[e2e] opening multiple TCP connections getting popular

Agarwal, Anil Anil.Agarwal at viasat.com
Fri Aug 31 09:12:14 PDT 2007


Lars wrote:
> On 2007-8-30, at 15:18, ext Michael Welzl wrote:
> > Does anybody know if there's a generally known, agreed upon 
> reason for 
> > not using Window Scaling? Google tells me that some broken routers 
> > can't handle it... but, interestingly, Wikipedia (via google :-) ) 
> > tells me that, since kernel version 2.6.8, the option is enabled in 
> > Linux by default, and that it's used (by default? don't
> > know) in Vista...  so what, are we already heading for trouble?
> Microsoft presented their findings related to window scaling 
> (and several other TCP extensions) at the IETF TSVAREA 
> meeting in Prague.  
> See http://www3.ietf.org/proceedings/07mar/slides/tsvarea-3/sld3.htm
> and the two following slides. Summary: Window scaling is 
> enabled in Vista, but limited to a factor of 2.

1. What are the default and maximum receive and transmit window size
values of Linux 2.6.x, Windows and Vista? If they are less than 64
kbytes, then enabling window scaling does not accomplish much, except
for applications that explicitly configure large maximum window sizes
both at the transmitter and the receiver.

2. Assuming that all routers, firewalls, etc. get fixed (LoL) and can
handle TCP packets with window scaling correctly, what would we suggest
the default and maximum TCP window values be? Is the "Internet" robust
enough to handle a maximum TCP window size of, say, 10 Mbytes for every
TCP connection? Will existing TCP congestion control mechanisms
(RFC2581) and existing router implementations and configurations (tail
drop, RED?, ECN?, buffer sizes, etc.) suffice (ignoring issues of
fairness for the time being, with apologies to Bob Briscoe)?


Anil Agarwal
ViaSat Inc.
20511 Seneca Meadows Parkway, Suite 200
Germantown, MD 20876
Anil.Agarwal at viasat.com
ViaSat Brings your Network to Life

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