The GSM A-bis Interface - 3 days

This three day course aims to give the student a thorough understanding of the GSM A-bis interface. The interface is first placed in the context of the total GSM system including the Air interface and the A interface. The functions and interrelationships of the BSC, BTS and TRAU are covered including the physical context of 64 kb/s links, TEI allocations and the mapping of TEI's to SCCP numbers at the BSC. The signalling relationships and flow between these elements and the MSC messages relating to the BSS and MS are covered. The complete signalling model of the BSSAP (BSSMAP, DTAP,) SCCP, MTP at the BSC, BTSM, L3, L2 and L1 at the BSC, L1, L2 and L3 at the BTS and RR, CM an CC at the mobile station is included. The functions of the LAPD transport mechanisms on the A-bis are covered.

The A-bis Common Channel management, Dedicated Channel management, Radio Link Layer management and the TRX management are covered in detail with the content of the layer 3 messages. The transparent messages MSC to mobile station and the structure of these layer 3 messages are also examined. Dimensioning of the A-bis link to cater for various traffic demands and BCCH carrier configurations is included. This is prefaced by an introduction to cell dimensioning.

The course includes a demanding exercise in completing the L3 and L2 signal flow across the A-bis and A interface given a group of Um messages. The students will leave the course with a clear understanding and confidence in their abilities to dealwith operational issues concerning the A-bis interface.

Introduction. BSC Functions. BTS Functions. TRAU Functions. A interface. Um interface. Physical links MSC-TRAU-BSC-BTS. The OML and the OMC function. TEI allocation and mapping to SCCP. Connection and connectionless communication.

Signalling Model MSC-BSS-MS. BSSMAP, DTAP, SCCP, MTP, LAPD, BTSM, RR, CM and CC.

Layer 3 Message Flow on the A-bis. . Common Channel Management - Paging - Channel Required - Delete Indication - BCCH Information SMS Broadcast Request - SMS Broadcast Command. Dedicated Channel Management - Channel Activation - Mode Modify - Mode Modify Request - Mode Modify Acknowledge - Mode Modify Negative Acknowledge - Handover Detection Intra BS - Handover Detection Inter BSS Encryption - Measurement Results - Preprocess Configure - Preprocessed measurement results - Deactivate SACCH - RF Channel Release - RF Channel Release Acknowledge - Power Control - Connection Fail Indicator - Physical Contex. Radio Link Layer Management - Establish Indication - Release Indication - Establish Request - Establish Confirm - Release Request - Release Confirm - Data Request - Data Indication - Unit Data Request - Unit Data Indication - Error TRX Management - Resource Indication - SACCH Fill - Overload

Structure of the A-bis Layer 3 Messages.

LAPD. A-bis LAPD. Operation of the LAPD Frames. Flow and Error Control in LAPD

Layer 1. The E1 and T1 structure. FAW. FDW. Alarms. Exercises. Completion of arrow diagrams for MO, MT calls, Handovers, mode change. A-bis dimensioning.