FCIP QoS text

[Black_David@emc.com]

At the last meeting I promised to provide some advice about
the DSCP and QoS text in the FCIP draft.  This email is sent
in my role as one of the authors of the Diffserv header and
architecture RFCs (2474 and 2475), rather than as a WG co-chair.

Section 5.3 of the FCIP draft says:

      DSCP (6 bits): The recommended DSCP field setting is 101110
      corresponding to the EF service.

As I would recommend replacing this text
with text describing the properties of the forwarding service
that are needed/desired (e.g., high bandwidth, low delay, low
variation in delay, essentially no loss), and then citing EF as
an example of a PHB that can be used to implement such a service
(overprovisioned AF will likely also work).  An actual diffserv
service is a combination of PHB and edge traffic conditioning
(for EF to behave as intended, there has to be a bandwidth
limit on the inbound traffic at the edge of the domain).

An important thing to understand about diffserv is that it's a
toolkit.  Neither EF nor AF have to be implemented in a diffserv-
compliant network - the only required PHBs are defined/described
in RFC 2474 (Default, and the PHBs mapped to the class selectors).
The approach I'm recommending provides guidance to the user of
the toolkit about what the required result should be (e.g., tighten
that nut) rather than overspecifying the tool to be used (e.g.,
requiring a crescent wrench when a socket will also work).  The
QoS discussion in Section 9.1 should also be revised to reflect
this toolkit philosophy.

Thanks,
--David

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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
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black_david@emc.com       Mobile: +1 (978) 394-7754
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