Subject: RE: [rddp] Let's discuss markers

From: "Williams, Jim" <[email-masked]>
Date: Tue, 3 Dec 2002 13:26:31 -0500

This was discussed for iSCSI.

See the following:
   http://www.pdl.cmu.edu/mailinglists/ips/mail/msg02410.html

Looks like modifying TCP was off the table at that point.
If proposed TCP modifications can now be considered, perhaps
this is worth a second look.

I don't fully recall, but I think there may have been other
reasons this was rejected around potential non-interoperability.
I can't reconstruct this argument, however.

> -----Original Message-----
> From: David Borman [mailto:[email-masked]]
> Sent: Tuesday, December 03, 2002 11:45 AM
> To: [email-masked]; [email-masked]
> Subject: Re: [rddp] Let's discuss markers
> 
> 
> Hi,
> 
> I've been thinking about the marker issue with TCP.  My understanding
> of the issue is that it boils down to this question:
> 
> 	If there is a hole in the TCP packet stream, is it possible
> 	to identify later DDP headers in the stream so that their
> 	data may be placed into the correct ULP buffers rather than
> 	forcing the NIC to buffer up the data, waiting for the missing
> 	TCP packet?
> 
> [...]  TCP already has a mechanism for identifying interesting
> points in the data stream, called the Urgent Pointer.
> 
> [...]
> 
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---

From: "Somesh Gupta" <[email-masked]>
Date: Tue, 3 Dec 2002 10:46:47 -0800

If you look at the urgent pointer related portions of RFC 793
(and if I recall correctly), the sender and reciever are required
to manage only one "urgent pointer variable". This means that
urgent pointers work as indicated by the user only when TCP can
keep sending data - and breaks down when the window is not open
or retransmission occurs. The window may not be open for many
reasons including slow start, congestion avoidance or other end
not acking. The behavior of middle boxes could be unpredictable
(BTW does anyone have an example of a resegmenting middle box - is
a proxy server considered one?).

BTW, some people have indicated that PSH flag could be used for
creating aligned segments. I believe that some 
implementations do not follow this when window is closed or
on retransmission.

Somesh

> From: [email-masked] [mailto:[email-masked]]On Behalf Of
> Williams, Jim
> Sent: Tuesday, December 03, 2002 10:27 AM
> To: 'David Borman'; [email-masked]; [email-masked]
> Subject: RE: [rddp] Let's discuss markers
> 
>