Level 3 of the Message Transfer Part (Message Transfer Part 3 – MTP3) resides at layer 3 of the OSI model and performs the SS7 protocol’s network functions. The primary purpose of this protocol level is to route messages between SS7 network nodes in a reliable manner. This responsibility is divided into two categories:

  • Signaling Message Handling (SMH)

  • Signaling Network Management (SNM)

Signaling Message Handling is concerned with routing messages to the appropriate network destination. Each node analyzes the incoming message based on its Destination Point Code (DPC) to determine whether the message is destined for that node. If the receiving node is the destination, the incoming message is delivered to the appropriate MTP3 user. If the receiving node is not the destination and the message has routing capability, i.e., is an STP, an attempt is made to route the message.

Signaling Network Management is a set of messages and procedures whose purpose is to handle network failures in a manner that allows messages to continue to reach their destination whenever possible. These procedures work together to coordinate SS7 resources that are becoming available or unavailable with the demands of user traffic. Network nodes communicate with each other to remain aware of which routes are available for sending messages so they can adjust traffic routes appropriately.

This chapter examines network addressing, how messages are routed, and the robust network management procedures instituted by the protocol to ensure successful message delivery with minimal disruption. The following sections address these topics:

  • Point Codes

  • Message Format

  • Signaling Message Handling

  • Signaling Network Management

  • Summary