Subject: Wedge between transport and ULP

From: Dave Crocker <[email-masked]>
Date: Wed, 3 Mar 2004 15:12:44 +0900

Folks,

Geoff mention an architectural choice that is not currently
represented by any proposals.  It places a multiaddressing wedge layer
between the transport layer and the applications layer.

Some MAST discussions explored this issue a bit, as did early BEEP
discussions.  For what they are worth, here are some observations:

The wedge fits rather nicely into that realm the OSI folks like to
call 'session layer'.  Things put at that layer tend to need to
replicate control (eg, reliability) mechanisms already done in
transport.  This will be particularly true if the layer is expected to
work across multiple transport associations.

Pekka N. noted the compelling requirement for having transport state
NOT cross machine boundaries.

This suggests that the kind of multiaddressing being discussed here
belongs no higher than the bottom of transport.

An application that wants to exists as a single logical entity, but
live across more than one machine, needs something like a
session-level multiaddressing feature.

d/
--
 Dave Crocker <dcrocker-at-brandenburg-dot-com>
 Brandenburg InternetWorking <www.brandenburg.com>
 Sunnyvale, CA  USA <tel:+1.408.246.8253>

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From: Iljitsch van Beijnum <[email-masked]>
Date: Sat, 6 Mar 2004 13:45:08 +0100

> between the transport layer and the applications layer.

We've discussed this a while ago (where you on the list yet back 
then?). I'm not sure if everyone agreed in the end, but my position was 
and is that this can't work in a sane way.

> work across multiple transport associations.

The problem is that you can't know how much data made it to the other 
end at any particular moment in time so retiring one TCP session and 
continuing over another means you have to resync. For some protocols 
(most HTTP, FTP) this can be done with relative ease, but solving the 
general case means effectively tunneling TCP over TCP, which makes no 
sense.