Hi!,
I think that the current Westwood algorithm implemented in the Linux kernel
(since 2.6.13) is not same with one described in its original paper.
In the Linux implementation, Westwood uses 'tcp_reno_ssthresh' function as a
'ssthresh' interface as below codes.
---------------------------------------------------
<tcp_westwood.c>
...
static struct tcp_congestion_ops tcp_westwood = {
.init = tcp_westwood_init,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.min_cwnd = tcp_westwood_bw_rttmin,
.cwnd_event = tcp_westwood_event,
.get_info = tcp_westwood_info,
.pkts_acked = tcp_westwood_pkts_acked,
.owner = THIS_MODULE,
.name = "westwood"
};
----------------------------------------------------
But, Westwood basically sets its ssthresh value based on bandwidth
estimation, not by cwnd/2 as Reno does.
In this case, Linux-Westwood would call 'tcp_reno_ssthresh' to set its
ssthresh value when retransmission timeout expires.
I don't know why Westwood uses Reno's ssthresh function.
In my opinion,
1) '.ssthresh' interface should be changed from 'tcp_reno_ssthresh' to
'tcp_westwood_bw_rttmin'.
Then, '.min_cwnd' interface can be removed.
2) In 'tcp_westwood_event()' function,
2.1) The case of 'CA_EVENT_COMPLETE_CWR' can be removed. (corresponding
codes are already executed)
2.2) In the case of 'CA_EVENT_FRTO', 'tp->snd_ssthresh =
tcp_westwood_bw_rttmin(sk);' can be removed because '.ssthresh' interface is
called before tcp_ca_event(sk, CA_EVENT_FRTO) is called.
Thanks,
Jaehyun Hwang
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