Does only decimal system work for data rate specification?
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
1) Why we prefer to only specify 10GE rather than suggest other
reasonable data rates related to gigabit Ethernet, say 2.5/5 gigabit
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
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
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
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
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
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