George,
I presume, that your question, was regarding Voice over IP
over Satellite links. Of course, satellites routinely carry voice traffic,
esp. international, using "circuit" based technologies such as ISDN, T1/E1,
and the like.
We (COMSAT) have experimented with Voice-over-IP over satellite links,
using commercial Voice-over-IP equipment (we demonstrated it at InterOp-97
in Paris). As we all know, voice is carried over UDP, not TCP and therefore
does not get affected by 'window size" limitations or round-trip-time.
Subjectively, we have found the the quality to be quite good.
The particular application we used in our network uses 8 kbps
compressed speech. The delay is obviously larger than terrestrial
links - but it is not annoyingly so. The delay factor is dominated by
the approx. 250 ms one way propagation delay, the delay introduced
by compression and the networking equipment is small.
We have also tried interactive video conferencing (over UDP/IP)
and found it to be quite satisfactory in performance.
One has to engineer the satellite links appropriately to get
satisfactory performance (things such as antenna size, transmit power,
forward error correction), which any seatellite vendor can help you with.
One more factor that affects performance is congestion (this
is true for terrestrial Internet links, as well). Presumably
if you have routers that can provide guaranteed QoS to voice traffic,
perhaps based on RSVP, then performance wont degrade under congestion
(we haven't tried this yet).
If you, or any one else, wants to "experience" Voice-over-IP-over-Satellite,
please give us a call - we currently have a satellite network between U.S and
South America, that includes Voice-over-IP equipment.
Hope this helps.
Anil Agarwal
COMSAT Laboratories
Clarksburg, MD 20871
[email protected]
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