Re-transmission Timeout - what does log entry mean

I do not understand this entry or recognise the ip address:

[2014-11-06 11:14:13] WARNING[2463] chan_sip.c: Retransmission timeout reached on transmission [email protected] for seqno 23139 (Critical Response) – See
Packet timed out after 31999ms with no response
[2014-11-06 11:14:13] WARNING[2463] chan_sip.c: Hanging up call [email protected] - no reply to our critical packet (see

Where you or someone else making a phone call at that time?

No, Just one incoming call. The problem is consistent to incoming voip calls and is reproducible. In the past I had a similar problem which, if I remember correctly, was due to the SIP setting in my router being on. I checked it and it is off. Unsure exactly how long this has been going on but about 5 - 7 days.
Incoming calls last about 30 - 40 seconds then go silent. Seems like a RTP problem but I didn’t change RTP settings before this began. I use Flowroute for VOIP in.

Turns out to be a problem with ALG in my router. Even though I had checked “Disable ALG”, somehow it was active. I was told by my VOIP vendor that this is a common problem with consumer routers (Linksys,Netgear,Buffalo). The problem shows up as connecting from another port than 5060 or whatever is configured.

This is good information to spread around as many may not be aware.