tailieunhanh - GSM Networks : Protocols, Terminology, and Implementation - Chapter 12

Chương này áp dụng cho các cơ sở kiến thức thu được của các chương trước để mô tả các hệ thống con GSM khác nhau thông qua giao thức báo hiệu. Mỗi kịch bản được trình bày là giải thích chi tiết. Trước khi trình bày những chi tiết, tuy nhiên, tính phổ biến, hoặc "sợi chỉ đỏ" của kịch bản nên được nhấn mạnh. Đối với mục đích đó, sơ đồ khối trong hình áp dụng đối với tất cả: Bộ Xây dựng (điện thoại di động có nguồn gốc cuộc gọi), MTC (điện thoại di động. | 12 Scenarios This chapter applies the acquired knowledge base of the previous chapters to describe the various GSM subsystems via signaling protocols. Every presented scenario is explained in detail. Before presenting those details however the commonality or red thread of the scenarios should be emphasized. For that purpose the block diagram in Figure applies to all MOC mobile originating call MTC mobile terminating call and LU location update . The following is an explanation of the individual blocks in Figure Only in a MTC does the network search for a particular subscriber paging . When the MS is located or when the MS initiates a call a control channel between MS and BSC has to be established. The MS uses the control channel for identification and indicates to the BSC in detail which service is requested. The BSC passes the service request of the MS to the NSS. For that purpose the BSS has to request an SCCP connection from the MSC. The NSS reacts on a connection request of any kind with a request for authentication except for an emergency call . Additionally the IMEI may be checked. Ciphering between BTS and MS is activated in successful authentication. Ciphering prevents tapping into the Air-interface. Additional information between MS and NSS are exchanged after activation of ciphering. The additional information either terminates 225 226 GSM Networks Protocols Terminology and Implementation Air-interface Abis-interface A-interface n MSC _J_I Search for the subscriber paging Request for assignment of a control cannel TCH assignment A-Interface Traffic channel assignment Air-interface Phase of active call exchange of payload Figure Block diagram of the base scenarios. a successful LU or in case of a connection request defines the details of that connection . directory number of the called subscriber required technical capabilities of the network and the MS . The process is synchronized between MS and NSS. The assignment of the TCH on the .