Patent GB-1325076-A (GB)
Title: Multi-stage time division multiplex highway switching network
IPC: H04M3/22
Filed: 1970-11-11
Abstract: 1325076 Automatic exchange systems COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 11 Nov 1970 [17 Nov 1969] 53747/70 Addition to 1286909 Heading H4K A three-stage time-division-multiplex switching network comprises an array of switches in its first stage connecting incoming to intermediate time division multiplex highways, an array of switches in the second stage connecting the intermediate highway outlets of the first stage to further intermediate highways giving access to a third stage of switches over which outgoing highways are accessible; each switch comprising channel stores for each incoming highway, a store in which all channels of all incoming highways are set up in parallel, channel stores for each outgoing highway and a control circuit for reading out to an outgoing channel from the storage section of an incoming channel; route selection across the network being effected by reference to an intermediate highway channel state record under direction of a processor which provides the identities of the first- and third-stage switches serving the incoming and outgoing channels to be connected, an idle channel to a first of the second-stage switches being sought, and, if such exists, an idle channel being sought from that first of the second-stage switches, the search being taken to other of the second-stage switches if necessary. The trunking of the intermediate highways is such that each first-stage switch has access over one highway to each second-stage switch and each second-stage switch has access over one highway to each third-stage switch. For each second-stage switch, therefore, only one incoming and one outgoing intermediate highway will be pertinent to a search for a route between identified terminals of the network. A store MCO, Fig.3, is provided with as many sections as there are intermediate highways and each section records the idle/busy state of the channels of a highway. An address register is set up with a 5-bit code ACI to identify those storage sections pertaining to all intermediate highways serving a particular second-stage switch. The register is also set up with a 5-bit code ACE/ ACS and a 1-bit code LRS/LRE to identify a particular one of the highways serving the indicated second-stage switch. The 5-bit code in ACE/ACS indicates the number of the incoming first-stage switch or of the outgoing third-stage switch. The one bit register section LRS/LRE indicates whether the highway is on the incoming or outgoing side of the second-stage switch. An address decoder effects read out of the selected highway channel states as a parallel array of bits, one per channel, to a register RLE for presentation to a left-most idle channel selector CC. The particular free channel selected by CC is indicated to encoder CDB which sets up the channel identity as a 5-bit code in RVT. In a route search operation, accessing MCO in this manner, the address represents the first-stage switch over which connection is desired and an arbitrary secondstage switch, and if no free channel exists the 5- bit code in ACI is incremented to try the next second-stage switch. When a free channel from the first-stage switch to a second-stage switch is found the identity of the channel in RVT is transferred for preservation in a common control and processor interface BLDC. In respect of the same second-stage switch indicated from ACI, the address of the third-stage switch over which connection is desired is put in ACE/ACS and LRS/LRE and a free channel in the intermediate highway so indicated is selected from the record in MCO and encoded into register RVT. If no such idle channel exists the search progresses to the next second-stage switch. If a free channel is so indicated it is transferred to the common control interface BLDC which sends to the processor the identity of the second-stage switch providing the route and the identities of the selected channels free in the incoming and outgoing highways serving that switch and giving access to the inlet and outlet to be connected. The common control interface BLDC also, by suitably addressing MCO and setting up the channel identities in register RVT, effects updating of the channel records in the highway sections of MCO, a decoder DBD being provided so that a channel address in RVT gains access to the particular channel bit in a storage section read out of MCO and set up on RLE. The records in MCO must also be updated whenever a connection across the network is released, the processor providing BLDC with address and channel particulars for the purpose. The store MCO may use magnetic cores or use semi-conductor elements constructed by integrated circuit techniques. The channels transmit 8-bit codes.