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Eicon Connections for Linux User’s Guide

page 77

APPENDIX C

Key Packet Formats

Details of the Packet Format for the X.25 Packets used in call establishment and call clearing

are provided in this section. It describes the fields that must be filled by the application.

Call Request Packet Format

The format for a Call Request Packet is shown below. 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 the CCITT X.25 Recommendation for

details.

*Semi-octet of zeroes is present only if combined total digits in DTE address block is odd

The first three octets (up to and including Packet Type Identifier) are handled by the Eiconcard

X.25 Development Kit. The rest of the octets are built from information supplied by the

application program.

General Format ID Logical Channel Group

Logical Channel Number

Packet Type Identifier

0 0 0 0 1 0 1 1

Calling DTE Address Length Called DTE Address Length

Called DTE digit-1 ...

Callled DTE digit-n Calling DTE digit-1

Calling DTE digit-2 ...

Calling DTE digit-n 0* 0 0 0

Facility Length

Facilities

...

Call User Data

...

Call Request Packet Format

Bit

7 6 5 4 3 2 1 0

1 2 ... 74 75 76 77 78 79 80 81 82 83 84 ... 90 91

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Eicon Networks S52 Guia do Utilizador Página 79