Command:

debug isdn q921


Mode:

Router#


Syntax:

debug isdn q921

no debug isdn q921

 

Syntax Description:

This command has no arguments or keywords.

 

Command Description:

To display data link layer (Layer 2) access procedures that are taking place at the router on the D channel (LAPD) of its ISDN interface, use the debug isdn q921 privileged EXEC command. The no form of this command disables debugging output.

The ISDN data link layer interface provided by the router conforms to the user interface specification defined by ITU-T recommendation Q.921. The debug isdn q921 command output is limited to commands and responses exchanged during peer-to-peer communication carried over the D channel. This debug information does not include data sent over the B channels that is also part of the router’s ISDN interface. The peers (data link layer entities and layer management entities on the routers) communicate with each other via an ISDN switch over the D channel.

A router can be the calling or called party of the ISDN Q.921 data link layer access procedures. If the router is the calling party, the command displays information about an outgoing call. If the router is the called party, the command displays information about an incoming call and the keepalives.

The debug isdn q921 command can be used with the debug isdn event and the debug isdn q931 commands at the same time. The displays will be intermingled.

Use the service timestamps debug datetime msec global configuration command to include the time with each message.


Example:

The following is sample output from the debug isdn q921 command for an outgoing call:

Router# debug isdn q921
Jan 3 14:52:24.475: ISDN BR0: TX -> INFOc sapi = 0 tei = 64 ns = 5 nr = 2
i = 0x08010705040288901801837006803631383835
Jan 3 14:52:24.503: ISDN BR0: RX <- RRr sapi = 0 tei = 64 nr = 6
Jan 3 14:52:24.527: ISDN BR0: RX <- INFOc sapi = 0 tei = 64 ns = 2 nr = 6
i = 0x08018702180189
Jan 3 14:52:24.535: ISDN BR0: TX -> RRr sapi = 0 tei = 64 nr = 3
Jan 3 14:52:24.643: ISDN BR0: RX <- INFOc sapi = 0 tei = 64 ns = 3 nr = 6
i = 0x08018707
Jan 3 14:52:24.655: ISDN BR0: TX -> RRr sapi = 0 tei = 64 nr = 4
%LINK-3-UPDOWN: Interface BRI0:1, changed state to up
Jan 3 14:52:24.683: ISDN BR0: TX -> INFOc sapi = 0 tei = 64 ns = 6 nr = 4
i = 0x0801070F
Jan 3 14:52:24.699: ISDN BR0: RX <- RRr sapi = 0 tei = 64 nr = 7
%LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to up
%ISDN-6-CONNECT: Interface BRI0:1 is now connected to 61885 goodie
Jan 3 14:52:34.415: ISDN BR0: RX <- RRp sapi = 0 tei = 64 nr = 7
Jan 3 14:52:34.419: ISDN BR0: TX -> RRf sapi = 0 tei = 64 nr = 4


Misconceptions:

The ISDN switch provides the network interface defined by Q.921. This debug command does not display data link layer access procedures taking place within the ISDN network (that is, procedures taking place on the network side of the ISDN connection).


Related Commands:

None.


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