Re: VoIP SIP and satellite

[Ben Teitelbaum <>]

Bob,

Tyler is right.  This is most definitely not a SIP problem.  

My guess is that your problem is due either to extreme jitter that
confuses the adaptive playback buffering in a Vonage gateway or is due
to packet loss.  I have not yet played with either Vonage or the
ATA-186.  Is it easy to make a point-to-point SIP call or are you
locked into placing calls through Vonage's gateways?  If you can SIP
me, you could call me tomorrow in the office and I could read the
upstream RTP stats off my phone.

-- ben (tel:+1-734-352-7031 or 
sip:)

P.S. Is the latency assymetric or just the bandwidth?  

P.P.S. There is another group with SIP and VoIP people on it--the VoIP
working group, whom I've CC'd.

Tyler Miller Johnson 
<>
 writes:

> I do not think it is a SIP issue. It has to do with the codec
> implementation and how large your buffers are. The more you buffer the
> data, the more you can handle network latency and jitter. But also the
> more audio delay you have. My sense is the h.323 products have more
> experience with codec management than do the SIP products, because
> they are newer to market.
> 
> The other complication is assymetrical performance, which most
> implementations don't expect.
> 
> I would also say that telephone folks tend to design for really low
> latency (too low) in an attempt to make the service more like an
> analog phone. I have seen this with h.323 phones as well.
> 
> Bob Dixon wrote:
> >>
> >>
> >> We have been trying to run SIP VoIP over a satellite link and it is
> >> not working very well.
> >> We are using the Vonage service, who use Cisco ATA boxes.  The
> >> audio quality in the downlink direction is good. But in the uplink
> >> direction it is poor to fair.  Yet if we run an H.323 video
> >> conference over the same link, the audio is fine in both
> >> directions. The satellite speed is 1500 Kb down and 512 Kb up.
> >> H.323 audio bandwidth is 64 Kb.  Vonage audio bandwidth is 90 Kb by
> >> default, but you can switch it to 30 Kb, which we did with a
> >> moderate improvement. There is nothing else running on the
> >> satellite link, so bandwidth is not a problem. Vonage tech support
> >> says they are aware of this satellite problem but cannot provide
> >> any actual explanations or cure, other than to refund our money.
> >> We have tried to reach Cisco so far without success.
> >>
> >> Is there a latency problem with this SIP implementation by Cisco?
> >> Any suggestions of what is causing this problem and how to fix it?
> >>
> >> I know this is a video group, but it is the only group I know of
> >> that has SIP and VoIP people on it.
> >>
> >> Thanks!
> >>
> >>                   Bob
> >>
> >
> 
> 
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