thanks for the feedback, i agree that techniques such as spoofing (splitting
the tcp connection) from companies mentioned like flash-networks & mentat,
and explict signalling NASA JPL's SCPS-TP, and other techniques given in tcp
pep, improve performance.
topology : (sender)x------G1- - - - G2-------y(receiver)
where G1-G2 is the satellite hop
But, spoofing would violate the end-to-end tcp semantics, as the sender
could receive an ack from the proxy receiver(G1) at one of the satellite
link ends, before the data packet reaches the actual receiver (y).
Calculating the correct round trip time could be crucial to some
applications. Moreover if data is lost over a terrestial link which is after
the satellite hop, then the sender won't be informed of the congestion loss,
as the other satellite link end (G2) would do the recovery.
Whereas in case of NASA's SCPS-TP, the hosts would require modification to
process the corruption signal from the satellite link. Any protocol which
requires the end hosts to be modified wouldn't be easy to deploy in the
existing network. If it is deployed partially at some hosts, other hosts
using the same satellite channel would be at a loss.
Still we don't have a protocol which is completely transparent and preserves
all existing semantics of tcp.
What i'm trying to say is why not attack the real problem. The root cause
for tcp's poor performace over satellite channels is that it fast
retransmits on receiving 3 duplicate acks (reducing its window), and as the
delay*bandwidth product over a satellite channel is large, the no. of data
packets in the end-to-end pipe are large, so a loss due to corruption,
results in a number of duplicates acks being generated, moving the sender
tcp to fast retranmission, and thus poor performance.
ketan
> > The issue i'm trying to raise here is why bother TCP to
> > distinguish between
> > packet loss due to corrution or due to congestion, why not make the
> > corruption loss transparent to sender tcp ? Some of the work
> > ive seen in
> > doing the above, are split-connection and berkeley snoop
> > designs. But they
> > are limited to a particular satellite network topologies, where the
> > satellite hop is the last hop of the end-to-end path. What about more
> > generic topologies ?
>
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This archive was generated by hypermail 2b29 : Mon Feb 14 2000 - 16:14:55 EST