RE: iSCSI: SNACK R2T/Data

["Julian Satran" <Julian_Satran@il.ibm.com>]

Matthew,

I am also in favor of such a mechanism.  It is easy to implement (another
form of SNACK) and we have already built-in a mechanism by which an inbound
stream can be marked for acking (the inbound sequence separator F bit).
It can also be specified as mandated only if the within-command recovery
class is present.

However I am reluctant to open again this issue except if there are more
supporters. Data ACKs where hastily dropped at the interim meeting in
Orlando.  I recall Somesh Gupta, Pierre Labat and Santosh Rao as being very
vocal against them (arguing complexity) and carrying the room with them.

Julo



                                                                                              
                    "BURBRIDGE,MATTH                                                          
                    EW                     To:     Julian Satran/Haifa/IBM@IBMIL,             
                    (HP-UnitedKingdo        ips@ece.cmu.edu                                   
                    m,ex2)"                cc:                                                
                    <matthew_burbrid       Subject:     RE: iSCSI: SNACK R2T/Data             
                    ge@hp.com>                                                                
                                                                                              
                    19-09-01 17:25                                                            
                    Please respond                                                            
                    to                                                                        
                    "BURBRIDGE,MATTH                                                          
                    EW                                                                        
                    (HP-UnitedKingdo                                                          
                    m,ex2)"                                                                   
                                                                                              
                                                                                              




I am very much in favour of having a positive ACK mechanism to control
buffer resources at the target.  If there is a very large transfer (e.g. 1
Mb) then the sender can release buffer space once it knows that the
receiver
has received the data.  It is worth pointing out that this mechanism is for
buffer control and is not for flow control which, as we all know, is
handled
by TCP.

Cheers

Matthew Burbridge
Senior Development Engineer
NIS-Bristol
Hewlett Packard
Telnet: 312 7010
E-mail: matthewb@bri.hp.com




-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Wednesday, September 19, 2001 6:28 AM
To: ips@ece.cmu.edu
Subject: Re: iSCSI: SNACK R2T/Data


There is no ACK mechanism. The group wisdom was that there is no need for
one.
Incoming data and R2Ts are not acked (a mechanism that did that existed and
was based on NOP-Out).

Julo

Michael Schoberg <michael_schoberg@cnt.com> on 18-09-2001 19:09:51

Please respond to Michael Schoberg <michael_schoberg@cnt.com>

To:   "'ips@ece.cmu.edu'" <ips@ece.cmu.edu>, Julian Satran/Haifa/IBM@IBMIL
cc:
Subject:  iSCSI: SNACK R2T/Data



Old subject, but I couldn't find any discussion on this:

When does the target know it no longer needs to hold R2T & Data PDUs?
StatSN responses are acknowledged through the ExpStatSN field received in
future I->T requests.  What's the acknowledgement method for R2T & Data
PDUs?  Is it tied to the original request and acknowledged through the
ExpStatSN acknowledgment of the request's response?

Thanks.