Re: Min PDU that can come in a TCP packet.

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

Paul,

It looks to me like the message:

 >> Is there a possibility that just one
byte of an ISCSI PDU can
 >> come in an ISCSI packet?

asks about iSCSI PDUs and in
theory even those can have a 1 byte useful payload but must be padded

Julo

Paul Koning <pkoning@equallogic.com>

24/01/03 18:07

To	Julian Satran/Haifa/IBM@IBMIL
cc	pverma@marantinetworks.com, ips@ece.cmu.edu, owner-ips@ece.cmu.edu
Subject	Re: Min PDU that can come in a TCP packet.

>>>>> "Julian" == Julian
Satran <Julian_Satran@il.ibm.com> writes:

 Julian> yes but it will have to be padded to 4.

True, but the question wasn't "how small can an iSCSI PDU be"
but
rather "can a (possibly large) iSCSI PDU come across in one byte TCP
segments".  

The answer is clearly yes -- TCP is a stream protocol, not a packet
protocol (unfortunately).  There is no required relationship between
TCP segment boundaries and application layer PDU boundaries.  An
application layer PDU may come across as one TCP segment; you may have
multiple application PDUs in one TCP segment; application PDUs may
cross TCP segment boundaries; or an application PDU may come across in
multiple TCP segments, theoretically in units as small as one byte per
TCP segment.

In practice I would assume that sensible implementers will not, or not
often, do some of the more extreme things permitted by TCP, but if you
want a reliabile implementation, you have to permit all sorts of
strange things.

                
paul

 >> Is there a possibility that just one byte of an ISCSI PDU can
 >> come in an ISCSI packet?

 >> Preetam Verma