[:BLIP:]Re: [Gllug] Bandwidth shaping

Simon Stewart sms at lateral.net
Wed Apr 3 14:51:23 UTC 2002

On Wed, Apr 03, 2002 at 03:02:13PM +0100, Stephen Harker wrote:
> How do those download managers like Gozilla and the Linux NT downloader
> regulate their download speeds then? Is that further up the OSI layer
> thingo?

Didn't think that they did that --- just thought they ran quietly in
the background picking up dropped downloads and attempting to resume
them. In any case, from my badly remembered networking lectures, you
could send source quench ICMP packets, which essentially ask a sending
host to slow down a bit, please.

I don't write download managers, but an alternative is based on the
fact that TCP/IP uses a "slow start" algorithm: it starts transmitting
slowly, and then builds up the transmission rate over time until
packets start getting rejected (that is, the ACK packets from the
recieving machine are dropped en route to the sending machine), so it
should be possible for the download manager to drop ACKs prematurely,
thus limiting bandwidth usage.

If you're interested, have a poke about in RFCs 2001 and 813 for



(if anyone can tell me why I'm wrapping everything in parentheses, I'd
 be interested to know. I'm sure I had a good reason to do it, I'm just
 not sure what it was.)  --- Nix

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