[e2e] Are we doing sliding window in the Internet?

[Joe Touch]

Detlef Bosau wrote:
> Venkata Pingali wrote:
>>
>>
>> Server end (i.e, end that has large
>> amount of data to transfer):
>>
>>     - Most connections are short (90% < 1sec)
> 
> Do you have any knowledge of the number of "rounds" the TCP connection
> has seen?  A couple of years ago I saw some similar result (don´t no the
> source at the moment) where 90 % of connections consist of not more than
> 20 packets.
> 
> Now, consider the initial slowstart, IIRC we start with 2 MSS (?) then
> we have:

I don't know if the current code starts with 2 MSS; it could start with 4.

> Round    CWND
>    1              2
>    2              4
>    3              8
>                            total of 14 packets up to now
>    4             16
>                            total of 24 packets up to now,

It doesn't double each RTT; it goes up by 50%. Remember, the window
grows by one MSS each ACK during the initial phase, but there is one ACK
for each two MSS's.

I.e., the sequence should be:

round	CWND
1	2	(assuming it starts with 2)
2	3
3	4
4	6
5	9
6	13

This assumes that the congestion window hasn't kicked in, at which point
the growth would be 1 MSS per round (RTT).

FYI,Internet MSS's are usually in the 500-byte range in general. A 5KB
file would take 10 packets and be over by the 4th round.

Joe

-- 
----------------------------------------
Joe Touch
Sr. Network Engineer, USAF TSAT Space Segment

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