SONET/SDH
First 3 columns are for system mgt. info.
- First 3 rows (of first 3 cols) contain section overhead
- Next 6 contain line overhead
Synchronous Payload Envelope (SPE) - the user data can start anywhere in the SONET frame.Useful when 1) a dummy frame is being constructed. 2) payload does not fit into a frame (we will study this in ATM)