Calls are failing to egress the local PSTN gateway that uses an E1 PRI circuit. Which debug command would be most useful in determining which dialed digits are being sent to the PSTN?

A.
debug voice dial-peer

B.
debug isdn q921

C.
debug isdn q931

D.
ccapi inout

Explanation:

Debug isdn q931 command to display information about call setup and teardown of ISDN network connections (Layer 3).In order to verify the layer 3 signaling we need to enable layer 3 signaling command. ISDN q921 is for layer2. Debug isdn q931 shows the calling number and called number. If the calls are failing, we can also see the ISDN cause codes from the debug isdn q931 command.

http://www.cisco.com/en/US/docs/ios/11_2/debug/command/reference/dipx.html#wp13263