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RE: Does only decimal system work for data rate specification?

Your comments on fixed decimal rate is bang on.

I think the question is largely irrelevant of whether long haul 10GbE should
be clocked at SONET speeds 9.98.. or exactly 10Gbps.

We believe that data variable 10GbE is critical, particularly for CWDM
systems.  In the CWDM system we are deploying in Alberta for example the
critical limiting factor is the distance between existing repeater huts.
The last thing we want to do is build new repeater huts.  A repeater hut is
a hell lot more expensive than any optical technology.  The problem with
CWDM is that you have different attenuation and dispersion rates at
different frequencies and so with fixed clock rates the link loss budget at
the frequency with the worst attenuation and dispersion (usually around
1310) drives your network design. But with variable data rate 10Gbe we could
lower the clock rate at those frequencies to achieve the same BER.  More
importantly at frequencies that exceed the link loss budget the clock rate
could possibly be increased to 14, 16, 18 , 20 Gbps.  This is a big
advantage of CWDM over DWDM as you don't have to worry about you modulation
skirt interfering with other wavelengths or being cut off by the DWDM

I understand the problem with frequency agile PLLs, but what I had in mind
is perhaps a GBIC like PHY which we could plug into the 10Gbe card.  I
believe the proposed 10Gbe standard will have a simple flow control
mechanism to allow for variable data rates.

I keep reminding vendors that we don't feel a standard for long haul 10GbE
is that critical to us.  Long haul 10GbE will have the same problems as
SONET transport and will require both ends to be carefully matched to
optimize performance and therefore most likely will require both ends to
come from the same manufacturer.  However the interconnection to the  long
haul segment should be along the lines recently proposed by the OIF for a 12
channel  inter-equipment 10GbE.  That is very important.

For LAN based 10Gbe the problem is more complex, because you definitely want
interoperability between equipment vendors, but I think a variable rate
10Gbe would still be useful.


Bill St. Arnaud
Senior Director Network Projects
+1 613 785-0426

> -----Original Message-----
> From: owner-stds-802-3-hssg@xxxxxxxx
> [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Fenghao Mu
> Sent: December 9, 1999 3:56 AM
> To: stds-802-3-hssg@xxxxxxxx
> Cc: Fenghao Mu
> Subject: Does only decimal system work for data rate specification?
> Hello,
> I have seen some of the emails, and also missed some.
> I am a designer for a single-chip solution of gigabit Ethernet switcher.
> I was a little bit confused by this discussion group. I have the
> following
> questions:
> 1) Why we prefer to only specify 10GE rather than suggest other
> reasonable data rates related to gigabit Ethernet, say  2.5/5 gigabit
> Ethernet?
> 2) Why we need Hari coding to tie four individual links together instead
> of sending data separately?
> 3) Does our data rate specification fit with market requirement and
> technology progress well?
> I think the last question is very critical. If a specification does not
> match the market and technology progress, it will die!
> I also have the following points:
> 1. From a customer point of view, only 1GE and 10GE give less choices
> for one to build a good switching structure. He has to chose between two
> possible data rates, either 1GE or 10GE. It might be very
> difficult for him
> to upgrade his data links, in other words, 10GE is too luxurious and 1GE
> is insufficient for his requirement. What is his best solution? Perhaps
> he has to wait until the price of 10GE comes down to an acceptable value.
> This acceptable value may never come if the standard does not fit to the
> market requirement. However, if there is a 2.5/5 gigabit Ethernet
> data rate,
> he could flexibly upgrade his network according to his real requirement.
> 2. Data rate evenly distributed networks are seldom met in
> reality, and it
> exists only in people's imagination. Designing a switcher fabric based on
> this imagination will cause a big waste of resource. For data
> rate unevenly
> distributed networks, multiple data rates can give one more solutions,
> therefore a relative optimum is easy to achieve. The future 10GE switcher
> will face a serious challenge of limited I/O capacity. How to efficiently
> use
> of the I/O pads is a very important issue. If we could use
> 2.5/5/10 GE data
> rates, we can individually assign a data rate for a path in a network
> according different requirements. Multiple data rates can be very helpful
> for
> optimal I/O pad usage.
> 3. There is no reason why we only specify 10GE, which bonds 4 individual
> links together. Probably there isn't any information source or sink today
> which has to be specified at 10Gb/s. Why we have to glue 4
> individual links
> together just for making more problems in design, test, and maintain? The
> only clue is the historical reason that Ethernet had migrated
> from 10ME to
> 100ME, and from 100ME to 1GE. Does only decimal system work for data
> rate specification?
>  4. If 4 individual links at 2.5Gb/s are glued together to form a 10GE,
> we need word synchronization, as someone suggested using Hari coding.
> Transmission at 10Gb/s (or 12.5Gb/s with 8B10B coding) are more difficult
> than sending 4 links individually. From reliability point of view, an
> encapsulation of several links will greatly reduce network reliability.
> For example, if one of the link is broken the whole frame of data is
> destroyed, therefore, nothing could pass even if the rest three links
> function well.
> 5. At today's technology, few devices could support 10GE within one link
> for a meaningful distance. From technology point of view, there isn't any
> remarkable breakthrough so that we can utilize a new and cheap device
> to implement 10GE links. For most of the transmission media, what we
> can utilize are the lower speed links. 10Gb/s data can only be
> transmitted
> at distance about a few dozens cm in PCB.  Long distance optical
> fiber link
> is an exception, and that means we only need 10GE at switcher interface
> to the long distance trunks.
> 6. In fact, we could simply extend the Gigabit Ethernet standard to
> 2.5/5 GE specification by adapting new speed as a smooth move. If we
> use 8B10B encoding, the speed will be 3.125/6.25 Gb/s, respectively.
> Simple and efficient! Why not?
> Thank you for your attention
> Regards
> ___________________________________________________
> Fenghao Mu
> e-mail:
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