
Eicon Connections for Linux User’s Guide
page 75
APPENDIX B
X.29 Call User Data Format
An overview of the Call User Data formats used in X.25 calls is provided in this section. It
shows how to format user data for X.25 call clearing.
The format for Call User Data consists of four protocol identifier octets followed by a maximum
of 12 octets of the call user data. Octets consist of bits numbered 7 to 0, where bit 0 is the
low order bit and is transmitted first. Octets are consecutively numbered starting from 1 and
are transmitted in this order.
See below for information on how bit 0 relates to bits 6 &7 of octet 1
Protocol Identifier octet 1 details are shown below:
When bits 7 and 6 are 00, bits 5 to 0 are 000001 to indicate PAD messages relating to the
PAD facility for the start-stop mode DTE. Other coding of bits 5 to 0 is reserved for future
standardization by the CCITT, subject to the rules of Recommendation X.244.
All bits of octets 2, 3, and 4 are set to 0. These octets are reserved for future use to provide
the called PAD or packet mode DTE with additional information pertinent to the calling party.
Octets of the call data field will contain the user characters received by the PAD from the
start-stop mode DTE during the call establishment phase. The coding of these octets is similar
to that of user sequences. The call data field is limited to 12 octets.
6
0 0
7 345 012
Octet
1
Protocol ID
Octet
2
Protocol ID
Bit
Call User Data
00 0000
Octet
3
Protocol ID
Octet
4
Protocol ID
Octet
5
User Data
User Data
...
...
Octet
16
User Data
User Data
0 000 0000
0 000 0000
See "Protocol ID (octet 1) Detail" below
67 345 012
Bit
Protocol ID (octet 1) Detail
0 100 0000
Bit Values
11
01
10
Future Use
Description
for CCITT use re: PADs
for national use
reserved for international user bodies
for DTE-DTE use
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