[Asterisk-Users] Asterisk IAX over VSAT satellite.

[Chad Wicker]

Remember that a ping is round trip so the other user should only
experience a 325ms delay on a 650ms circuit.  What you would be
expieriecing is the overlap in conversations as a result of the delay. 
i.e. when someone stops talking, it takes about 300ms for the other side
to start getting the pause and then 300 more ms for the persons responce
to get back to the original speaker.  

While there are many other pitfalls to VoIP and TCP-IP over satellite
(I can expond on many of them as I work for a company in the buisiness)
it still is a viable option in many situations.  Mobile sites, remote
locations, maritime, quick responce and many other unique situations
make satellite a very viable option for many users.

As far as dropouts are concerned,  a well designed satellite system can
operate at 99.995% availability or more.  For licencing concerns, Ku is
prefered over C.  Most systems sold as consumer systems are also sharing
bandwidth which would cause some additional concerns for the importance
of the data being transported.  (I can expound if anyone is interested.)
 I have a testbed up here constantly and can go for about a month before
noticing any downtime.

Chad C. Wicker
Systems Engineer
Petrocom

>>> woodheads at gonegardening.com 5/29/2003 2:39:16 PM >>>
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/ 
> _______________________________________________
> Asterisk-Users mailing list
> Asterisk-Users at lists.digium.com 
> http://lists.digium.com/mailman/listinfo/asterisk-users 
>


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