VoIP over satellite link?

[Ramon F Herrera]

We have a customer in a remote area, relatively near the equator
(their ISP is too). They don't have much voice coverage (no land lines
and scant cell) but they have a satellite-based DSL Internet link. I
would like to try to solve their problem with a VoIP ATA from
Linksys, because its configuration parameters can be tweaked at will.

I have the obvious concerns: how much will the delay affect voice
quality? Is there some TCP/UDP window that should be adjusted? Any
question I haven't addressed?

TIA,

-Ramon F Herrera

[Rick Jones]

Post by Ramon F Herrera
We have a customer in a remote area, relatively near the equator
(their ISP is too). They don't have much voice coverage (no land
lines and scant cell) but they have a satellite-based DSL Internet
link. I would like to try to solve their problem with a VoIP ATA
from Linksys, because its configuration parameters can be tweaked at
will.
I have the obvious concerns: how much will the delay affect voice
quality? Is there some TCP/UDP window that should be adjusted? Any
question I haven't addressed?

Did you ever use one of those old satelite links for a
long-distance/overseas call? I suspect that VoIP over a
satellite-based DSL link wouldn't even be that good. I have vague
memories of speaking with my grandfather over one of those a few times
and it did not lend itself to a normal flowing dialog.

Assuming we are talking about a geosync satellite here, that is at
least one hop of ~46000 miles each way, which translates to a one-way
latency of ~250 milliseconds. (Handwaving math...) And then add-in
whatever happens once their voice data hits the regular pots (?)
network, and whatever other delays there might be on the IP side at
the ISP or whatnot.

So, your customer would say "boo!" and it would be a full half-second
before you could say "eek!" No tweaking of TCP windows (UDP has no
window) or other stuff could change that. While at first blush half a
second might not sound like a big deal, there was a very compelling
reason the telcos/whatever put all those trans-oceanic links in :)

rick jones

[alt]

Post by Rick Jones

Post by Ramon F Herrera
We have a customer in a remote area, relatively near the equator
(their ISP is too). They don't have much voice coverage (no land
lines and scant cell) but they have a satellite-based DSL Internet
link. I would like to try to solve their problem with a VoIP ATA
from Linksys, because its configuration parameters can be tweaked at
will.
I have the obvious concerns: how much will the delay affect voice
quality? Is there some TCP/UDP window that should be adjusted? Any
question I haven't addressed?

Did you ever use one of those old satelite links for a
long-distance/overseas call? I suspect that VoIP over a
satellite-based DSL link wouldn't even be that good. I have vague
memories of speaking with my grandfather over one of those a few times
and it did not lend itself to a normal flowing dialog.
Assuming we are talking about a geosync satellite here, that is at
least one hop of ~46000 miles each way, which translates to a one-way
latency of ~250 milliseconds. (Handwaving math...) And then add-in
whatever happens once their voice data hits the regular pots (?)
network, and whatever other delays there might be on the IP side at
the ISP or whatnot.
So, your customer would say "boo!" and it would be a full half-second
before you could say "eek!" No tweaking of TCP windows (UDP has no
window) or other stuff could change that. While at first blush half a
second might not sound like a big deal, there was a very compelling
reason the telcos/whatever put all those trans-oceanic links in :)
rick jones

Hi Rick:

I've set up a lot of VoIP-over-Satellite systems. Yes, the latency is a
bit of an issue, but for the most part you can have some well flowing
conversations. And as long as you don't have any packet loss or large
packet jitter, the sound will be very clear and clean because it is
all-digital. I routinely see 300ms-350ms of latency and the customers
don't seem to mind.

That being said, if you can get terrestrial, get it, for all the reasons
you've laid out above.

[wildeyed]

You could just try a standard satellite phone if you can afford th
charges, but I should warn you they are not cheap! :(

This is a VOIP forum not a satellite telephony forum. :

--
wildeye
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[Stefan Pfefferkorn]

You could just try a standard satellite phone if you can afford the
charges, but I should warn you they are not cheap! :(

This is a VOIP forum not a satellite telephony forum. :o

This is not a forum - this is a newsgroup :-)