tcp window concept

[Valdis.Kletnieks at vt.edu]

On Mon, 17 Jun 2013 10:03:02 -0400, Greg Freemyer said:

> The solution from the very start of tcp/ip in the late 70's was to
> have a sliding window of un-ack'ed data.  The normal default is 4 x
> MSS (iirc).  That means the sender can send 4 large packets worth of
> data without getting a single ACK.  (The default can be overridden up
> to 64K bytes max (iirc).)

Up to 64K if you don't support RFC1323 window scaling, which pretty much
everybody does, because even at 10mbit speed, 64K only allows a 6.4ms RTT
before a full window prevents you from using more bandwidth (in other
words, if your RTT is over 6.4ms, your performance starts dropping). And
if you're at 100mbit or gigabit or higher, the allowable RTT drops even more.

With RFC1323 window scaling, the windows can get to multiple megabytes
in size - enough to do line-rate 40 gbit/sec cross country.  And even faster:

http://www.extremetech.com/extreme/141651-caltech-and-uvic-set-339gbps-internet-speed-record


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