If you can provide data on this, it would be most welcome J Thank you, Francois From: Francois Menard [mailto:fmenard@xxxxxxxxxxx]
Sent: Thursday, February 25, 2016 9:48 AM
To: Marek Hajduczenia
Cc: STDS-802-3-NGEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_NGEPON] ONU ASIC and wavelength plans
My point about four wave mixing remains valid for other slots in the O-Band. I do not insist on 1260-1280.
Sent from my mobile device. Apologies for any typo. Francois, Just one note: we are already using 1260 – 1280nm band for 10G-EPON. XGS-PON is nothing more than 10G-EPON in disguise (yes, they did change a few things at logical layer, so what). I am not sure though what point you’re trying to make – reuse of 1260-1280 band for NG-EPON would block the coexistence / backward compatibility with 10G-EPON, which is one of our goals for the project. If we forgot backward compatibility with 1G-EPON, we have plenty of real estate in O band to work with, without the need to kill off compatibility with 10G-EPON. Marek Barry wrote > I agree with Ed that the second, third fourth channel is where we can start adding the cost and this is where a tunable may make sense. Of course the cost of a tunable must not exceed 2x the cost of a non-tunable. Barry, are you making the point that until such time the OLT has a Gen2 or Gen3 transceiver on the PON, it makes no sense for the ONU to be tunable ? My view is that even if the OLT has a Gen2 or Gen3 transceiver, it would still make sense for a Gen1 ONU to be tunable across all two channels of a Gen 2 OLT transceiver or across all four channels of a Gen 3 OLT transceiver. To the same end, a Gen2 ONU could be tunable on both of its channels, so it could roam on any of the four channels of a Gen3 OLT transceiver. Only Gen3 ONUs would not take advantage of tunability, for having a quad transmission / receiver array. Of course, if the number of channels is greater than four ( NG-PON2 already has eight), such as the use case I’ve pointed to earlier where two NG-EPON instances on two sets of four channels could be there on the same PON and the 100 Gbps ONU could roam any of its four channels onto any of the channels of the two instances of NG-EPON on the same PON. Barry wrote > If the goal is to just provide a lot of inflexible cheap incremental bandwidth (not a bad goal) than we can declare that all ONU will use 4 CWDM channels in the O band and be done with the discussion. I’m not sure CWDM is an adequate solution at this bitrate. I’ve been meaning to run some simulations on the effect of four wave mixing in the O-band at high bitrates. I like the idea that gain chips with quantum dots are potentially easier to make in the O band (and less expensive) than in the C band, allowing better resiliency to back reflections and possibly sparing the costs of having to package an isolator in the ONU. Finally, I’m not sure CWDM technology lasers have the required linewith to combat chromatic dispersion at such a high bitrate, even if its 25 Gbps over distances of 20 km. I think there is merit in being able to consider the 1260-1280 spectrum proposed for XGS-PON for more than a single channel. Absolutely. A gen-1 25 Gb/s single-lane EPON should provide 2.5x more bandwidth than 10G EPON at less than 2.5x the cost. That won’t happen if you toss in a tunable laser (and tunable receiver filter) in the ONU, and put wavelengths on a DWDM grid. Let’s defer that cost and complexity to the 2nd lane. Ed Somehow, just because the end target is 100G-EPON, people think that we need to utilize the 100G EPON capacity from day one. And if we don’t have 100G ONUs at day one, then we have to fill this capacity with 25G ONUs. This is not what we set to do. The generation 1 is a single-lane EPON. Yes, starting with tunable optics and utilizing 4 lanes will provide 4x of sustained throughput per ONU. But that would be at more than 4x the cost. According to my latest market data, the cost of tunable ONU optics today is ~9x that of 10G/10G-EPON ONU optics. Projections out to 2020 show it to drop to 3.5x the cost of 10/10 ONU optics, which is still very high. Is this not why after completing NG-PON2 standard, SG15 shifted focus to XGS-PON that uses a fixed single wavelength 10/10 optics? If the same cost ratio between tunable and fixed optics remains for the 25G tunable and 25G fixed, then the cost of 50G ONUs will likely be lower than tunable 25G ONUs. A 50G ONU obviously can burst at 50Gb/s peak rate, but additionally can operate as a 25G ONU on either of the channels, or even can operate as two independent 25G ONUs. So, we may spend time and efforts developing the first generation based on tunable optics, but then why wouldn’t operators just skip gen 1 and go directly to 50G ONUs with 2 fixed channels? Glen Here is what I understand so far: Per what Glen has presented: The OLT starts with a Gen 1 transceiver, which is stuck at 25 Gbps until it is replaced with a Gen 2 at 50 Gbps. Only the OLT transceiver is replaced with a Gen 3 transceiver, would it then become possible to add 100 Gbps ONUs on the PON. With a Gen 1 OLT transceiver on the PON, 100 Gbps ONUs would be limited to 25 Gbps. However, in NG-PON2, the use of an external WM allows for different OLT ports (or different OLT’s) to be the source of the additional instances of 10 Gbps channel (up to 8 from 8 different line cards or OLT shelves is allowed). Therefore this allows pay as you grow, in service, with no downtime without requirement of retiring out OLT transceivers. Is this a benefit or a pain in the rear end for operators ? Benefits allow for greater reliability, pay as you grow from cheaper 10 Gbps fixed XFPs/SFP+ with burst mode receivers. Pain in the butt means dealing with the WM and increased footprint. With regards to the benefits of being able to get a 25 Gbps Tunable Tx / Tunable Rx ONU to roam across channels, here are the benefits: - Serviceability of the PON port. If an ONU can move to another channel while the one that is down is being serviced, then everybody is happy.
- Enhanced average throughput on the PON at the expense of peak speed. For instances, with 32 ONUs and 8 lambdas @ 25 Gbps, average throughput would be 25 Gbps / 4 = 6.25 Gbps rather than 25 Gbps / 32 = 0.78 Gbps, which is 8 times greater. Perhaps this is not required for all applications, but as soon as you have mobile fronthaul, or business services on the PON, this capability becomes important.
- As soon as the tuning range at the ONU exceeds the number of users on the PON (and you have an equally sized multi-wavelength Comb laser + Rx Array in the OLT transceiver like what is being done in the OpenOptics MSA), then it becomes possible to turn off burst mode operation both for transmission on the ONU as well as for reception in the OLT. You’re now doing WDM-PON on power splitters. Each user gets a dedicated channel. This is where we want to go in the end with all of this.
- Achieving greater 4 times the throughput of the maximum line rate of a single channel, is all about packaging the cost structure of 4 tunable ONUs in one ONU and to have the MAC and ASIC to deal with the four transceivers. It is perfectly possible to imagine the OLT transceiver would support 32 channels and that an ONU would only be able to bond 4 channels. Then the question becomes which 4 channels to bond in a pool of 32. If the ONU is not tunable, then you are not able to take advantage of assigning different bonded channels to different ONUs.
Francois Menard
CTO & Co-Founder
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