Troubleshooting ISDN Connections - Internetworking Troubleshooting - page 506

For outbound ISDN calls, debug isdn q931 and debug isdn events are the best tools to use. Fortunately,
debugging outbound calls is very similar to debugging incoming calls. A normal successful call might
look like this:

*Mar 20 21:07:45.025: ISDN BR0: Event: Call to 5553759 at 64 Kb/s
*Mar 20 21:07:45.033: ISDN BR0: TX -> SETUP pd = 8 callref = 0x2C
*Mar 20 21:07:45.037: Bearer Capability i = 0x8890
*Mar 20 21:07:45.041: Channel ID i = 0x83
*Mar 20 21:07:45.041: Keypad Facility i = 0x35353533373539
*Mar 20 21:07:45.141: ISDN BR0: RX <- CALL_PROC pd = 8 callref = 0xAC
*Mar 20 21:07:45.145: Channel ID i = 0x89
*Mar 20 21:07:45.157: ISDN BR0: received HOST_PROCEEDING
Channel ID i = 0x0101
*Mar 20 21:07:45.161: -------------------
Channel ID i = 0x89
*Mar 20 21:07:45.313: ISDN BR0: RX <- CONNECT pd = 8 callref = 0xAC
*Mar 20 21:07:45.325: ISDN BR0: received HOST_CONNECT

Note that the CONNECT message is the key indicator of success. If a CONNECT is not received, you
may see a DISCONNECT or a RELEASE_COMP (“release complete”) message followed by a cause
code:

*Mar 20 22:11:03.212: ISDN BR0: RX <- RELEASE_COMP pd = 8 callref = 0x8F

*Mar 20 22:11:03.216: Cause i = 0x8295 - Call rejected

The cause value indicates two things. The second byte of the 4- or 6-byte value indicates from where in
the end-to-end call path the DISCONNECT or RELEASE_COMP was received. This can help you to
localize the problem. The third and fourth bytes indicate the actual reason for the failure. See the tables
that follow for the meanings of the different values.
Note : If you see this line, the likely reason is a higher-protocol failure:

Cause i = 0x8090 - Normal call clearing

PPP authentication failure is a typical reason. Turn on debug ppp negotiation and debug ppp
authentication before assuming that the connection failure is necessarily an ISDN problem.

Cause Code Fields

Table 17-9 lists the ISDN cause code fields that display in the following format within the debug
commands:

i=0x y1 y2 z1 z2 [ a1 a2 ]

Table17-9 ISDN Cause Code Fields

Field Value—Description

0x The values that follow are in hexadecimal.

8-ITU-T standard coding.

y1