"This standard is applicable to the interconnection of data processing terminal equipment and data communication equipment. It defines a means of exchanging control signals and binary serialized data signals between data processing terminal equipment and data communication equipment@ and is of particular importance when each is furnished by a different company. This standard is applicable for data transmission when used in conjunction with electronic terminal equipment. There is no implication that the speeds in the two directions of transmission are necessarily the same. This standard applies to all classes of data communication@ both synchronous and asynchronous@ including the following: A. Private line service@ either tow-wire or four-wire. Consideration is given to multipoint operation. B. Switched network service@ either two-wire or four-wire. Consideration is given to automatic answering of calls@ but it should be noted that this standard may not include all the interchange circuits that may be required for establishing the connection. C. It also applies equally to both sides of separate equipments which provide other functions required by the communications system and which may be inserted between the data processing terminal equipment and data communication equipment. It is intended that the signal interchange point shall be located on the customer's premises and that the interchange circuits shall convey signals over relatively short distance (i.e.@ less than fifty feet). The data communication equipment may include transmitting and receiving signal converters@ The term ""signal converter' refers to the equipment which changes the data signal into a form suitable to the transmission medium@ or the reverse. In general@ separate signal converters are provided for transmission and for reception. A data set may include signal converters and control circuits. Other functions@ such as pulse regeneration and error control@ may or may not be provided. Equipment to provide these other functions may be included in the data processing terminal equipment or in the data communication equipment@ or it may be separate equipment@ as described in paragraph 1.3 (C). It is not intended that when other functions are provided within the data processing terminal equipment or data communication equipment@ that this interface standard apply other than to the interchange circuits between the two classes of equipment."