While this thread is already in the archives, I'll throw my opinion on the table, too.
The latency is about .25 seconds to and .25 seconds from the satellite. There is additional propagation delay in the system. Also, TCP/IP relies on propagation delay to optimize traffic, but doesn't handle delays this long well. There is special purpose hardware available the sends the traffic to an from the satellite with a different protocol. This helps the satellite calls quite a bit.
http://www.mentat.com/skyx/skyx-whitepaper.html
John Todd reamed me out the last time I suggested that you need this hardware, he says he has voice working fine over a satellite link. And he knows what he's talking about. I thought I would save him some time, this time, by putting this in. ;-)
Again, for the archives, I'll comment on why this hardware/software probably isn't useful for VoIP. :-)
All of the satellite accelerators are based on TCP spoofing, which ACK's TCP packets before the other side actually sends the ACK. This keeps things flowing faster because it "breaks" the way TCP functions. Since VoIP is almost always UDP, this doesn't do any good. Plus, since VoIP is real-time human-perceived communication, you can't make it any faster than it currently is - the speed of radio waves in a vacuum (and a short duration in the "slower" atmosphere) is fixed. Geosync satellites are ~22,000 miles away - there is no speeding up that process or predicting what is being said before it's actually said.
I have used SIP RTP over satellite, and while the delay is uncomfortable it is workable if that is the only method to get to the endpoint at a reasonable cost. As previously noted, discomfort is a function of cost; the more expensive the transport, the less discomfort one is willing to suffer through.
Quality of sound in UDP-based VoIP services are 100% a function of available bandwidth, and not a function of delay, though with IAX2 I can't say if that's the case or not since I am unaware of how it handles unreasonable duration between frames of send/receive. The trunking features of IAX2 may help tremendously in saving transmission bandwidth, though - the removal of the IP overhead from subsequent sessions (after the first one) is a huge savings over SIP or H.323, so you should be able to get much more out of your very expensive bitstream than you would ordinarily be able to get with other VoIP protocols, so from that perspective (to the original poster or anyone else with IAX2 over satellite transport) please let us know how you make out with testing.
PS: To answer the original question, the _theoretical_ maximum for channels through 128kbps is 18 calls with LPC10, based on my codec comparisons (see the archives) with IAX2. LPC10 sucks, and adding a satellite delay would make it infuriating for anyone except the most hardened cheapskate. A more reasonable codec would be G.729, at a theoretical maximum of 11 calls, but you'd probably really only get 8 or 9 without starting to get loss or buffer issues.
JT
There is, of course, also the problem of the upload speed. The consumer grade satellites don't offer much upstream bandwidth. You can get better upload speed from some of the commercial satellite carriers.
http://www.tachyon.net/
Paul
Paul Mahler mail:[EMAIL PROTECTED] phone: 650.207.9855 fax: 877.408.0105
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bisker, Scott (7805) Sent: Wednesday, December 17, 2003 7:06 AM To: [EMAIL PROTECTED] Subject: RE: [Asterisk-Users] 128 kbs satelite link
Similar to online gaming, I would think that the propagation delay with the satelite connection would make calls unbearable. Half-duplex at its worst.
my $0.02
-sb
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Senad Jordanovic Sent: Wednesday, December 17, 2003 9:49 AM To: [EMAIL PROTECTED] Subject: [Asterisk-Users] 128 kbs satelite link
Hi all,
Anyone has experience using * through 128 kbs (or bigger) satelite link?
In particular I am interested to hear how many calls could be put through 128Kbs satelite link simultaneously?
Ta SJ
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