1. Multiplexing

4. PDH

5. Multiplexing Plesiochronous digital hierarchy (PDH) -each TDM stream was derived using a separate timing source -Justification bits Synchronous digital hierarchy (SDH) -all equipment is synchronized to a single master clock -Synchronous transport module level 1 or STM-1 is 155.52Mbps -A section is a single length of transmission cable -Section Termination equipment (STE) : repeater -A Line extends across multiple cable sections and is terminated by a line termination equipment (LTE) -> multiplexers and switching nodes -A path is an end-to-end transmission path through the complete transmission system -Each frame comprises 2430 bytes and repeats every 125 microsec. -A frame comprises nine 270-byte segments each of which has a 9- byte header associated with it and a 261-byte payload