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[802.3af] Register proposals for IEEE 802.3af


At the July IEEE P802 Plenary I volunteered to produce a set of register and MIB
definitions for IEEE P802.3af. I have now produced two submission in response to
this which can be found on the IEEE P802.3af documents area on the web site. The
first proposal is an update to the 802.3 MIB, Clause 30, this can be found at
the URL -
The second proposal is a set of register definitions that would be placed in
Clause 33, this can be found at the URL - As the basis
of this work I used the IETF Power Ethernet (DTE Power via MDI) MIB and the
notes from the Management ad-hoc meeting held 8th January at the IEEE P802.3af
January Interim meeting in Irvine, CA. These notes can be found at the URL -

One choice I had to make in producing these proposals related to which register
space to use, either the 10/100/1000Mb/s Clause 22 register space or the 10Gb/s
Clause 45 register space. As you will see in the submission I have chosen the
Clause 22 register space, the reasons for this I have covered below. I would
however point out it would be a simple editorial task to change the register
space used to Clause 45 if desired.

Please considers these two submissions work in progress. As I first want to
gauge reaction to their content, I have provided the main body of the text, the
IEEE 802.3 Clause 30 MIB and the register definition. If these submissions don't
produced significant adverse reaction I will then produce the updates to Annex
30A & 30B and a set of updates to Clause 22 to reflect the use of two currently
reserved registers by Clause 33. I will then formally submit this as a comment
on draft 1.2 for consideration by the Task Force during comment resolution.

   David Law

Clause 22 vs Clause 45 registers

The following summarizes some of the positive and negative features of the two
registers spaces that I could think of. I am sure there are others and I would
welcome comments from others.

Clause 22

+ The same MDC/MDIO specification as existing 10/100/1000 PHYs.
+ Ease of eventual integration of PSE/PD and PHY registers is to one device.
- If the device containing the PD/PSE function is not part of the PHY, using the
Clause 22 register space could become a pain as Clause 22 only provides one set
of registers per port. Some form of shadowing may be required where some
registers are returned from one device and others are returned for the PD/PSE

Clause 45

- New electrical specification (1.2V vs 3.3/5V for Clause 22).
+ Supports the concept of MDIO Manageable Device (MMD). This provides support
for multiple devices for a single port.
+ Has provision for mixing Clause 45 and Clause 22 register access on the same
- An existing MDC/MDIO Bus Master may not be able to support the new Clause 45
start of frame (ST) encoding of 00.

On reviewing the above I decided to produce the proposal using Clause 22
registers. The reason for this is to provide the ability to integrate the PD/PSE
registers within 10/100/1000 PHYs and be able to connect these PHY to a existing
Clause 22 MDC/MDIO Bus Master.