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Re: PMD discussion




Jay,

I agree with you. However, I believe that we are loosing sight of the ultimate
goal of the WAN PHY: Compatibility with the SONET/SDH infrastructure. 

I'd like to address a comment regarding our objectives that was made during the
Ottawa meeting on several occasions: It was said that a LAN PHY with a WIS (for
SONET/SDH compatibility) does not meet the HSSG objectives. I'm having trouble
understanding why a solution which "exceeds" the objectives, and is highly
likely to be lower in cost, is inferior to one which "meets" the objectives.

The specific objective in question is as follows:

Define two families of PHYs
 A LAN PHY, operating at a data rate of 10.000 Gb/s
 A WAN PHY, operating at a data rate compatible with the payload rate of
OC-192c/SDH VC-4-64c

It has been proposed, and there is general agreement (i.e. lack of any other
proposal) that the WIS, a layer 1 (PHY) sublayer is used to encapsulate Ethernet
packets, using 64B/66B for a PCS, for transport over SONET/SDH. The latest
relevant proposals from Ottawa are:

http://grouper.ieee.org/groups/802/3/ae/public/may00/bottorff_1_0500.pdf
http://grouper.ieee.org/groups/802/3/ae/public/may00/nicholl_1_0500.pdf
http://grouper.ieee.org/groups/802/3/ae/public/may00/walker_1_0500.pdf

The location of the WIS in a WAN PHY can be illustrated as follows:

    +-----+    +-----+        +-----+    +-----+ 
--->|     |--->| PHY |------->|     |--->|SONET|
    | MAC |    |     | medium | PHY |    |  \  |
<---|     |<---|(WIS)|<-------|     |<---| SDH |
    +-----+    +-----+        +-----+    +-----+ 
    (rate
  controlled)   |<--- WAN PHY ---->|
   
Alternatively, the location of the WIS in a LAN PHY can be illustrated as
follows:

    +-----+    +-----+        +-----+    +-----+ 
--->|     |--->|     |------->| PHY |--->|SONET|
    | MAC |    | PHY | medium |     |    |  \  |
<---|     |<---|     |<-------|(WIS)|<---| SDH |
    +-----+    +-----+        +-----+    +-----+ 
    (rate
  controlled)   |<--- LAN PHY ---->|

Note that the WIS function simply moves to the right (towards SONET/SDH) and the
same PHY, a LAN "UniPHY" if you will, may be used to achieve full SONET
compatibility. MAC/PHY rate control is not issue between the two methods. I
understand how to implement it either way.

Please point out the flaw(s) with the LAN UniPHY in supporting Ethernet over
SONET. Is it that there is a unwritten requirement for a WAN PHY to support
payloads other than Ethernet over SONET/SDH? I'd call any such requirements out
of the scope of IEEE 802.3.

Best Regards,
Rich
   
--

jay.hoge@xxxxxxxxxxxxxx wrote:
> 
> In order for the WAN PHY to do its job, it cann't use a line code or else
> the data rate will exceed that of OC-192. Scrambling anyone?
> 
> Jay
                                   
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