SPA112 gets one way (inbound) audio problem when connected to a (allegedly) better router

[Witold Grabysz]

The first 2-25 seconds (this duration seems to be random number) of incoming voice are ok, then it begins to be choppy, sometimes improves for a while. Outbound voice is ok.

The router: Fritz!Box 3272, connected via ADSL.

Previous router was delivered by the ISP. Private label, so I can't say what it was, but I suspect it was really cheap. I had problems with stability of the connection, so decided to buy a "real" one. But with the previous router there was no one way audio problem! I did a test and replaced the new router by the old one and it was ok again.

VoIP connections from a PC connected to the same router are fine. I regret, because I hoped to use Wireshark to pin down the cause. I can't use Wireshark to monitor packets coming to SPA112. (Or can I? Is there a way to put a PC between the router and gateway?)

Tried to tinker with codecs, jitter parameters, port forwarding, NAT options, STUN, prioritization of traffic over the router. Fritz!Box and SIP trunk providers failed to help.

I don't expect a simple solution to cure the problem, but are open to do whatever diagnostic to find the reason.

I hope someone has an idea where to search.

Best regards,

Witold

[Dan Lukes]

Is there a way to put a PC between the router and gateway?

Yes, but it's easier to put network HUB in-between and connect the PC to other HUB's port.

Switch with SPAN/monitor feature properly configured can be used as well.

Also, "real" router should offer a diagnostics tools to you.

[Witold Grabysz]

Thank you, Dan. The hub solution is genial in its simplicity, however, I did it wrong too. I've bought a "hub" which turned out to be a switch, so I couldn't see other packets. But the loss of 10 bucks stimulated me to investigate further. As soon as I learned a magic word "promiscuous" I was able to find an undocumented feature of my router - capturing traffic on all interfaces in Wireshark format. The problem is that the capture by the router (of the internal interface) substantially differs from the direct capture by Wireshark as far as RTP streams are concerned. For the same VoIP connection (listening to an automatic message) the router reported 1705 packet up and 2 down, whereas direct capture by Wireshark shows 1502 packets down. Because I haven't uttered a single word but was only listening, I'm inclined to believe the latter is correct.

I have just sent two capture files to the manufacturer of the router.

Best regards,

Witold

[Witold Grabysz]

The support of the router sent me the procedure and asked to reset the router by uploading its firmware again. As soon as I did it all started to work perfectly. I will never know what the real culprit was. The support claims I set undocumented options using third-party software. It's true I downloaded such informal configuration stuff, but as I remember I was only watching settings, not touching them. I'm inclined to think, that during the installation I attempted to use a wrong password. Unaware of this I was tinkering with all options I could find. Most likely I came up with a combination not foreseen by the manufacturer.