rizwan602
join:2004-03-20
Gilbert, AZ
 ·Cox HSI
| [General] Questions about t.38 and fax and modems and voip provi
Hello,
I have a series of questions that I have been unable to resolve on my own - so I would like some help in clarification.
1) Does VOIP.MS support t.38? If not, who does?
2) At our work we have analog modems that dial out to gates at various communities for programming access codes. Can we put these modems in our office on a VOIP line and make it work that way? What will be needed other than an ATA? I tried this with a linksys pap2 and it failed miserably...
3) Is t.38 required to do #2? Or is that just a fax only protocol?
4) What is a good ATA (without a router) to use for t.38?
5) What else should I know about all of this? |
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toro
join:2006-01-27
Scarborough, ON
 ·TekSavvy Solutions..
| Re: [General] Questions about t.38 and fax and modems and voip p
I can answer some questions for you:
2) I don't think T.38 will help you with a regular modem transmission. It's for faxing only. For modem transmission I would try forcing the g711 codec and a low transmission speed in your modem software.
4) I've had good results with PAP2v2 flashed with the GrauerFuchs's patched RTP300 firmware (obviously the RTP300 works as well, but you asked for an ATA without router). An SPA2100 has worked well for me as well, but although I could see in the packet capture that was using T.38, the web interface was showing G711. With the PAP2v2 and RTP300, it shows T.38
5) When using T.38, all fax calls start using g711 and then the ATA and the gateway renegotiate the protocol once they detect the fax tone. In my experiments, the T.38 re-negotiation worked only when my ATA/router had a public IP address. Again, if you're doing just modem transmission, probably the two parties won't even try to re-negotiate the protocol. |
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trev
join:2009-06-29
Victoria, BC
| reply to rizwan602
These steps should help maximize your chances of success:
- Disable echo cancellation
- Disable all codecs but G.711
- Set your modem to use 14.4 kbps or less, maybe even 9600 bps.
- T.38 will not help your case, it is only for faxes
However, you'd be better off converting the gates to use IP or sticking with your analog/digital hard lines and not using VoIP for the modems. VoIP is VOICE over IP, not telephone over IP.
Good luck! |
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joako
Premium
join:2000-09-07
/dev/null
 ·AT&T U-Verse
| reply to toro
I do T.38 w/ G729 start codec on Grandstream HT-496 (CRAP... don't recommend these at all) and it works fine.
I have found the success rate using T.38 isn't as good as a normal analog line, but it is not bad.
--
PRescott7-2097 |
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SteveinNC
join:2007-07-19
Greensboro, NC
| reply to rizwan602
»www.youtube.com/watch?v=Zf0ZyoUn7Vk |
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Juilo
join:2007-08-10
New York, NY | reply to rizwan602
t.38 work for fax only, I tested modem communication on it in many case. no lucky.
There are different standard for modem over ip, like v.150. the audiocodes MP202 ata or it's copy Xia302 has this seperate option for modem over ip. you may try. |
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