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:
- 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=-
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Francois Menard
CTO & Co-Founder
AEPONYX inc.
Cell: +1 (819) 609-1394
E-Mail: francois.menard@xxxxxxxxxxx