On 4/20/24 21:36, borg@uu3.net wrote:

Erm, WAN-PHY did not extend into 40G because there was not much
of those STM-256 deployment? (or customers didnt wanted to pay for those).

With SONET/SDH, as the traffic rate increased, so did the number of overhead bytes. With every iteration of the data rate, the overhead bytes quadrupled. This was one of the key reasons we did not see field deployment of STM-256/OC-768 and STM-1024/OC-3072. For example, if SONET/SDH had to transport a 100G service, it would require 160Gbps of bandwidth. That clearly wasn't going to work.

At the time when STM-256/OC-768 was being developed, DWDM and OTN had come a long way. The granularity SONET/SDH required to stand up a service had become too small for the growing data rate (primarily VC-3, VC-4 and VC-12). If you look at OTN, the smallest container is 1.25Gbps (ODU0), which was attractive for networks looking to migrate from E1's, E3's, STM-1's, STM-4's and STM-16's - carried over VC-12, VC-4 and VC-3 SDH circuits - to 1GE, for example, rather than trying to keep their PDH/SDH infrastructure going.

DWDM and OTN permitted a very small control overhead, so as data rates increased, there wasn't the same penalty you got with SONET/SDH.
WAN-PHY was designed so people could encapsulate Ethernet frames
right into STM-64. Once world moved out of SDH/SONET stuff, there was
no more need for WAN-PHY anymore.

Technically, what you are describing is EoS (Ethernet over SONET, Ethernet over SDH), which is not the same as WAN-PHY (although the working groups that developed these nearly confused each other in the process, ANSI/ITU for the former vs. IEEE for the latter).

WAN-PHY was developed to be operated across multiple vendors over different media... SONET/SDH, DWDM, IP/MPLS/Ethernet devices and even dark fibre. The goal of WAN-PHY was to deliver a low-cost Ethernet interface that was SONET/SDH-compatible, as EoS interfaces were too costly for operators and their customers.

As we saw in real life, 10GE ports out-sold STM-64/OC-192 ports, as networks replaced SONET/SDH backbones with DWDM and OTN.

Mark.