Re: a vote for asymmetric connections in a session

["Randall R. Stewart" <randall@stewart.chicago.il.us>]

Charles Monia wrote:
<snip....snip>
> 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:
> 

Any time you get ANY retransmissions in TCP you will create a
"head-of-line"
blocking scenario. This does not matter if it is from flow control as
you state or network congestion where a packet is dropped by a router.
You will have situations where the TCP is holding data waiting for the
retransmissions of an earlier packet... this is one of the reasons
that sigtran developed SCTP...


> 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

-- 
Randall R. Stewart
randall@stewart.chicago.il.us or rrs@cisco.com
815-342-5222 (cell) 815-477-2127 (work)