It's sometimes useful to look at SIP conversations in retrospect.  If you have
a troublesome system, enable sip debug (in the CLI: sip set debug on), set up
logger.conf to log it to some file and then you can use the two scripts here to
extract the SIP converssations as seen by asterisk.

find_call_ids.sh:

This script will locate Call-ID values given an A and B number. Just invoke it with:

find_call_ids.sh /path/to/log A-num B-num

eg:

find_call_ids.sh /var/log/asterisk/debug 102 105

To find the Call-IDs for calls going from ext 102 to ext 105 (depends on your
exact setup and the actual values being passed in the SIP INVITE packets)

find_call_sip_trace.sh

This script will extract a SIP conversation from the log for one or more
Call-ID values.  Invoke with:

find_call_sip_trace.sh /path/to/log Call-ID [...]

Eg:

find_call_sip_trace.sh /var/log/asterisk/debug 12341665haf434qgrq3@192.168.0.5 123123@192.168.0.3

This will find the SIP packets for those two conversations from the log
(interleaving the packets in the order asterisk output them - useful for
analysing the two SIP legs of the same call).