Personally, I'm a network guy and I like to use Wireshark to evaluate network traffic. Sure SipViewer shows you what the PBX is seeing for SIP traffic, but I want it all...
To capture directly on the sipXecs server, use the following command:
sipXecs: tcpdump -n -s 0 -i any -w filename.cap
Then you'll be able to use winscp to copy the file to your PC and open it with wireshark.