lux limitation. The second interface in common usage is the V.35 and merit some discussion. On the simplest level, an interface recommendation supplied via a 34 way connector, its electrical consists of three parts, a protocol, an electrical specification and a characteristics providing for balanced (carrying equal and opposite mechanical connector. The protocol describes the logical attributes voltages) interchange circuits. Neither lead is at ground potential. which typically include the meaning of the electrical signals on each Balanced circuits provide a cancellation effect which bestows pin, the interrelationship between the signals and the means to higher immunity to interference and, due to lower capacitance, exchange information. allows extended transmission distances in comparison to RS232C. The electrical and mechanical specification in turn specify the Originally specified at 48kbit/s operation, it is common to find U.S. physical attributes of the electrical signals on the pins and the developed equipment rated at up to MegaStream speeds. Later dimensions and construction of the connector itself. A successful standards developed for higher rates and operating distances origin- connection is dependent on the combination of all three. The best ated initially as EIA RS423 and RS422 which were subsequently known of these is the ubiquitous Electronic Industries Association adopted by the CCITT as recommendations V.10 and V.11 respec- (EIA) RS232C specification which formed the basis of the CCITT tively. Because their electrical characteristics were suitable for V.24 recommendation. Whereas RS232C described both physical public data network interfaces they have also been assigned as X.26 and logical attributes, V.24 describes only the logical and is sup- and X.27 respectively. plemented by recommendations V.28 and ISO2110 for electrical The potential for confusion increased when EIA released RS449 and mechanical characteristics. to cover the non electrical aspects, as well as updating RS232C. The use of the 