Taxonomy
Tandem derives from the Latin adverb tandem meaning "at length," and is used in English to mean a group of two people or machines working together, usually in series. A "tandem switch" is used to connect two other switches to each other via one or more trunks. Thus, trunk switches are always part of a series of switches and lines that connect telephone callers to each other.
Read more about this topic: Class 4 Telephone Switch