CWND Stats

tcptrace reports statistics on the estimated congestion window with the -W option when used in conjunction with the -l option. Since there is no direct way to determine the congestion window at the TCP sender, the outstanding unacknowledged data is used to estimate the congestion window. The 4 new statistics produced by the -W option in addition to the detailed statistics reported due to the -l option, are explained below.

surya:/home/mani/tcptrace-manual> tcptrace -lW malus.dmp.gz

1 arg remaining, starting with 'malus.dmp.gz'
Ostermann's tcptrace -- version 6.4.6 -- Tue Jul 1, 2003

32 packets seen, 32 TCP packets traced
elapsed wallclock time: 0:00:00.026658, 1200 pkts/sec analyzed
trace file elapsed time: 0:00:00.404427
TCP connection info:
1 TCP connection traced:
TCP connection 1:
	host a:        elephus.cs.ohiou.edu:59518
	host b:        A17-112-152-32.apple.com:80
	complete conn: yes
	first packet:  Thu Jul 10 19:12:54.914101 2003
	last packet:   Thu Jul 10 19:12:55.318528 2003
	elapsed time:  0:00:00.404427
	total packets: 32
	filename:      malus.dmp.gz
   a->b:			      b->a:
     total packets:            16           total packets:            16
           . . .                                  . . .
           . . .                                  . . .
     avg win adv:           22091 bytes     avg win adv:           33304 bytes
     
     max owin:                451 bytes     max owin:               1449 bytes
     min non-zero owin:         1 bytes     min non-zero owin:         1 bytes
     avg owin:                 31 bytes     avg owin:               1213 bytes
     wavg owin:               113 bytes     wavg owin:               682 bytes
     
     initial window:          450 bytes     initial window:         1448 bytes
           . . .                                  . . .
           . . .                                  . . .          
     throughput:             1113 Bps       throughput:            44957 Bps

• max owin The maximum outstanding unacknowledged data (in bytes) seen at any point in time in the lifetime of the connection.

• min non-zero owin The minimum (non-zero) outstanding unacknowledged data (in bytes) seen.

• avg owin The average outstanding unacknowledged data (in bytes), calculated from the sum of all the outstanding data byte samples (in bytes) divided by the total number of samples.

• wavg owin The weighted average outstanding unacknowledged data seen. For example, if the outstanding data (odata) was 500 bytes for the first 0.1 seconds, 1000 bytes for the next 1 second, and 2000 bytes for the last 0.1 seconds of a connection that lasted 1.2 seconds, wavg owin= ((500 x 0.1) + (1000 x 1) + (2000 x 0.1)) / 1.2 = 1041.67 bytes an estimate closer to 1000 bytes which was the outstanding data for the most of the lifetime of the connection. Note that the straight-forward average reported in avg owin would have been (500+1000+2000)/1.2 = 2916.67 bytes, a value less indicative of the outstanding data observed during most of the connection's lifetime.