Debugging Q931 – one tip

When I started working at telephony technology first it was easy to debug calls using Q931. I analyzed small systems with small number of calls, so there was no problem to follow one call entire debug.
One day I had to debug a huge cluster with gateway with 4 E1 interfaces and huge amount of calls. Using filters loaded CPU too much so the unique solution was to grab all logs.
The question was “How should I know which line of logs I need to take regarding a call that is interesting for me.
Extracted part of log for one call below:
So first of all we need to catch first part of call with TX -> SETUP, Calling Party Number and Called Party Number. The key info is callref in our case equal 0x1517.

Oct 3 13:18:19.659: ISDN Se0/1/2:15 Q931: TX -> SETUP pd = 8 callref = 0x1517
Sending Complete
Bearer Capability i = 0x8090A3
Standard = CCITT
Transfer Capability = Speech
Transfer Mode = Circuit
Transfer Rate = 64 kbit/s
Channel ID i = 0xA98395
Exclusive, Channel 21
Calling Party Number i = 0x0083, '49928853291'
Plan:Unknown, Type:Unknown
Called Party Number i = 0x80, '44344112683'
Plan:Unknown, Type:Unknown
Oct 3 13:18:20.130: ISDN Se0/1/2:15 Q931: RX <- CALL_PROC pd = 8 callref = 0x9517
Channel ID i = 0xA98395
Exclusive, Channel 21
Oct 3 13:18:20.144: ISDN Se0/1/2:15 Q931: RX <- PROGRESS pd = 8 callref = 0x9517
Progress Ind i = 0x8188 - In-band info or appropriate now available
Oct 3 13:18:23.760: ISDN Se0/1/2:15 Q931: RX <- ALERTING pd = 8 callref = 0x9517
Oct 3 13:18:33.109: ISDN Se0/1/2:15 Q931: RX CONNECT_ACK pd = 8 callref = 0x1517
Oct 3 13:18:49.370: ISDN Se0/1/2:15 Q931: RX RELEASE pd = 8 callref = 0x1517
Oct 3 13:18:49.396: ISDN Se0/1/2:15 Q931: RX <- RELEASE_COMP pd = 8 callref = 0x9517

You can see callref is 64bits id in HEX. Within all logs our call transmitting part is with callref = 0x1517. First digit for receiving part is with 8 added. So RX callref is 0x9517.
That’s all.

Debug and less logs by filtering

To debug an issue it is always easier to focus on our source and destination. No one likes to dig into a lot of unwanted text.
I found out this by an accident and had forgotten about that a few time. Solution is simple. I show only an example.

configuration as below

call filter match-list 1 voice
incoming calling-number 442248123

and enable debugging (example)

debug condition match-list 1 exact-match
debug ccsip calls

what you will see is

show debug
CCSIP SPI: SIP Call Statistics tracing is enabled (filter is ON)

Just short, simple and so useful. You will see in logs only what you need. To match by other values just see documentation.