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RE: [EFM-P2P][EFM] PMD considerations

Quick comment:

All three of the OAM transport proposals (ipg, preamble, in-frames) will
cost about the same to implement in 1GE p2p (in our experience /
expectation). In-frames may cost a little more if one has to add a MAC, even
then it's peanuts. I would think that we will all be using similar
'available today' ICs for this.

I would imagine that the same is true for p2mp. I can't guess at copper. May
be Hugh can have a stab at that one.



-----Original Message-----
From: George, John Emanuel (John)** JV ** [mailto:johngeorge@xxxxxxxxxx]
Sent: 21 December 2001 18:56
To: 'Bob Barrett'; Ulf Jönsson F (ERA);
stds-802-3-efm-p2p@xxxxxxxxxxxxxxxxxx; stds-802-3-efm@xxxxxxxxxxxxxxxxxx
Subject: RE: [EFM-P2P][EFM] PMD considerations


One question that might assist the decision regarding PMDs is to what degree
may existing Ethernet PMDs be used within an 802.3ah network.

1) Some in the group state that the 802.3 document structure would allow the
use of existing 802.3 PMDs in an EFM network. This would permit service
providers to benefit from the low cost of existing high volume PMDs.

2) Others have stated that if OAM&P functions are integrated within the PCS,
such legacy Ethernet PMDs would require changes to be used in an 802.3ah
network. Even with these changes to silicon, however, the PMD would still
benefit from the use of existing high volume low cost optics (or copper).
But would it still be 802.3ah compliant?

3) If an existing 802.3 PMD must be changed to accommodate OAM&P to be EFM
compliant, maybe a simple statement in the standard that "existing 802.3
PMDs employing the OAM&P functions defined in 802.3ah are 802.3ah compliant"
would be appropriate.

Is 1 or 2 or both correct? If one had to incorporate EFM OAM&P into an
existing 802.3 PMD, what would be the cost impact?

John George
OFS - Fitel
Fiber Offer Development Mgr
770-798-2432 (v)
770-798-3872 (fax)

-----Original Message-----
From: Bob Barrett [mailto:bob.barrett@xxxxxxxxxxxxxxx]
Sent: Tuesday, December 18, 2001 5:00 PM
To: Ulf Jönsson F (ERA); stds-802-3-efm-p2p@xxxxxxxxxxxxxxxxxx;
Subject: RE: [EFM-P2P][EFM] PMD considerations

Dear all

I went to a customer meeting today and had them tell me that 100M SMF was an
EFM work in progress. News to me :-). He may not have been correct, but he
is the customer.

The point being that this customer was deploying 100M SMF and would like it
to be standardised. I advised them to at least visit the email archive on
the reflector, if not join the mailing list.



-----Original Message-----
[]On Behalf Of Ulf
Jönsson F (ERA)
Sent: 17 December 2001 19:49
To: stds-802-3-efm-p2p@xxxxxxxxxxxxxxxxxx;
Subject: [EFM-P2P][EFM] PMD considerations

Hi all,

The following text brings up some considerations regarding the EFM optical
PMD from a component perspective. It has been written with great help from
our Ericsson internal experts on the optoelectrical component side.

For the physical medium, i.e. the O/E-converters and the fiber connecting
them, a few aspects may be high-lighted:
1. Data rate
2. Single or multimode fiber
3. Single or dual fiber

We will discuss these aspects in more detail and will also try to draw a
conclusion. Hopefully this will start a discussion on the reflector that may
make it easier for us to agree on a (few) baseline proposal(s) in March.

1. Data rate
The choice is between 100Mbps and 1000Mbps. Of course one must pay a premium
for a tenfold speed increase, throughout the entire system (A more detailed
cost analysis will be presented at the January interim). Optimizing an O/E
converter design for 100Mbps instead of 1000Mbps means

* inherent improvement of receiver sensitivity.
* lowered demands on output optical power (consequence of above).
* lowered demands on thermal management (both inherent, due to lower speed,
and consequence of above)
* lower crosstalk

All these factors will facilitate the module design, simplify the assembly
and increase the yield, thus substantially lower the costs. The argument for
1000Mbps, that the higher volumes for this product will yield lower cost,
neglect the impact of EFM as a cost driving application itself. This
application should in itself be enough to create sufficient production
volumes. Thus, it does not seem optimal to let the vast majority of
connections where 100Mbps is sufficient pay that cost premium, especially as
a P2P topology allows for relatively easy individual line upgrades. On the
other hand, 1000BASE-X will in a P2P topology be appropriate for premium
subscribers and for aggregate traffic higher up in the access network and it
will of course be appropriate to use in a P2MP network. Hence, we see a need
to include both a 100Mbps PMD and a 1000Mbps PMD in EFM.

2. Singlemode or multimode fiber
As of now, multimode systems are significatly more low-cost than singlemode
systems. Though this difference will decrease as the singlemode component
volumes increase, a certain difference will always remain, due to the less
stringent geometrical tolerances in a multimode system. For those
applications where multimode systems are appropriate, there is no need to
pay the singlemode premium. What is important is that a large number of
connections require singlemode systems, both due to present distance
limitations and to future upgradeability.

3. Single or dual fiber
O/E converters for a single fiber system are inevitably more expensive than
those for a dual fiber system, due to the higher complexity. Just as
inevitable is the fact that this difference will be more than compensated at
very long link lengths. The question is the cross-over distance, and the
distribution of potential installations below and beyond this cross-over,
respectively. If it is regarded necessary to include both options in the
standard, how can that be made with a minimum of effort? Let us examine the
implications on the basic parameters.

3.1. Power budget
A dual fiber system can, and should, allow for a wide output power range, in
order to achieve high production yields in a low-cost assembly process.
If wavelength separation is used in the single fiber case, the power
specification should be equal for dual and single fiber. The extra
attentuation caused by the splitters are hidden inside the converters, and
just has to be compensated for by extra laser power and increased internal
receiver sensitivity, respectively.

The single wavelength case is more difficult, due to constraints imposed by
the reflection crosstalk. In order not to have completely unrealistic
back-reflection demands, the span of the allowed output power must be
minimized. Otherwise, the transmitted power from a "low-end" module would
drown in the reflected power from a relatively high power module. Assume
e.g. a power span of 10dB, a link budget of 10dB and a required SNR of 10dB.
This implies a total allowed near-end reflection of below -30dB, which is
not easily achieved.

Thus, if the output power range for dual fiber is e.g. -5dBm to -15dBm, the
single fiber version should probably be a part of that, something
like -12dBm to -15dBm.

3.2. Wavelength
For dual fiber systems, the operating wavelegth window can, from a component
perspective, be selected freely within the SM fiber window 1300-1600mn. A
wavelength separated single fiber system of course have strict requirements
regarding this matter. For such a system it is also required to have two
types of transceivers, for each end of the connection. Depending on the
actual implementation of the components for a single wavelength single fiber
system, some wavelength restrictions could be needed, as the splitters might
have a wavelength dependence.

3.3. Connectors
For dual fiber, several types of standard connectors should be allowed, e.g.
MT-RJ, LC, MU, etc. The requirements on connector performance can be kept
low, to reduce costs, since the desired power budget is easily achieved, and
there is no back-reflection problem.

The same should be valid for single fiber WDM systems, even though the power
budget is a bit harder to meet in this case. Possibly the connector
attenuation must be a bit tighter specified.

For non-WDM single fiber, the crosstalk problem make low reflection
connectors necessary throughout the entire system.

Eight different P2P relevant configurations, each with its own merits and
drawbacks, can be distinguished. These are:

100 Mbps MMF dual fiber
100 Mbps SMF dual fiber
100 Mbps SMF single fiber
100 Mbps SMF single fiber WDM
1000 Mbps MMF dual fiber
1000 Mbps SMF dual fiber
1000 Mbps SMF single fiber
1000 Mbps SMF single fiber WDM

of these three already exist as standards within IEEE 802.3, namely

100 Mbps MMF dual fiber
1000 Mbps MMF dual fiber
1000 Mbps SMF dual fiber

100 Mbps SMF dual fiber is at present not an Ethernet standard. Still,
components exist and are used when needed. ANSI has standardized a PMD for
100Mbps FDDI over SMF (ANSI X3.184-1993). The corresponding FDDI standard
for MMF is used as a reference for Ethernet 100BASE-FX.
The need to incorporate 100 Mbps SMF dual fiber within the Ethernet family
is obvious. Since it also seems to be the most appropriate choice for a
large number of EFM connections, it should be the first choice for an EFM
PMD. This PMD should of course to a large extent be based on the 100BASE-FX,
with the physical media specifications optimized for low-cost components
with sufficient performance.

To give a variety of options, it seems reasonable to also incorporate
100Mbps MMF dual fiber as well as 1000Mbps dual fiber in EFM. As already
being Ethernet standards, this should be possible without much extra work.

Single fiber systems are a bit more complicated, since the requirements are
more closely connected to the actual implementation, and a PMD are more
different from existing standards. One way to go, since the requirements
(with wavelength for the WDM solutions as a possible exception) is within
the dual fiber specification, only tighter specified, would be to use the
dual fiber PMD as a base and have different categories within that. These
could be one or two single fiber options, but also extended temperature and
extended range dual fiber options. Depending on the progress of the work,
the single fiber options can either be tightly defined within the base PMD,
or kept rather open for different manufacturer implemenations. The important
issue is to let the time-schedule be set by the most straightforward, dual
fiber, solution.

Best regards,
Ulf Jönsson & Hans Mickelsson