STM-1 is a physical layer framing format that provides a 155.52 Mb/s synchronous bit stream for the transport of ATM cells in SDH networks. STM-1 framing can be carried over both optical and electrical physical layers.
It consists of three components:
- S-OH (Section Overhead) of 81 bytes per frame
- P-OH (Path Overhead) of 9 bytes per frame
- VC (Virtual Container) of 2340 bytes per frame (carries tributary signals across the synchronous network)
The information is suitably conditioned for serial transmission on the selected media at a rate which is synchronized to the network.