point code (PC)

SS7 networks use addressing information to route the call from one network node to the next through the network. The actual addressing scheme is based on a logical address that identifies each individual SS7 node, including the Service Switching Points( SSP), the Signalling Transfer Points( STP) and the Signalling Control Points ( SCP).

The logical addresses are called point codes(PCs). They are located in the third layer of the protocol stack of SS7 signaling. The Point Codes are used in conjunction with the Circuit Indentification Code( CIC), the calling party number and the called party number for processing and forwarding.

Point codes ( PC) in SS7 networks are divided into Adjacent Point Code( APC), Destination Point Code( DPC) and Originating Point Code( OPC). There are various point code formats, such as the ANSI point code and the ITU point code. According to ANSI, a point code consists of three octets of 8 bits each, i.e. a total of 24 bits. The logical address is divided into three individual sections separated by dots. The first section identifies the network, the second the cluster, which are the logical groups of network nodes, and the third the member nodes connected to the clusters. The corresponding ANSI point code could have the following structure: 15.55.20.

The ITU format is slightly different. Like that of ANSI, the logical address consists of three data fields, although they may differ in the number of bits. The first data field identifies the geographical area, the second data field stands for the network identifier and the third data field for the Signalling Point Identifier( SPID).