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Unread 05-19-2006, 06:46 AM   #1
pmerrill
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Question DID pointing to Voxalot and Call Quality

I've currently got my DID pointing to my voxalot account xxxxxx@voxalot.com and I've registered my ATA with voxalot as well. I have two VSP providers set up, SIPME and ASTRATEL. My DID was provided by SIPME but they have "redirected" it to my Voxalot account as requested.

For incoming calls using my DID, who actually gets involved with the call and how do the codecs get chosen? What would prevent the call being connected using my preferred codec, g711a?

It "appears" that when I call using the Sydney sipbroker access number, followed by *010XXXXXX, the call IS connected using g711a and the quality is great. However, when I call home via my DID, it seems to connect via g729 and the quality is not as good.

What EXACTLY is going on here?
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Unread 05-19-2006, 08:09 AM   #2
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Codecs are negotiated between the 2 end points. So what is happening is your DID provider and your ATA are negotiating on what Codec to use.

If your DID provider only allows g729 then that's what you will end up with. One thing to try, is to update your ATA to only allow g711 and see if the DID accepts this.

VoXaLot is just proxying the INVITE request from the DID and plays no part in the Codec negotiation.
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Unread 05-19-2006, 09:52 AM   #3
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Thanks Martin.

I verified it tonight. I rang out from my home phone PSTN and called my DID. The call connected with g.729. I also rang the sip broker pstn, dialed the voxalot access *010 and my voxalot account and got g.711a with corresponding better quality!

All I really need to find is a DID provider who will allow me to forward the DID to voxalot and who HAS g.711a for off-net. I understand that SIPME (my DID provider) only does g.729 for off-net calls. AstraTEL, when they work, will do g.711 for off-net, BUT, they won't forward the DID to Voxalot. Damn!

Does anyone know where I can secure a DID at the cheapest rate, does g.711a for off-net calls AND will allow me to re-direct the DID to Voxalot?
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Unread 05-19-2006, 10:10 AM   #4
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Quote:
Originally Posted by martin
Codecs are negotiated between the 2 end points. So what is happening is your DID provider and your ATA are negotiating on what Codec to use.

If your DID provider only allows g729 then that's what you will end up with. One thing to try, is to update your ATA to only allow g711 and see if the DID accepts this.

VoXaLot is just proxying the INVITE request from the DID and plays no part in the Codec negotiation.
Another question.

I have two providers, AstraTEL (supplies g711a for off net) and SIPME (supplies g729 for off-net). I've tried a couple of dial plans so that calls can get routed via SIPME or AstraTEL. I would EXPECT that if I routed a call via SIPME I would get the g.729 codec and if I routed a call via AstraTEL I would use the g.711 codec. However, when I tested it I could only get the g.729.

Ideas as to why this did not work?
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Unread 05-19-2006, 12:39 PM   #5
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Have a look at the Codec setting for each of the providers within VoXaLot. If you would like g711 to take priority over the other Codecs then list it first:

e.g. default is:

g729;ilbc;gsm;ulaw;alaw

make it:

ulaw;alaw;g729;ilbc;gsm
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Unread 05-19-2006, 11:16 PM   #6
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Martin,

The codec line for AstraTEL is

alaw;ulaw;g726;g729;g723

and for SIPME is

alaw;ulaw;g726;g729;g723

I'm thinking that since AstraTEL have been having lots of problems of late, maybe they have disabled g711a and g711u so that they can handle more calls with g729?

Is there anyway to see exactly what's happening between AstraTEL and my ATA? I assume from previous discussions that Voxalot does not get involved in the negotiations between my ATA and AstraTEL about which codec to use?
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Unread 05-22-2006, 12:11 PM   #7
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I sorted the problem out so I just thought I'd tell everyone.

On a Draytek 2100V you cannot force a codec, only indicate your preferred one.

AstraTEL queries your ATA to determine if it can use G.729 and if that's true, then it uses it. Many ATAs will say they can use G.729, especially if there is a preferred list (i.e., try g.711a, then g.711mu and then g.729). Astral forces your ATA to use g.729 if it is somewhere in the list (even 3rd place!).

Solution, in your Voxalot provider list set up AstraTEL so that it ONLY provides alaw;ulaw. When you make an outgoing call, Voxalot forces g.711a and the net result is that you get a high quality outgoing call!
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Unread 05-22-2006, 06:52 PM   #8
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I've encountered that with other VOIP providers before, so it is not completely unknown for them to prefer a low-bitrate codec and select that for your conversation even if it is third or fourth on your list, and your preferred is u-law. The solution I had to use to get u-law was to disable G729 and G723.1 on my line.
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Unread 05-22-2006, 11:38 PM   #9
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Quote:
Originally Posted by ctylor
I've encountered that with other VOIP providers before, so it is not completely unknown for them to prefer a low-bitrate codec and select that for your conversation even if it is third or fourth on your list, and your preferred is u-law. The solution I had to use to get u-law was to disable G729 and G723.1 on my line.
Yes. Some ATA's allow you to specify only one. Unfortunately, the Draytek 2100V does not allow that. Draytek told me that they are researching the idea of locking one in but only on the 2800V, so I'm out of luck unless I upgrade.

Having said that, the Voxalot solution works perfectly, so I'm not going to worry for now.
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Unread 05-23-2006, 12:20 AM   #10
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Thanks for sharing pmerrill
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