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
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