According to some sources, SONET is physical layer.

But some sources say that SONET can carry IP directly. Also, SONET defines its own frame -- it has a header and a payload. That must make SONET a data link.

What is the truth about SONET? Also, where can you see SONET equipment and fiber optic lines?


SONET defines a physical layer (or variants thereof) and a common data link layer, similar to Ethernet.

(Circuit-switching) SONET used to be a popular carrier technology but has largely been replaced by (packet-switching, much more efficient) Ethernet.

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