TABLE OF CONTENTS This chapter discusses Message Transfer Part (MTP) level 3 functions as used in channelized networks. Some of these functions have been implemented in new Internet Protocol (IP) protocols specifically for the transport of Signaling System 7 (SS7) over IP networks. The purpose of adding the functions and procedures discussed in this chapter to IP networks is to ensure the reliability of the signaling network and guarantee the delivery of signaling messages when using Transmission Control Protocol /Internet Protocol (TCP/IP) facilities.
Therefore, it is important to understand MTP level 3 even though you may not be using time-division multiplexing (TDM) networks. You will find that MTP level 3 is still supported in the signaling nodes [ service switching points (SSPs), signal transfer points (STPs), and service control points (SCPs)], although IP is the transport.
There are two categories of functionality at this level: signaling message handling and signaling network management. Signaling message handling is used for routing messages to the appropriate link and determining if messages will be addressed to the received node or if they will be forwarded. Signaling network management is used to reroute traffic to other links when nodes become unavailable.
MTP level 3 relies on the services of level 2 for the delivery of all messages. The interface between the two levels consists of a set of primitives. Primitives enable parameters to be sent to level 2 for routing over the network in the form of SS7 messages.
