On Monday, March 31, 2014 7:04 AM, wi...@mncomm.com <> wrote: > So, the scenario would be the CO goes into a gateway device to convert to > digital, goes over the LAN to the other gateway device. That device hooks > up to the fax machine. If someone has done this before can you share the > products you may have used? The products we have say they will work this > way, but no luck, just voice transmission. I may have a bad device as > well.
If you are talking about a private point-to-point wireless link shot between two buildings across a parking lot or whatever, with excellent link quality characteristics and low jitter and latency, there is no reason that I can think of why moving the fax machine over wouldn't "just work". Perhaps you could share with us the following: 1. Model of the Grandstream gateways in question. 2. How you have the gateways configured (e.g., codec being used and such). 3. What equipment you are using to do the wireless shot. 4. Average throughput, latency, and jitter across that link. 5. Whether the link is for phone use only, or is combined voice and data. 6. ...if combined, whether any kind of QoS is being employed to promote voice transmission ahead of data. ...and, most importantly... 7. What exactly happens when you try to send or receive a fax over the gateway devices. A vague "it doesn't work" description never helped anybody solve anything. :-) Give us details. How does it fail, exactly? How far along does it get? Is it able to transmit a partial page and then the connection drops? Or can it not even complete the handshake with the other fax machine? If it works for voice, I very much doubt you have a "bad device", unless it is a software/firmware issue on the device(s). If the device was physically bad, I suspect the defect would present itself in other ways as well. General things to try out and to look out for: If you are using some fancy, efficient voice codec like G.729, turn that crap off. Limit both gateways to negotiate G.711u with each other only. If they have a T.38 option, make sure it is either enabled on both sides, or disabled on both sides...if there is a mismatch, some SIP stacks behave very badly if/when their re-INVITE to T.38 is rejected by the other peer. If the gateway devices support T.38 and it happens to be enabled, try turning it off. The T.38 spec is so vague as to often be useless, and there can be interop problems even between two identical devices (I swear that sometimes vendors don't test their own products...it's infuriating). And on a private, short-haul link like that, I would sure think that using G.711u PCM for both voice and fax transmission would be sufficient and pose no problems. On the other hand, if latency and jitter are sometimes a problem and the quality of the link is in doubt, and you haven't been using T.38, then by all means give T.38 a try, assuming your Grandstream devices can act as T.38 gateways (it's not enough for them to have T.38 passthrough support, they must have GATEWAY functionality). Once you finally get past all of the interop issues, T.38 really can work magic for "FoIP" on uncontrolled IP links. If you are using T.38 (or, heck, even if you aren't using T.38), try forcibly lowering the maximum modulation rate that their fax machine will attempt to handshake to the other side with. It is still (sadly) incredibly common for most production T.38 implementations these days to be based off of version "0", which does not include support for gatewaying V.34, only V.17. If they have a "Super G3" fax machine, the T.38 gateway feature should in theory just ignore the handshake and not even engage and try to re-INVITE to T.38, but you never know...could be buggy. Or if you aren't using T.38, V.34 modulation rates could be more sensitive to timing and jitter issues. So limit the fax machine to 14400bps or 9600bps. Hope this helps, -- Nathan Anderson First Step Internet, LLC nath...@fsr.com _______________________________________________ Wireless mailing list Wireless@wispa.org http://lists.wispa.org/mailman/listinfo/wireless
