[EFM] Re: [EFM-Copper] Long Reach Copper Presentations in Vancouver
I have to jump in here.
We could think of Ethernet as a service. We could think of Ethernet as a banana
(see other thread).
The fact of the matter is that it is neither. Please take the time to read the
802.3 document. Ethernet defines a MAC (just one!) and a limited set of physical
layer interfaces. If you have any other perception of Ethernet then I suggest
that you are reading the wrong document.
You may consider this a way to cut through the knot. I think that most of the
authors of the Ethernet standard would consider it cutting through the heart of
All that has an MII is not Ethernet (and, of course, vice-versa).
John Farnbach wrote:
> Steve, and all,
> Steve makes some good points below. It seems to me that the most compelling
> point is that the Ethernet standards have always specified the physical
> layer. 22 years ago when Ethernet was first being developed, it was necessary
> to specify it all the way down to the physical layer. Otherwise, how could
> you connect one ethernet port to another?
> Only consider this: What if we think about Ethernet as a service, rather than
> a physical network? Service providers today are very good at physical layer
> connectivity, they do it all the time over a variety of links, including HDSL,
> ADSL, and SHDSL. There would be less, not more, confusion by defining EFM
> above the byte pipe layer. Steve asks, which version of EoCu would a carrier
> install... They would install the byte pipe of their choice and layer
> Ethernet on top of that. Only one version of Metro Ethernet, not many. There
> is not any confusion in saying that EFM operates over any byte pipe--They
> already know how to make byte pipes work.
> And what about the carriers who have a kind of byte pipe installed tht may not
> be the one chosen for EFM? It would be much easier for them to provide
> Ethernet service over any byte pipe than to have to change out all their
> physical links to the one that might be chosen.
> Just seems to me that there is a simpler way to cut through the knot.
> Steve Jackson wrote:
>> Threaded response:
>> -----Original Message-----
>> From: John Farnbach [mailto:john.farnbach@xxxxxxxxx]
>> Sent: Thursday, December 19, 2002 2:37 PM
>> To: Steve Jackson
>> Subject: Re: [EFM-Copper] Long Reach Copper Presentations in
>> Steve, thanks for the info. You're welcome.I may be wrong, but it
>> seems to me that it is technically and logically possible to
>> define the MAC and the 'gamma" interface for an EoDSL layer and
>> leave the lower layers open. It is technically and logically
>> possible, of course.Seems like that would be very effective and
>> would guarantee interoperability, provided that the two ends of a
>> link interoperated at the PMD layer. Um, no. Doing so would
>> create massive market confusion. Tell me, how many versions of
>> EoCu would show up on the market? Six? Eleven? Which one does
>> BellSouth use? Verizon? France Telecom?See what I mean?Are you
>> saying that the original PAR requires that 802.3ah must define the
>> physical layers as well?
>> Yes. The 5 requirements include "broad market acceptance" and
>> "technical feasibility" among other definitive statements.
>> That seems counter-effective.
>> Hmmm. 100BASE-T specifies a PHY (actually, several) for example.
>> Most implementations have an embedded MII. Are you saying that we
>> should have just said "oh, use whatever you like, the MII is
>> spec'd out" and let vendors ensure PMD interoperability?
>> No, you couldn't mean that. ;-) What did you mean?
>> As demonstrated by the ADSL/SHDSL debate, over defining the
>> standard just gives more room for debate. Is it possible to go
>> back and modify the PAR?
>> The ADSL / SHDSL debate is caused by the semiconductor vendors who
>> have megabucks invested in DMT and QAM development. It's not a
>> real argument in and of itself. If SHDSL is approved, it's seen
>> as a huge advantage to the VDSL SCM vendors, and vice-versa.
>> Realistically, we're too far down the road to even re-write the
>> objectives, much less rewrite a PAR and start over. More likely,
>> we'd just drop the whole standards effort first.
> John Farnbach, Managing Partner
> Farnbach Associates
> tel/fax: 303-448-9852
> 4022 Old Westbury Court, Suite 202, Boulder CO 80301