Poor quality echo cancellation on Linksys RT31P2?

Posts: 2 · New Forum Member Joined: Mar 06, 2005 Posts: 2

I recently signed up for Vonage. In general, the audio quality is fine. However, I've noticed one extremely annoying behavior that I believe is due to the echo cancellation built into my ATA (Linksys RT31P2). Shortly after (roughly 1/2 second) I speak, the incoming audio is briefly cut off. This means that if I happen to speak at about the same time as the person on the other end, I miss what they say. The problem is worse the louder I speak. As an extreme, if I whistle very loudly, the incoming audio cuts out entirely until I stop. The end result is that the incoming audio sounds choppy (or non-existent) whenever I talk. This is annoying enough that I can't live with it.

One reason I'm confident this is related to echo cancellation is that if I speak (or whistle) quietly enough, I can hear a faint echo (about ~500ms delayed - rough estimate). I'd much rather have the faint echo than no sound at all. Note that I've tried this on phone calls to several different people with several different TelCos and it has been quite consistent (so I doubt that it's, for example, a particularly bad far-end hybrid or handset causing excessive echo).

So first of all, the 500ms round-trip time is very surprising to me. I've run several broadband speed tests (including the vonage-forum one) and the results have all been great. RTT is usually around 100ms, packet loss almost alway 0, downstream 1.3Mbps and upstream 300kbps. Because of this, and the fact that my Vonage service is otherwise fine, I do not believe that this is a problem with my Internet connection. What is the normal end-to-end (including the PSTN) latency I should expect? Assuming the 100ms IP RTT time is accurate, I'm amazed the PSTN loop would add another ~400ms to that. Is there any golden-phone number or something I can call which will accurately measure the full end-to-end voice round-trip-time? Perhaps there is an underlying latency problem here which is causing the echo cancellation to malfunction.

Regardless of the delay, I'd be content if I could just prevent the audio from cutting out. I just got off the phone with Vonage tech support, and he wasn't aware of any way to disable the Linksys echo cancellation (and of course I'm locked out from all of the VoIP configuration). Instead he said he'll try "lowering the packet size from 020 to 010", but it is not clear yet to me if this has had any affect on the problem (that can't be bytes, can it? 20 - or 32 if it was hex - bytes for a UDP frame is WAY to small to be efficient.).

Has anyone else experienced a similar problem? I'm considering switching to SpeakEasy VoIP (my ISP - who claim their private network allows them to prioritize VoIP traffic end-to-end to maintain very low latency).

Thanks
Rick

Posts: 89 · Posted: Mon Mar 07, 2005 12:17 pm Post subject:

I have the exact same problem. One difference is that I have the RT31P2. I have narrowed it down to only happening on local calls. The long distance calls are fine. I have tried Tech support and they changed the FXS Gain, I told them that I didn't think this would help because it only happens on local calls. He told me to try it and call him back. Rolling Eyes

It didn't help.

I did read a thread on dslreports from a person that had a similar problem. Their problem was resolved with having her local calls moved to another switch. The tech looked up the thread on dslreports and said that was not possible. I have tried PM SSantana but have not gotten a response.

If you can get an answer or fix please post.

Posts: 492 · Posted: Mon Mar 07, 2005 12:36 pm Post subject:

There is one item missing in your discourse. Who and where are you calling?
Echo is usually generated elsewhere. All telephones have echo, it's usually not noticed. Poor wiring on the PSTN is a classic cause. A poor quality telephone without echo reduction circuits can also be the problem.

http://www.vonage.com/help_knowledgeBase_article.php?article=266

Posts: 89 · Posted: Mon Mar 07, 2005 12:54 pm Post subject:

It is not a normal echo. It is very hard to explain. It is like you hear a few of your own words repeated back on your end. It is more like feedback then echo. I am sorry I am not explaining it very well. It doesn't happen all the time or with the same people. But it is always local calls. I am in Upstate NY.

Posts: 2 · New Forum Member Joined: Mar 06, 2005 Posts: 2

I think my problem is different from yours jockey. I do experience it on all (or at least most) calls (including long distance). And it's not the echo I'm complaining about (I know that isn't always avoidable). It's the silence that is presumably created by blocking of the echo.

Posts: 4 · New Forum Member Joined: Jun 24, 2005 Posts: 4

I've also experienced the echo. Echo is dealt with throughout the network. Vonage should be placing echo cancellers at gateways to POTS and between its own switches. There are other VOIP providers out there and I am going to keep my eye on my Vonage phone quality and reviews of other VOIP providers.

There are two reasons I can think of for small voice packets.

One is to reduce the delay: The larger the packet, the longer it takes to unbundle it. This will add to the delay of a received voice. Why would you want to unbundle and check the packet before starting to deliver the first bits to the receiver? because the packet may be so garbled as to be interpreted by the receiver as an annoying clip of noise.

The second reason, and probably more important, is to reduce the effect of corrupted/lost packets. Losing 10 or 20 bytes of voice to a corrupted or lost or out-of-order packet may not be as noticeable as losing a 100 or larger-byte packet.

With today's large bandwidths, in the backbone and at the home (remember Vonage requires broadband), packet efficiency is not as important. Also when the technician talks about 10 or 20, is that just the data content of the packet and not including the UDP header?

What is a good size for a voice packet - I recall it to be something in the range of 32 to 64 bytes.

Posts: 646 · Posted: Sat Jun 25, 2005 2:46 am Post subject:

The 10 or 20 is referring to milliseconds per packet. At 8khz, 8-bit sampling, 1ms is equivalent to 8 bytes.

So, at 20ms, each packet contains a 160-byte payload.

Posts: 4 · New Forum Member Joined: Jun 24, 2005 Posts: 4

Thanks that does make sense.

but what is Vonage doing about the annoying echos everyone seems to be getting on occasional calls? Since it is not every call, I don't think ikt is in my phone or router. Rather Vonage seems to not to have the best network equipment. i hope Vonage plans to do something to improve its overall quality.

Posts: 89 · Posted: Sat Jun 25, 2005 10:02 am Post subject:

I fixed this by changing to another VOIP provider. It is funny how Vonage kept telling me is was an ISP problem but when I switched VOIP providers the problem disappeared. I have been using the same ISP ( Roadrunner) all along. Also as a fringe benefit when I call customer service now my new company answers within a few minutes and speaks english!!