RE: new iSCSI draft - 02.txt

["David Peterson" <dap@cisco.com>]

The problem is: at that layer there is simply not a byte stream. The data
is contained in socket buffers which are most likely mbuf clusters for most
implementations. To "simply insert a few extra bytes" requires mbuf
manipulation.
Mbuf manipulation can processing intensive. Depending on how the mbuf data
is
packaged a small DMA operation may occur for these few extra bytes also.
Dave

-----Original Message-----
From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
Matt Wakeley
Sent: Wednesday, January 03, 2001 7:21 PM
To: IPS Reflector
Subject: Re: new iSCSI draft - 02.txt


David Peterson wrote:
>
> I believe there was agreement to remove the Urgent-Pointer framing
mechanism
> but don't recall any agreement to replace it with an in-stream marker. For
a
> software implementation it would be hard to support this type of framing
> mechanism. I believe a TCP option indicating the message boundry or a
> fixed-length PDU at a granularity to minimize overhead are much better
> solutions and are workable for both software and hardware implementations.
I
> have not seen an agenda but I would hope this issue would be discussed at
> the upcoming meeting in Orlando.
> Dave

What is so difficult for software to insert a few extra bytes in the byte
stream?  It's simply a layering problem:

iSCSI layer <-> marker layer <-> TCP

Normally, the marker layer simply transfers the bytes from the iSCSI layer
to
the TCP. Every X number of bytes, the marker layer inserts the marker into
the
byte stream.

Since your software will probably not benefit from the receipt of the
markers,
it would negotiate not to receive the markers.  It would only send markers
*IF* the remote node requested them to be sent.

-Matt Wakeley
Agilent Technologies