Telecommunications transmission security arrangement

Claim 1

A telecommunications transmission security arrangement connected to a dual path ring transmission system wherein transmission in one path occurs in a direction opposite to transmission in the other path comprising first and second transmission paths, each path having first and second serially connected circuit means, said first circuit means of said first path being arranged to be connectable to said second circuit means of said second path, and said first circuit means of said second path being arranged to be connectable to said second circuit means of said first path, each second circuit means is arranged to constantly monitor alarm conditions of the transmission paths and based upon an alarm condition monitored by said second circuit means, the second circuit means are arranged to select a transmission path by way of the first circuit means of the first path and the second circuit means of the second path when the first path is determined not suitable for transmission by the second circuit means, and to set up a transmission path by way of the first circuit means of the second path and the second circuit means of the first path when the second path is determined not suitable for transmission, by the second circuit means, because of a monitored alarm condition, and wherein connection to the ring system is made by way of two add/drop multiplexers, a first of which is arranged to transfer traffic to and from an upper transmission rate synchronous stream and the second of which is arranged to transfer traffic to and from a lower transmission rate synchronous stream, each add/drop multiplexer including a switching arrangement which transfers a number of tributaries from the ring system in a defined order.