Time division telephone switching exchange

Claim 1

In an exchange for a time-division-multiplex communication system serving a multiplicity of subscriber lines identified by individual addresses, in combination: a primary and a secondary processor each including a circulating caller memory, a circulating responder memory and a circulating monitoring memory, each of said memories being divided into a predetermined number of service phases and conversation phases representing respective time slots in a recurrent memory cycle, the conversation phases of said caller and responder memories serving for the storage of addresses of subscriber lines initiating a call or engaged in a conversation, the conversation phases of said monitoring memory serving for the storage of data relating to a call initiated or in progress from a subscriber line whose address is entered in a corresponding conversation phase of the associated caller memory; timing means for stepping all memories of both processors in synchronism through consecutive memory cycles; scanning means in each processor for periodically sampling said subscriber lines in a service phase of successive memory cycles and ascertaining the activity thereof; test means responsive to said scanning means for determining the absence of an entry of the address of an active subscriber line in any conversation phase of each caller and responder memory; first allocation means in each processor controlled by the associated monitoring memory for entering the address of any previously unentered active subscriber line in the first free conversation phase of the associated caller memory; preference means controlled by both monitoring memories for inhibiting the entry of an address in the first free conversation phase of the caller memory of said secondary processor upon a coincidence of said first free conversation phase with a first free conversation phase of the caller memory of said primary processor; malfunction-detecting means responsive to a fault indication from either processor for limiting the operation of said first allocation means to the caller memory of the other processor, sadi preference means being ineffectual upon the occurrence of a fault indication from said primary processor; and second allocation means responsive to entry in a conversation phase of either monitoring memory, corresponding to a phase allocated in the associated caller memory to an active subscriber line, of an identification of a called subscriber line for entering the address of the latter subscriber line in the corresponding phase of the associated responder memory preparatorily to the establishment of a connection between the two subscriber lines so entered.