[Asterisk-Users] SIP / IAX over satellite

[John Todd]

[post re-ordered chronologically]

>-----Original Message-----
>From: asterisk-users-admin at lists.digium.com
>[mailto:asterisk-users-admin at lists.digium.com] On Behalf Of Tilghman
>Lesher
>Sent: Saturday, October 11, 2003 4:03 PM
>To: asterisk-users at lists.digium.com
>Subject: Re: [Asterisk-Users] SIP / IAX over satellite
>
>
>On Saturday, Oct 11, 2003, at 17:04 America/Chicago, Paul Mahler wrote:
>
>>  Which satellite system?
>>
>>  I think you need some specialized support, even special hardware. 
>>  Check
>>  out
>>
>>  http://www.groundcontrol.com/igvoip_001.htm
>>
>>  You may need to replace TCP/IP
>>
>  > http://www.mentat.com/skyx/skyx-gateway.html
>
>I don't know why he'd need to replace TCP/IP when both SIP as well as
>IAX use UDP/IP.  There may be substantial latency, however.
>
>-Tilghman


>Well, it's that stack that needs to go. Check out the link.
>
>Paul
>
>
>Paul Mahler
>pmahler at signate.com
>phone: 650-207-9855
>fax: 877-408-0105


It's unlikely that the TCP/IP stack "needs to go".  IP applications 
work quite well over satellite, no matter what people tell you.  They 
just get really, really slow if they're TCP due to ACK response 
delay, and UDP has the aforementioned 500ms lag as well.

The skyx stuff is just a forward-ACKing spoofer for TCP, and probably 
some smart squid derivatives to boost HTTP transfer speeds.  Not 
useful for VoIP, but probably useful if you're doing anything that's 
not UDP based.

For VoIP with IAX, there may be application layer issues that are 
smudging your results.  I would suggest that you try to get SIP 
working over satellite, as I have had that working with no difficulty 
in the past (excepting the delay issues, of course.)  If you can get 
"raw" RTP working with SIP, but not IAX2, then perhaps the issue 
needs to be patched in the IAX source code if there is some timer 
that is expiring inside the IAX protocol.  Let us know how your 
results with SIP work.

Again: VoIP works JUST FINE over satellite, at least as far as the 
voice quality goes, as long as you have decent bandwidth available. 
Latency is another issue, but there's nothing  you're going to be 
able to do when you're pushing a radio wave 33,000 miles out and 
33,000 miles back - physics doesn't allow for better QoS.  :-)

JT