tailieunhanh - GSM Networks : Protocols, Terminology, and Implementation - Chapter 6

Abis giao diện là giao diện giữa BTS và BSC. Nó là một giao diện PCM 30, giống như tất cả các giao diện trên mặt đất khác trong mạng GSM. Đó là quy định của ITU trong G-series các khuyến nghị. Tốc độ truyền là 2,048 Mbps, được phân chia thành 32 kênh 64 Kbps. Các kỹ thuật nén GSM sử dụng gói lên đến 8 kênh lưu lượng truy cập GSM vào một kênh duy nhất 64-Kbps. GSM không bao giờ quy định Abis giao diện trong từng chi tiết, như trường hợp với giao diện-B (giao diện. | 6 The Abis-Interface The Abis-interface is the interface between the BTS and the BSC. It is a PCM 30 interface like all the other terrestrial interfaces in GSM. It is specified by ITU in the G-series of recommendations. The transmission rate is Mbps which is partitioned into 32 channels of 64 Kbps each. The compression techniques that GSM utilizes packs up to 8 GSM traffic channels into a single 64-Kbps channel. GSM never specified the Abis-interface in every detail as was also the case with the B-interface the interface between the MSC and the VLR . The Abis-interface is regarded as proprietary which leads to variations in the Layer 2 protocol between manufacturers as well as to different channel configurations. The consequence is that normally a BTS from manufacturer A cannot be used with a BSC from manufacturer B. Channel Configurations Figure presents two possible channel configurations of the Abis-interface. Note the fixed mapping of the air-interface traffic channels Air0 Air1 . onto a time slot of the Abis-interface. This fixed mapping has the advantage that it is possible to determine which Abis time slot will be used when a particular air-interface channel is assigned. 51 52 GSM Networks Protocols Terminology and Implementation bit TS 7 6 5 4 3 2 1 0 0 1 FAS NFAS TRX1 Air 0 Air 1 Air 2 Air 3 2 Air 4 Air 5 Air 6 Air 7 3 Air 0 Air 1 Air 2 Air 3 TRX5 4 Air 4 Air 5 Air 6 Air 7 5 Air 0 Air 1 Air 2 Air 3 TRX2 6 Air 4 Air 5 Air 6 Air 7 7 Air 0 Air 1 Air 2 Air 3 TRX6 8 Air 4 Air 5 Air 6 Air 7 9 Air 0 Air 1 Air 2 Air 3 TRX3 10 Air 4 Air 5 Air 6 Air 7 11 Air 0 Air 1 Air 2 Air 3 TRX7 12 Air 4 Air 5 Air 6 Air 7 13 Air 0 Air 1 Air 2 Air 3 TRX4 14 Air 4 Air 5 Air 6 Air 7 15 Air 0 Air 1 Air 2 Air 3 TRX8 16 Air 4 Air 5 Air 6 Air 7 17 not used 18 not used 19 partial O M data 20 not used 21 O M signaling 22 TRX 8 signaling 23 TRX 7 signaling 24 TRX 6 signaling 25 TRX 5 signaling 26 not used 27 TRX 4 signaling 28 TRX 3 signaling 29 TRX 2 signaling 30 TRX 1 .