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Concept of Point Codes



Each signaling point in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling points to identify the source and destination of each message. Each signaling point uses a routing table to select the appropriate signaling path for each message. Signalling Points codes can be categorized as Local/National Point Codes or International Point Codes. Signalling Nodes which are connected on International Signalling Network is assigned International Point code. Normally, GMSC(Gateway Mobile Switching Centre) of a mobile network is given International Point Code which would be unique throughout globe. Whereas internal signaling nodes are given local/private signaling points and are not accessible outside mobile operator’s network. E.g. IVR System, SMSC etc.

All types of signaling units carry an Origination Point Code (OPC) and a Destination Point Code (DPC). Point codes are unique identification numbers for signaling points. If traffic is transferred between two Siganlling Points say A & B , then A would be called OPC (Origination Point Code) and B would be referred as DPC (Destination Point Code)

Point Code Formats

Point code format are different in ANSI and CITTU network.
Formats are as follows:

NNNN (CITTU) - e.g., 2345
In case of CITTU or ITU-T, Point codes are indetified by a 14 bit unique identifier with in a network. Digits in a CITTU point code tell MTP Level 3 the following about a signaling point's location:

These point codes can further be categorized as Local or Private Point Codes and Global Points Codes. These can be termed as Private IP address and Public IP address if compared to TCP/IP world.

NNN-NNN-NNN (ANSI) - e.g., 123-456-789
Digits in an ANSI point code tell MTP Level 3 the following about the location of a signaling point: When the destination point code in a message indicates the receiving signaling point, the message is distributed to the appropriate user part (e.g., ISUP or SCCP) indicated by the service indicator in the SIO. Messages destined for other signaling points are transferred provided that the receiving signaling point has message transfer capabilities (like an STP).

International Point Code Numbering
International Signalling Point Codes (ISPCs) are 14-bit binary codes used to establish direct SS7 signalling links and interconnection with overseas networks. The 14 bits of the ISPC are commonly represented by three decimal numbers (e.g. 5-047-0):

  1. the first decimal, with the range of 0 to 7, represents the three (3) most significant bits; It identifies world geographical zone
  2. the second decimal string, with the range of 000 to 255 represents the following eight (8) bits; The sub-field of 8 bits identify a geographical area or network in a specific zone.
  3. and the third decimal, with the range of 0 to 7, represents the three least significant bits. The sub-field of 3 bits (CBA) should identify a signalling point in a specific geographical area or network. The combination of the first and second sub-fields could be regarded as a signalling area/network code (SANC).

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