Subject: [Tsvwg] RE: [rdma] a proposal for a different No-Data-Touch framer for TC P

From: "THALER,PAT (A-Roseville,ex1)" <[email-masked]>
Date: Thu, 14 Feb 2002 17:13:09 -0700

Jim,

I don't understand what you are suggesting. It seems like an "aligning FIM"
approach could only work for a ULP that had fixed length PDUs - which would
make it a pretty narrow solution. If the PDUs aren't fixed length, then the
markers which are at fixed intervals won't necessarily fall into the same
PDU as the aligned packets so it doesn't ensure ability to place the aligned
packet right after a packet drop. Therefore, it isn't clear tha anything is
gained by alignment.

Or do you just mean that FIM and one of the PDU alignment schemes can be
applied to the same stream so that FIM can be used if resegmentation
destroys the alignment? That would be possible, but it is kind of a belt and
suspenders approach. 

Regards,
Pat

-----Original Message-----
From: WENDT,JIM (HP-Roseville,ex1) [mailto:[email-masked]]
Sent: Wednesday, February 13, 2002 11:16 AM
To: 'Stephen Bailey'; Julian Satran
Cc: [email-masked]; [email-masked]
Subject: RE: [rdma] a proposal for a different No-Data-Touch framer for
TC P

> I see it clearly.  However, this seems to be a case where we can't
> have everything.  If we want to touch the data we can have a
> synchronization technique which can also be used to determine PDU
> alignment (COWS).  If we don't want to touch the data, we can have PDU
> alignment (TUF or NDT) OR synchronization (FIM), but not both.

Not to muddy the waters, but isn't an "aligning FIM" possible
(not that anyone would want to do it), where ULP PDUs (possibly
chunked) are aligned into TCP segments allowing direct placement
of each TCP segment payload, and with FIM to allow location of
subsequent ULP PDUs after a packet drop?

Jim

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---

From: Stephen Bailey <[email-masked]>
Date: Fri, 15 Feb 2002 14:31:18 -0500

Pat,

> I don't understand what you are suggesting.

Actually, it seems you do understand what he's suggesting, but are not
buying it :^)

The way I'd define it, it's not that the ULP PDUs are fixed length,
but that the framing protocol may add padding within a finite
interval.  For best transport efficiency, you would need to do what
TUF calls `ULPDU packing'.  You may end up with more than one ULPDU
per finite interval.

It actually seems like it might be a pretty good scheme.  Your finite
interval would be EMSS, and the segmentation algorithm would be
similar to the current TUF except to get markers at the beginning of
segments.

This might be a new leading candidate.  It's no touch and completely
safe.  The cost is that you must either do ULPDU packing (the
unpacking is actually the burdensome part, but I personally never
thought it was too horrible), or live with inefficient transport of
small messages.  For bulk data protocols (e.g. storage) the
overwhelming majority of the data you carry is in large
(interval-sized) PDUs, so a small loss of transport efficiency for the
control PDUs won't hurt.

Alright, you've done it again Jim!  By muddying the waters we clarify
them :-?

Steph

---

From: Stephen Bailey <[email-masked]>
Date: Fri, 15 Feb 2002 20:07:05 -0500

> make it a pretty narrow solution.

The other thing about aligning FIM is that if the ULP is capable of
padding its PDUs, you don't actually need a marker in the stream at
all.  I'm not sure that's a useful property, but it's cute.  You know
for sure that a ULPDU begins every finite interval.

Steph