Hi all,
I'm having trouble getting reliable voip service to work via my Draytek 2930Vn router, and having got as far as snooping packet flows still can't see what's wrong - so I'm hoping someone wise and experienced on the forum might have some ideas!
My setup is as follows:
Router
Draytek 2930Vn. Built-in VoIP disabled (all entries blanked, and ports renumbered in GUI, and "sys sip_alg 0" run via telnet). Running NAT between WAN (single static IP) and LAN.
Router Model: Vigor2930 series Version: v3.2.3 English
Profile version: 3.0.0 Status: 1 (0xe2f80502)
Router IP: 172.30.0.1 Netmask: 255.255.0.0
Firmware Build Date/Time: Fri Jul 24 11:44:21.21 2009
Revision: 13868 2930
Port forwarding configured to forward SIP and RTP through to the SIP CPE (have also tried configuring the SIP box as the DMZ host - no change)
Firewall and DoS detection features all disabled.
SIP CPE
Siemens A580 IP DECT base station. Static (internal) IP. SIP on port 5060, RTP on ports 4000-4999. Registered (multiple registrations) to gradwell's SIP service, using all Gradwell's recommended settings (nat proxy, no STUN, etc)
The Problem
Intermittently (initially rarely but then more and more frequently until I reboot the router at which point it usually works fine for a little while) I get no incoming audio, at the start of calls. Usually it's about 10 seconds, which is really annoying as it basically guarantees that by the time audio cuts through the other person is already doing the "hello, hello, can you hear me" thing which is not the best way to open a conversation!
I've run test calls while snooping traffic on both the LAN and WAN sides of the router (and can provide wireshark captures if anyone's interested).
What happens is
1. The usual call setup SIP flows go back and forth, and we get to 180 Ringing
2. Inbound and outbound audio start flowing as expected
3. About a second later, inbound audio suddenly stops passing through the Draytek router - packets continue arriving at the WAN side, but none are sent from the LAN side. Outbound audio is unaffected.
4. Around 10 seconds later, inbound forwarding suddenly restarts.
The unforwarded packets are never transmitted on, and the packets that are forwarded are always sent onwards promptly. During the period that audio is not being forwarded, RTCP messages from the far end into the LAN are correctly forwarded (they're on the UDP port one higher than the RTP stream).
There are no other related messages flowing at the time of the start or end of the problem, and I can see nothing different about the structure or payload of the non-forwarded packets. It simply seems that the router just decides for a few seconds that it's not going to bother running port forwarding.
The problem only occurs at the start of calls - though as noted above it's not actually from the very start - there's usually around 1 second of good audio followed by 10 second gap, followed by the rest of the call working fine.
Any suggestions? I can easily reproduce this so can try out ideas or gather snoops etc.
Thanks,
Matt
