Enterprise Telephony (ET) is a business telephone system that provides basic business features, such as call hold, three-way calling, call transfer, and call forwarding. ET shares many similarities with the Public Switched Telephone Network (PSTN), but there are many key differences. This chapter details both the similarities and differences between these two networks, the ways in which they interoperate, and typical ET network designs.
The PSTN and ET are similar in the following ways:
Circuit Switching—Both networks are based on the time-division multiplexing (TDM) switching of 64-kbps circuits.
Common Infrastructure Model—Bearer channels, call-control, and service planes are ...