On Tue, 31 Oct 2006 15:25:16 -0800
"Xiaoliang (David) Wei" [off-list ref] wrote:

On 10/31/06, Stephen Hemminger [off-list ref] wrote:

quoted

I reran the tests, this time using my DSL line to home (80ms 1Mbit/sec).
        http://developer.osdl.org/shemminger/tcp/2.6.19-rc4/dsl

The only obvious problem is Vegas looks broken.

Thanks, Stephen.

It seems that the default Vegas alpha parameter in the rc4 is 1...

I observed similar situation with the NS2Linux simulator (with 2.6.16
code) and found that if alpha=1, delayed ack will make it broken
(keeping cwnd very low without real congestion)

See details at http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegas

(Basically alpha==1 means Vegas seeks to see a delay of about 1 packet
worth. With delayed ack, 1 packet worth of delay is common even with
no congestion.)

To make Vegas work, I'd suggest to raise alpha to at least 2 or 3.
(and beta has to be at least as large as alpha.)

-David

I ran with the current default:
	alpha = 1 (scaled 2)
	beta  = 3 (scaled 6)
	gamma = 1 (scaled 2)




-- 
Stephen Hemminger [off-list ref]