Patent GB-965670-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H04L7/10
Filed: 1961-02-02
Abstract: 965,670. Multiplex pulse signalling. WESTERN ELECTRIC CO. Inc. Feb. 2, 1961 [Feb. 2, 1960], No. 3984/61. Heading H4L. Relates to an arrangement for maintaining synchronization of a plurality of interconnected units in a complex system, e.g. in a pulse code modulation system, which carry out preassigned operations co-ordinated by synchronizing signals, in which not all the units (nodes) are operative simultaneously but may be switched in or out as required, and in which the synchronizing information normally originates with one pre-assigned unit (the primary master node), but is self-reorganizing if different conditions prevail or faults occur. As shown in Figs. 2A to 2C, the nodes 1 to 8 of a complex system are numbered sequentially in order of precedence, number 1 being the primary master which may be determined, for example, by the stability of the timing oscillators positioned at each node. The connecting links between nodes are shown dashed in Fig. 2A to show that before the system is activated no synchronizing channels have been established. In the absence of a signal from an adjoining node each particular node generates and registers its own distinctive signature consisting of a four-digit code of the form j o jj, where j is the numerical rank of the particular node. As the selforganization starts, Fig. 2B, the first three digits of every node signature are transmitted to each adjoining node and these compared with the first, second and fourth digits of the signature registered. The second digit is a measure of the distance between the primary master and the particular node in terms of the number of links involved and thus before comparison each received signature has its second digit augmented by unity to account for the additional link used in the transmission from the preceding node (immediate master). For example at node 4 the signatures compared with the registered signature 404 are 111 from node 1, 212 from node 2, and 313 from node 3, and the control circuit associated with the timing oscillator at node 4 decides that the signal from node 1, 111 is of the highest order and the signature registered at 4 is modified by having digit 3 (the digit identifying it) replace the digit 3 of the signature from 1, producing a new signature 1141. The other signatures are modified as shown. At node 8 the immediate master chosen is node 2 but the signature at 2 cannot be sent to node 8 immediately. When the organized control circuits begin transmitting their signatures to their neighbours, the control circuit at 2 relays the digits 112 so that the signature at 8 becomes 1282, Fig. 2C. Similarly, node 5 is of higher rank than its immediate neighbours and during the transistional period its self-signature remains. When the control circuits transmit the new signatures, the modified signature at 6 is recognized at node 5 so that the final signature at 5 becomes 1256. Thus in the signatures finally registered, digit one denotes the master node, digit 2 denotes the distance between the master and the particular node as measured by the number of links, digit 3 is an identification of the particular node, and digit 4 denotes the preceding node (immediate master). When a failure of the timing signal occurs, which may be due to a failure of the primary master or an intervening link, or an increase in the registered signature takes place due to a re-organization at intervening nodes due to such a failure, the system may be arranged to operate alarm signals and will re-organize itself automatically to a new primary master node in the manner described. For example, if nodes 1 and 2 are faulty, node 3 will take over as primary master. Fig. 4 shows the apparatus at say node 8 connected by links with nodes 2 and 5 of the complex system via transceivers 11-2, 11-5, each receiver receiving supervisory and timing information via channels 13-2, 14-2 and 13-5, 14-5 respectively. The timing information is passed to a control timing selector 18, and before selection of the appropriate timing lead 21-2 or 21-5 local operations are directed by a local clock pulse generator 22. A start pulse closes a preset gate 27 and the register 25 stores the selfsignature 8088 produced by generator 28. The incoming signatures mn2 and pq5 have their second digits augmented by unity in a translator 40 which passes the signatures to a scanner 45 where they are successively sampled and supplied to a comparator 50. At the comparator 50 they are compared with the signature stored in the register 25 and if of higher rank the gate 60 is closed and the new signature stored at 25, digit D3 designating the rank of the local node remaining unchanged. Digit D4 operates the timing selector 18 causing it to select the appropriate timing signal. The first three digits D1, D2, D3 of the stored signature are relayed along with the timing signal selected by digit D4, to the adjoining nodes by means, not shown. Fig. 5 shows the same arrangement but in which alarm signals are provided. A signature monitor alarm 82 operates to select the line 84-2 or 84-5 which provides the signature stored at 25 at a given instant, the fourth digit D4 in the register controlling a selector 83 similar to the timing selector 18. The first two digits of the incoming signature are continuously compared with corresponding digits D1, D2, stored at 25 and whenever the selected incoming signature increases, a delay generator 70 is energized to inhibit a gate 72, the delay thus introduced allowing all, disabled units of the system to clear themselves of signatures no longer valid. During the delay a gate 27 is operated and the self-signature from the generator 28 is stored at 25 and termination of the signal from generator 70 allows reorganization to proceed. If the timing signal should fail although the supervisory signal continues to be received it is detected by a timing alarm monitor 93. The digit D4 from the register 25 operates a selector 95 to select the appropriate timing lead and if the timing signal stops the delay generator 70 is started and the control circuit operates as before. The complete control circuit at a node in a pulse code modulation system is described, Figs. 6A to 6H (not shown).