Abstract: A method for configuring an interface device and a protection device in a digital communication system. The interface device has a first port for communicating with other devices, the first port being in a high-impedance state when the interface device fails. The protection device has a second port for replacing the communication of the interface device when the interface device fails, the second port being in a high-impedance state when the protection device is not in the replacing state. The primary winding of a first transformer is in series connection with the first port, and the primary winding of a second transformer is in series connection with the second port. The secondary winding of the first transformer and the secondary winding of the second transformer are connected in parallel. The resultant configuration makes the system simplified, compact, economic and easy for maintenance.

Abstract: A method of failure protection in a digital transmission system having a plurality of transmission elements connected in a ring configuration over metallic media, said ring configuration being formed by at least two paths, one path as a normal path for the transmission at the normal status, another path as a backup path which forms a closed loop and has no connection with said normal path at the normal status, said normal path and said backup path having opposite transmission directions, said method comprising the step of connecting said normal path and said backup path in said transmission element through hardware when a failure happens in said normal path so as to maintain the transmission. A digital transmission system with less expensive transmission elements and better failure protection can be obtained accordingly.

Abstract: A method and device for determining whether a stream of digital words, each comprising a plurality of binary digits, represents data signals, or represents digitized voice is disclosed. The method comprises the step of testing the steadiness or randomness of an individual bit within a predetermined sequence of each said digital words. If the individual bit is tested to be random, the stream of digital words represents data signals; and if the individual bit is test to be steady, the stream of digital words represents voice signals. The device comprises a shift registers to store the predetermined sequence of the digital words, a counter to control the shift register, and a gate arrays to determine steadiness or randomness of the individual bit within the predetermined sequence of each said digital words.