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350-801 · Question #400

An engineer is troubleshooting a Primary Rate Interface that fails to come up on a H.323 production voice gateway. Layer 1 and Layer 2 configurations were validated successfully. Which Cisco IOS…

The correct answer is D. debug isdn q931. To troubleshoot a PRI issue on an H.323 gateway where Layer 1 and 2 are confirmed functional, debug isdn q931 is the most appropriate command to inspect Layer 3 ISDN signaling with minimal performance impact.

Voice Gateways and Session Border Controllers

Question

An engineer is troubleshooting a Primary Rate Interface that fails to come up on a H.323 production voice gateway. Layer 1 and Layer 2 configurations were validated successfully. Which Cisco IOS command must be run to debug the issue with the least impact on network performance?

Options

  • Adebug vtsp session
  • Bdebug ccsip messages
  • Cdebug all
  • Ddebug isdn q931

How the community answered

(37 responses)
  • A
    3% (1)
  • B
    5% (2)
  • C
    8% (3)
  • D
    84% (31)

Why each option

To troubleshoot a PRI issue on an H.323 gateway where Layer 1 and 2 are confirmed functional, `debug isdn q931` is the most appropriate command to inspect Layer 3 ISDN signaling with minimal performance impact.

Adebug vtsp session

`debug vtsp session` is used for debugging voice termination service provider sessions, which is not directly related to ISDN PRI Layer 3 signaling issues.

Bdebug ccsip messages

`debug ccsip messages` is used for debugging SIP call signaling messages, but the question specifies an H.323 voice gateway with a PRI, not SIP.

Cdebug all

`debug all` enables all possible debugging and generates a massive amount of output, severely impacting the production gateway's performance and making it unsuitable for troubleshooting in a live environment.

Ddebug isdn q931Correct

The `debug isdn q931` command specifically displays detailed information about the ISDN Q.931 Layer 3 signaling messages, which are crucial for establishing and maintaining calls over a PRI, and since Layer 1 and Layer 2 are validated, the issue likely resides at Layer 3. This command provides targeted debugging for PRI issues without the excessive output of broader debug commands.

Concept tested: Cisco IOS ISDN PRI Layer 3 debugging

Source: https://www.cisco.com/c/en/us/td/docs/ios/dial/command/reference/dia_d1.html

Topics

#PRI Troubleshooting#ISDN Q.931#Cisco IOS Debug#Voice Gateways

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