Re: [802.3_NGEPON] ONU ASIC and wavelength plans

[Marek Hajduczenia <marek.hajduczenia@xxxxxxxxx>]

Francois

 

NG-PON2 aside (we are not trying to do just what they did – their decision process and requirement were different at design time), the use of external muxing is messy, operationally complex, adds failure points in the hub, and extra loss in the signal path. I believe the beauty and power of current multi-rate OLTs supporting 1G and 10G-EPON is that a single port can do both, and a customer upgrade in this case is trivial – replace the ONU and it comes up on 10G-EPON with no further reconfiguration needed on the OLT. I would love to have the same flexibility in the future and avoid the need for external filtering components and spaghetti running between OLT ports and some shelf located underneath it.

 

As far as the arguments in favor of tuneability go:

 

·         I can agree with 1 – it makes sense, but most outages are caused by fiber cuts, and these cannot be resolved by tuning to a different range. Data on failure rates of a single channel in multi-channel transceiver is something to consider, for sure, but I do not have data on it right now to assess how valuable this is.

·         Item 2: this does not work that well. Once CIPRI hits rates above a few Gb/s, cell towers would have to be moved to 50G or 100G solution to avoid moving them around too often. This is a controlled bandwidth increase and moving them around to different 25G wavelength will not solve the growth curve.

·         Item 3: I do not think the scope of the project is to do a WDM-PON – a vendor can always design it, but we set out to do something different.

·         Item 4: this is the 50G and 100G solution we are talking about. I am not sure why this is a argument in favor of tuneability, really …

 

Marek

 

From: Francois Menard [mailto:fmenard@xxxxxxxxxxx]
Sent: Tuesday, February 23, 2016 10:02 AM
To: STDS-802-3-NGEPON@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_NGEPON] ONU ASIC and wavelength plans

 

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:

1. 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.
2. 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.
3. 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.  
4. 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=-

--

Francois Menard
CTO & Co-Founder

AEPONYX inc.

Cell: +1 (819) 609-1394
E-Mail: francois.menard@xxxxxxxxxxx