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Re: Clock Tolerance and the WAN PHY


What you are actually referring to is Ethernet over SONET/SDH.  I will be 
attending ITU-T SG7 next week and participating in the approval process of 
x.86, a version of Ethernet over SDH.  T1X1 is also looking at 
standardizing a version of Ethernet over SONET.  I attempted to get 802.3 
interested in participating in these, but they did not seem to recognize 
what was happening.  These standards will allow Ethernet data switches to 
connect to the simple point to point SONET and SDH transmission 
infrastructure with very low equipment costs.  It will also allow small and 
medium size IT organizations to build long distance extended LAN networks 
instead of WAN networks that need expensive WAN protocol support.  The 
10GbE WAN PHY will allow larger companies to do the same thing.  The whole 
landscape of long distance data networking is changing.

One of the major miss-conceptions regarding the WAN PHY and EoS is the that 
EoS is required for optical sub-rate bandwidths that will be TDM 
multiplexed by the service provider.  The WAN PHY is designed for full 
optical services that are not TDM multiplexed by the service provider.  A 
lot of the overhead bytes that are not implemented in the WAN PHY have to 
do with active TDM multiplexing network elements.  The tighter clock 
tolerance, even in the OTN is a function of attempt to maintain the same 
old multiplexing nature of SONET and SDH, instead of the just the 
operational management of the optical services.  The vendors that are 
pushing for the tighter clock tolerance in the OTN at the ITU have a vested 
interest in wanting to be able to multiplex a very expensive "digital 
wrapper" around the customer's optical signal.  At present, there are so 
many options for the digital wrapper that none of the different vendors 
wrappers are fully interoperable.  Personally, I don't believe that the OTN 
"digital wrapper" solution will make it in the market long term.

Thank you,
Roy Bynum

At 08:59 AM 1/24/01 -0500, Steve  Augusta wrote:
>Assume that a router had a WAN PHY which provided all of the SONET
>bytes (not just the subset being utilized by 802.3ae) and automatic protection
>switching.  Why could this router not be utilized as part of the core
>Steve Augusta
>Roy Bynum wrote:
> > Boaz,
> >
> > There are two major miss-conceptions about POS.  The first is that it
> > directly connects to SONET transmission systems.  It does not.  POS
> > interfaces to customer facing, reduced function SONET facilities.  The
> > primary function that causes the most problem with SONET systems, and
> > requires a change in service provisioning methodologies has to do with
> > protection switching.  Standard SONET has it, POS interfaces invariably do
> > not.  The second is that IETF creates globally standards.  Because of the
> > way that the IETF standard was written, many of the POS interfaces that
> > work well with SONET do not work well with SDH because of overhead byte
> > usage incompatibility.
> >
> > I was involved with the development of POS several years ago.  Almost all
> > of us within the transmission industry thought that we could make a router
> > part of the transmission network.  We were wrong.  A router is data
> > equipment, not transmission equipment.  The level within the OSI stack that
> > routers operate at is two layers above SONET.  There is almost a total
> > disconnect between the operation of the router, as a router, and SONET
> > transmission systems.  The attempt to make a router be part of the
> > transmission system is perhaps one of the reasons that POS interfaces are
> > so expensive, per megabit, compared to GbE.
> >
> > One of the reasons that I have been pushing 10GbE WAN PHY to not be full
> > SONET compliant is to prevent network implementers from falling into the
> > same trap, that an Ethernet data switch could be an active part of the
> > transmission network.  Other reasons are that by reducing the management
> > overhead bytes to a minimum, a set that is common between SONET, SDH, and
> > SDHJ could be provided, making 10GbE fully interoperable, as a passive
> > managed element to all of the transmission systems in the world. Another
> > reason for the Ethernet WAN PHY is reduced cost.  The less complex
> > management overhead, compared to POS, gives Ethernet an additional
> > opportunity to come in a greatly reduced cost, compared to POS.
> >
> > I hope that this helps you understand why 10GbE WAN PHY will be used in
> > place of POS.  In addition, I wonder how many people have recognized that
> > the ability to use the Ethernet tag and queuing functionality is similar to
> > what MPLS is advertised to be going to do.  This is a customer
> > implementation issue, but I would speculate that a lot of customer are
> > looking very hard at this as well.
> >
> > Thank you,
> > Roy Bynum
> >
> >