для Cisco Cisco IOS Software Release 12.4(2)XB6

ISDN call failures are most commonly attributed to the following issues:

Dial-on-demand routing (DDR)

ISDN layers 1, 2 and 3

Point-to-Point Protocol (PPP): including link control protocol (LCP), Authentication, or IP Control 
Protocol (IPCP) related issues.

Use the following commands to troubleshoot integrated data and voice for ISDN interfaces:

debug dialer events—Used to display debugging information about the packets received on a dialer 
interface.

debug isdn q931—Used to check outgoing dial-peer matching for an ISDN incoming call. Enable 
this command on both sides of the call. The output indicates whether the messages are generated by 
the calling party router (indicated by TX ->) or by the called party router (indicated by RX <-).

debug tgrm inout—Used to check voice or DDR channel selection request and return status. From 
the output, you can determine what type of call enabled the preemption and which timeslot is 
selected from which trunkgroup.

debug voip ccapi individual 146—Used to troubleshoot the call control application programming 
interface (CCAPI) contents. The individual 146 command option is used to log call preemption 
indication information.

debug voip ccapi inout—Used to show how a call flows through the system. From the output, you 
can see the call setup and teardown operations performed on both the telephony and network call 
legs. 

show call history voice | i Cause—Used to gather DisconnectCause information from the show call 
history voice command line display.

 name [preference-number]

Router(config-dial-peer)# trunkgroup 1

Defines the trunk group associated with this dial peer.

name—Label of the trunk group to use for the call. 
Valid trunk group names contain a maximum of 63 
alphanumeric characters.

preference-number—Preference or priority of the trunk 
group. Range is from 1 (highest priority) to 64 (lowest 
priority).

{flash-override | flash | 

| priority | routine}

Router(config-dial-peer)# preemption level 

flash

Sets the preemption level of the selected outbound dial peer. 
Voice calls can be preempted by a DDR call with a higher 
preemption level. The default is routine.

flash-override—Level 0 (highest)

flash—Level 1

immediate—Level 2

priority—Level 3

routine—Level 4 (lowest)

The preemption level flash-override setting can 
prevent the call to be preempted by a DDR call.