Re: Why not have both?
I concur with Howard's proposal in using a bridge in the model to high-light the
differences between the LAN and the WAN operating characteristics. The model in
and of itself doesn't require the bridge in the real implementation. However,
given our experience with GE buffered repeater, I don't see the market picking
up the 10GE buffered repeater either. If anything, it may even be a L3 switch
at the edge of the LAN/WAN.
"Henry Ngai" <hngai@xxxxxxxxxxxx> on 09/09/99 10:59:16 AM
Sent by: "Henry Ngai" <hngai@xxxxxxxxxxxx>
cc: (Peter Wang/HQ/3Com)
Subject: Re: Why not have both?
I believe you are right in shooting for two different PHYs. However, I do
not think bridge is a good way to join the two MACs and PHY together. Unless
we impose the implementation of a bridge with all its overhead on the WAN
link. A better approach to explain the simplicity of such a device may be a
As a buffering repeater, there is no need to worry about how STA works in
this environment, nor is there need for bridge MIBs.
Rate differences, in case of over 95% utilization at the 10G side of the
network, can be handled by XOFF protocols.
----- Original Message -----
From: Howard Frazier <hfrazier@xxxxxxxxx>
Sent: Wednesday, September 08, 1999 5:51 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.
> Howard Frazier
> Cisco Systems, Inc.