Re: ISCSI: Urgent Flag requirement violates TCP.

[Silvano Gai <sgai@cisco.com>]

At 11:47 AM 11/13/2000 -0800, Matt Wakeley wrote:
>Silvano Gai wrote:
>
>> At 04:28 PM 11/7/2000 -0800, Matt Wakeley wrote:
>>
>> ...
>>
>> >For example, if the following iSCSI messages are sent:
>> >
>> >Command A sent to target  ->
>> >Command B sent to target  ->
>> ><- target sends data/status for command A
>> ><- target sends data/status for command B
>>
>> In the previous example, if Command A and Command B are transmitted in the same segment, do you care to specify if the urgent pointer points to the first or second command?
>
>It would be great if the urgent pointer pointed to the first command.  However (current off the shelf) TCP coalescing will have the urgent pointer point to the second command.
>
>The important thing to remember is that the urgent pointer is only utilized to regain iSCSI PDU framing in the presence of dropped frames.  

I understand that "regaining iSCSI PDU framing" may be useful for iSCSI protocol analyzers (I assume protocol analyzers don't reconstruct the TCP stream across multiple packets), but I am not able to figure out how this can allow more efficient hardware implementation of iSCSI (you need anyhow to receive the bytes in order). Can you comment ?

Thanks

-- Silvano



Silvano Gai               
Cisco Systems                  Empowering the Internet Generation
170 West Tasman Drive                         Tel. (408) 527 2690
San Jose, CA, 95134-1706                      Fax. (408) 527 2690
                                                   sgai@cisco.com