rsync transfer rates over ssh

[J.P. Trosclair]

This is just an inquiry about how rsync calculates its transfer speeds.

I'm using rsync over ssh to pull data from our central office to another 
office. Our central office is connected to the internet via T1 and the 
other office is connected to the internet via DSL. rsync is being run at 
the remote office to pull data down from the central office so I expect 
to see transfer speeds at a maximum of ~150KB/s, or so. Instead I'm 
seeing this on a ~310mb file (just one example):

            0   0%    0.00kB/s    0:00:00
     13372944   4%   12.75MB/s    0:00:23
     22294152   7%   10.63MB/s    0:00:26
     32173104  10%   10.23MB/s    0:00:26

    ....

    313022664  99%    2.63MB/s    0:00:00
    314732544 100%    6.05MB/s    0:00:49 (xfer#223, to-check=133384/557231)

The transfer took 49 seconds total so there must be some truth to the 
speeds I'm seeing. I don't understand how this is being calculated 
because we don't have that kind of bandwidth on either side of the 
connection. The transfer in question is an update to the file, it 
already existed at the remote office. Is the speed a result of how rsync 
is transferring the changed file?