Implementing and Operating Cisco Collaboration Core Technologies (CLCOR) — Question 398

A collaboration engineer is troubleshooting issues with a T1 PRI. The engineer wants to confirm if the router received an ISDN Set Asynchronous Balanced Mode Extended message and responded with an Unnumbered Acknowledge frame. Which Cisco IOS command is used to debug ISDN Layer 2 issues?

Answer options

• A. debug voice q921
• B. debug isdn q921
• C. debug isdn q931
• D. debug voip ccapi inout

Correct answer: B

Explanation

The correct answer is B, as the 'debug isdn q921' command specifically targets ISDN Layer 2 issues, allowing the engineer to monitor Q.921 protocol messages. Options A, C, and D do not focus on Layer 2 debugging for ISDN; A pertains to voice protocols, C relates to Layer 3 Q.931 messages, and D is for debugging VoIP call control APIs.