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Re: Hari


Multiple proposals aired in Kauai and I have already explained that Hari is simply a "better" interface for attaching a MAC/PCS/PMA to a PMD. As Dan Dove of HP has explained, Hari would at most be an optional interface as was the case with both the TBI (closest Hari equivalent in GbE) and GbE's GMII. Hari is a serial-based interface, and as such requires a transmission code. 8B/10B was deemed to be the best choice for Hari. That's it! I encourage you to propose a better interface than Hari for its intended purpose or a better transmission code for Hari. In the absence of either, I saw an awful lot of support for Hari in Kauai and will continue to do my best to improve upon the current proposal.

Roy Bynum wrote:


I'm not sure what gave you the idea that Hari was favorable to serial PHYs.  I do know that
it is not favorable to anything other than the legacy fiber channel 8B10B LAN PHY.  Hari is
NOT a PHY neutral device interconnect.  Some LAN vendors have very huge boards and they want
something that will support their 8B10B encoding over the distance of their board, and also
the back plane if needed.  By introducing Hari as the standard for device interconnect
between the PMA and the PMD,  they are specifically, and possibly knowingly,  hampering the
development of the agreed on WAN PHY.  There is no mechanism for rate controlling over
Hari.  This is in violation of the agreed objective in this regard.  Hari is an attempt by a
specific camp to control the development of 10GbE and limit development of anything other
than the 10.0 only rate PHY.

On the rate control issue: 8B/10B encoding, with it's special code-group support provides a means to support a myriad of out-of-band functions such as rate control. In fact, the Insert/Remove protocol proposed for Hari provides one very simple rate control signaling method. I encourage you and other WAN PHY proponents to take a good look at the Kauai Hari presentation material.
As you will remember, I called the presenters and floor on the issue of what Hari really
was.  It was admitted that it was a LAN extension interconnect by the individual that
responded.  For those of us that are attempting to bring 802.3 into the 20th century by
making a truly ubiquitous MAC, we have been astounded by the brazen push of this
"interconnect".   Chip makers will confirm that Hari specifically makes the WAN PHY
extremely difficult to implement.  Since Hari truly is not common to all of the PHYs as
specified in the objectives, I suggest that it be withdrawn from consideration as part of
the 10GbE standard.
Once again, I've pointed out that LAN Serial PMDs including binary and multi-level signaling benefit from stripping off 8B/10B code and recoding the serial stream with a considerably different transmission code. Henning Lysdal of Giga did a great job illustrating  in his Kauai presentation entitled: "Serial LAN PMD Architecture Options" The WAN PHY can do the same if it chooses to use the optional Hari interface. If you don't like this optional interface, please suggest an alternate optional interface for the WAN PHY.

Best regards,


Thank you,
Roy Bynum

Rich Taborek wrote:

> Roy,
> I thought that Hari was clearly presented in at least half a dozen presentations by at
> least the same number of presenters who all explained it in the same way in Kauai. I'll
> try one more time here.
> Hari is the same as the Serial interface of the 10 GMII as presented to the HSSG by
> Howard Frazier of Cisco in Montreal, York and Kauai. A group of Ethernet, Fibre Channel,
> InfiniBand and even OIF folks have gotten together over the past several months to try
> and arrive at a common interface for passing 10 Gbps of data continuously in each
> direction between a PCS/PMA element (which may be integrated with the MAC and the PMD
> (i.e. transceiver module).
> Note that a typical Ethernet PHY, like 1000BASE-X contains the PCS, PMA and PMD
> sublayers. Hari is NOT a PHY nor is it a PHY sublayer. Hari is an interface between
> sublayers and is very similar in nature to the Ten-Bit Interface (TBI) of 1000BASE-X,
> which is fully described in Clause 36 of that standard.
> Hari has nothing at all to do with WWDM although it clearly may be used to attach a WWDM
> PMD to its MAC/PCS/PMA.
> Hari may be used to attach a Parallel Optical PMD to its MAC/PCS/PMA in much the same
> fashion as for WWDM
> Hari usage to attach a MAS PMD to its MAC/PCS/PMA has been described in all my MAS
> proposals to the HSSG including the latest update presented in Kauai:
> Hari usage to attach a Serial PMD to its MAC/PCS/PMA along with a proposed coding to
> maintain a line rate of ~10 Gbaud has been described in the Kauai proposal by Rick
> Walker and Richard Dugan of Agilent:
> Therefore, Hari provides a common interface for all major classes of PMDs proposed to
> the HSSG to date in addition to being strongly considered as a common interface for
> other ~10 Gbps standard and industry interfaces.
> The principal strengths of Hari are:
> 1) Low pin count
> 2) Self-timed (doesn't need a clock with data)
> 3) Supports reasonable distances over inexpensive medium (e.g. 20" of FR4 traces)
> 4) Good synergy with traditional Ethernet MAC/PHY framing
> 5) Sufficient robustness to not compromise a 10E-12 link BER
> 8B/10B encoding has been proposed for Hari since it has been proven time and time again
> in multiple forums that 8B/10B is a very robust serial link transmission code. However,
> Hari is not a PCS and an alternate code could have been proposed for Hari. I consider
> the Hari usage of 8B/10B to be analogous to a parity bit for a traditional parallel
> interface. The "parity bit" can be generated at the source and discarded after checking
> at the destination. The MAS and Serial PMD proposals referenced above use Hari in
> exactly this fashion and result in the lower line rate possible for those respective
> interfaces when compared to a PMD coding which would carry forward the 8B/10B overhead.
> Hari is being proposed for inclusion into the 802.3ae standard as an interface as
> described above. However, Hari does not dictate the encoding of data transported over
> the Medium. Hari simply enables the transport of that data over the medium in a manner
> commensurate with the 5 criteria of 802.3ae.
> As such, I would also recommend that Hari be considered for the WAN PHY.
> Best regards,
> Rich


Richard Taborek Sr.   1441 Walnut Dr.   Campbell, CA 95008 USA
Tel: 408-330-0488 or 408-370-9233           Cell: 408-832-3957
Email: rtaborek@xxxxxxxxxx or rtaborek@xxxxxxxxxxxxx