[e2e] Satellite Date Rates

Arjuna Sathiaseelan arjuna at dcs.kcl.ac.uk
Fri Nov 26 01:27:54 PST 2004

Dear Lloyd,
  Thanks for your explainations. I am writing down the details provided by
Sally Floyd's RR-TCP:Reordering Robust TCP paper:

Satellite links have very long RTTs, typically on the order of several
hundred milliseconds. To keep the pipe full,link-layer retransmission
protocols for such links must continue sending subsequent packets while
awaiting for an ACK or NAK for a previously sent packet. Here, a
link-layer retransmission is reordered by however many packets were sent
between the original transmission of that packet and the return of the ACK
or NAK.
[C.Ward, H.Choi and T.Hain. A datalink control protocol for LEO satellite
networks providing a reliable datagram service. IEEE/ACM Transactions on
Networking, 3(1):91-103,Feb 1995.]

I was wondering whether this causes any reordering in GEO satellites?


>> Reordering in satellites occurs mainly due to link level retransmissions
> It does? Can you give us evidence supporting that claim?
> (People tend to presume a satellite channel is more errored than it
> is. You need a BER better than 10e-5 to carry IP traffic well, so you
> dimension coding for the channel appropriately. A 45MHz transponder
> with an HDLC serial stream going through it may have no link layer to
> speak of.)
> If the link layer is causing massive reordering, it may not be
> designed well for IP traffic - see RFC3366 section 3.1.

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