RE: Why not have both?
I firmly believe the consensus to have both LAN/PHY and WAN/PHY is the right
direction for HSSG, which has been required by market for a while. It will
enable us to share the Internet-wealth with WAN people who are looking for
LAN people's help to further expand the market.
We have to appreciate many people in the last two months devoted so much
time on the reflector to explore all issues and gradually build up the
consensus to move to enable both LAN/PHY and WAN/PHY proposals. Not to
mention Roy's persistent effort, there were many counter views to shape the
WAN/PHY model to a realistic, cost-effective concept.
Both Howard and H.W Chin responded timely to propose
LAN/PHY-bridging-WAN/PHY model, and a detailed OC-192c PHY were greatly
appreciated by many of us, including myself.
It is the time for us to move forward to develop MAC, LAN/PHY, and WAN/PHY
specifications. I believe we can develop a common MAC/PLUS to serve both
LAN/PHY and WAN/PHY, as the example of other Ethernet MACs with a common MII
interface, or 10GMII for 10xGbE. As they were discussed on the reflector,
there are so many issues of LAN/PHY and WAN/PHY waiting for us to resolve
them to convert into specifications.
Howard's LAN MAC/PHY-BRIDGE-WAN MAC/PHY model is a great picture to ignite
rally among us to support two PHYs. It proved "a picture is worth 10 Giga
Nevertheless, it seems that interconnecting LAN MAC/PHY and WAN MAC/PHY is
the vendor implementation choices, rather than a standard issue.
As long as we are using a common MAC for both PHYs, there are many ways of
tying the I/O side of both MACs depending on the market needs. With some
kind of simple congestion control in a MAC chip, we can directly OR-TIE both
I/Os of LAN/MAC and WAN/MAC (common bus). A simple buffered repeater as
someone suggested, or one may add a peripheral controller for flow control.
Implementing level-3 switch to have much more flexibility and complexity to
achieve various data rates, addresses, frame sizes...etc. Of course, we can
go to the higher level, if we want. Furthermore, the WAN MAC/PHY does not
have to connect to a LAN MAC/PHY, instead, it can connect to other MACs;
namely, 1xGbE, 100 Ethernet ..etc. I believe, those innovative vendors will
come up with variety of conversion approaches to meet the market needs.
NetWorth Technologies, Inc.
I would like to request, in behalf of the HSSG, a presentation at the York
meeting regarding the applicability of the "Gigabit Ethernet Model (i.e.,
Hanson; Cunningham spreadsheet)" for use in our work on "ten Gig."
This model was extremely helpful to us in 1000BASE-X in discussing
Variations to the specifications and resolving issues. I expect, as with any
model, that there are certain underlying assumptions which might have to be
corrected (or at least tuned) for application in 10 Gig. At very least,
there will be new techniques needed to use it for multilevel encoding, as an
Some things to consider:
1. Use of truly single mode LW lasers (Vs multiple longitudinal; single
1.1 Compensated by adjusting K only?
1.2 Measurement of spectral width (rate of drift of "single mode" Vs
Characterization of spectra)
2. The inherent difference between rise and fall times
3. Assumptions about ISI penalty maximums for a link
4. Simultaneous support for:
4.1 Serial up to 12.5 Gig
4.2 Parallel / WDM down to ?
4.3 Support of various multi-level schemes
4.4 Channel to channel crosstalk issues
4.6 Assumptions for SMF and high performance BW MMF
5. Replacement of the E/R (per FC proposals)
6. The various recommendations made by Petar Pepeligoski (IBM)
[mailto:email@example.com]On Behalf Of Howard
Sent: Wednesday, September 08, 1999 8:52 PM
Subject: Why not have both?
>From the various statements posted to this reflector over the past
few months, it has become obvious to me that the LAN and WAN
markets have different needs when it comes to the physical layer
of a network interface. I would also say that it is apparent that
the HSSG is at an impasse. I doubt very much that either the
LAN devotees or the WAN devotees will be able to
persuade their opposite numbers to abandon their well thought out
and closely held beliefs and settle on a single Physical Layer
definition that will serve both markets.
Therefore, I encourage the HSSG to consider the development of
two distinct PHYs for 10 Gigabit Ethernet. Let's call one the
LAN PHY, and the other, the WAN PHY. Each of these specifications would be
optimized for the intended application.
As others have already stated, it is possible to build a relatively
simple, low cost, low complexity device that will bridge these
interfaces together. A layer diagram of such a device is shown in
the attached PDF file.
Referring to the diagram, on the left side, we have a cloud labled
"LAN infrastructure". This is made up of the switches, routers,
hubs, NICs, firewalls, gateways, servers, desktops, etc, etc,
that communicate via Ethernet. On the right side, we have a
cloud labled "WAN infrastructure". This is made up of the
transponders, multiplexors, regenerators, amplifiers, etc,etc,
that conform to SONET specifications.
In between these two clouds, we have a bridge. In the context
of 802.3 standards, this is an 802.1D bridge, but in practice,
it could have more or less functionality than required by 802.1D.
The primary purpose of this device is to hide all of the details
of the underlying LAN and WAN PHYs from each other. The
PHYs can use completely different signaling methods, they can
use different physical media, they can run at different rates.
They can also have different management attributes.
I assert that the cost of such a device is dominated by the cost
of the PMD (the optical components) associated with the
WAN interface. I can't throw dollar figures around, but I can
state with conviction that the sum of the costs for the LAN PMD,
the LAN PHY, the LAN MAC, the Bridge, any associated memory,
any associated microprocessor, the WAN MAC, and the WAN
PHY, and associated management, is about 1/25th of the cost
of the WAN PMD and its associated clock oscillator. That's
right. Relatively speaking, the WAN optics cost about 25 times
as much as the rest of the components in the box combined.
That tells me that such a device will definitely not be a barrier
to the use of 10 Gigabit Ethernet in the WAN, and it might even
be considered an "enabler", because it can connect to the LAN
infrastructure just about anywhere you wish. Of course, since
I am suggesting that we specify a WAN PHY as well as a LAN
PHY, it is possible to build an interface for an "Enterprise" LAN
switch that provides a WAN PHY and PMD, and maybe this
will happen. The "Two PHY" approach allows inovation and
optimization to keep pace with technology development, and
the needs of the market.
It will also let us get going in the HSSG, and put some of the
arguments behind us. To that end, I suggest that we:
1) Adopt an objective to specify a PHY optimized for LAN
2) Adopt an objective to specify a PHY optimized for WAN applications.
3) Settle the "speed" objective by stating that the MAC/PLS
interface always runs at 10.0000 Gb/s.
This speed will work with either PHY. For various reasons,
the WAN PHY will require at least a packet's worth of buffering
in each direction. If you have to have the buffer, you might
as well use it to match the 10.0000 Gb/s MAC/PLS rate to
the 9.95328 baud rate on the WAN medium.
4) Agree that a pacing mechanism of some sort can be employed
if necessary to throttle the MAC's transmit data rate down to a
rate which is compatible with the payload rate of a WAN PHY.
With a packet buffer in the PHY, this pacing mechanism can
operate on a packet by packet basis.
Note: If you were to design an integrated MAC and WAN PHY,
you could get rid of the buffer and the pacing mechanism.
5) Agree that the two PHYs need to be individually justified in
the "5 Criteria". I am not suggesting that two PHYs means two
standards projects (i.e. two PARs), but I do think that we need
to answer the 5 Criteria for both PHYs, so that the rest of the
world understands why we are doing this. I think it will be
easier to come up with words which justify the two PHYs
individually than it would be to agree to one set of words that
embraces both PHYs.
Please give this suggestion some serious thought.
Cisco Systems, Inc.