Patent GB-1473552-A (GB)
Title: Control apparatus for protection switching systems and to systems including such apparatus
IPC: H04B1/74
Filed: 1974-06-03
Abstract: 1473552 Multichannel communication system protection WESTERN ELECTRIC CO Inc 3 June 1974 [6 June 1973 20 Dec 1973] 24578/74 Heading H4L In a communication system having a number of regular channels and at least one protection channel and being such that in the event of failure or degradation, a regular channel is automatically replaced by the protection channel, a network is incorporated in the automatic replacement circuitry which contains a number of segments, one associated with the protection channel and the remainder a respective regular channel. On the occurrence of a fault, the segment associated with the protection channel is first enabled, and then subsequently the regular channel segments are enabled in sequence. A control arrangement operates in response to regular channel failure and enablement of the associated circuit segment to initiate substitution of the protection channel for the associated regular channel. Such an arrangement is said to simplify modification of the system when it is desired to incorporate more (or fewer) regular elements. General operation.-In an embodiment of the system, shown in outline in Fig. 1, regular channels A-F are monitored by channel monitors 21-A to 21-F, and two protection channels X, Y provided, each having a carrier and pilot generator 14, 15, load 19, 20 and monitor 21-X, 21-Y. If a monitor detects a faulty regular channel, and one or other of the protection channels is satisfactory and free, the switch control apparatus 23 is operated to signal via path 26 to the transmitter and of the system 13 to cause the faulty channel to be switched to a protection channel, and also to signal to the receiver switch 18 to make the appropriate connections. The generator and load of the selected channel are switched out. Switch control apparatus operation (Figs. 2A, 2B).-The apparatus is sectionalized (parts 23-A, 23-B ... 23-F, 23-X, 23-Y) in accordance with the number of channels. Each section incorporates a status circuit 35-A- 35-Y which normally delivers "1's" on two outputs SR and ECR in response to input signals from the respective channel monitor 21 indicating that the monitored channel is satisfactory. If the carrier on any regular channel is lost, the noise level becomes too high, a "1" is delivered to the status circuit and the outputs of this become zero. The ECR output is delivered to an enabling circuit 36 for a sequential pulsing circuit (SPC). There are two sequential pulsing circuits, each associated with a respective protection channel, and the channel status circuits are primarily apportioned to one or other of these; thus status circuits 35-A, 35-C, 35-E are such that they enable the X channel sequential pulsing circuit (XSPC). The enabling circuit 36-X will be disabled if the X protection channel is unsatisfactory, otherwise it will apply a pulse to the protection channel XSPC segment 31-XX. This pulse circulates through the other segments of the XSPC, 31-XA, 31-XB &c. .... As it passes each segment, a pulse is applied to a corresponding assignment and memory logic control circuit 34-XA &c. If this is also receiving a "0" from the SR output of the corresponding status circuit 35, signals are issued to initiate the appropriate switching operations at the transmitter and receiver terminals.  Further logic connections in the system, involving the actuating circuits 37, enable the alternative protection channel to be used should the primary one be in use or unsatisfactory. The logical arrangement of the XSPC is explained in the Specification (with reference to Fig. 3, not shown).