[Bismark-devel] How to measure the initial TCP impulse generated by a web browser?

[Dave Taht]

Jim has been worrying about the size of the initial impulse being 
generated by the increase in the initial windows across multiple 
operating systems from 4 to 10 or more, and how to look at that brief, 
transient impulse, and later, its effect on TCP window scaling.

He messaged me earlier today with:

The best thing I've been able to think is to get a packet capture, 
having triggered a bunch of simultaneous HTTP get's on a web server.

Current browsers are doing 6 over the same path (and FF may do 15 under 
  some circumstances).  If you have a sharded web site, you can get yet 
more packets in flight, as the web browser doesn't know it's actually 
the same web site.

On sites like google images, the connections may be persistent, and the 
window size may be growing further when you scroll to the next page.  Dunno.

Here's a rough computation
    # connections    IW        Size of "splat"    Comments
        2                     4              8 packets       RFC 
2068/2616 behaviour
        6                     4              24 Packets     Current 
browser + old IW
        6                    10             60 packets     Current 
browser + new IW proposal

Not pretty.


Then from timestamp data (even best if it is TCP timestamp data), one 
should be able to figure out how long a broadband link is saturated by 
the packet burst that arrives.