On 5/8/23 21:53, Phil Bedard wrote:

I guess let’s not confuse two things.  The optical network is made up of the photonic portion and then the transponder/muxponder portion.   A single term like “DWDM” can be confusing since it can refer to both.


Indeed.

I am short-handing to mean DWDM on the line side and grey on the client side.


   It will take a long time (maybe never) to remove the photonic switching part of the network.


There was a time when my intention was to do just that. But that was prior to expecting to ever run links larger than 10Gbps :-).


  However, it’s always been cheap to deploy because optical vendors tended to subsidize that network using sales of the other portion, the transponders, which you buy more and more over time.  Those photonic components are expensive.   


It depends on the application... either you want performance, space and power cost optimization or functional integration of previously disparate system-level features. This will determine whether you focus on pluggables or embeddeds, with pluggables promoting cost reduction, while embeddeds push performance.


On the DWDM signal portion, I’m not talking about 100ZR compared to 100G on a transponder or DWDM line system.  100ZR has had to deal with the power limitations of QSFP28 ports, which QDD/OSFP do not suffer from.



Right - 100ZR is short-reach (80km). It's really for the metro edge where 400Gbps is not needed.


  There are quite a few QDD pluggables in production today capable of supporting 100G signals over 1000s of km or 400G near 1500km.


I think the more interesting QSPF-DD (or OSFP) development is OpenZR+, which is an MSA project to standardize 400ZR+. The plan is to be able to support 100Gbps up to 5,800km, and 400Gbps up to 480km (EDFA) or about 1,000km (EDFA + Raman). With a 4x 100Gbps mode supported on QSFP28 router ports, you can have one muxponder talking to 4x routers at 100Gbps each.


  Now that’s not what you can get out of some external transponders, so those will still have their place in high performance applications.   When you move to 800G, 1.2Tbps single channel they also have their own distance limitations.  So it really depends on the application and the network. 


800Gbps and 1.2Tbps applications are really for long haul use-cases, especially if you used 400Gbps pluggables before and run out of distance (so less than 1,000km). They are also preferred for submarine use-cases.

I can't wait to see what happens when the CMOS gets down to 5nm and 3nm.

Mark.