X.25 Facilities

X.25 Facilities are generally used for communicating with the network, although many are also of end-to-end significance. Indeed, there is a class of facilities (X.25 Annex-G) reserved for end-to-end usage.

Facilities include such things as:

  • Packet and Window size negotiation
  • Throughput Class negotiation
  • Reverse Charging
  • Closed User Groups
  • NUI selection
  • Charging information
  • Call deflection selection and redirection notification

Certain facilities are allowed in certain packet types – most can appear in Call Requests, but others, for example charging information, appear in Clear Indication packets and DCE Clear Confirmation packets.

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X.25 Networking Guide