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Topic # 57776 24-Feb-2010 15:42
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Hi all


A bit (lot) of background


I have either a Dynalink RTA1320 or a Linksys AM300 modem (depending on how I'm feeling) connected to a WRTP54G-AU using half bridge mode. The phone out from the router goes to a dsc alarm, then to all of the phones in our house. I have a fast-ish / stable connection to the internet (~15Mb/.9Mb). The line into the property goes directly to the 1 modem jackpoint only (no filters / splitters / other jackpoints etc).


We don't have alarm monitoring via a company (ie - don't use contact id / sis etc), but have set the alarm to residential dial. What this means is that the alarm will ring my cellphone and emit a tone (1300 Hz for 500 ms every 2 sec). During this time, the alarm is listening for a handshake. This handshake is me sending back a dtmf tone (not 3,6,9) to the alarm. 


Unfortunately, the alarm is not correctly receiving the dtmf handshake back from my mobile phone, so, gives up after 30 seconds, and trys for 2 more times (settings I've set in the alarm).


I have a nokia 6220c phone, and I'm selecting to send dtmf tone when I answer the call. I can't set the duration of the tones generated, as, I expect they would be sent out of band to 2 degrees where I presume they are generated, however, I would expect the duration to be adequate. I suspect that the tone is being destroyed by being carried inband over the vfx call, and the codec not being "nice" to dtmf tones.


Does anyone know if it is possible to select a different codec that is "nicer" to dtmf tones being carried inband so I can see if this resolves the issue, or, have any other suggestions?


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  Reply # 301901 24-Feb-2010 19:31
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I've helped a few people with related issues, so trust me and try this. Get an ADSL line filter and connect it between the modem and the VFX box. On the filter the plug that normally goes to the wall is electrically the same as the socket that normally goes to the ADSL modem, so use only the "phone" and the "modem" sockets on the filter, don't bother trying to find the correct adapters to use the "line" connection.

So the setup is dial-up modem connects to "phone" socket of filter, VFX box connects to "modem" socket on filter, and "line" plug is not connected. Or you can swap "phone" and "modem", it does not matter.

The theory in very loose terms (tired, can't be bothered thinking) is that the VFX box does not expect DTMF tones which contain high frequency overtones, so you get image frequencies and other artefacts (you might be aware of digital imaging artefacts, similar things happen when digitising sound). The ADSL line filter is just a low pass filter so it removes unimportant overtones and artefacts.

This works for me when we had an AC Neilson barcode scanner which you use to scan all your groceries and every night it's modem sent the data to AC Neilson. It also worked for someone with an EFTPOS machine. I still have to try it with my Sky box which does not work over VFX (when the box dials out automatically) but can't be bothered looking for my box of line filters.

In addition you can also ask XNet for the higher bit rate CODEC.




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  Reply # 302005 25-Feb-2010 11:18
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Hmm, the quick reply I just wrote disappeared. Hmm,
here's a quick summery of what I wrote.

Cool, will give the low pass filter a try as it's just plug in.

And clarified that no analogue to digital conversion was happening at my end for anything critical (just a 1300Hz tone for me to listen to), and that the incoming dtmf is what was not being recognised.

Oh, and possibly won't be able to test this until the weekend...

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  Reply # 302266 25-Feb-2010 19:05
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The issue I have had with incoming DTMF on voip is that you get a burst of the audio DTMF from the other end, then it cuts to the generated DTMF from the ATA that it plays from the out of band signalling. Sometimes there is enough of the audio signal for it to detect that as a digit, sometimes there is not, so sending 1 2 3 # became 1 1 2 3 3 # # when recieved.

That was on a cheap device that would read back to me. Am trying it on a VF@home box now to see how it goes but have better things to do at the moment.




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  Reply # 302284 25-Feb-2010 19:41
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You can try getting your codec changed to alaw or ulaw but this isn't any guarantee. Fast DTMF and Contact ID is very much a best effort scenario.



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  Reply # 302324 25-Feb-2010 22:03
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sbiddle: You can try getting your codec changed to alaw or ulaw but this isn't any guarantee. Fast DTMF and Contact ID is very much a best effort scenario.


I'll see how it goes in the weekend with the filter, otherwise, will ask about the codec change. It's not fast DTMF or Contact Id, just a manually sent dtmf tone back to the alarm panel from my mobile.

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  Reply # 302366 26-Feb-2010 07:01
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A codec change is the first thing I'd do.

The downside is that unless you internet is rock solid you've face possible issues with voice quality. ulaw or alaw require around 3x the bandwidth of a G.729 call and are more likely to suffer from quality issues with things such as jitter.


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  Reply # 302470 26-Feb-2010 13:50
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I found that I had more problems with dtmf on ulaw than on g729 - with g729 the small burst of the audio wasnt good enough to trigger the device, on ulaw it was.

But I prefer using ulaw for phonecalls because it doesnt sound like crap.




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  Reply # 302485 26-Feb-2010 14:39
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You can't carry DTMF tones inband in G.729 - it's all RFC2833 and carried in signalling since it's a compressed codec.

Using ulaw or alaw you can carry DTMF inband which can fix some issues.



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  Reply # 302825 27-Feb-2010 22:52
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Have tried with the filter - no go.
What's the process for getting the codec changed to G.711?

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  Reply # 302859 28-Feb-2010 00:57
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dolsen: Have tried with the filter - no go.
What's the process for getting the codec changed to G.711?

Phone up Xnet Tech. Support on 0800 14 9638 and ask them to change it Smile

You will have to wait until 8am Monday before doing this.





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  Reply # 302873 28-Feb-2010 07:32
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Or send an e-mail to support (not sales). I've done all my requests via e-mail as it gives a record of what I've requested.




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