Analog Modem over SIP

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HugoMAL
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Analog Modem over SIP

Post by HugoMAL » 24 Nov 2016 13:12

Hi all.

I have a particular situation with a customer. It's a security company and they use very old analog modems such as US Robotics and MD-12 to enter their alarm systems.

They have a problem with their copper lines (with cable that enters the building) so the solution was to purchase to an ISP a fiber solution and to use VoIP.

So after everything completed and the OXO configured with SIP (and working properly) we decided to test the modems using analog extensions.

And here's my headache. The software that they use signals the modem into calling the number they need to enter the alarm system, the number is dialed and the otherside answers and sends some information so they can be synced and start trading information. This is what it should do EVERYTIME (unless busyline and other things that i'm excluding).

The problem is that sometimes it works, sometimes it doesn't.. And i know that is not from another external situation because they still have an copper line (ADSL) and works fine.

From my research (and believe me, two weeks on google searching) I finally think that the solution is "inside" the OXO. The transformation of the signal into analog-digital-analog is not happening in the right way and I'm almost sure the it's because of codecs (usually G711 works they say) or the fact SIP uses UDP and not TCP to "transport" the packets. (packet loss)


So, and sorry for the long post, as any of the users of this forum tried a solution like this (modem on analog extensions through SIP) or if anyone as some sort of idea what is happening or what i can try on the VoIP options..

Again, sorry for the long post and I appreciatte the time you wasted on helping me.

Thanks,

Hugo

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cavagnaro
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Re: Analog Modem over SIP

Post by cavagnaro » 24 Nov 2016 14:09

Not a good combo at all
You need G711 and a stable connection. Internet is not that.
TCP helps only on packet size, retransmission is discarded as doesn't work on voip, imagine a nightmare by you listening words you spoke a few seconds ago.
Modem is a very sensitive as FAX, information.
So, I would suspect the issue is your architecture rather and inside OXO.
If you want reliable and stability, then VOIP over ADSL is not the solution you are looking for.

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Re: Analog Modem over SIP

Post by HugoMAL » 24 Nov 2016 15:01

Hi cavagnaro and thanks for your quick reply.

Yes, the architecture maybe is the problem but theoretically.. shouldn't this work? I say theoretically cause, and correct me if i'm wrong, here in Portugal one of the ISP (i.e MEO-PT) when you buy a service with internet+voice they "transport" both services let's say with fiber, they convert that signal in a media converter (fiber to copper) and then use a router that provides both internet access and a RJ11 port so you can connect your analog phone (that works with a SIP/VOIP account internally). And that "analog line" is basically is the same thing that I create when doing what i'm doing isn't it? But I'm using an OXO "in the middle".

And in that way (ISP way) it works with the modems because I tested and it works :( that's what's bugging me and I suspect it's inside configuration from VoIP inside the OXO because the difference between the two systems I described (mine and the ISP) is one uses the router and the other uses OXO.

Maybe I'm overthinking but I would love to solve this (if it has some sort of solution)

Thanks again mate.

Hugo

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Re: Analog Modem over SIP

Post by cavagnaro » 24 Nov 2016 19:05

You think they as carrier wouldn't add QoS to their own services? That is why it works, again, OXO has nothing to do, it is your architecture. In theory yes, but with a lot of variables which you don't control

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Re: Analog Modem over SIP

Post by HugoMAL » 05 Dec 2016 13:28

Hello again everyone.

I have found a solution that until now is working.

Forced the G722 codec on all SIP Gateways, activated some RTP functions that were in the VOIP configuration, changed the QOS preference and did some jitter and framing tweaks that i found after reading the OXO Expert Manual.

After some tests we realized that the connections we made were stable and in 50 attempts only 3 weren't successuful but it could be a busy line or some other issue (we hope). It's better than the 50/50 chances that we had before the tweaking.

I hope it will work in the future and if someone has the same problem, the solution is "easy".

Best regards,

Hugo.

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Re: Analog Modem over SIP

Post by tgn » 05 Dec 2016 18:03

thanks for sharing! :)
have you tried to deliver some kilo- or megabytes? how stable is a long modem connection?

regards...


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Re: Analog Modem over SIP

Post by HugoMAL » 07 Dec 2016 17:59

Hi tgn,

honestly I still didn't measure how much data is traded between the connections. The only thing I can see in the software that they use is "upload events" and the maximum number is 500 and it takes.. maybe 5 minutes to download that data.

The modems works in a very slow rate (300 or 1200) so I suspect maybe some kilo or a few (very few) megabytes.

30 minutes was the longest connection with no failures.

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Re: Analog Modem over SIP

Post by tgn » 10 Dec 2016 14:49

tyvm :)

regards...


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Re: Analog Modem over SIP

Post by cavagnaro » 10 Dec 2016 23:08

Nice! Thanks for sharing :)

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Re: Analog Modem over SIP

Post by fe80 » 08 Jan 2019 05:15

I can't believe this because OXOs DSP is unable to encode G.722

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