Question about VOIP over satellite

[jamalyusuf]

I was thinking of setting up a VoIP system using my VSAT connection. But the problem was, the VSAT system only works with TDMA enabled VoIP gateways.

Can you please help me out on what VoIP gateways that will work with my VSAT connection, am thinking of a SOHO system.

Best regards,

Jamal

[scottmac]

I'm pretty sure that VoIP (by any vendor I'm familiar with) is not functional over a satellite link. The problem is the latency of sending a signl 45,000 miles (22.5k up, 22.5k back) is just too long for voice. Try Telnetting something: the character echo time should give you an idea of what trying to talk VoIP over satellite would be like. I believe the spec is something like ~100milliseconds: satellite is 10-20 times over that (include encode/decode/translate & buffer time through the satellite each way).

If you need voice from a remote location, maybe look into InMarSAT or whoever bought out the Iridium project.

Good Luck

Scott

[asapun]

Jamal,

I've put together a VoIP toll-bypass solution over a satellite leased b/w, and the quality is just as good as any toll call. If you're running only voice packets through it then you should be just fine, if you're mixing voice and data then make sure that you have proper QoS in place. Im using G.729 codec and on top of that I'm compressing the RTP header. By doing that you increase the daley even more, but you don't loose much in quality.

Voice over a sattelite link will give you delay in terms of conversation due to propagation delay of approx 600ms. The quality of the voice itself however can be quite good because the delay is usually constant so jitter buffer values don't need to adjust much dynamically. The main effect of sattelite delay is that when the speaker stops talking he will encounter delay hearing the

listener respond. People usually adjust to this delay within 30 seconds of conversation (the human mind is very adaptive).

Your best bet would be (depending on how many voice channels you need) to use AS5400 (preferably AS5400HPX) access server, it can handle

384 VAD ON and 240 VAD OFF voice calls

75-80% CPU utilization on average taken up for:

Any codec type: G.711, G.729a, G.723.1 - 20 msec sampling rate.

Hope this helps.