Telecommunication control unit

{{Short description|Device attached to a computer multiplexer channel which supports multiple terminals}}

{{Use dmy dates|date=April 2025}}

A telecommunication control unit (TCU), line control unit, or terminal control unit{{cite book|title=System analysis handbook|date=1986|publisher=Fort Benjamin Harrison (Ind.). Computer Science School, United States Army Soldier Support Institute|page=3-118|url=https://books.google.com/books?id=ecMrAAAAYAAJ|accessdate=30 July 2016}} (although terminal control unit may also refer to a terminal cluster controller) is a Front-end processor for mainframes and some minicomputers which supports attachment of one or more telecommunication lines.{{cite book|last1=Arick|first1=Martin R.|title=Data Communications: Concepts & Systems|date=1987|publisher=QED Information Sciences|location=Wellesley, MA|isbn=9780894351501|page=76|url=https://books.google.com/books?id=WNoiAAAAMAAJ|accessdate=30 July 2016}} TCUs free processors from handling the data coming in and out of RS-232 ports. The TCU can support multiple terminals, sometimes hundreds. Many of these TCUs can support RS-232 when it is required, although there are other serial interfaces as well.

The advent of ubiquitous TCP/IP has reduced the need for telecommunications control units.