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Tech Stuff - Q.931 Information Elements

Information Elements (IEs) must appear in numerically ascending order within ascending codeset order. Not all IEs are valid with all message types. IEs take two formats; one-octet IEs or variable length IEs.


The documentation defines four codesets being:

One-Octet IEs

These IEs are all shift types (escape codes in non-ITU language) between various code sets.

Value Meaning
0x95 Locking Shift to Codeset 5
0x96 Locking Shift to Codeset 6
0x9D Non-Locking Shift to Codeset 5
0x9E Non-Locking Shift to Codeset 6

NOTE: Those of you still awake will have spotted that the top bit (bit 8 in ITU-speak) is always set on single octet IEs.

Variable Length ITU IEs (Codeset 0)

All the IEs shown are in 'C' type hexadecimal values rather than the more normal bit format of ITU documentation - for our ease of use. You are welcome to convert them back to binary if that is easier to work with!!

Standard ITU one-octet messages

Value Name Notes
0x00 Segmented Message  
0x04 Bearer Required bearer service e.g. voice, data etc.
0x08 Cause Error/termination code/status.
0x0D Extended Facility  
0x14 Call State  
0x18 Channel Id Defines B channel being used.
0x1C Facility  
0x1E Progress Indication Information about call in progress.
0x27 Notification Indication  
0x2C Keypad Dialed digits.
0x32 Information Request  
0x34 Signal Call progress info including
0x38 Feature Activation one-octet format
0x39 Feature Indication  
0x3A SPID infamous Service Profile Identification.
0x3B Endpoint Identifier  
0x40 Information Rate Packet Mode (PMD)
0x43 Transition Delay Packet Mode (PMD)
0x44 Packet Layer Binary Params Packet Mode (PMD)
0x45 Packet Layer window Size Packet Mode (PMD)
0x46 Packet Size Packet Mode (PMD)
0x4C Connected Number If a disconnect during CONFERENCE indicates the remaining caller.
0x6C Calling Party Number Who is calling
0x6D Calling Party Subaddress  
0x70 Called Party Number Who we are calling.
0x71 Called Party subaddress  
0x74 Redirecting Number  
0x76 Redirection Number  
0x78 Transit Network Selection  
0x79 Restart Indicator  
0x7C LLC Lower Layer Compatability
0x7D HLC Higher Layer Compatability
0x7E User-User User-User Information

National Specific IEs (Codeset 5)

Since these message types are National they are listed under the country/region. These IE's are preceded with a locking (0x95) or non-locking (0x9D) shift to codeset 5.

North America - NI-1, 2 and 3

Value Name Notes
0x01 Operator System Access Only in originating SETUP (User-Network)
0x2A Display Text Formatted text for display

Network Specific IEs (Codeset 6)

Since these message types are typically proprietary or National they are listed under the vendor (or country) value. These IE's are preceded with a locking (0x96) or non-locking (0x9E) shift to codeset 6.

North America - NI-1, 2 and 3
Value Name Notes
0x3E Protocol Version Control  
0x41 Closed User Group  
0x42 Reverse Charging Indication  
0x75 Redirecting Subaddress  
0x7B Call Appearance Call Appearance number being used (Key system IE)


Value Name Notes
0x02 User Code Provides authorization info for calls (voice or data)
0x21 Associated Type Provides call status for key systems
0x22 Selected Call appearance Network says use this call appearance
0x23 Origination Call Appearance The call appearance we are using for this call
0x25 Destination Call Appearance On incoming call - should be same as last SCA
0x26 Endpoint Identifier  
0x32 Keypad Control  
0x36 Switch hook 0 = on-hook, 1 = off-hook
0x37 Other Call Reference Used in CONFerence operations
0x38 Feature Activation two-octet format
0x39 Feature Indication  
0x3A Adjunct Control  
0x3B Display Control  
0x3C Display Field 5ESS is very verbose
0x7A Management used in MAN_INFO message types

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