Reference:ISDN Cause Codes

This document lists the ISDN cause codes defined by Euro-ISDN.

• traces,
• as well as in syslogs and
• call detail records

Note that cause codes are coded differently in traces and syslogs.

How to decode cause codes from traces

Within traces, you will find sequences similar to this:

0:0432:491:0 - TEI0.0 -> Q931.0 : LL_RECV_RESULT
     data(13),FALC
     08 02 80 02  45 08 02 82  81 1e 02 82  88            ....E........

if you have ticked the “trace” checkmark in the “interface configuration”.

Additionally, you will see something like

0:0432:491:3 - R_CALL.7 -> RELAY.0 : SIG_DISC
     CAU = 82 81

if you have ticked the “trace” checkmark in the “protocol configuration”.

In the example, the cause code thus is 82 81.

FIXME: not yet completed

The first byte (82) gives the Coding-standard and location. It is made up of: bit 8, 7, 6 and 5 usually 1000. Bit 4, 3, 2, 1 gives the location (that is, the entity generating the cause code). If bit 8 to 5 are unequal to 1000, the cause code is non-standard. The location is usually 0010, so that the second byte is usually 0x82 (10000010).

The second byte (81) contains the cause code within the lower 7 bit (1). So you need to clear the MSB to look up the cause code in Table 1, using the “Cause (hex)” column. You may also look it up directly using the “Cause, bit 8 set to 1 (hex)” column.