18. A text compression unit for disposition between a local text encoding and decoding station of a telecommunication network and the communications network interface for communication with remote stations which may or may not be equipped with a similar text compression unit comprising: multiplex means for coupling the unit between the local text encoding and decoding station and the network interface unit, and data processing and storage means coupled to the multiplex means for automatically receiving a standard data stream from the local station, compressing the standard data stream to produce a compressed data stream, and sending the compressed data stream to a remote station, and for receiving a compressed data stream from a remote station, decompressing the compressed data stream received from the remote station, and sending the decompressed data stream to the local station and for compiling a library of data units in a memory during compression of the data by writing each data unit into the memory upon the first occurrence of each data unit and for each occurrence thereafter compiling the address of the data 1 unit in the library instead of an original representation of the data unit.
18. A text compression unit for disposition between a local text encoding and decoding station of a telecommunication network and the communications network interface for communication with remote stations which may or may not be equipped with a similar text compression unit comprising: multiplex means for coupling the unit between the local text encoding and decoding station and the network interface unit, and data processing and storage means coupled to the multiplex means for automatically receiving a standard data stream from the local station, compressing the standard data stream to produce a compressed data stream, and sending the compressed data stream to a remote station, and for receiving a compressed data stream from a remote station, decompressing the compressed data stream received from the remote station, and sending the decompressed data stream to the local station and for compiling a library of data units in a memory during compression of the data by writing each data unit into the memory upon the first occurrence of each data unit and for each occurrence thereafter compiling the address of the data 1 unit in the library instead of an original representation of the data unit. 19. The text compression unit of claim 18 wherein the data processing and storage means further includes means for: storing call-up instructions for establishing communications with the remote station and at least a portion of a standard message received from the local station, automatically and repeatedly executing the call-up of the remote station until the remote station answers-back, determining from the answer-back whether the remote station is equipped to decompress a compressed message, and either sending a compressed or standard message to the remote station in accordance with the capability of the remote station as signalled by the answer-back.