At 12:03 PM 3/25/98 -0500, you wrote:
>I could claim the lower-layer mitigation regarding FEC (from the draft):
>
> "The use of forward error correction coding (FEC) on a satellite
> link should be used to bring the performance of the link to at
> least fiber quality."
>
>is not related to TCP and therefore out of scope. Thankfully, I don't
>believe that would be a valid or useful position; though the "at least
>fiber quality" is an expensive hurdle.
Unfortunately, in the real-world of satellite communications, one can be
assured of one thing: your path will degrade, or be degraded, to below
"fiber quality" more often than you would expect. No matter which form of
FEC you're running, if the noise floor comes up too high, BER goes up too
much for the system to cope with, and if the application systems can't
determine thios has happened you are in trouble.
Overloading of transponders by unauthorized users, or users inadvertantly
increasing power, or jackleg video-uplink-truck operators who use the
"ready-fire-aim" approach to lighting up their HPA's, or due to imermod
products, or spurious emmissions, or any number of other causes, will
reduce effective Carrier to Noise and therefore EB/No and BER performance
of any link. It happens a LOT. (My firm services over 300 networks,
domestic and internationally, and hardly a day goes by, somewhere, where
someone isn't glitched .... [sigh]
If spoofing techniques are in place, the users never know they've missed a
bit or two - until they try to run that latest 10mB version of Eudora,
which is corrupt.
I'm sure that the same things happen in the terrestrial world, courtesy of
BillyBob's BackHoe Services, etc., and that's why TCP is so good ... it
never passes corrupt data. As a satellite network provider, I really don't
want my clients to suffer corruption - ever. Yes - there's a two or three
billion dollar global market waiting for REAL FAST TCP/IP over satellite,
and that is a real incentive to speed things up. But - in my own opinion,
we should maintain the integrity of the application data to the greatest
degree possible as we work to deliver the goods at true link speeds. Any
satellite operator who says they can "guarantee" a BER of 10-E14 all the
time ... is kidding themselves and their clients. Unlike digital audio or
video, which has the occasional dropout which is momentarily irritating to
the user ... 'net applications are such that one bit missed will crash the
user's application, and error correction over the link requires more than a
blind FEC scheme ... in my opinion, anyway.
Bill
****************************************************
Bill Sepmeier VP NSN Network Services
mailto:[email protected] http://sepmeier.com
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"Things change ... " The Dalai Lama
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