On 4/21/24 08:12, Saku Ytti wrote:

Key difference being, WAN-PHY does not provide synchronous timing, so
it's not SDH/SONET compatible for strict definition for it, but it
does have the frame format. And the optical systems which could
regenerate SONET/SDH framing, didn't care about timing, they just
wanted to be able to parse and generate those frames, which they
could, but they could not do it for ethernet frames.

Correct.

In those days, WAN-PHY was considered "SONET/SDH-Lite".

I think it is pretty clear, the driver was to support long haul
regeneration, so it was always going to be a stop-gap solution. Even
though I know some networks, who specifically wanted WAN-PHY for its
error reporting capabilities, I don't think this was majority driver,
majority driver almost certainly was 'thats only thing we can put on
this circuit'.

SONET/SDH did have similar reach as OTN back then, just less bandwidth for the distance. It had FEC support for STM-16, STM-64 and STM-256.

I really think the bigger driver was interface cost, because EoS had already been selling for 1GE alongside STM-16 for 2.5G. In those days, if you needed more than 1G but less than 10G, it was a toss-up between 2x 1G EoSDH vs. 1x STM-16. Often times, you took the 2x 1G EoSDH because 2x 1GE ports were cheaper than 1x STM-16 port, even though you ended up losing about 405Mbps of capacity in the process, which was a huge deal.

The backbone providers did not like selling EoSDH services, because it was too much admin. for them (VC container management), and they ended up paying more for transponders on their side than their customers did for Ethernet ports on theirs :-).

But by and large, the majority of networks in our market maintained SDH services long after coherent became commercially available. It was a perception thing, that SDH was more superior to Ethernet, even if that Ethernet was transported over a DWDM network.

In the end, SDH port costs were too hard to ignore due to router vendors maintaining their mark-up on them despite dying demand, which then led to the migration from SDH to EoDWDM growing significantly from about 2016. Optical vendors also began de-prioritizing SDH transponder ports, which had a massive impact on the SLTE (submarine) side in making the decision to encourage customers away from SDH for wet services.

Mark.