Which command is used to troubleshoot calls as they enter and leave a PRI connection?

Q.931 is the ISDN Layer 3 protocol responsible for call control signaling on PRI interfaces, carrying messages such as SETUP, CALL PROCEEDING, ALERTING, CONNECT, and RELEASE. The 'debug isdn q931' command displays these messages in real time as calls enter and leave the PRI, making it the definitive tool for troubleshooting PRI call flow and diagnosing issues like call rejection, incorrect numbering, or failed negotiations.

'show voice call summary' is a show command that displays a snapshot of currently active voice calls and their states - it does not provide real-time signaling message detail for PRI troubleshooting.

'debug voip dialpeer' traces dial-peer matching logic within the IOS VoIP engine and does not capture the ISDN Q.931 signaling layer used on PRI connections.

'show dial-peer voice summary' displays the configured dial peers and their statistics in a tabular format - it is a static configuration view, not a real-time signaling debugger.