RE: a vote for asymmetric connections in a session

[Charles Monia <cmonia@NishanSystems.com>]

Hi All:

> -----Original Message-----
> From: Matt Wakeley [mailto:matt_wakeley@agilent.com]
> Sent: Thursday, September 07, 2000 3:47 PM
> To: ips@ece.cmu.edu
> Subject: Re: a vote for asymmetric connections in a session
> 
> 
> As Julian has stated in a different thread, the purpose of 
> the "sliding
> windows" in iSCSI is not for congestion management.  It is 
> simply there to
> handle the case where if a connection goes down in a multiple 
> connection
> session, it prevents the remaining connections from 
> overwhelming the target
> with new commands that it can't process due to missing 
> commands that where on
> the broken connection.
> 
> Since all of this runs on top of TCP, and TCP performs 
> congestion management,
> why must iSCSI perform congestion management on top of TCP?
> 
> -Matt Wakeley
> Agilent Technologies
> 

I'm not sure what is meant by "congestion."  If we're talking about
congestion in the TCP/IP transport, I'm in agreement.  However, I thought we
were referring to the sort of congestion that  the application on top of
iSCSI might see if it received more commands than it had room for. 

Unless I misunderstood your point, threfore, I think there might be an
issue. The only way I can see flow control in the tranport layer being used
to avoid dropping commands is if higher layer congestion results in back
pressure to the iSCSI pipe.  I believe that behavior is undesirable because
it introduces "head-of-line" blocking, with the following consequences:

a) It effectively shuts down the flow of commands to all logical units.

b) It blocks the flow of task management commands (Abort Task, Clear task
set, etc).


<snip...snip>

Charles Monia
Senior Technology Consultant
Nishan Systems Corporation
email: cmonia@nishansystems.com
voice: (408) 519-3986
fax:   (408) 435-8385