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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.
F.
From: Harstead, Ed (Nokia - US) [mailto:ed.harstead@xxxxxxxxx]
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
From: EXT Glen Kramer [mailto:glen.kramer@xxxxxxxxxxxx]
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 From: Francois Menard [mailto:fmenard@xxxxxxxxxxx]
Marek, 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:
-=Francois=- -- Francois Menard AEPONYX inc. Cell: +1 (819) 609-1394 |