a digital line card for interfacing a remotely located digital telephone to a central office system by a two - wire connection is disclosed . the digital line card consists of a line interface connected to the two - wire connection . the line interface provides a full duplex transmission link with the remotely located digital telephone over the two - wire connection . a buffer is connected between the line interface and the central office system . the buffer converts data between the line interface and the central office system . the line card further comprising a protocol controller connected to the line interface . the protocol controller performs a packet protocol for communications with the remotely located telephone . to complete the line card , there is provided a processor connected to the protocol controller and to the central office system , under the direction of the central office system , the processor controls the operation of the digital line card and , through the protocol controller means , communicates with and controls the remotely located digital telephone .