Subject: I-D ACTION:draft-ietf-pilc-asym-04.txt

From: [email-masked]
Date: Mon, 21 May 2001 06:59:35 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Performance Implications of Link Characteristics Working Group of the IETF.

	Title		: TCP Performance Implications of Network Asymmetry
	Author(s)	: H. Balakrishnan, V. Padmanabhan et al.
	Filename	: draft-ietf-pilc-asym-04.txt
	Pages		: 32
	Date		: 18-May-01
	
This document describes TCP performance problems that arise because 
of asymmetric effects. These problems arise in several access 
networks, including bandwidth-asymmetric networks and packet radio 
networks, for different underlying reasons. However, the end result 
on TCP performance is the same in both cases: performance often 
degrades significantly because of imperfection and variability in 
the ACK feedback from the receiver to the sender.

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From: [email-masked]
Date: Wed, 30 May 2001 17:50:55 -0400

Hello Everyone,

I would like to make the following comments on the IETF Internet Draft document
entitled, "TCP Performance Implications of Network Asymmetry"
(draft-ietf-pilc-asym-04.txt).

Section 4.1 Bandwidth Asymmetry

The second paragraph of the section provides some very useful calculations on
when an upstream bottleneck becomes saturated before the downstream bottleneck
does.  Unfortunately, it makes an assumption that a client has the ability to
occupy the full capacity of the downstream link, which may not be true in all
cases.  For example, consider a T1 (1.544 Mbit/s) wireless link with an RTT of
about 650 milliseconds.  If the maximum TCP window is 65,535 bytes then the
calculated throughput this client could achieve (over an individual connection)
is limited to 806 Kbit/s, which is obviously less than the full capacity of the
channel.  Moreover, this would have a significant impact on the normalized
bandwidth ratio, k.  There should be some discussion of this situation in the
section, since it would possibly lead to a very inaccurate result, if taken
literally.

Section 5.8 Enhanced Backpressure

To reiterate Lloyd Wood's comment, a clear definition of the term 'backpressure"
would be useful and would make the section easier to understand.  Moreover, it
would also be useful if the authors could offer some ideas on how backpressure
could be implemented to avoid uplink congestion.

Rod Ragland
Hughes Network Systems