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Re: Leveraging OC-192c - 802.3x flow control

Hon Wah,

I agree in general with your thoughts on leveraging elements of the OC-192
infrastructure including EDFAs and regenerators for use with 10 GbE equipment.

The only question I have is with respect to 802.3x flow control: My
understanding is that 802.3x flow control is limited to a single link. Is this
your understanding also? I believe we need to clear up this matter as we
continue to try and determine the correct HSSG speed objective.

A second point you make is to raise the possibility of using 802.3x AND other
pacing mechanisms in a link. I don't believe that it's a good idea to mix
mechanisms that control the flow of packets within a link. This speaks in favor
of 802.x as being the only flow control mechanism for 10 GbE.

Best Regards,


Hon Wah Chin wrote:

> The discussion about a MAC/PLS pacing mechanism would be more
> important if the interface were typically exposed.  If it is
> not exposed (and that's my guess), how it works is an internal
> implementation issue.  The PHY would clock information from the upper
> protocol layers however it needs to.
> This would simplify the discussion and eliminate the question of
> how 802.3x interacts.  Use of the 802.3x mechanism in this pacing
> AND allowing flow control from the other end of the link probably
> conflicts with the assumption in 802.3x that flow control packets
> are not forwarded.  As observed previously (Mick Seaman?), generating
> such packets at the MAC/PLS interface AND forwarding such packets (without
> extra internal state) received from the link can cause confusion.
> The "bit time" used in the various calculations (IFG, 802.3x pause..)
> can be defined at 10G or some other standard rate, probably with less
> controversy.
> Still, the question of a THROUGHPUT RATE TARGET interacts with
> the signaling rate and packet formating to be used on the link.
> Leveraging the OC-192 equipment still requires defining the packet
> formating, and without flexibility in the signalling rate we have to
> work on tradeoffs in the framing/formating vs throughput.
> It seems to me that the leverage from the OC-192 deployment is mostly in the
> regenerators.  Current SONET ADMs would do not transport OC-192c trib
> traffic,
> The current LINE side is about 10Gb/s so there's no multiplexing or
> add/drop.
> The OC-192 components are ahead in volume right now, but the prospects
> for 10Gb/s Ethernets would provide enough volume on their own to justify
> tweaks to the component specifications, assuming no attempt is made
> to push the performance 25%.  The other advantage of the defined OC-192
> structure is the overhead already reserved for link performance monitoring.
> This saves definition work if this style of OAM&P is desired for extending
> the reach of 10 Gb/s Ethernet using the deployed SONET OC-192 regenerators.
> Overall, if you believe in significant 10Gb/s Ethernet volumes, leveraging
> the deployed OC-192 regenerators is useful but not compelling.  On a
> buildout
> of new links, new regnerators that clock at a slightly different clock
> rate can be installed as well as old design regenerators that do exactly
> what SONET OC-192 defines.  Within the 40km target, regeneration would
> not typically be used at all.  Maybe making the physical layer
> work with EDFAs will be more important than with OC-192 regenerators.

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