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Tech Stuff - Q.931 Cause Information Element

The Cause Information Element provides one or more octets that may help in diagnosing network or CPE problems.

Cause Format

The Cause IE is variable length with the following format:

8 7 6 5 4 3 2 1 Octet
0 Cause IE (0x08) 1
length of the Cause Information 2
1 coding std. 0 Location 3
1 Class Value 4

NOTE: Bit 8 of octets 3 and 4 above is the Extension bit and is coded as follows:

  1. Extension bit = 0 more information for this field follows.
  2. Extension bit = 1 last octet of this field.

Coding Standard

7 6 Meaning
0 0 ITU standardized coding
1 1 Standard specific to Location field


4 3 2 1 Meaning
0 0 0 0 User
0 0 0 1 Private network serving location user
0 0 1 0 Public network serving local user
0 0 1 1 Transit network
0 1 0 0 Public network serving remote user
0 1 0 1 Remote private network
0 1 1 1 International network
1 0 1 0 Network beyond interworking point


7 6 5 Meaning
0 0 0 Normal event
0 0 1 Normal event
0 1 0 Resource unavailable
0 1 1 Service or option not available
1 0 0 Service or option not implemented
1 0 1 Invalid message (e.g. parameter out of range)
1 1 0 Protocol error (e.g. unknown error)
1 1 1 Interworking


The Class and Value fields are normally treated as one. The following table shows the hexadecimal value with the extension bit set, without the extension bit set and the decimal value (without the extension bit set).

CCITT standard Values
w Ext
wo Ext
Dec Meaning
0x81 0x01 1 Unassigned number
0x82 0x02 2 No route to specified network
0x83 0x03 3 No route to specified transit network
0x86 0x06 6 Channel Unacceptable
0x87 0x07 7 Call awarded and being delivered in an established channel
0x90 0x10 16 Normal, clearing
0x91 0x11 17 User busy
0x92 0x12 18 No user responding
0x93 0x13 19 User alterting
0x95 0x15 21 Call rejected
0x96 0x16 22 Number changed
0x9A 0x1A 26 Non-selected user clearing
0x9B 0x1B 27 Destination out of order
0x9C 0x1C 28 Invalid number format (incomplete)
0x9D 0x1D 29 Requested facility rejected
0x9E 0x1E 30 Response to STATUS ENQuiry
0x9F 0x1F 31 Normal, unspecified
0xA2 0x22 34 No channel available
0xA3 0x23 35 Call queued
0xA9 0x29 41 Temporary failure
0xAA 0x2A 42 Network congestion
0xAB 0x2B 43 Access information discarded
0xAC 0x2C 44 Requested channel not available
0xAF 0x2F 47 Resource unavailable, unspecified
0xB2 0x32 50 Requested facility not subscribed
0xB9 0x39 57 Beare capability not authorized
0xBA 0x3A 58 Bearer capability not presently available
0xBF 0x3F 63 Service or option not available
0xC1 0x41 65 Bearer service not implemented
0xC5 0x45 69 Requested facility not implemented
0xCF 0x4F 79 Service or option not implemented, unspecified
0xD2 0x52 81 Invalid call reference
0xD8 0x58 88 Incompatible destination
0xE0 0x60 96 Mandatory IE missing
0xE1 0x61 97 Message type non-existent or not imp-lemented
0xE3 0x63 99 Information element non-existent or not implemented
0xE4 0x64 100 Invalid IE contents
0xE5 0x65 101 Message not compatible with call state
0xE6 0x66 102 Recovery of timer expiry
0xEF 0x6F 111 Protocol error, unspecified
0xFF 0x7F 127 Interworking, unspecified
National Specific
0x84 0x04 4 Vacant code
0x88 0x08 8 Prefix 0 dialed in error
0x89 0x09 9 Prefix 1 dialed in error
0x8A 0x0A 10 Prefix 1 not dialed
0x8B 0x0B 11 Excessive digits received, call is proceeding
Network Specific
0x88 0x08 8 Call is proceeding
0x8D 0x0D 13 Service denied
0x9C 0x1C 28 Special Intercept Announcement
0x9D 0x1D 29 Special Intercept announcement, undefined code
0x9E 0x1E 30 Special Intercept announcement, number unassigned
0x9F 0x1F 31 Special intercept annoucement, call blocked due to group restriction
0xA3 0x23 35 Blocked due to group restrictions, call queued
0xB3 0x33 51 Call type incompatible with service request
0xB5 0x35 53 Service operation violated
0xE5 0x65 101 Protocol error, threshold exceeded
Custom Lucent
0xB4 0x34 52 Outgoing calls barred
0xB6 0x36 54 Incoming calls barred
0xC2 0x42 66 Channel type not implemented
0xD3 0x53 82 Identified channel does not exist
0xDB 0x5B 91 Transit network does not exist
0xE2 0x62 98 Message not compatible with call state

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