It is sometimes required to analyze protocol messages in a given link in order to troubleshoot call problems. Wanpipemon makes possible to create a pcap file with all D-channel data which can then be examined using Wireshark.
What makes it so convenient is that this method is independent from the application you’re using (Asterisk, FreeSWITCH or whatever). You basically have the capability to tap into the D-channel, pretty much like using tcpdump to monitor TCP/IP traffic.
wanpipemon -i w1g1 -pcap -pcap_file isdn.pcap -prot ISDN -full -systime -c trd
You can refer to the Sangoma Wiki for other details (and SS7 tracing commands too): http://wiki.sangoma.com/wanpipe-wireshark-pcap-pri-bri-wan-t1-e1-tracing
Next time your D-channel link does not come up, fire up wanpipemon and take a look in Wireshark to what’s going on!