RE: Concensus Call on Urgent Pointer.

["GUPTA,SOMESH (HP-Cupertino,ex1)" <somesh_gupta@hp.com>]

One possible alternative that has not been discussed (might have been
discussed in the old design team) is ensuring alignment of iSCSI header
at fixed intervals (the intervals could be fixed by spec or negotiated
in each direction at login time) - i.e. an iSCSI header appears every
mod n = 0 bytes in the TCP byte stream. Multiple iSCSI PDUs will appear
in an interval, but the last one will be followed by pad bytes.

This has 2 implications - one is that the largest iSCSI data PDU must be
less than the negotiated interval. Second there is some wasted bandwidth
- the percentage is probably inversely proportional to the length of
the interval.

This is nowhere near as efficient as tightly coupled iSCSI/TCP
implementations
either sending out iSCSI headers aligned at TCP segment boundaries or
using URG pointer in a particular way. However, it does enable
recovery of sync (except for the pathological case). If the connections
have negligible loss/out-of-order delivery, or if the implementation has lot
of buffer memory (host stacks or some other offload implementations) then a
very very large interval can be negotiated. If the connections are in a
lossy environment (or where the tolerance for packet loss is low), 
a smaller interval can be negotiated (probably causing even more loss
in an already poor environment). 

> -----Original Message-----
> From: HAAGENS,RANDY (HP-Roseville,ex1) [mailto:randy_haagens@hp.com]
> Sent: Friday, November 17, 2000 4:06 PM
> To: 'Dick Gahan'; Daniel Smith
> Cc: ips@ece.cmu.edu; Matt Wakeley (E-mail)
> Subject: RE: Concensus Call on Urgent Pointer.
> 
> 
> I disagree with making a solution to the framing problem optional.
> 
> The framing problem is real.  Without a solution to it, iSCSI 
> will fail.
> Failure is not an option.
> 
> Those who doubt the importance of finding a solution to the 
> framing problem
> should argue that point directly, without trying to negate proposed
> solutions by making them optional.
> 
> Those who accept the framing problem, but disagree with the 
> urgent pointer
> mechanism as a solution, can contribute constructively by (a) 
> exhibiting an
> alternative solution; (b) fully explaining their reservations 
> about use of
> the urgent pointer mechanism.
> 
> I myself am not yet convinced that the urgent pointer 
> mechanism is a viable
> solution to the framing problem.  But I do applaud Matt's 
> attempts to find a
> solution.
> 
> R
> 
> Randy Haagens
> Director, Networked Storage Architecture
> Storage Organization
> Hewlett-Packard Co.
> e-mail: Randy_Haagens@hp.com
> tel: +1 916 785 4578
> fax: +1 916 785 0391
> 
> 
> -----Original Message-----
> From: Dick Gahan [mailto:Dick_Gahan@eur.3com.com]
> Sent: Friday, November 17, 2000 10:14 AM
> To: Daniel Smith
> Cc: ips@ece.cmu.edu
> Subject: Re: Concensus Call on Urgent Pointer.
> 
> 
> 
> 
> I agree with Daniel smiths wording.
> 
> >"During login, if the target reqests use of the Urgent 
> Pointer (UP) then
> >.this should be taken as meaning that the target will operate more
> >efficiently when the UP is used.  The initiator should make 
> an effort to
> use
> >the UP.  If it is unable (or unwilling, because of user 
> intervention*) to
> >use the UP then it must indicate its non-compliance to the target."
> 
> 
> Neither the target or the initiator must support it but 
> either or both can
> request it.
> The requested party does not have to support it to be complient.
> 
> Dick Gahan
> 3com
> 
> 
> 
> I apologize for the advertizing in my last memo - some MIS people have
> enabled
> this and I havn't had time
> to turn it off.
> 
> Dick
> 
> 
> 
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>