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Barry, While it is simple on paper, the number of supported data rate combinations would be staggering and that will translate into silicon complexity, which I imagine will not be simple slam dank to begin with. We need analysis of the impact it will have because I do not see another way to settle this Marek From: Barry Colella [mailto:barry.colella@xxxxxxxxxxxxxxxxxxx] I agree that tunable and DWDM is costly. However, I’m not advocating tunable optics as a requirement. My original point was that, although I agree with most of Glen’s presentation from last Thursday, I was thinking that only having 25G ONU on a single wavelength was a drawback in a 100G capable PON. I suggested that we design the standard so that we can accommodate both fixed and tunable as a way to overcome this if possible given the lack of support (understandable) for different fixed wavelength 25G ONU. 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. 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. 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 |