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Brad, Thanks for the clarification. I think the parallel
detect specified in 802.3ap would be inadequate for optics speed negotiation.
The 802.3ap parallel detect function was only intended to detect two legacy PHY
types that could interoperate with the newly defined 802.3ap PHYs. I don’t
think it would scale to support a large number of PHY types and it does not allow
a PHY to advertize more than one speed of operation. Clause 8 of the Fibre Channel
Framing and Signaling specification describes a method of link speed
negotiation where the transmitter shows off its abilities by operating at different
speeds in sequence while the receiver detects the one it wants to use, however this
seems fairly complex and I think it would make more sense for 802.3 to reuse Clause
37 for optics speed negotiation and to contradict what I said below to consider
if the Clause 73 AN protocol could be used over optics. Arthur. From: Brad Booth [mailto:Brad_Booth@xxxxxxxx] Arthur, Clarification: -
I support using Clause 73 AN for P802.3bj. -
Sequence ordered sets could provide fast FEC on/off switching
that having to restart AN. -
Sequence ordered sets could provide a means to exchange FEC
abilities, etc. in optical media. -
Speed negotiation in optics could use parallel detect specified
by 802.3ap. Hopefully that clarifies
things a bit better.
From: Arthur Marris [mailto:arthurm@xxxxxxxxxxx] Brad, Let me make a
few comments. For 802.3bj it
is necessary to use Clause 73 for auto-negotiation because Clause 73 already
supports port types for four-lane twinax and back-plane. If new 100G port types
are being added for these media, they need to be included in Clause 73. Clause
73 also gives you FEC negotiation for free. Clause 73
clearly does not work over optical media. You can use
ordered sets for exchanging ability and requests, but this only works if both
sides of the link are running at the same speed and the error ratio is not too
bad. For next generation optics you are going to need to decide whether you
need to negotiate speed in addition to determining FEC operation (for example
you might want to negotiate between 40GBASE-SR4 and 100GBASE-SR4). If you do
decide to negotiate speed you could consider re-using Clause 37 for
auto-negotiation (which operates at a 1.25G data-rate). If you are not
negotiating speed but are just concerned about bit errors, then the task being
performed is really link training rather than ability resolution. Arthur. From: Brad Booth [mailto:Brad_Booth@xxxxxxxx] Stephen, It depends on the FEC
protocol adopted, implementation requirement, and the associated latency. The
discussion got started around the idea of using Clause 73 AN for FEC ability
exchange in the optical domain. Considering we’re still
in the study group phase, some of those questions cannot be answered as we have
not adopted an FEC proposal. If an exchange protocol is required, then IMHO the
use of sequence ordered sets would be preferred over creating of a new autoneg
protocol. Cheers, |