Download

8SS7 MESSAGE TRANSFER PARTThe Message Transfer Part (MTP) of SS7 has two main functions. In the first place,it handles the transfer of MTP-user messages across the SS7 signaling network.In the second place, it includes functions to keep the message traffic flowingwhen failures occur in the signaling network.8.1 INTRODUCTION TO MTP8.1.1 Structure of MTPMTP is divided into three parts, located at levels 1, 2, and 3 of the SS7 hierarchy.The main functions of these parts are outlined below [1–5].MTP Level 1 (MTP1). MTP1 is the physical signaling data link (SDL), whichconsists of a pair of 64-kb/s digital transmission channels, and transports SS7signal units between two signaling points. MTP1 is described in Section 8.2.MTP Level 2 (MTP2). A signaling link (SL) between signaling points A and Bconsists of a SDL between the signaling points and MTP2 functions located atboth signaling points (Fig. 8.1-1). The MTP2 functions relate to individual signalinglinks and include synchronization and the detection and correction of errors inmessage signal units (MSUs). MTP2 is discussed in Sections 8.3 through 8.6.MTP Level 3. MTP3 is the interface between MTP and the MTP-users (level-4protocols) at a signaling point. In addition to providing services for the transfer ofuser messages, MTP3 includes procedures to reroute messages when a failureoccurs in the SS7 signaling network. MTP3 is discussed in Sections 8.7 through 8.9.Signaling in Telecommunication Networks, Second Edition, by John G. van Bosse and Fabrizio U. DevetakCopyright # 2007 John Wiley & Sons, Inc.167