Subject: [PWE3] PWE3 Fiber Channel draft

From: Stewart Bryant <[email-masked]>
Date: Fri, 07 Nov 2008 15:00:24 +0000

The PWE3 chairs have reviewed the Fiber Channel draft:

Encapsulation Methods for Transport of Fiber Channel frames
Over MPLS Networks
 
http://tools.ietf.org/html/draft-ietf-pwe3-fc-encap-08
 
and have spent a long time thinking about how this fits in
with the overall PWE3 architecture.
 
It is our view that the work really describes two components:
a reliable, congestion aware FC specific transport, which is
then carried over a conventional PW. The PW signaling
protocol is used to provide a number of parameters to the
transport function.
 
We think that it would be better if the draft was split into
two components to reflect this.
 
One draft should describe the transport protocol and the
rational for developing it. This element of the protocol
should be seen as residing in the NSP.
 
The other draft should describe the PW for carrying that
transport protocol and the signaling extensions needed to
support it. This would be a regular PW.
 
We feel that this partitioning of the work would underline
the concept of a PW as being a relatively simple stateless
switching function and would be more consistent with the
multi-segment model.
 
This restructuring means no change to the on the wire protocol.   

We have discussed the above with the authors and with
David Black and they have  agreed to do this split.

One concern that we have is with the use of LDP to signal the
congestion state and request a shutdown.

Although FC is expected to be used in relatively low density
applications, there is nothing to prevent high density
implementations being built and in any case we do not want to
set a precedent for newer PW types. We therefore think that
work needs to be done to limit the number of PWs within an
LDP session simultaneously requesting shutdown, perhaps by a
restriction on the density or perhaps by introducing a group
shutdown request. That is we should apply the PWE3 group ID
concept to this type of PW.

Finally as a WG we need to consider the tradeoffs that apply when
an NSP wishes to take advantage of the PW signaling
mechanism. Matthew and I propose to write a draft describing
the use of PW signaling by the NSP, what constraints apply etc.

Regards  

Stewart & Matthew

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