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Re: Long distance links


In your Montreal presentation
page 5, you show a transponder performing a bridge function between a DWDM
photonic network and a L2/L3 WAN access switch. I have a couple of comments
about this implementation:

1) It seems that you require a very specific SONET WAN PHY on both the Ethernet
side of the Transponder and WAN side of the L2/L3 access switch. Specifically,
you require that the Ethernet frames be scrambled NRZ, that the MAC/PLS rate of
at least the switch is 9.58464 Gbps, and that no special symbols be used.
Essentially, your requirement is that the "Ethernet" link PHY is the same as
SONET OC-192. Is this not exactly true? If not, please point our my

2) I'll even go along with you if your answer above is "Yes, IEEE 9.58464 GiGE
is really OC-192". As a matter of fact, I'll support it in committee as an
alternative 10 GbE PHY option, call it the "WX" family of PHY's (could be
different wavelengths). However, this PHY is ill suited for the LAN environment
and forces every demarcation point between "old Ethernet" and "new SONENET" to
do protocol conversion.
Besides the OC-192 PHY not being cost effective in the LAN for reasons I've
belabored in previous notes to this reflector, an additional cost which cannot
be ignored is the cost/performance penalty assessed by forced protocol
conversion in ALL LAN environments including LAN environments with no WAN
access requirements. Am I wrong about this protocol conversion requirement?

3) It seems to me that your presentation portrays one of many possible
implementations of 10 GbE use in the WAN. The complete set includes WANs which
do and do not utilize DWDM technology. By your own words you indicate that DWDM
equipment may be code dependent (i.e. proprietary). It seems very reasonable
then to shield 10 GbE from the special purpose, high cost and proprietary
interfaces such as DWDM. Please help enlighten me as to how standardizing a
non-standard WAN PHY as 10 GbE helps Ethernet customers in general?

4) As far as implementations go, one possible implementation would be to feed
10 GbE at 10.0 Gbps directly into the DWDM photonic network. Since DWDM is
still relatively in its infancy, I foresee more direct WAN implementation which
may benefit from some of the more cost effective PHYs already proposed for 10
GbE, especially if common interfaces are developed for these PHYs. The use of
these PHYs would enable perhaps the most cost effective implementations of
metro and wide area DWDM networks which can STILL tie into the existing WAN
infrastructure via routing or bridging. It's not much of a stretch to envision
WAN access routers with DWDM interfaces on the WAN side and 10 GbE interfaces
on the LAN side. Is this latter implementation impossible? I think not. What is
the signaling protocol on the DWDM side in this case? The point here is that I
view your DWDM photonic network as only one possible implementation of a DWDM
photonic network. Please don't encumber the rest of the Ethernet community with
implementation specific and special requirements.

I have to apologize for being so harsh in my trying to the bottom of this
issue. But I believe that my strategy in doing so sooner rather than later will
prove to be beneficial. Please also don't take the issues personally. I'm
trying very hard to stick to the issues.

Best Regards,


Paul Bottorff wrote:

> Dan:
> I also think we are getting closer to understanding. A few comments.
> Cheers,
> Paul
> At 05:49 PM 9/1/99 -0600, DOVE,DANIEL J (HP-Roseville,ex1) wrote:
> >
> >Paul,
> >
> >While we may not be coming closer to agreement (or maybe we are?) I
> >believe we are at least coming closer to understanding.
> >
> >More in context below...
> >
> >> >So if I understand this model, we have a 10Gig link (campus backbone)
> >> >that is connected to a campus switch. That switch wants to connect to
> >> >a WAN and thus will have a WAN port that operates at 9.58464 by using
> >> >its XGMII "hold" signal.
> >>
> >> Provided people built networks to this configuration, then it
> >> works just
> >> fine.
> >> The IEEE has not yet decided to build 2 PHYs. I believe that
> >> the WAN PHY
> >> being talked about does not have a distinct identity from the LAN PHY.
> >
> >This is one point at which we clearly have different perspectives. I
> >believe that there will be sufficient distinction in cost between a
> >DWDM laser for the WAN, and a (WWDM or serial) solution that is
> >limited to a few Km for the campus. Otherwise, why do we need an XGMII?
> I agree that a PHY which included a DWDM laser would have a distinct
> identity. However, I don't believe this interface is the current topic of
> standardization. How I see the system being built is that the DWDM network
> will be terminated in a shelf which provides 10 GigE access ports. On one
> side of the shelf will be IEEE standard 10 GigE on the other side of the
> shelf will be a DWDM photonic network. The device in the middle at the
> demarcation point will be a transponder/repeater. For a router to access
> the photonic network it will attach a 10 GigE interface to the photonic
> network access port.
> A typical 10 GigE WAN link which attaches to a photonic network would be
> built using 3 or more link segments. If you refer to my slides from
> Montreal the 5th slide provides a picture of such a network. The link
> segments which attach from the router to the photonic network need to
> provide the 9.584640 data rate since this is all the data the photonic
> network can carry due to historic reasons. The PHYs in the router do not
> have DWDM photonics.
> >
> >> Because I don't have a good criteria for distinct identity
> >> I've found no
> >> reason to believe the committee should build 2 PHYs. My
> >> assumption is that
> >> any PHY developed may run on SMF and may be deployed in the
> >> wide area. This
> >> is what is currently happening with 1 GigE.
> >
> >Actually, there is LX, SX, CX and 1000BASE-T not to mention a few
> >proprietary links for long-haul 1550nm. There is no reason not to
> >believe that 10G will follow the paradigm that allows multiple
> >PHYs for multiple cost/performance domains.
> Access to the photonic network described above can (and will in some cases)
> be less than 100 meters. It may use 850, 900, 1300, for 1550 nm lasers. It
> may be serial or CWDM. Finally it may have a different encode that the DWDM
> network (though I dislike this).
> >
> >> >
> >> >I agree that THAT switch will require buffering to handle the rate
> >> >mismatch, but that would be required in the event that it has more
> >> >than 10 Gigabit links feeding it anyway. This is OK.
> >>
> >> In the configuration I described it is the buffer at a
> >> transponder/repeater
> >> located at the junction between the IEEE segment and the DWDM
> >> segment which
> >> requires buffering to rate match. At this juncture there are only two
> >> ports. One side is the IEEE 10.00 Gbps and the other side is
> >> the 9.9584640
> >> Gbps DWDM cloud. The buffer size covers only the rate mismatch not the
> >> normal overload seen in packet switches. The photonic network
> >> appears as a
> >> new segment in the link between switches, not as a separate link.
> >
> >This looks like a specific implementation restriction. I doubt that
> >I would implement it that way.
> >
> >Regards,
> >
> >Dan Dove
> >
> >
> Paul A. Bottorff, Director Switching Architecture
> Enterprise Solutions Technology Center
> Nortel Networks, Inc.
> 4401 Great America Parkway
> Santa Clara, CA 95052-8185
> Tel: 408 495 3365 Fax: 408 495 1299 ESN: 265 3365
> email: pbottorf@xxxxxxxxxxxxxxxxxx

Richard Taborek Sr.    Tel: 650 210 8800 x101 or 408 370 9233
Principal Architect         Fax: 650 940 1898 or 408 374 3645
Transcendata, Inc.           Email: rtaborek@xxxxxxxxxxxxxxxx
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Palo Alto, CA 94303-4305    Alt email: rtaborek@xxxxxxxxxxxxx