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Re: [8023-10GEPON] Upstream Wavelength Selection



Title: Upstream Wavelength Selection

Dear Jim,

 

You know, the technical business is a funny thing.  When you talk to the applications engineers, you get one story.  When you negotiate the contract, you get quite a different one.  What I’ve heard from my friends in North America that buy the fiber and passives is that the specifications only go to 1550nm – that is what the big contract says. I have to believe that the 1625nm spec was dropped for a reason, shouldn’t I?  That is the puzzling factor.  Maybe your Corning contact can comment on that.    

 

On a different matter, I have heard that the SCTE should be sending us a liaison regarding their work on a new sort of PON system called RFOG (radio frequency over glass).  This system is completing the downstream-only video overlay scheme that we started with the 1550 to 1560nm wavelength by adding an analog upstream transport.  They are looking at using the 1590 or 1610 bands, and they will need 20nm of width (most likely) because these upstream lasers are at the ONTs.  If we want to coexist with this system (admittedly a new request), then we should think twice about using up the entire spectrum.  As it is, if we stick to 1577, then this system could use 1610 with a nice 20nm guard band.  If we spread out to 1600nm, then where does that leave them?  

 

If I can elevate the discussion for a moment, the evolution of PON has been marked with the tendency to spend our spectrum like water.  When it came time to add new features and upgrades, we were forced to go back and revise our systems to narrow the windows, add blocking filter specifications that should have been in there in the first place, jump through multi-rate TDMA hoops, and so on.  This is not a good path.  The 1577nm option is a small step towards being more conservative in our allocation of spectrum.  But I’ll admit that this sort of argument in not strictly in our scope – it is more a general concept position… just take it for what it’s worth.  

 

Sincerely,

Frank E.

 

 

 

 

 

 


From: Jim Farmer [mailto:Jim.Farmer@xxxxxxxxxxxxx]
Sent: Wednesday, October 22, 2008 5:12 PM
To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-10GEPON] Upstream Wavelength Selection

 

Sorry to have let this lie for a few days - had to go off and earn a little money.

 

Thanks for the replies.  It seems Pete has established that existing fiber and passives should work up to 1625 nm.  We have gotten similar information from a large vendor of optical fiber and components.  He tells me that the oldest long distance fiber he knows of being deployed in the US is -A fiber.  So the likelihood of finding fiber in the access network that is not good to 1625 nm is minuscule.  How much should we base specification of the latest product on fear for fiber performance that may not exist in the field, and almost certainly not where we are going (access)?

 

In addition, please see the note from Corning below (they have agreed to let me post it with their name), which establishes a latest date for the introduction of G.562B fibers.

 

We are content to let PR(X)30 operate at 1577 nm, and if the market decides that is all that is needed, so be it.  With due respect, it may be that vendors who are working on 1577 nm product are doing so because of the perceived initial market for a 10 G product, which may be a slightly specialized market.  But we remain concerned about two things: The cost of meeting the narrow bandwidth, both in terms of money and power, and the filter used to separate the downstream RF overlay from the lower 1577 nm wavelength.  This latter would not be an issue except it is a filtering function that must be done at the ONT, where we worry about every penny of cost.  I've been trying to get solid numbers from vendors, but I, too, am having trouble finding consensus.

 

The narrow bandwidth (+/- 3 nm) issue is an OLT issue, and so is not quite of as much concern as is anything at the ONT, but we still worry about it.  I can accommodate the bandwidth by measuring the wavelength of each laser and determining the temperature at which the cooler must operate to keep its wavelength centered in the window.  This works, but does cost money and power for the cooler and control circuit, as well as an extra step in production.  While traditional telecom markets may not be concerned, we feel that emerging deployers, such as municipalities and cable companies, may not tolerate increased costs.  We don't see how a product with a cooler will be competitive with something that does not have to be cooled, all else being equal.

 

Regarding the issue of filtering the 1560 nm maximum video wavelength from the 1574 nm minimum data wavelength, I, too, have not been able to get a quantitative answer.  But intuitively, the narrower you make the transition region, the more costly the filter, and the more loss it will have.  We had one discussion with a company that buys filters and packages them, and at first they thought this was a non-issue based on their experience with CWDM filters.  But then we pointed out that we need a lot more rejection at the reject band (probably on the order of 50 dB), and we have to do it at ONT prices.  This made them worry.  Right now, with current-generation product, we have a transition region from 1500 to 1550 nm - 50 nm transition - and we are talking about reducing it to 20 nm or so.  I hope someone with filter design experience can give us guidance.  We continue to seek same.

 

In answer to Marek's question, while we normally talk about 1550 nm for broadcast use, the actual band over which transmitters are available is 1550 - 1560 nm, corresponding to the actual amplification band of commonly-available EDFAs.  It may be possible to restrict the actual wavelengths used to 1550 - 1555 nm.  (The transmitters use a cooled DFB laser with good stability, so the occupied band is relatively narrow, but transmitters are produced at various wavelengths.)  I have already floated this idea by the RFoG reflector, and as usual, initial reaction was mixed but generally unfavorable.  But I think we could ease the filtering requirements some by doing this.  Now if I just knew where the cost curve flattens out, so I'd know if I was tilting at windmills or addressing a real concern...

 

Regarding the bending issue, I think the primary issue occurs in or near the end customer, and this is likely to be new fiber anyway.  We have bend-insensitive fiber available now from all vendors.

 

This thread seems to have bifurcated last week due to time zone differences.  I think I have all the responses below, in the correct temporal order.

 

Thanks,

jim

 

From Corning:

The G.652B standardization added the PMD requirement in October 2000.  Prior to the above date, there was not a standardized method to deterimine PMD.  Different manufacturers tested differently.  So, fibers made earlier may have met the standard but they were not measured.   G.652B fibers can be integrated with later fibers such as G.652D; however, system capabilities are limited to that of the legacy fiber.

The oldest spec sheet we have quoting performance at 1625nm is December 2000.

Chris Kalivoda
Applications Engineer
828-901-5573
CORNING CABLE SYSTEMS
HICKORY, NC

Jim Farmer, K4BSE
Chief Network Architect,
Enablence Technology
FTTx Networks Division.
1075 Windward Ridge Parkway
Alpharetta, GA 30005 USA

678-339-1045
678-640-0860 (cell)
jim.farmer@xxxxxxxxxxxxx
www.enablence.com

 

 


From: Frank Effenberger [mailto:feffenberger@xxxxxxxxxx]
Sent: Thursday, October 16, 2008 9:31 AM
To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-10GEPON] Upstream Wavelength Selection

Dear Pete,

 

Thank you for your additional information.  I had missed that 2006 amendment on the splitters.  

 

On the status of real PON deployments, it is difficult to get really solid information.  Since I work for an equipment vendor company, I don’t have direct access to what the operator’s measure on their fibers.  All I have to go on is what they tell me.  What they tell me is mixed.  Many companies are deploying PONs which are guaranteed to work out to 1600nm.  Other companies only go out to 1580nm (at least, that is what their specifications / measurements go to). Yet others are interested in using OTDR equipment, and so the long wavelengths need to be reserved for that.  

 

Actually, I’m glad that we are having this discussion – hopefully the interested parties who have access to the data will come forward, and we can hear the first-hand story of what is really out there.  Based on that information, we can make a better informed decision.  

 

Sincerely,

Frank Effenberger

 

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

From: Marek Hajduczenia [marek_haj@xxxxxxx]
Sent: Thursday, October 16, 2008 5:27 AM
To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-10GEPON] Upstream Wavelength Selection

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: Pete Anslow [mailto:pja@xxxxxxxxxx]
Sent: Thursday, October 16, 2008 5:18 AM
To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [8023-10GEPON] Upstream Wavelength Selection

 

Frank,

 

While not wishing to enter the debate on what the wavelength choice for 10G EPON should be, your statement “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.“ is not really correct.

 

G.671 Amendment 1 (03/2006) available here:

http://www.itu.int/rec/T-REC-G.671-200603-I!Amd1/en

adds an “Optical branching component (wavelength non-selective) for PONs” which is specified from 1260 to 1360 nm and 1450 to 1600 nm.

 

For the loss of G.652 type fibre, some information was presented in:

http://www.ieee802.org/3/av/public/2007_03/3av_0703_anslow_1.pdf

see slides 5 to 11.

 

The red curve on slide 6 is derived from measurements of 1549 fibres at 1550 and 1625 nm together with full spectrum measurements of uncabled fibres.  The only room for uncertainty between these results and your requirements is whether the bends seen in a PON environment produce a significantly different curve from those seen in the transport environment.

 

Regards,

Pete Anslow

 

Nortel Networks UK Limited, London Rd, Harlow, Essex CM17 9NA, UK

External +44 1279 402540 ESN 742 2540

Fax +44 1279 402543

 


From: Frank Effenberger [mailto:feffenberger@xxxxxxxxxx]
Sent: 16 October 2008 01:00
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]
Sent: Wednesday, October 15, 2008 5:59 PM
To: STDS-802-3-10GEPON@xxxxxxxxxxxxxxxxx
Subject: [8023-10GEPON] Upstream Wavelength Selection

 

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 Seoul, we have a good bit of concern over cost and performance, and would like to propose a return to the originally-planned wavelength of 1590 +/-10 nm for PR(X)10 and 20 downstream data.

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
Alan Brown
Enablence Technologies (Wave7 Optics)
================
From September meeting:
IEEE 802.3av Draft 2.0 IEEE 802.3av d2.0 10G-EPON comments Intermediate Responses
Cl 75 SC 75.1.4 P 51 L 16 # 2158
Comment Type T
This comment concerns the downstream wavelength for the PR10, PR20, PRX10, and
PRX20 PMDs, which is currently specified at 1580 to 1600nm. When this was selected, it
was thought that it would enable cheaper transmitters. However, there are a couple of
issues that argue against this wavelength choice:
1. The 1590nm sources seem to be less available than the 1577nm sources, so any cost
savings due to the wider window will be cancelled out by this effect.
2. The use of wavelengths beyond 1580nm has become increasingly uncertain, since the
fibers and couplers are not fully specified at those wavelengths.
We should also consider that if we use a single downstream wavelength for all PMD types,
then early volumes will be increased and the manufacturing community will be given a
clearer message on what wavelength sources to build.
SuggestedRemedy
Change the downstream wavelength range for all PMD types to 1574 to 1580nm.
This occurs in Table 75-1, 75-5, 75-11, 75-12, 75-13, and 75-20, and throughout section
75.6.1.1.
ACCEPT.
I approve the resolution suggested in the comment:
Yes: 10
No: 0
Abstain: 15
[Accepted]
[COME BACK, review ad-hoc material and revisit]
If accepted, this change will affect Clause 75 draft in a number of places: Table 75-1, 75-5,
75-11, 75-12, 75-13, and 75-20, and throughout section 75.6.1.1. Align figures where
necessary e.g. Figure 75-8.

 

 

 

Jim Farmer, K4BSE
Chief Network Architect,
Enablence Technology
FTTx Networks Division.
1075 Windward Ridge Parkway
Alpharetta, GA 30005 USA

678-339-1045
678-640-0860 (cell)
jim.farmer@xxxxxxxxxxxxx
www.enablence.com