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.