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Karl, Figured I would respond to you on this
issue. First, let me address your Terabit
Ethernet comment. The reason why I made the statement that I did can be
explained by looking at Page 22 of the HSSG Tutorial (http://www.ieee802.org/3/hssg/public/nov07/HSSG_Tutorial_1107.zip)
If we forecast the growth for network aggregation, it is easy to
see the need for Terabit. Other analogies can be drawn from data in www.Top500.org which covers the HPC industry. Two of the participants responded to your
question regarding PCS, but their answer is more specific to the specification
in its current state. So I will try to provide some background.
First, the HSSG efforts are very intense, and there was a desire to try and
come up with an architecture that would be scalable for future speeds. Next,
as the group was addressing the architecture, it was not clear what the solution
today or in the future would be, so an architecture that could be used with
different optical / electrical physical specifications and interfaces was
desirable. For example, for 100G, there was discussion about 10x10, 5x20,
4x25, 2x50, and 1x100 specifications. 20 winds up being the least common
denominator of all of these possibilities. Therefore, 20 PCS lanes was
chosen, and then in the PMA sublayer, you can essentially do the demuxing /
muxing to and from PCS lanes to get to the right width interface at both ends
of the PMA sublayer. It is very important to note that an
architecture has now been developed that can be scaled to future solutions of
different widths and rates in the future. Hope this helps out. Feel free to contact
me in the future. Regards, John From: Fritz, Karl
[mailto:fritz.karl@xxxxxxxx] Greetings Task Force Members, My name is Karl Fritz and I work for the Special Purpose
Processor Development Group at the Mayo Clinic in However, I do have a question related to
the way the signals are grouped for 100GbE protocol. It appears that the
data will be striped across 20 lanes, then down to 10 lanes (for the
CAUI protocol) and then again possibly muxed down to 4 and then 1
(according the the Ethernet Alliance November 2008 Technology Overview
document). Being that 10Gbps serdes exist, why does the standard start at
20 lanes (5 Gbps each)? If this standard is expected to be scaleable, it
appears things could get rather messy if we want to scale this to Terabit
speeds (effectively multiplying all this by 10). Could somebody enlighten me a bit or point me as to why 20
lanes was selected as a standard? Why not go directly to 10 lanes at 10
Gbps? thanks Karl Fritz Lead Engineer Special Purpose
Processor Development Group (SPPDG) Phone: 507-538-5466 Fax: 507-284-9171 E-mail: fritz.karl@xxxxxxxx _________________________________________________ Mayo Clinic 200 |