[e2e] MSS and cwnd increase

[Ian McDonald]

On 7/2/06, Salman Abdul Baset <salman at cs.columbia.edu> wrote:
> I am wondering how the Linux 2.6 updates its congestion window when a CBR
> stream (packet size << MSS) is sent over TCP.
>
> In general, if I am sending 100 packets every second with a packet size
> of one byte and assuming each packet is ACKed, then increasing window by
> one every RTT (during congestion avoidance) will artifically inflate the
> window. Thus, the cwnd calculation should not assume that the last packet
> sent contained MSS bytes of data.
>
> The rfc and the code and seem to imply that cwnd increase is MSS-based. I
> haven't confirmed either way (still testing it) and will like to know:
> 1) What is the RFC suggested way?
> 2) How Linux 2.6 is implementing it?
>
Linux has changed to use RFC 3465 Appropriate Byte Counting (ABC) for
exactly this sort of reason. This can be turned off or on but is on by
default.

Ian
-- 
Ian McDonald
Web: http://wand.net.nz/~iam4
Blog: http://imcdnzl.blogspot.com
WAND Network Research Group
Department of Computer Science
University of Waikato
New Zealand