[Iccrg] SSDT Scope - summary
lachlan.andrew at gmail.com
Tue Apr 8 21:50:29 BST 2008
> Lachlan Andrew wrote:
> > But when we first start, we don't know if we're talking to a 300bps
> > mote or a 100GbE supercomputer. After a single timeout, we will
> > generally (???) be using a "similar" network.
> In times of QoS this assumption may be very wrong. E.g. You have two
> wires to the internet. One 1MB and one 100MB, but for the 100MB only
> HTTP is allowed all other protocols have to use the 1MB link. If youre
> first connection is an HTTP one, then the 1MB link will be overshot, the
> other way round you'll have to wait for a long time to satisfy the 100MB
> if you increase just linear.
> The first mentioned problem, with 1MB link get 100 MB data could be
> solved in one RTT, but in this case 99MB data get dropped. This would be
> an overshot of the factor 100 and much worser than slowstart.
If only one is HTTP, then they're probably different TCP connections.
Even ignoring that:
1. going from 100Mbit/s to 1Mbit/s, you will overshoot in the first
RTT, when the rate is much less than 100Mbit/s, get a time-out, and
start a normal exponential slow-start. I'm not suggesting going
straight from the current rate to the final rate.
2. going from 1Mbit/s to 100Mbit/s, either way slow start will stop
when ssthresh is reached, when the source is sending at ~1Mbit/s.
Lachlan Andrew Dept of Computer Science, Caltech
1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA
Ph: +1 (626) 395-8820 Fax: +1 (626) 568-3603
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