Method of automatically testing the serviceability of a data transmission system

A method of automatically testing the transmission quality of a data transmission system, comprising the steps of:

• transmitting from a testing station during actuation of a first key a bit group containing data bits having a given marking polarity and at least one additional bit corresponding to a spacing condition,
• receiving said bit group in a receiving station,
• analyzing said received bit group for transmission disturbances,
• producing a visual indication is said receiving station in the event of mulitple undisturbed reception of said bit group,
• connecting, in the event of multiple undisturbed reception of said bit group, a receiver in said receiving station to a transmitter therein and retransmitting said bit group to said testing station,
• analyzing said retransmitted bit group for transmission disturbances,
• producing a visual indication in said testing station in the event of multiple undisturbed reception of said retransmitted bit group and
• blocking data input and output circuits in said testing and receiving stations during performance of the foregoing testing method.