So, I'm reviewing the different IEEE transmission standards for an exam, and I've noticed that for the 10GBASE-X standards, there's two different sets of fiber-optic standards, 10GBASE-xW and 10GBASE-xR. It's noted that the W standards are for WANs and a bit of googling turns up that they're "SONET capable", but I don't really know what that means.
They have the same ranges, same data rates (or at least, not difference is noted), use the same wavelengths (I mean, yes, SW/SR uses a different wavelength of light than LW/LR, but the W and R ones don't differ), and they're both IEEE 802.3ae specifications.
and importantly, I haven't seen separate specifications for WAN/SONET and LAN fiber-optic transmission standards in the lower speeds---gigabit and 100M fast ether net just have one set of IEEE fiber-optic transmission standards
So why are there separate specifications for the 10 gigabit standards? what does it mean to be "SONET capable" and why did we only need that for 10 gigabit speeds?