Subject: Does window scale solve long fat pipe issue?

From: Jun Huang <[email-masked]>
Date: Thu, 28 Oct 1999 11:52:40 -0400

Hi

I did a few simulations of client-server ftp sessions over geostationary
on-board ATM processed satellite using OPNET simulation tool with almost all
default values provided by OPNET Modeler6.0, and find that window scale
extension described in RFC1323 does not provide the throughput great than
1Mbps (64Kbytes/500ms) on a 2Mbps link. 

Does that mean we have to use performance enhancement proxy to boost/ shape/
accelerate/ optimize the TCP over long fat satellite pipe?

Anybody does the similar work? And is so kindly to give me a Tip?

Best Regards,

Jun Huang
Sr. Network Architect, System Research, 
SpaceBridge - a Newbridge/ComDev company,
115 Champlain, Hull, QC J8X 3R1, Canada
Phone: (819) 7765664 ext 6004
Fax: (819) 776 4179
http://www.spacebridge.com

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From: Mark Allman <[email-masked]>
Date: Fri, 29 Oct 1999 09:09:36 -0400

> By the way, what's the state of Floyd's proposal to have an
> initial congestion window size of 4 packets instead of 1. This may
> help during slow start.

The following RFC provides an *experimental* change to TCP whereby
the initial cwnd can be 2, 3 or 4 segments, based on segment size.

    Mark Allman, Sally Floyd, Craig Partridge. Increasing TCP's
    Initial Window, September 1998. RFC 2414.

Also note that RFC 2581 allows a 1 or 2 segment window as standard.

allman

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From: "Spencer Dawkins" <[email-masked]>
Date: Fri, 29 Oct 1999 12:03:25 -0500

And, of course, 1-segment initial windows interact with delayed ACKs to
provide a no-extra-charge, for-limited-useful-purpose delayed ACK timer
timeout of 200-500 milliseconds at the beginning of the connection (sender
waiting for first ACK before sending second segment, receiver waiting to see
if another segment will be received before sending an ACK). 

http://search.ietf.org/internet-drafts/draft-montenegro-pilc-ltn-03.txt
(which has been approved by IESG for publication as an Informational RFC)
recommends an initial congestion window size of two segments, for this
reason.

And, I notice, the BCP-track PILC documents don't contain this
recommendation (memo to self - "snarl", on to version 03 after DC)...

Spencer

> -----Original Message-----
> From:	Mark Allman [SMTP:[email-masked]]
> Sent:	Friday, October 29, 1999 9:10 AM
> To:	Omar Elloumi
> Cc:	Godard, Julien [HAL02:HM90:EXCH]; 'Jun Huang'; [email-masked]
> Subject:	Re: Does window scale solve long fat pipe issue?
> 
>