Davis Sylvester III wrote:
Thanks for the quick response. But how do other VoIP Service Providers like vonage provide fax capabilities?
Inevitably what I say here is going to be countered from some Vonage customer saying, "You're wrong! It always has worked for me." Vonage even advertises fax service. I think that you have to pay extra for it, but they claim to provide it. However, I've also known many unhappy Vonage customers who couldn't get a fax through to save their life. Read the doc I suggested, and hopefully you'll understand why their experience can simply be a luck of the draw.
Now, I'm not a Vonage expert... so I don't know exactly what they're doing. So I don't know what is happening differently for those happy Vonage customers. But let me tell you some things that could be happening to mitigate their situation.
1. The distance or number of hops between the user and their Vonage-controlled gateway could be very, very short... which would allow Vonage a lot better chance of controlling the problematic fax-over-VoIP factors.
2. Vonage could actually be using T.38 (or perhaps T.37) in their ATAs and gateways. I think that this is unlikely, but possible.
3. Undoubtedly the Vonage ATA uses QoS, and if everyone in the path between the user and the Vonage gateway honors that QoS to some degree or another, then maybe that's helping and making the difference.
4. Vonage could be employing some fax-specific kind of jitterbuffer on both ends of the VoIP connection. This would help control the jitter-related problems... but again, it wouldn't solve the problem of audio corruption happening.
5. Vonage could be acting as a store-and-forward fax relay, employing an extremely tolerant set of fax protocols to mitigate the jitter issues. I think that this is unlikely, but possible.
6. They could be using some combination of the above or something else that I've not thought of right now.
As for my guess... I'd suspect that they're using #3 and #4 together, and that #1 comes into play more frequently than we would normally think.
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