| Term | Definition |
| Circuit Switching | It is used for call routing in the telephone network. Circuit switching refers to the mechanism of communication in which a dedicated path with allocated bandwidth is set up in an on-demand basis before the actual communication can take place. |
| On-demand | On-demand means that the path is set up quickly when the request is made. The dedicated path is released immediately when the communication is over. |
| Trunkgroup | It refers to a group of circuits or trunks on a link between two directly connected switches; a trunkgroup is also referred as an inter-machine trunk (IMT) while considered in the context of connecting two switches. |
| Time-Division Multiplexing (TDM) | It is a type of multiplexing that combines data streams by assigning each stream a different time slot in a set. TDM repeatedly transmits a fixed sequence of time slots over a single transmission channel. Within T-Carrier systems, such as T-1 and T-3, TDM combines Pulse Code Modulated (PCM) streams created for each conversation or data stream. |