| Thread Links | Date Links | ||||
|---|---|---|---|---|---|
| Thread Prev | Thread Next | Thread Index | Date Prev | Date Next | Date Index |
|
Dear all,
Speaking as a member of this group, I believe Frank has one
very strong point which we cannot forget about - at the beginning of the project
we set forth to provide 10G-EPON specs which will be backward compatible with
the existing 1G-EPON deployments. If we are to live up to that promise, I would
expect nothing less than a situation in which I can replace ONUs and OLTs on
both sides of the ODN and run 10G-EPON at the magnificent data rate of
10.3125 Gbps. As a carrier, I would not want to go out and requalify my ODN. I
would not want to go and change my splitters. As a matter of
fact, I would not want to touch anything apart from ONUs and OLTs.
That said, consider how much fiber is deployed and which
does not meet more stringent G.652-B specifications. Some of carriers who enter
the fibre deployment phase only right now will not have any problem meeting 1625
nm marker (newer fiber and PLC splitters), other will have tremendous
constraints moving past 1580 nm, for whatever technical reason (ODTR, additional
filters, poor fiber or splitters etc. etc.), but mainly due to the fast that
their fiber is simply older and will not qualify (probably) for more stringent
G.652-B specifications. There is a parallel discussion on the same topic going
on at FSAN and I believe (Frank, correct me if I am mistaken here) this is
exactly what the conclusions were. We do not have however the possibility of
defining optional wavelengths for the same PMD, as some are proposing for FSAN
NG-PON. As far as I understood IEEE approach to defining
specifications, we try to boil the available options down to the set of common
features. That means that we need to guarantee support for a more narrow
wavelength range in this case i.e. stick with 1580 nm limit upper, at least for
certain PMDs.
Our project was born with a set of constraints we have to
live with, when considering the target deployment scenarios. Additionally, we
have to also look at what is happening on the market of optical components. I
agree with Frank's comment from the last recirculation here - I have been
also tracking progress in several companies developing optical subassemblies and
for now I have only seen products focusing on 1574 - 1580 nm band, while
1580 - 1600 nm band seems to be pushed much further in the future. Additionally,
companies seem to be unwilling to invest into development of components the
volume of which may be much more limited. In short, most people I have spoken to
so far seem to bet more on PR(X)30 type devices than 10 and 20
classes. That seems to follow the trend from the past and if we believe it
happens, than application will indeed drive adequate volume to get the cost down
at the target wavelength, despite the fact that it might be more narrow than
standard CWDM band of 20 nm. If we are to look at the problem at hand through
the prism of backward compatibility, then indeed PR(X)30 type PMDs are in a
better position to be deployed, mainly because of the quantity of compatible
ODN. The main problem I see here is that we are trying to predict what market
does at times when I think we all learnt that market is not predictable.
An interesting point to note in favour of
PR(X)30 PMDs: if any of the current GPON favouring carriers were to switch to
EPON technology, PR(X)30 would be exactly the PMD they would need to use. Much
as it seems unlikely, I did receive querries from a few large carriers on such a
possibility. In such a case, PR(X)10 and 20 PMDs could not be used for obvious
reasons. Additionally, when considering harmonization with FSAN/ITU-T NG-PON
systems, PR(X)30 PMDs are yet again the ones which will receive the main focus,
since they are considered for reuse for XG-PON systems. Should that move
forward, this will represent a clear signal to the manufacturers to focus on
these devices. In the long run, the cost of a more narrow band PR(X)30 OLT PMD
may be comparable if not lower than uncooled DML based PR(X)10/20 PMDs. Jim and
Alan are right here - the bigger the volume and more companies in the segment,
the better the prices.
Concerning filter cost: I have seen already presentations
on this topic done at our group and at FSAN and conclusions are contradictory.
Some say a decrease to 15/14 nm isolation between video and data channel should
have minimum impact on the filter cost, others say it is going to hurt us
bad. If I recall right, we had only one presentation on this topic at our group.
I am not an expert in this area myself so I rely on others for data and
information. Yet in the view of conflicting information, I find myself
wondering where we really are. Perhaps people workign with filter
design could contribute with more down to the ground relative cost comparison
for 20, 15, 10 nm channel separation ?
Just a mental note - aren't RF Video systems supposed to
operate at 1550 nm ? Who would push them to 1560 nm ?
Regards
Marek From: Frank Effenberger [mailto:feffenberger@xxxxxxxxxx] Sent: quinta-feira, 16 de Outubro de 2008 1:00 To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx Subject: Re: [8023-10GEPON] Upstream Wavelength Selection Dear Group,
Let's not forget that it is not just
splitters and the raw fiber we need to worry about at 1600nm, but also the
effects of bends. And that is something that is more field operations
dependent. This is the biggest uncertainty that has made my operator
contacts concerned about using wavelengths longer than 1580nm. I will
point out that the data I’m getting from network operators is very sporadic and
somewhat contradictory. But, if there is doubt, then I think the right way
to go is to assume the worst case. There is another thing to
consider: We may consider proprietary specifications all we want, but in
the end we should be more standards driven. If I look at the G.652-A fiber
recommendation, all it tells me is that the loss (both basic and with bends) is
specified at 1550nm at the longest wavelength. Only G.652-B specifies the
losses at 1625nm. The G.671 standard for couplers specifies the two
traditional windows: 1260~1360 and 1480~1580. So, if we continue to
specify that our ODN is composed of fibers recommended in G.652 and couplers
recommended in G.671 then we really shouldn't go beyond 1580nm.
The alternative would be to require
the fiber to conform to G.652-B, and then to require the couplers to conform to
a revised G.671. But that sort of defeats the whole idea of backward
compatibility with existing PONs, which did not have such restrictions. So
that is our problem. I realize that the window is
somewhat narrow, but it seems to be the only safe choice at this point.
Sincerely, Frank
E. From: Jim
Farmer [mailto:Jim.Farmer@xxxxxxxxxxxxx] Before submitting a formal comment,
we wanted to run this by the reflector for comment. Regarding the upstream
wavelength action reflected below, from the September meeting in Cost and power dissipation:
The use of a tight wavelength band (e.g., 1577 +/-3 nm) at any wavelength is
going to significantly increase the cost of the laser, both due to the
manufacturing tolerance imposed and by the need for heating the laser. Any
DFB laser so far as we know, has a temperature drift of about 0.1 nm/deg.
C. If one were to provide for a normal indoor temperature range, which can
cover 60 degrees, then one will have a 6 nm wavelength shift due to drift.
We have found that there is market demand for wider temperature range OLTs,
which can easily have a wavelength drift of 10 nm over their operating
temperature range. Of course, the answer is to temperature-stabilize the
laser, but this requires an added heater/cooler and control, and the best
estimate we can make right now is that it will add 2-4 watts per PON to the OLT
power dissipation when operated at room temperature. Granted, this is
small compared with the total power dissipated by the OLT, but in an age in
which we are trying to minimize the power draw of all equipment, it is going in
the wrong direction. And it will cost money, not to mention that the laser
will have to be specified to a tight wavelength tolerance (or the wavelength
tuned by the cooler), adding more cost. Concerning the availability of
devices, we expect that this application will drive adequate volume to get the
cost down at whatever wavelength we choose. We’ve been told by one laser
manufacturer that the wavelength specified has little bearing on cost, though of
course, tolerance and volume play a big part in determining the
cost. Specification: We question the
statement that fiber and couplers are not fully specified beyond 1580 nm.
Some people are using 1610 nm for OTDRs. A check with a couple of major
manufacturers of fiber and couplers indicates that specifications are controlled
out to 1625 nm. See, for example, http://www.corning.com/WorkArea/showcontent.aspx?id=15535, and
http://www.ofsoptics.com/resources/AllWaveFLEX136web.pdf. As
for couplers, I understand that planar couplers are fine over this wavelength
range, though fused biconic couplers may not be as
good. Yet
another concern we have with the 1577 nm selection is the filtering when a 1550
nm video carrier is used. The video optical carrier can be as high as 1560
nm. For a 1577 nm downstream data carrier, which can go as low as 1574 nm
by specification, the WDM to separate the wavelengths has a 14 nm transition
region. If we use 1590 +/-10 nm for data, the transition region expands
43%, to 20 nm. This can help reduce ONT cost, as well as the cost of the
WDM at the OLT. For
these reasons, we seek reconsideration of the decision to abandon 1590 nm.
We would like to receive comments from the reflector, then we are planning to
submit a formal comment before the deadline. Thanks, Jim
Farmer, K4BSE |