Patent GB-1236887-A (GB)
Title: Improvements in or relating to automatic telecommunications exchange systems
IPC: H04Q3/545
Filed: 1969-10-01
Abstract: 1,236,887. Program-controlled exchange systems. SIEMENS A.G. 1 Oct., 1969 [2 Oct., 1968], No. 48143/69. Heading H4K. A program-controlled exchange system, in which the network comprises a number of exchange groups each of which is constituted by a number of switching groups each comprised of a number of individual multiple switches, and in which connections are established from any one inlet of the first rank of switches of the network into the network and back to any other such inlet of the first rank, the number of switching stages involved in a connection being as a matter of choice small or large according to the separation between the inlets being connected, and in which incoming and outgoing relay sets for each other-exchange direction are distributed over the network inlets, the system processor having a record of idle/busy conditions of the relay sets for each other-exchange direction together with an indication of whether the grade of provision of such sets is relatively large or small, search for a free set in a particular wanted direction being conducted by the processor in steps each such step embracing more or less of the exchange inlets according to the grade of provision of the sets. In a first arrangement the storage layout in the processor is such that given the identity of the wanted direction of a network relay set access is first made to a store peculiar to that direction and containing a statistical record of the number of free relay sets serving that direction together with an indication of the grade of provision of such sets. If there are no free sets the process terminates but if at least one free set is available access is directed to a store peculiar to the exchange group from which the connection demand originates such store giving an indication of the number of sets in the wanted direction that are free within the group. If such a free set exists and the grade of provision is small, access is directed to a complete record of the idle/busy states of all relay sets in the wanted direction, only that section of the record corresponding to the originating exchange group being searched for the first free set. Should no free relay set be indicated in the originating exchange group, the search is diverted to an arbitrarily nominated other exchange group and from there, if necessary, to the remaining exchange groups in sequence. If the grade of provision is large and a free set exists in the originating exchange group, access is directed to a record of how many idle sets exist in the originating switch group of the exchange group and, should one be available, access is then directed to the corresponding small section of the complete record of idle/busy states to seize the first free set. Should no idle set be available in the originating switch group, search is continued in an arbitrarily determined other switch group and, if necessary, over the remaining switch groups of the exchange group in sequence. In a second arrangement the other-exchange directions are served by relays sets with a grade of provision that may be large, medium, or small and the distribution of sets over the exchange inlets is such that no multiple switch serves more than one set of a given direction with a large grade of provision, no switch group serves more than one set of a direction of medium grade, and no exchange group serves more than one set of a direction of small grade. Separate stores are provided per switch group for the idle/busy conditions of sets serving each direction with a large grade of provision. Search starts from that set serving the same multiple switch from which demand for the connection originated, the search continuing within the switch group and being extended to other switch groups in the exchange group and to other exchange groups as necessary. Separate stores are provided per exchange group for the idle/busy conditions of sets serving directions with a medium grade of service, search starting from the set of the originating switch group and being extended as necessary. A single store is provided the idle/busy conditions of sets serving directions with a small grade of provision search starting with that set of the exchange group from which demand originated. The storage position of seized sets establishes their identity. The grade of provision of a wanted direction is obtained by initial access to a general store which also keeps a statistical record of relay sets free in each direction. In a third arrangement, after initial access to determine grade of provision, access is directed to one of three storage arrangements according to grade. If the grade is one of large provision the process is steered to a store peculiar to that direction and which records the identity of the set standing idle the longest and the identity of the last set to be released out of a list of free sets served by the switch group in which demand for a connection originated. The list is compiled as a chain with each set being associated with the identity of the set released next, and so on. If these records are zero no set is idle in the switch group and search steps to the cyclically next switch group for which a similarly indicated list of free sets is provided. If within the exchange group, no free set is available, search continues in an arbitrarily nominated other exchange group and from there, if necessary, cyclically over remaining exchange groups. If, the grade of provision of relay sets in a wanted direction is medium, access is directed to a store containing next-for-use and last-to-be-freed identities of sets served by each of the exchange groups, and for small grade of provision a single list is available covering the whole network. In each search the lists are examined to find a free set which is as close as possible to the originating network inlet. A statistical record of the traffic in each exchange group may be taken.