Does Vonage support T.38

Posts: 187 · Vonage Forum Master Joined: Feb 14, 2007 Posts: 187

Here is a pretty good write-up about fax over VoIP:

http://www.soft-switch.org/foip.html

Does Vonage support T.38 fax relay? I know the vta-vr does, what about the Vonage pstn gateways?

Is it possible that some of the things you get with a "dedicated fax line" are T.38 support and turning off things like echo cancellation and silence suppression (not in the fax machine of course but in the adapter itself)?

Mark

Posts: 83 · Vonage Forum Senior Joined: Oct 26, 2006 Posts: 83

Vonage does support T38, all their gateways do but only for inbound faxes becuase not all PSTN gateways support it yet. However their Sonus Gateways support it for inbound and outbound, but if you number is a LEVEL 3 number, level 3 does not support T38 on any of their gateways so it would not be used for a dedicated fax line in that case

echo cancellation and stuff of that nature is not really something that can be changed on the user end, and often is disabled by default on a dedicated fax line

the only Vonage devices that support T38 are the TI devices, any device with a "P2" such as WRT54GP2 or all other Sipura devices do not support T38

as far as silence suppression their are ways that tech support and modify send and receive gains to lower "noise" on a fax line

Posts: 187 · Vonage Forum Master Joined: Feb 14, 2007 Posts: 187

"Vonage does support T38, all their gateways do but only for inbound faxes becuase not all PSTN gateways support it yet"

I'm confused - the only PSTN gateways that would be used would be Vonage's gateways, wouldn't they?

If some gateways support T.38 and some don't, the ones that don't couldn't handle it inbound, either.

Thanks for any clarification.

Mark

Posts: 83 · Vonage Forum Senior Joined: Oct 26, 2006 Posts: 83

clarification:

If i have a POTS line and send you a fax and the carrier that I have supports T38 on their outbound gateways then you are all set because that fax will be sent to the Vonage inbound gateway and then routed to the Vonage customer and that gateway is able to handle T38

Vonage uses different gateways for inbound and outbound calls and faxes. Some PSTN carrier's Gateways are not able to negotiate T38 so Vonage has not yet set it up so that all the outbound gateways support it because essentially there is no point until the Gateways that they route to on the PSTN side are able to negotiate T38 as well. Vonage does have one gateway group, SONUS, that does use T38 for inbound and outbound but htat is the only one

T38 is a codec essentially that all vonage inbound gateways can negotiate so if they receive a fax with on T38 then they are able to receive it

It would be like making an outbound call from Vonage to Verizon and lets say that Vonage could only use the G711 codec (the highest codec) and Verizon could only negotiate G726 and G729a then the two would not be able to talk to each other because the gateways would not know how to talk to each other but if you set it up so that the inbound gateways at Vonage could negotiate G726 and G729a then there is no issue if you place a call from Verizon to Vonage because they both speak the same language

not sure if that clarifies it for you or if it made it more confusing

Posts: 187 · Vonage Forum Master Joined: Feb 14, 2007 Posts: 187

I guess where I'm having a conceptual problem is that in my experience, a gateway operates between two protocols.

My d-link vta for example is a gateway between voip and analog/pstn protocols/service.

In your first paragraph example pstn fax to vonage customer, you make reference to the pstn carrier's outbound gateway and Vonage's inbound gateway. Why two gateway's?

You've got pstn on one side and voip on the other. A single gateway would do the trick. And it would need to be T.38 compliant.

Most carrier-class pstn/voip gateways I've seen have a pri or channelized T1 on the pstn side and an ethernet on the voip side.
The SONUS units you reference would seem to fit this model.

Mark (still slightly confused)

Posts: 6 · Posted: Thu Jul 19, 2007 12:07 pm Post subject:

BUMP

Can someone clarrify Vonages position on T.38 and are they using it on all there gateways now?

Also what about the major telco companies like Bell Canada, AT&T, Bell South etc etc are they using T.38 ?

I am considering cancelling my fax line since it does not work with my fax modem. Do i have a better chance using a fax machine that supports T.38 ? Vonage custommer support could not recommend or explain anything to me, seemed like i knew more than them?!