On 4/20/24 14:41, Dave Cohen wrote:
LAN PHY dominates in the US too. Requests for WAN PHY were almost exclusively for terrestrial backhaul extending off of legacy subsea systems that still commonly had TDM-framed services. It’s been a couple of years since I’ve been in optical transport directly but these requests were essentially non-existent after 2018 or so. OTN became somewhat more common from 2014 onward as optical system interop improved, but actually was more common in the enterprise space as providers would generally go straight to fiber in most use cases, and with dark fiber opex costs coming down in many markets, I see OTN requests as winnowing here as well.
What really changed the game was coherent detection, which breathed new life into legacy subsea cables that were built on dispersion-managed fibre. Post-2014 when uncompensated (and highly dispersed) fibre has been the standard for subsea builds (even for SDM cables), coherent optical systems are the mainstay. In fact, because linear dispersion can be accurately calculated for the cable span, uncompensated cables are a good thing because the dispersion compensation happens in very advanced coherent DSP's in the optical engine, rather than in the fibre itself.
WAN-PHY did not extend to 40G or 100G, which can explain one of the reasons it lost favour. For 10G, its availability also depended on the type of device, its NOS, line card and/or pluggable at the time, which made it hard to find a standard around this if you built multi-vendor networks or purchased backhaul services from 3rd party providers that had non-standard support for WAN-PHY/OTN/G.709. In other words, LAN-PHY (and plain Ethernet) became the lowest common denominator in the majority of cases for customers.
In 2024, I find that operators care more about bringing the circuit up than using its link properties to trigger monitoring, failover and reconvergence. The simplest way to do that is to ask for plain Ethernet services, particularly for 100G and 400G, but also for 10G. In practice, this has been reasonably reliable in the past 2 - 3 years when procuring 100G backhaul services. So for the most part, users of these services seem to be otherwise happy.
Mark.
