mail us  |  mail this page

contact us
training  | 
tech stuff  | 

Tech Stuff - Q.931 Packet Format

Generic Format

This is the generic format of a Q.931 packet carried within a LAPD (Q.921) frame.

Humble Pie: Until pointed out by Andreas Hagerer we had incorrectly stated that the call originator set the call reference flag = 1, the call originator sets the flag = 0 the other side sets the flag = 1. Thanks to Andreas for taking the time.

Name Octets Notes
Protocol Discriminator 1 Always 0x08 for ISDN
Call Reference 1,2 or 3 The call reference field.
Message Type 1 or 2 The message type value.
Information Elements various Information Elements (IEs) may or may not be present.

Call Reference

The call reference value may take any of the following formats.

8 7 6 5 4 3 2 1
0 0 0 0 CR length
Flag Optional call reference
Optional extended call reference

Notes

  1. Call Reference length = 0 (with no further octets) is called the NULL (or Dummy) Call Reference and is used to carry information of global significance for the line i.e. it is not relevant to a specific call.

  2. Custom LUCENT also uses an alternate format for a NULL call reference with a length of 1 and a call reference value = 0 (a.k.a. the Global call reference).

  3. Call Reference values are unique for any given user-network interface. They are not significant on an end-to-end basis.

  4. The call originator (either user or network side) sets flag = 0, the other end will always set flag = 1.

  5. Single octet call reference values lie in the range 1 to 127.

  6. Dual Octet call reference values lie in the range 1 to 32768 (and are typically only used in Primary Rate Interfaces).



Problems, comments, suggestions, corrections (including broken links) or something to add? Please take the time from a busy life to 'mail us' (at top of screen), the webmaster (below) or info-support at zytrax. You will have a warm inner glow for the rest of the day.

Tech Stuff

RSS Feed Icon

If you are happy it's OK - but your browser is giving a less than optimal experience on our site. You could, at no charge, upgrade to a W3C standards compliant browser such as Firefox

Search

web zytrax.com

Share

Icons made by Icomoon from www.flaticon.com is licensed by CC 3.0 BY
share page via facebook tweet this page

Page

email us Send to a friend feature print this page Display full width page Decrease font size Increase font size

Standards

ISO (International)
IEC (International)
ANSI (US)
DIN (Germany)
ETSI (EU)
BSI (UK)
AFNOR (France)

Telecom

TIA (US)
ECIA (US)
ITU (International)
IEEE (US)
ETSI (EU)
OFCOM (UK)

Internet

IETF
IETF-RFCs
IANA
ICANN
W3C

Electronics

JEDEC
ECIA (US)

Site

CSS Technology SPF Record Conformant Domain
Copyright © 1994 - 2024 ZyTrax, Inc.
All rights reserved. Legal and Privacy
site by zytrax
hosted by javapipe.com
web-master at zytrax
Page modified: January 20 2022.