RE: Hari
Hi Rich,
Actually, I have to disagree with your relation of HARI to the TBI.
I believe that the un-specified SERDES interface is a more appropriate
model as it is;
a) Differential
b) High Speed
c) Asynchronous (ie: Clocks are derived rather than sent discretely)
However, the industry might have gained from standardization of that
interface. If you are aware (and I am sure you are) there are now AC
coupled and DC coupled versions of the SERDES interface that just
complicate board designs.
I support the HARI concept, although I believe that we need to work on
it a bit to understand the impact of splitting the 8B10B codes onto
separate channels will have.
As for Roy's concerns about that interface complicating things, I
believe that concern is resolved (or should be) by the fact that HARI
would at most be an optional interface.
Best Regards,
Dan Dove
PS: Have a nice Thanksgiving
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-----Original Message-----
From: Rich Taborek [mailto:rtaborek@earthlink.net]
Sent: Friday, November 19, 1999 12:47 AM
To: HSSG
Subject: Re: Hari
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:
http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/taborek_2_1199.p
df
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:
http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/walker_1_1199.pd
f
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
--
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
> >
(http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/taborek_1_1199.
pdf)
> > and "Word Striping on Multiple Serial Lanes"
> >
http://grouper.ieee.org/groups/802/3/10G_study/public/nov99/ritter_1_1199.pd
f)
> > 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@earthlink.net