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.