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AIXLink/X.25 1.1 for AIX: Guide and Reference

Appendix E. Supported Facilities for X.25 Communications

The X.25 program supports both standard X.25 facilities and CCITT-defined facilities.

Several types of facilities may be requested in a call packet. Standard X.25 facilities are the most usual but you may find also non-X.25 facilities specific to your network or CCITT-defined facilities to be used with the OSI network services. Ask your network provider which facilities are available.

Facilities Format

Nonstandard facilities are preceded by a facility marker: 0x0000, 0x00FF or 0x000F. The Facilities Format figure shows the format of these facility markers:

X.25 facilities
non-X.25 facilities provided by the local network
non-X.25 facilities provided by the remote network
CCITT-specified DTE facilities
Facilities Format

If any section is not required, both it and the preceding facility marker can be left out.

Within each section, the facilities format is defined as a series of facility codes, followed by a number of bytes of arguments. The number of bytes of arguments is defined by the first two bits of the facility code as shown in the Facility Code Format figure.

0 Class        |       |       |       |       |               |       |       |       |       |       

The class can have one of the following values:

00 Class A. This has a single-byte parameter field.
01 Class B. This has two bytes as a parameter.
10 Class C. This has three bytes as a parameter.
11 Class D. The next byte defines the length of the parameter.

One special facility code, 0xFF, is reserved for extension of the facility codes. The octet following this code indicates an extended facility code having the format A, B, C or D class. Repetition of the facility code 0xFF is permitted, resulting in additional extensions.

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