[clug] VOIP over Satellite broadband

Keith Goggin kgoggin at bigpond.com
Thu Feb 28 07:17:15 GMT 2008

Update to my first message which didn't seem to get through anyway.

Switched from Linksys SPA2000 to Linksys WRT54GP2.

VOIP over satellite now works OK for TX but still broken up for RX.

So some progress :-)

Also perhaps I should have said I'm running Linux x86_64 
(openSUSE10.3) on AMD Athlon64 X2 4800+ with 2x1 GB DDR2 667

I currently run VOIP over ISDN (too far from town for ADSL).

It works tolerably well provided I do my own QoS by pausing uploads/downloads 
for the duration of any calls.

I've just been connected to Aussie Broadband / IPStar (512/128 kbps) and VOIP 
is unusable.

While ping time (satellite) is of the order of 900 ms RTT. Phone users are 
conscious of only half of that which is just tolerable. 

I've run a tcpdump -c 1000 on my IPCop box (Promiscious mode from my desktop 
doesn't catch the VOIP traffic) while VOIPing my landline from both ISDN and 
Satellite. I've run both these files through Wireshark and to my untrained 
eye there's no obvious difference.

However when I stream radio over satellite and run Wireshark I see some 
evidence of buffer overrun (tcp zerowindow).

I do realise streaming radio uses TCP while VOIP uses UDP but beyond that I am 
about out of my depth.

Can anyone advise me what else to look for?

PS. ISDN Home finishes in December, regular ISDN charge for data and the 
nearest NextG tower is 42 Kms away. Not much choice really.  

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