tcp window concept

Greg Freemyer greg.freemyer at
Mon Jun 17 10:59:03 EDT 2013

On Mon, Jun 17, 2013 at 10:45 AM,  <Valdis.Kletnieks at> wrote:
> 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:


It's been 10 years since I did a deep dive into TCP/IP sliding windows
and it was for a 19.2KB satellite based network, so window scaling was
not used.


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