Signaling points are identified using Destination Point Codes (DPCs). DPCs can be a number, up to 24 bits, based on the variant (for example, ITU has 14 bit DPC, ANSI has 24 bit DPC). In MTP3 software, each point code can be uniquely identified as a local SS7 point code or a remote SS7 point code.
In MTP3 software, each signaling point is additionally identified by a network identifier (ID) which is unique to all signaling point codes within the network. This addressing is useful for simultaneously supporting multiple variants of MTP3 where each signaling point can be addressed by MTP3 using the combination of DPC and network ID. (Note: By virtue of the network ID, MTP3 can support the same DPC value for more than one signaling point if each of the signaling points that have the same DPC value belongs to a different network.)
The Destination Point Code (DPC), Origination Point Code (OPC), and Signaling Link Selection (SLS) fields are part of the routing label in MTP3. The service indicator and network indicator are part of the Service Information Octet (SIO) of the MSU. The service indicator is four bits and can indicate an MTP service user or signaling network management service. The network indicator is two bits and can indicate a national or international network.