GSM PROTOCOL SUITES :
The layers are
The physical layer handles all radio specific functions.
1. Creation of burst in any one of 5 format.
2. Multiplexing burst into a TDMA frame.
3. Synchronization with BTS.
4. Detection of idle channel.
5. Channel Quality measurement.
6. Channel coding and error detection and correction.
The Um interfaces use GMSK for modulation and perform encryption and decryption.
The protocol architecture of GSM is shown below:
LAYER 2 :
For signaling between entitites in GSM network this layer is used. The protocol used is LAPDM. LAPD stands for link access procedure for D channel. LAPDM has no buffers has to follow Um interface patterns. The functions of the layer are namely:
1. Reliable data transfer
2. Reseqeuncing of data
3. Flow control
LAYER 3 : NETWORK LAYER
The network layer has sublayers. They are,
1. RADIO RESOURCE MANAGEMENT:
This is the lowest sub layer and it‘s a part of RR and RR‘ is implemented by BSC. The function of RR are Setup, Maintenance, Release of radio channels. RR directly access the physical layer. It supports BTS management. The function of RR‘ are supported by BSC via BSTM.
2. MOBILITY MANAGEMENT:
The main function of Mobility management are Registration, Authentication, Identification, Location Updating, Providing TMSI, IMSI.
LAYER 4 : CALL MANAGEMENT:
This layer contains three entities. They are Call control, SMS, Supplementary services. Call control provides point to point connection between two terminals and also used for call clearance, change of call parameters. SMS allows messages transfer using control channels. The supplementary services discussed already is to be reproduced here.