Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: Hari


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

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,


Roy Bynum wrote:

> Rich,
> I am confused here.  Is Hari being proposed as a PHY for the LAN compatible PHY of
> 10GbE?  I have recognized that Hari only needs the WWDM optical interface to be a 4
> wavelength parallel short reach PHY.  When it was first presented, the way that it
> was presented reminded me of a "solution looking for a problem".  It certainly looks
> like there are a lot of people have been working on this for some time.  All of the
> conversations on the reflector are starting to treat Hari as a PHY, not a device
> interconnect.  I am confused why an interconnect suitable to be a full LAN PHY would
> be proposed first as a device interconnect.  As a 500m  and less LAN PHY, I am
> neutral on Hari.  As something else, I confused by the way it was presented and have
> my doubts as to the overall impact of Hari as a device interconnect and the
> limitations that it inherently makes on the PCS/PMD relationship.
> Hari as a device interconnect requires specific functionality.  It forces the
> physical coding functionality of non parallel PHYs to exist at the PMD, not the
> PCS.  I have been told by a Hari supporter that the PCS/PMA/PMD relationship is
> purely for the standard and has little relationship to how protocols are implemented
> and devices are actually designed.  If device and protocol implementation has little
> to do with the standard, why have the standard?  If the protocol implementation is
> specific to the standard, then Hari is a PCS specific to a particular PHY and is
> exclusive of other PCS definitions for other PHY definitions.
> If Hari is a PCS, let us recognize it as such and move on with other PHY
> definitions.  If it is not a PCS then let us recognize that it will alter the nature
> of the relationships of the PHY functionalities for the non-WWDM PHYs dramatically.
> A silicon designer can best determine if the increase in complexity of the PMD is
> countered by the pin count benefits of Hari as something other than a PCS.   Hari as
> a device interconnect needs to be removed from the table.  Hari as a PCS, with minor
> modifications can be evaluated as such.
> Thank you,
> Roy Bynum
> Rich Taborek wrote:
> > The purpose of this note is to clear up confusion regarding Hari, a
> > proposed 4-lane serial interface for 10 GbE and train-up sequences.
> >
> > It should be clear that NO TRAINING SEQUENCES are proposed for Hari.
> > Both the "Hari Coding Objectives" presentation
> > (
> > and "Word Striping on Multiple Serial Lanes"
> >
> > make a point of noting that no train-up is required Hari to deskew.
> >
> > The Hari Coding Objectives proposal uses the standard Idle sequence
> > proposed by Howard Frazier of Cisco to deskew multiple parallel lanes
> > while simultaneously acquiring code-group synchronization on all lanes.


Richard Taborek Sr.   1441 Walnut Dr.   Campbell, CA 95008 USA
Tel: 408-370-9233     Cell: 408-832-3957     Fax: 408-374-3645
Email: rtaborek@xxxxxxxxxxxxx