[Asterisk-Users] Asterisk IAX over VSAT satellite.

[Simon Woodhead]

Hey Jim,

All sounds good.

We tried a satellite system here a few months ago but couldn't get on with
it. Glad you've had more success. In theory, it shouldn't matter whether the
TCP/IP link between your sites is going over satellite, modem or any other
medium but the issues we found with satellite that would be particularly
damaging for VoIP were as follows:

- Latency. You're onto this one already by the sounds of it. We were seeing
750ms pings so you're looking at delays of around 1 second; 1.5-2 seconds
for someone to hear what you've said and reply. That doesn't prevent a
conversation but might make it sound a little strange to the other party who
doesn't know what is going on.

- Upstream. We had a system with 2Mbps downstream but since the upstream is
the expensive part for providers to provide it is usually much much
smaller - ours was only 128k. That is one call for many codecs without
allowing for any other use you'll be making of the line. G.729 would improve
this a lot as you've spotted.

- Drop-outs. A satellite system should theoretically provide continuous
service like a leased line or modem connection so you shouldn't get call
dropouts. However, we found that we'd lose all connectivity from our
provider for several seconds at a time. It could have been a peculiarity of
the way they were prioritising traffic, routing, excessive contention or
even the non-TCP/IP method for the dish<>sat<>dish part of the link but it
seems whenever other customers were making heavy downloads others would slow
down to just a few bps or drop out completely. That wouldn't be good for the
quality of any calls in progress even if the connection was maintained.

I'm not meaning to be negative or dash your enthusiasm but if I had a choice
of links to do VoIP over, satellite would be at the bottom, even below
modems. Our experience could be unique of course and if you own both ends of
the link then you have far more control over the issues I've mentioned,
other than latency of course.

All the best,
Simon

----- Original Message ----- 
From: "Jim Ockers" <ockers at ockers.net>
To: <asterisk-users at lists.digium.com>
Sent: Thursday, May 29, 2003 7:47 PM
Subject: [Asterisk-Users] Asterisk IAX over VSAT satellite.


> Hi all,
>
> For some reason VSAT or Satellite Internet services are not mentioned
> (or searchable) in this list's archives.  I thought I'd let you know
> that I tested Asterisk using IAX (not IAX2) to make a phone call from
> an analog phone hooked up to an Asterisk system behind a Linksys router
> connected to a Gilat VSAT satmodem, and it worked.
>
> The "other end" (gateway) is a P200MMX with a X100P FXO card.  I have
> bi-directional calling set up so that the VSAT-phone can make outbound
> calls using the X100P in the gateway, and if the X100P gets a ring it
> answers and transfers the call to the analog phone on the other side
> of the VSAT.
>
> There is about a 1-2 second propagation delay in voice from the VSAT
> phone, as expected.  The echo is not bad at all, and the voice quality
> is quite good.
>
> I don't think the VSAT network was very busy so I don't know how well
> this will work if the available bandwidth is less.  We are not using the
> G.729 codec - just gsm.  I have tos=reliable set in iax.conf.  I didn't
> get disconnected during my test calls, but they weren't very long in
> duration.
>
> I haven't tried a fax but maybe I will.
>
> Anyway congratulations Mark et al on your fine work making such a robust
> VoIP system.  Thanks!
>
> -- 
> Jim Ockers, P.Eng. (ockers at ockers.net)
> Contact info: please see http://www.ockers.net/
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