Routed optical networks

Tue May 9 06:03:00 UTC 2023

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.
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