Re: Routed optical networks

[Phil Bedard <bedard.phil () gmail com>]

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

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

Phil

From: NANOG <nanog-bounces+bedard.phil=gmail.com () nanog org> on behalf of Mark Tinka <mark@tinka.africa>
Date: Friday, May 5, 2023 at 12:55 AM
To: nanog () nanog org <nanog () nanog org>
Subject: Re: Routed optical networks

On 5/4/23 19:32, Phil Bedard wrote:

It’s my personal opinion we aren’t to the days yet of where we can simply build an all packet network with no photonic 
switching that carries all services, but eventually (random # of years) it gets there for many networks.  There are 
also always going to be high performance applications for transponders where pluggable optics aren’t a good fit.

I think every time the IP space gets close to running an all-packet network, the Transport folk come out with an easier 
way to do it, that it's too hard to ignore.

Based on that, I think they will always be one step ahead, with the key advantage being reliability of capacity over 
the distance, for the cost.

The farther your fibre has to run, the costlier it gets to do it without DWDM.

I mean, it's only now that 100G-ZR is becoming a reality for packet networks, and we are talking thousands of US$ for 
optics to get us 80km - 120km distance. Meanwhile, DWDM vendors can get you 800Gbps per wavelength in the same distance 
(or 30X that distance) far less cheaply.

I get the appeal of not needing DWDM gear to underlay your packet network... it's neater and offers fewer points of 
failure. But unless you are dealing with very short distances and can ride a reasonable balance between service 
features and switching/forwarding capacity in your router/switch, it's going to be hard to ignore the DWDM gear if you 
are trying to be a serious operation, at that scale, over a wide area.

Mark.