Re: [EFM] EFM - reasons I withdrew my material
Bob:
We are still in the mode of hearing good technical proposals. Talking to
802.1 is a good idea.
Bruce Tolley
Cisco Systems
At 03:35 PM 7/15/01 +0100, Bob Barrett wrote:
Two reasons why I withdrew:
1) The material as submitted did not match the revised approach that I
want to take to this topic.
2) Having re-read the minutes of the interim, and paid particular
attention to the motion madness surrounding the issue of the OAM side
band, I thought it better to await the outcome of that issue before
raising my topic.
If the EFM task force decides that there will be no change to the p2p PHY
to enable side band OAM, then my suggestion of a 50M-100M uncommitted
side band (in which vendors could implement what they wish e.g. pseudo
isochronos circuits) is dead in the water. Even the smallest change to
the PHY for OAM would mean new PHY chips in order to get the economies
that we (the group) are always quoting as a justification for the
economic feasibility. Furthermore, if the PHY were to be changed (and new
PHY chips were required) then it would be very easy to add an uncommitted
side band at the PHY level with a small gate count and very little
cost.
Now, there is another way that this approach could find its way into EFM.
If we look at the degenerate case of EPON i.e. a two node system, that is
effectively p2p. I would envisage that it will be necessary to re-define
the PHY for EPON, in order to support the contention mechanism without
changing the MAC (if the MAC is inviolate and EFM can't do anything above
it that only leaves the PHY doesn't it). Most EPON vendors are specifying
systems that support both packet and TDM / circuit service points, one
way or another.
My assertion is that it is much simpler to support circuits in side bands
rather than as circuit emulations over packet with QoS. At the PHY it's a
low gate count and a bounded delay issue, 'bits in equals bits out' with
minimal buffering. At the MAC (or above) it is no longer a 'bits in
equals bits out' issue. It becomes a T1/E1 frame into a packet issue, and
by the way how many frames do we have to buffer to overcome the MAC
latency and stat. muxing (even with tags). Probably 100 times as many
gates required (not that I am an engineer you understand, but my
engineers have implemented both a PHY approach and a MAC circuit
emulation solution, and that is the information that I am getting back
from them).
There is circuit support in the metro right now in the form of SONET/SDH
infrastructure. If the carrier / service provider removes the circuits
that carry data from this SONET/SDH infrastructure and puts them (the
data services) onto a packet based metro using switches and routers
(probably on a separate lambda), then the circuit capacity freed up on
the current (paid for) SONET/SDH infrastructure can be used to generate
additional revenue from circuits. The business case for putting circuits
over packets in the metro is not as compelling for an ILEC as it is
(was??) for a CLEC. Any comments from xLECs on this point would be
welcomed.
Best regards
Bob
If the group decides
not
to change the 1GE p2p PHY to include an OAM side band
then I have a reasonable chance by taking a position along the lines of
'if we are going to change the PHY then we may as well add some real
value'. I need to talk with Tony Jeffree about the architectural
implications of my proposal too, as again, there is no point in pitching
it if 802.1 will rule it as being outside of the scope of
802.