Problem w/ 2 voip calls at once 1.5.9 on TP Link TL-WR1043ND

[Ragnor]

Hi guys,

As per the subject we have a TP Link TL-WR1043ND running 1.5.9 and use a hosted voip provider and are seeing a problem when we have two calls active at once.

One incoming call works fine, if there is a second incoming whilst one call is active it rings the phones as expected but when someone picks up there is no answer.

The provider has looked at their SIP logs and they believe is no ack/reply from end for the 2nd call indicating a router problem.

Details:
Router: TP Link TL-WR1043ND running 1.5.9
IP Phones: Cisco 303's
VOIP Provider: Hosted service (Asterisk/SIP based)
QoS: Basically default settings but I added an voip class based on providers fixed ip address.

What's the best way to look into/troubleshoot what's going on at the router end?

[pbix]

Problems with NAT routing of VoIP traffic traffic are complicated and difficult to solve. I have notice myself that one phone works OK but more than one phone can be a problem. The voice part comes on RTP packets and having trouble hearing incoming calls is the classic symptom of routing problems.

This not actually a Gargoyle issue but is common to all Linux based systems and VoIP. The SIP protocol used is not very compatible with NATing routers.

I do not know the solution but I have used siproxd in the past and it seems to work pretty well. This can be installed as a package on your router using opkg. It is designed to solve routing issues. You should read about it and experiment IMHO.

[Ragnor]

I'll have a look at siproxd.

Seems strange that 1 call works perfectly for us, it just hates two calls at once. Everything else works great and the QoS is working really well.

[Ragnor]

Haven't had time to investigate siproxd yet but I put in my spare old Linksys WRT54GL running TomatoUSB and 2 SIP calls at once works perfectly, the problem seems to be an OpenWRT thing.

I'll have another go and getting Gargoyle/OpenWRT to work later.

[pbix]

I struggled recently with VoIP routing issues recently myself until I unloaded the kernel modules ip_nat_sip and ip_conntrack_sip. These have been loaded automatically by OpenWRT since around Gargoyle 1.5.8. I can find little documentation about them. While in theory they are supposed to make life easier for SIP users at least in my case they did the opposite.

So you might try unloading them and see what happens.

[Ragnor]

Yes I think you're onto something there.

I found this NAT Analyzer that uses a Java applet to perform various tests on UDP and NAT and ran it on the devices involved:

TP Link TD-8840, my DSL modem I normally use this in PPPoA half bridge/ip extension to my router but I set it back to a normal connection for this test:
http://nattest.net.in.tum.de/individual ... a8d990ec22

TP Link TL-WR1043ND Gargoyle 1.5.9:
http://nattest.net.in.tum.de/individual ... 37b69a53b5

Linksys WRT54GL running TomatoUSB 1.28
http://nattest.net.in.tum.de/individual ... 05c3079196

The result for Gargoyle 1.5.9/OpenWRT indicates SIP INVITE packets are being modified. Most voip provider now use STUN or some other method of UDP hole punching and SIP ALG just messes things up.

Unloading those modules should do the trick, stupid question how do I do that? Is there some documentation with the steps, presume I need to ssh/telnet to the router and use modprobe or something like that?

[pbix]

rmmod can be used to temporarily remove modules.

If you discover this helps you you can make it perminent by removeing them from the file in /etc/module.d that loads them. I cann't remember which one right now but if you look you will find them there.

There are many sources in google which can show you how to remove modules in openwrt.

[Ragnor]

Got around to doing this, old WRT54GL running Tomato USB out and TP Link TL-WR1043ND running Gargoyle/OpenWRT back in..

Here's what I did:

Assuming you are on Windows PC connected to the router via LAN...

1: Download/Install WinSCP
http://winscp.net/eng/index.php

2: Settings for WinSCP:

File Protcol: SCP
Host Name: IP Address of our router (eg: 192.168.1.1)
User Name: root
Password: The password you set in Garogyle web admin

3: Once connected I got an error message about groups, just click ok and the file browser/navigator should be showing the root dir, hit ... to go up one directory. Then go into etc then into modules.d

4: Edit the 45-ipt-nathelper-extra file and remove the line nf_nat_sip

Note: You do not need to remove nf_conntrack_sip as this just tracks connections and doesn't modify the packets (as far as I can tell).

5: Disconnect WinSCP and reboot the router.

Screenshots (click on the image to see full size):