MTP 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 [l-5]. MTP Level 7 (MTp7) is the physical signaling data link (SDL), which consists of a pair of 64 kb/s digital transmission channels, and transports SS7 signal units between two signaling points. MTPl is described in Section 8.2. MTf Level 2 (MTf2).