My understanding is ATM is data link packet switched Wan solution like FRame relay .
Sonet means ( fiber optics) links over which ATM frames(cells) travel. So In this sense, sonet should be mapped to physical layer of OSI layers.
Is my understanding correct ?
Thanks a lot and have a nice weekend !
from the OSI point of view SONET provides L1 services to data networks.
The Sonet framework and its associated protocols and features like path protection, reroute can also be classified up to OSI layer3.
In communication world Sonet/SDH is seen as a transport framework (not OSI transport layer)that provides a structured synchronus service to transport TDM circuits from E1/T1 to OC-1 and above.
Hope to help
So In this sense, sonet should be mapped to physical layer of OSI layers.
Actually, SONET is considered a transport protocol. Check this link so you can see how a SONET frame looks like: