION( TRAFFIC) SIGNALLING INFORMATION (CONTROL) LOGICAL CHANNELS USER INFORMATION( TRAFFIC) SIGNALLING INFORMATION (CONTROL) 11/9/2018

Logical Channels Logical Channels Common Channels Dedicated Channels Control Channels Traffic Channels Broadcast Channels Common Control Channels TCH (Full-Rate) TCH (Half-Rate) TCH (EFR) SDCCH SACCH FACCH FCCH SCH BCCH RACH PCH AGCH 11/9/2018

Common channels are used to broadcast different information to MS & for setting up signaling channels between the MSC/VLR & the MS Common Channels Broadcast Channels Common Control Channels 11/9/2018

Broadcast Channels FCCH (Frequency Correction Channel) – Provides the frequency correction information used by the mobile station. SCH (Synchronization Channel) – Contains the Base Station Identity Code (BSIC) and the TDMA frame number used for synchronization of the mobile station to the frame structure of a new BTS. BCCH (Broadcast Control Channel) – Used to broadcast general information, related to network, to all mobile stations. 11/9/2018

Broadcast Channels….. FCCH:- This channel do not contain any information, this have a stream of 142 zeros. So, the frequency that have this sequence helps MS to identify the BCCH frequency among all transmitted frequency 11/9/2018

SCH(Synchronization Channel):- BTS sends TDMA frame number on SCH by which MS synchronize it self with GSM system. SCH Down link Down link TDMA Frame Number TDMA Frame Number BSIC 11/9/2018

Broadcast Control Channel(BCCH):- System Type 900/1800 LAI Neighbor Cell BCCH Information Frequency hopping used or not? Type of Training sequence used Max power allowed in cell 11/9/2018

Common Control Channels (CCCH) PCH (Paging Channel) – Used to page the mobile station. PCH information is transmitted over the downlink It contain IMSI or TMSI. RACH (Random Access Channel ) – Used by a mobile station to Request access to the system. RACH information is transmitted over the uplink. AGCH (Access Grant Channel) – Used to assign a SDCCH for call setup. AGCH information is transmitted over the downlink. 11/9/2018

It used when MS want to uplink first time Used for Emergency Call RACH:- It used when MS want to uplink first time Used for Emergency Call Answer to paging Initiate O/G call Location update request 11/9/2018

It show which SDCCH is allotted to MS AGCH (Access Grant Channel) – Used to assign a SDCCH for call setup. AGCH information is transmitted over the downlink Down link It show which SDCCH is allotted to MS 11/9/2018

Dedicated Control Channels (DCCH) SDCCH (Stand alone Dedicated Control Channel) – Carries signaling information during call setup SACCH (Slow Associated Control Channel) – Transmits call Control data and measurement reports during the call. FACCH (Fast Associated Control Channel) – Carries urgent Signalling information for handover etc. . 11/9/2018

Dedicated Control Channels (DCCH)…. SDCCH (Stand alone Dedicated Control Channel) Call Set up Authentication Transmission of SMS Location Update 11/9/2018

ALLOWED LOGICAL CHANNEL COMBINATIONS Channels are grouped into 26-multiframe - payload / voice – summarizes the bursts of TCHs and associated SACCHs and FACCHs 51-multiframe – signaling data – puts together all bursts of traffic channels without SACCHs and FACCHs GSM uses certain predefined pattern of channel combinations: CC1: TCH/F + FACCH/F + SACCH/TF CC2: TCH/H (0,1) + FACCH/H(0,1) + SACCH/TH(0,1) CC3: TCH/H(0) + FACCH/H(0) + SACCH/TH(0)+TCH/H(1) CC4: FCCH + SCH + BCCH + CCCH CC5: FCCH + SCH + BCCH + CCCH + SDCCH/4(0,1,2,3) + SACCH/C4 (0,1,2,3) CC6: BCCH + CCCH CC7: SDCCH/8 + SA 11/9/2018

Communication Systems GSM – frames, multiframes, superframes Why 26, 51:An active call transmits/receive in 25 frames, except the last one In this last frame, it can monitor the BCCH of this (and neighbor) cell This particular numbering allows to scan all BCCH slots during a superframe Important slots while call is active: frequency correction FCCH and sync SCH - needed for handover Why multiframes - determine how BCCH is constructed, e.g. which specific information transmitted on BCCH during a given multiframe Superframes are composed of multiframes Used as input parameter by encryption algorithm 11/9/2018

TDMA Bursts in GSM 3 8.25 FB 1 142 fixed bits 3 SB 3 39 data 64 bit Training seq 8.25 Dummy Burst 3 26 bit Training seq 3 8.25 8 41 bit Training seq 36 data 3 68.25 Access Burst 11/9/2018

Normal Burst Tail bit 3 57 Data bits 26 bit Training seq 57 Data bits 8.25 Bit GP Stealing Flags 11/9/2018

DATA ENCRYPTION IN GSM network MS Authentication What signed response (SRES) are you able to derive from the input challenge RAND by applying the A3 algorithm with your personal key Ki (Ki is per subscriber)? RAND network A3 algorithm Ki MS A3 algorithm Ki SRES Ki RAND (128bit) SRES 11/9/2018

DATA ENCRYPTION IN GSM BTS MS Encryption Digital technology – easy to encrypt voice data A5 derives a ciphering sequence of 114 bits for each burst independently XOR 114 bits of a radio burst with 114 bits of a ciphering sequence generated by A5 A5 algorithm Kc (64 bits) MS frame number (22 bits) BTS Kc S1(114) deciphering S2(114) ciphering S1 ciphering S2 deciphering S1 11/9/2018

GSM Mobility Management GSM architecture overview Network layout Protocols Addresses & identifiers Location management Call delivery + location update Security Handover management 11/9/2018

GSM network layout GSM Network (PLMN) MSC region MSC region MSC region PLMN: Public Land Mobile Network MSC: Mobile Switching Center BTS: Base Transceiver Station BSC: Base Station Controller GSM Network (PLMN) MSC region MSC region Location area Location area BSC BSC MSC region BTS BTS 11/9/2018

GSM network layout PSTN ISDN OMC MSC GMSC BSC HLR EIR VLR AUC BTS A Abis E B,C EIR HLR AUC VLR BTS Um 11/9/2018

GSM MAP protocol GSM MAP similar to IS41 MAP MAP uses Transactions Capabilities Part (TCAP) of the SS7 stack MAP functions: Updating of location information in VLRs Storing routing information in HLRs Updating and supplementing user profiles in HLRs Handoff of connections between MSCs 11/9/2018

LOCATION REGISTRATION Geographic based Time Based ON/OFF Based 11/9/2018

MOBILE IDENTIFICATION Mobile identification is used to identify the MS when the VLR does not recongnize the TMSI sent by the MS. 11/9/2018