From the Top Down: Channel Multiplex to Interleaver—Layer 2 and Part of Layer 1

As these chapters progress down the NRSC-5 protocol stack, the relationship between the information content and the protocol structure becomes more abstract. Coded Program Service Audio and Program Service Data were merged and encapsulated via the Audio Transport protocol. Parallel to these processes are other processes that will be addressed in Chapters 10 and 11—Station Information Service (SIS) and Advanced Data Service (ADS). The next step down in the stack is the Channel Multiplex, known as Layer 2 for the simple reason that it is the second layer above the transmission medium or physical layer.