A line card or Digital Line Card is a modular electronic circuit on a printed circuit board, the electronic circuits on the card interfacing the telecommunication lines coming from the subscribers (such as copper wire or optical fibers) to the rest of the telecommunications access network.
A line card commonly interfaces the twisted pair cable of a POTS local loop to the public switched telephone network (PSTN). Telephone line cards used in PSTN perform multiple tasks such as analog-to-digital and digital-to-analog conversion of voice, off-hook detection, ring supervision, line integrity tests, and other BORSCHT functions. In some telephone exchange designs the line cards generate ringing current and decode DTMF signals. The line card in a Subscriber Loop Carrier is commonly called a Subscriber Line Interface Card (SLIC).
A line card can terminate a line supporting voice POTS service, ISDN service, DSL service, or proprietary ones. Some line cards are capable of terminating more than one type of service.
Since an access network element is usually intended to interface many users (typically a few thousands) some exchanges have multiple line terminations per card. Similarly, it is common to have many line cards in the same network element.
Line Card less often refers to a brochure listing manufacturers and products sold by a third party, for example a distributor or representative..