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

ULf, Hans,

What you are attempting to discuss here is so broad as to defy 
quantification.  Each physical infrastructure deployment will be different 
based on the specifics of the physical plant requirements.  These will, for 
the most part, be highly engineered facilities.  For residential 
environments, each neighborhood will be different, with mixes of buried and 
areal deployment.  The buried deployments will be very dependant on the 
type of soil and climate(hot or cold).  The areal deployments will be 
dependant on the humidity and other climate weather conditions.  The cost 
of all of these will vary so greatly that only very broad speculations can 
be made.  The cost of the same type of construction will vary greatly from 
one locale to another.  What will cost one thing in one area, will cost 
something totally different in another area.  Even the cost of the 
equipment may vary between countries/states because of taxes etc.

About the only generalizations that I can find to be consistent between 
locations is that because of the cost of splices and interface ports, PON 
seems to be more cost effective for deployment than P2P in residential 
areas.  At the same time, in business environments, even with the higher 
costs, P2P may be what gets more deployment in building risers because of 
the ability to support private line services, which at the present time, 
PON can not.  Where there is legacy copper that the incumbent service 
providers want to leverage, the Ethernet over extended distance copper will 
be used.

Thank you,
Roy Bynum

At 08:49 PM 12/17/2001 +0100, ERA wrote:

>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