tcp_moderate_cwnd()

This function is one in the linux kernel which is non-IETF standard. It basically changes the value of the current cwnd to that of the total number of packets in flight + max burst (usually max burst=3).

There is currently talk as to whether this function should be incorporated into the kernel by people like Brian Tierny and Sally Floyd.

The effect of this 'moderation' is apparent on the graph below; it shows the cwnd (in red) as a function of time for a high speed, long delay link (DataTAG). As you can see, we achieve a window size of about 25Mb, which is dynamically right sized for the duration of the test. There are no losses or major reordering on the link and thus the cwnd should be well behaved (capped at the recv window). However. we can see that there is a wide spread of cwnd values, which account for about a quarter of the absolute value of the cwnd.

Note that there are also some 'undos' within the test sample, however, these were infrequent and hence negligable compared to the effects of the moderate_cwnd().

Wed, 23 July, 2003 13:07