Path finding system for large switching networks

Claim 2

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network which includes at least five matrix stages interconnected by links to provide plural paths between circuits connected to opposite ends of the network, and wherein each stage is divided into separate matrix groups, and wherein the matrix groups in each of the two end stages at each opposite end of the multistage network are connected to form a plurality of individual two stage networks, each two stage network providing paths for intErconnecting any circuits connected to opposite ends of the two stage network; means for selectively marking circuits connected to matrix groups in the stages at opposite ends of the multistage network; switching means in the matrix groups in the plurality of two stage networks at both ends of the multistage network for providing signals designating the busy-free condition of individual link interconnections to the two stage networks; detection means sequentially scanning the individual link interconnections to the two stage networks at one end of the multistage network and simultaneously therewith scanning the corresponding link interconnections to the two stage networks at the other end of the multistage network, so that the busyfree condition of the link interconnections that form separate paths through the network for interconnecting said marked circuits are sequentially scanned, and circuit means, responsive to the simultaneous detection of a free condition of link interconnections to each of said two stage networks at opposite ends of the multistage network defining a free path through the multistage network between marked circuits, for completing the connection through the multistage network including the free path.

Claim 3

A switching system as defined in claim 1 wherein said circuit means includes: a plurality of groups of switch means, a separate group of switch means for each of the two stage networks at at least one end of the multistage network, and wherein separate ones of said switch means in said plurality of groups are connected in series with individual ones of said link interconnections to the two stage networks; means for sequentially applying enabling signals synchronized to said detection means to said switch means at a rate wherein said switch means do not respond to said enabling signals; means for selecting the group of switch means associated with the two stage network that includes paths for interconnecting marked circuits, and means for stopping said applying means when a free path is detected so that an enabling signal is applied to one of the switch means in the selected group in said free path for a sufficient period of time to complete a connection through the multistage network between marked circuits at opposite ends of said multistage network.

Claim 4

A switching system as defined in claim 1 wherein said circuit means includes: a plurality of groups of switch means, a separate group of switch means for each of the two stage networks at at least one end of the multistage network, and wherein separate ones of said switch means in said plurality of groups are connected in series with individual ones of said link interconnections to the two stage networks; means for sequentially applying a first signal synchronized to said detection means to a selected group of switch means; means for stopping said first signal applying means when a free path is detected so that said first signal applying means applies a continuous signal to the switch means in said free path, and means for applying a second signal to the switch means in said free path when said first signal applying means is stopped so that said switch means in said free path is actuated by the simultaneous presence of said first and second signals to complete a connection between marked circuits on opposite ends of said multistage network.

Claim 5

A switching system as defined in claim 1 wherein: the multistage network includes a first, second, third, fourth and fifth matrix stages and wherein the matrix groups in he first and second stages are interconnected as a plurality of individual two stage networks and the matrix groups in the fourth and fifth stages are interconnected as a plurality of individual two stage networks; said switching means are included in matrix groups in said first, second, fourth and fifth stages, and said detection means is connected to the link interconnection connected to the switching meaNs in said second and fourth stages.

Claim 6

A switching system as defined in claim 4 wherein: said switching means are included in the third stage and are interconnected by links to the switching means in the first, second, fourth and fifth matrix stages to correspond with the paths through said first, second, third, fourth and fifth matrix stages.

Claim 7

A switching system as defined in claim 1 wherein: the multistage network includes first, second, third, fourth, fifth and sixth stages and wherein the matrix groups in the first and second stages, the third and fourth stages and the fifth and sixth stages are interconnected to form three groups of a plurality of two stage networks.

Claim 8

A switching system as defined in claim 6 wherein: said switch means are included in each of the first, second, third, fourth, fifth and sixth stages and are interconnected by links to correspond with paths through said first, second, third, fourth, fifth and sixth stages.

Claim 9

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including at least five matrix stages interconnected to provide plural control paths and corresponding plural switch paths between circuits connected to opposite ends of the network, wherein each stage is divided into a plurality of separate matrix groups, wherein each matrix group includes a plurality of cross-point switching devices arranged to form a matrix switch with the crosspoint devices connected in the control paths and the switches of the crosspoint devices connected in said switch paths, and wherein the matrix groups in each of the two end stages at opposite ends of the network are interconnected as a plurality of individual two stage networks providing paths for connecting any circuits connected to opposite ends of the two state network; means for selectively marking the control path interconnections of the circuits connected to opposite ends of the multistage network; first switching means in the matrix groups in the plurality of two stage networks at both ends of the multistage network interconnected to provide signals designating the busy-free condition of control path interconnections to the two stage networks; a plurality of second switching means connected in series with the control path interconnections to one of said plurality of two stage networks; means for selecting the two stage networks at opposite ends of the multistage network that include paths for interconnecting said marked circuits at opposite ends of said multistage network; detecting means sequentially monitoring the signals provided by the first switching means in a selected one of the two stage networks and simultaneously therewith sequentially monitoring the signals provided by the first switching means in a selected other one of said two stage networks so that the busy-free condition of the pairs of the control path interconnections that define separate control paths through said multistage network between the marked circuits are sequentially detected, and circuit means responsive to said detecting means for actuating one of said plurality of said second switching means in the free control path to complete a connection through the multistage network via the two free control path interconnections.

Claim 10

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including at least five matrix stages interconnected to provide plural control paths and corresponding plural switch paths between circuits connected to opposite ends of the network, wherein each stage is divided into a plurality of separate matrix groups, wherein each matrix group includes a plurality of cross-point switching devices arranged to form a matrix switch with the crosspoint devices connected in the control paths and the switches of the crosspoint devices connected in said switch paths, and wherein the matrix groups in each of the two end stages at opposite ends of the network are interconnected as a plurality of individual two stage networks providing paths for connecting any circuits connected to opposite ends of the two state network; means for selectively marking the control path interconnections of the circuits connected to opposite ends of the multistage network; first switching means in the matrix groups in the plurality of two stage networks at both ends of the multistage network interconnected to provide signals designating the busy-free condition of control path interconnections to the two stage networks; a plurality of second switching means connected in series with the control path interconnections to one of said plurality of two stage networks; means for selecting the two stage networks at opposite ends of the multistage network that include paths for interconnecting said marked circuits at opposite ends of said multistage network; detecting means sequentially monitoring the signals provided by the first switching means in a selected one of the two stage networks and simultaneously therewith sequentially monitoring the signals provided by the first switching means in a selected other one of said two stage networks so that the busy-free condition of the pairs of the control path interconnections that define separate control paths through said multistage network between the marked circuits are sequentially detected, and circuit means responsive to said detecting means for actuating one of said plurality of said second switching means in the free control path to complete a connection through the multistage network via the two free control path interconnections.

Claim 11

A switching system as defined in claim 8 including: means for stopping said detecting means when the free control path interconnections are detected, and means for restarting said detecting means after a preset period of time.

Claim 12

A switching system as defined in claim 8 wherein said circuit means includes: scanning means for applying sequential scanning signals in synchronism with said detecting means to said plurality of second switching means for a time duration that is insufficient to permit enabling of said second switching means, and circuit means for stopping said scanning means when a free control path is detected and wherein a scan siGnal of sufficient duration is applied to the second switch means in the free control path to switch the cross-point devices and complete the free path.

Claim 13

A switching system as defined in claim 8 including: means for stopping said detecting means when signals indicating a free control path have been detected, and means applying a switching signal to said one of said second switching means when said detecting means is stopped so that said second switching means in a control path interconnection of said free control path is actuated to complete the connection through the multistage network.

Claim 14

A switching system as defined in claim 8 wherein: the network includes first, second, third, fourth and fifth stages; said first switching means are included in matrix groups in first, second, fourth and fifth stages, and said detecting means is connected to receive signals from said first switching means in said first and second stages and in said fourth and fifth stages.

Claim 15

A switching system as defined in claim 12 wherein: said first switching means are included in the third matrix stage and are interconnected to the first switching means in the first, second, fourth and fifth matrix stages to correspond with the control paths through said first, second, third, fourth and fifth matrix stages.

Claim 16

A switching system as defined in claim 8 wherein: the multistage network includes first, second, third, fourth, fifth and sixth stages and wherein the matrix groups in the first and second stages, the third and fourth states and the fifth and sixth stages are interconnected to form three groups of a plurality of two stage networks.

Claim 17

A switching system for effecting interconnection of telephone circuits through a switching network comprising: a multistage network including at least five switching matrix stages wherein each stage is divided into separate matrix groups, wherein each matrix group includes a plurality of crosspoint devices arranged to form a matrix switch including control leads and switch leads, wherein the control leads and switch leads of crosspoint devices in the matrix groups in two end stages at each opposite end of the multistage network are interconnected to form a plurality of individual two stage networks, and wherein the control leads and switch leads of the two stage networks are connected by links to the control leads and switch leads, respectively, of the matrix groups of other adjacent stages to provide plural paths between telephone circuits connected to opposite ends of said multistage network; means for selectively marking the control leads of telephone circuits connected to the two stage networks at opposite ends of said multistage network; first switching means in the plurality of matrix groups in at least the two stages forming each two stage network for providing signals designating the busy-free condition of the link interconnections between the said two stage networks and the matrix groups of the stages adjacent said two stage networks; circuit means for selecting the two stage networks including control path interconnections for completing paths between said marked telephone circuits; a plurality of second switching means in series with the control lead link interconnections between one of said two stage networks and the matrix groups of an adjacent stage; scanning means for sequentially enabling the plurality of second switching means connected in the control link interconnection to the selected two stage networks for a time duration insufficient to eanble the second switching means to switch the crosspoint devices, and means for simultaneously detecting a signal from the selected two stage networks indicating a free condition of a control lead interconnection through the multistage network and for stopping said scanning means so that a second switching means in the detected free control lead interconnection is enabled for a sufficient time duration to switch crossPoint devices in said plurality of stages to complete the control path between marked telephone circuits on opposite ends of said multistage network.

Claim 18

A switching system for effecting interconnection of telephone circuits through a switching network comprising: a multistage network including at least five switching matrix stages wherein each stage is divided into separate matrix groups, wherein each matrix group includes a plurality of crosspoint devices arranged to form a matrix switch including control leads and switch leads, wherein the control leads and switch leads of crosspoint devices in the matrix groups in two end stages at each opposite end of the multistage network are interconnected to form a plurality of individual two stage networks, and wherein the control leads and switch leads of the two stage networks are connected by links to the control leads and switch leads, respectively, of the matrix groups of other adjacent stages to provide plural paths between telephone circuits connected to opposite ends of said multistage network; means for selectively marking the control leads of telephone circuits connected to the two stage networks at opposite ends of said multistage network; first switching means in the plurality of matrix groups in at least the two stages forming each two stage network for providing signals designating the busy-free condition of the link interconnections between the said two stage networks and the matrix groups of the stages adjacent said two stage networks; circuit means for selecting the two stage networks including control path interconnections for completing paths between said marked telephone circuits; a plurality of second switching means in series with the control lead link interconnections between one of said two stage networks and the matrix groups of an adjacent stage; scanning means for sequentially enabling the plurality of second switching means connected in the control link interconnection to the selected two stage networks for a time duration insufficient to eanble the second switching means to switch the crosspoint devices, and means for simultaneously detecting a signal from the selected two stage networks indicating a free condition of a control lead interconnection through the multistage network and for stopping said scanning means so that a second switching means in the detected free control lead interconnection is enabled for a sufficient time duration to switch crossPoint devices in said plurality of stages to complete the control path between marked telephone circuits on opposite ends of said multistage network.

Claim 19

A switching system as defined in claim 15 wherein: the crosspoint devices comprise relay switches having mark and sleeve relay coils, wherein the mark coils are interconnected by said control leads, wherein said sleeve coils are interconnected by sleeve leads and by contacts of their respective relay switches to form plural hold current paths, and wherein other contacts of said relay switches are interconnected to form plural signal paths, and said first switching means comprises a separate contact from each of said realy switches in each of said matrix groups in at least said matrix groups in said two stage networks, and wherein the contacts are interconnected in the matrix groups in each of the two stage networks to provide separate busy-free signals for each of the control lead interconnections to said two stage networks and so that when one of the relays connected to a control lead interconnection is activated, the contacts of the activated relay provide a busy signal for the control lead interconnection to the two stage network.

Claim 20

A switching system as defined in claim 15 wherein: the network includes first, second, third, fourth and fifth stages and wherein the matrix groups in the first and second stages are interconnected as a plurality of individual two stage networks and the matrix groups in the fourth and fifth stages are interconnected as a plurality of individual two stage networks; said first switching means are included in at least said first, second, fourth and fifth stages, and said detecting means is connected to receive signals from the first switching means in said first and second stages and in said fourth and fifth stages.

Claim 21

A switching system as defined in claim 17 wherein: said first switching means are included in the third matrix stage and are interconnected to the first, second, fourth and fifth matrix stages to correspond with the paths through said first, second, third, fourth and fifth matrix stages.

Claim 22

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including at least five matrix stages interconnected to provide plural paths between circuits connected to opposite ends of said multistage network, wherein each stage is divided into separate matrix groups, and wherein the two stages at each opposite end of the multistage network are interconnected to form two groups of a plurality of individual two stage networks in a manner to provide paths for connecting any circuits connected to opposite ends of the two stage networks; means for selectively marking circuits connected to matrix groups in the stages at opposite end of the network; switching means in the plurality of matrix groups in stages interconnected to form the two stage networks providing signals designating the busy-free condition of individual link interconnections between the two stage networks and the matrix groups of an adjacent stage; detection means sequentially scanning the signals provided by the switching means in the two stage network connected to a marked circuit at one end of the multistage network and simultaneously therewith sequentially scanning the signals provided by the switching means in the two stage network connected to a marked circuit at the other end of the multistage network, so that the busy-free condition of the link interconnections that define separate paths through the multistage network for interconnecting the marked circuits are sequentially detected, and circuit means responsive to the simultaneous detection of a free condition in a link interconnection to a two stage network at opposite ends of the multistage network to complete a path through said multistage network between marked circuits connected to opposite ends of said multistage network.

Claim 23

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including at least five matrix stages interconnected to provide plural paths between circuits connected to opposite ends of said multistage network, wherein each stage is divided into separate matrix groups, and wherein the two stages at each opposite end of the multistage network are interconnected to form two groups of a plurality of individual two stage networks in a manner to provide paths for connecting any circuits connected to opposite ends of the two stage networks; means for selectively marking circuits connected to matrix groups in the stages at opposite end of the network; switching means in the plurality of matrix groups in stages interconnected to form the two stage networks providing signals designating the busy-free condition of individual link interconnections between the two stage networks and the matrix groups of an adjacent stage; detection means sequentially scanning the signals provided by the switching means in the two stage network connected to a marked circuit at one end of the multistage network and simultaneously therewith sequentially scanning the signals provided by the switching means in the two stage network connected to a marked circuit at the other end of the multistage network, so that the busy-free condition of the link interconnections that define separate paths through the multistage network for interconnecting the marked circuits are sequentially detected, and circuit means responsive to the simultaneous detection of a free condition in a link interconnection to a two stage network at opposite ends of the multistage network to complete a path through said multistage network between marked circuits connected to opposite ends of said multistage network.

Claim 24

A sWitching system as defined in claim 19 wherein said circuit means includes: switch means connected in series with individual ones of said link interconnections to one of said two groups of said two stage networks; scanning means for sequentially applying enabling signals synchronized to said deection means to the switch means connected in series with the interconnections to a two stage network connected to a marked circuit at a rate wherein said switch means do not respond to said signal, and means for stopping scanning when a free path is detected for applying an enabling signal of sufficient duration to the switch means in said free path to complete a connection between marked circuits on opposite ends of said multistage network.

Claim 25

A switching system as defined in claim 20 wherein: said network includes first, second, third, fourth, fifth and sixth stages; said matrix groups in said first and second, said third and fourth and said fifth and sixth stages are interconnected to form three separate groups of a plurality of two stage networks, and said switching means are included in the matrix groups of said first, second, third, fourth, fifth and sixth stages.

Claim 26

A switching system as defined in claim 19 wherein said circuit means includes: switch means connected in series with individual ones of said link interconnections to one of said two groups of two stage networks; scanning means for sequentially applying first partial enabling signals synchronized to said detection means to said switch means; means for stopping said scanning means when free link interconnections defining a free path are detected, and means for applying a second partial enable signal to the switch means connected in series with the interconnections to the two stage networks connected to marked circuits after said scanning means stopped so that said switch means is actuated by the simultaneous presence of said first and second signals to complete a path between marked circuits on opposite ends of said multistage network.

Claim 27

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including a plurality of matrix stages interconnected by links to provide plural paths between circuits connected to opposite ends of the network, and wherein each stage is divided into separate matrix groups, and wherein at least the two end stages on each opposite side of the multistage network are connected to form two groups of a plurality of two stage networks; means for selectively marking circuits connected to matrix groups in the stages at opposite ends of the multistage network; first switching means in the plurality of matrix groups in the two groups of two stage networks for providing signals designating the busy-free condition of individual link interconnections to the two stage networks; a first group of link check circuits, one for each of said plurality of two stage networks in one group at one end of the multistage network, coupled to the link connections to individual ones of the two stage networks for monitoring the busy-free signals from said first switching means; a second group of link check circuits, one for each of said plurality of two state networks, in the other group at the other end of the multistage network, coupled to the link interconnections to individual ones of the two stage networks fo monitoring the busy-free signals from said first switching means; a plurality of groups of switching means, one group for each of the plurality of two stage networks of at least one group wherein separate switching means are connected in series with individual ones of the link connections to the two stage networks; first circuit means, responsive to the marking of the circuits connected to said one end of the multistage network, for selectively enabling one of said first groups of link check circuits monitoring link connections forming a portion Of paths through the network to the marked circuits, and for enabling corresponding ones of said groups of switching means; second circuit means, responsive to the marking of the circuits connected to said other end of the multistage network, for selectively enabling ones of said second groups of link check circuits monitoring link connections forming a portion of paths through the network to the marked circuits; counting circuit means for providing a series of sequential scanning pulses; third circuit means coupled to apply the scanning pulses to said first and second groups of link check circuits so that the link check circuits enabled by said first and second circuit means simultaneously scan the busy-free condition of the link interconnections to their corresponding two stage networks; fourth circuit means for stopping said counting circuit means in response to a simultaneous free condition signal from the first and second enabled link check circuits; fifth circuit means for applying said scanning signal to the groups of switching means enabled by said first circuit means so that the switching means in the detected free path is enabled when said counting circuit means is stopped, and circuit means for restarting said counting circuit means.

Claim 28

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including a plurality of matrix stages interconnected by links to provide plural paths between circuits connected to opposite ends of the network, and wherein each stage is divided into separate matrix groups, and wherein at least the two end stages on each opposite side of the multistage network are connected to form two groups of a plurality of two stage networks; means for selectively marking circuits connected to matrix groups in the stages at opposite ends of the multistage network; first switching means in the plurality of matrix groups in the two groups of two stage networks for providing signals designating the busy-free condition of individual link interconnections to the two stage networks; a first group of link check circuits, one for each of said plurality of two stage networks in one group at one end of the multistage network, coupled to the link connections to individual ones of the two stage networks for monitoring the busy-free signals from said first switching means; a second group of link check circuits, one for each of said plurality of two state networks, in the other group at the other end of the multistage network, coupled to the link interconnections to individual ones of the two stage networks fo monitoring the busy-free signals from said first switching means; a plurality of groups of switching means, one group for each of the plurality of two stage networks of at least one group wherein separate switching means are connected in series with individual ones of the link connections to the two stage networks; first circuit means, responsive to the marking of the circuits connected to said one end of the multistage network, for selectively enabling one of said first groups of link check circuits monitoring link connections forming a portion Of paths through the network to the marked circuits, and for enabling corresponding ones of said groups of switching means; second circuit means, responsive to the marking of the circuits connected to said other end of the multistage network, for selectively enabling ones of said second groups of link check circuits monitoring link connections forming a portion of paths through the network to the marked circuits; counting circuit means for providing a series of sequential scanning pulses; third circuit means coupled to apply the scanning pulses to said first and second groups of link check circuits so that the link check circuits enabled by said first and second circuit means simultaneously scan the busy-free condition of the link interconnections to their corresponding two stage networks; fourth circuit means for stopping said counting circuit means in response to a simultaneous free condition signal from the first and second enabled link check circuits; fifth circuit means for applying said scanning signal to the groups of switching means enabled by said first circuit means so that the switching means in the detected free path is enabled when said counting circuit means is stopped, and circuit means for restarting said counting circuit means.

Claim 29

A switching system as defined in claim 23 wherein: said counting circuit means, when stopped, provides a continuous signal corresponding to the scanning pulse at which the counting means is stopped, and said fifth circuit means is responsive to a signal from the fourth circuit means to apply the continuous signal from said counting circuit means to said switching means enabled by said first circuit means to activate the switching means and complete the path through the network.

Claim 30

A switching system as defined in claim 23 wherein: said counting circuit means provides said scanning signals at a sufficiently rapid repetition rate so that said switching means do not respond to the scanning signal from said counting circuit means until the counting circuit means is stopped.

Claim 31

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including a plurality of matrix stages interconnected to provide plural control paths and plural holding paths between circuits connected to opposite ends of the network, wherein each stage is divided into a plurality of separate matrix groups, wherein each matrix group includes a plurality of crosspoint relays arranged to form a matrix switch, wherein each relay includes a hold winding connection in series with contacts of the relay and includes a control winding, with the control windings of each relay being connected in the control paths, and the hold windings of each relay being connected through the series contacts in corresponding holding paths, and wherein two stages at each opposite end of the multistage network are interconnected to form two group of a plurality of individual two stage networks, each group being at opposite ends of the network; means for selectively marking circuits connected to the matrix groups in the stages at opposite ends of the network; detection means sequentially scanning the individual holding path connections to the two stage network connected to a marked circuit at one end of the multistage network and simultaneously therewith sequentially scanning the individual holding path connections to the two stage network connected to a marked circuit at the other end of the multistage network, so that the busy-free condition of the link interconnections that define separate paths through the multistage network for interconnecting the marked circuits are sequentially detected, and circuit means, responsive to the simultaneous detection of free holding path connections to each two stage networks at opposite ends of the multistage network defining a free path through the multistage network between marked circuits, for completing the interconneCtion through the multistage network including the free path.

Claim 32

A switching system for effecting interconnection of circuits through a switching network comprising: a multistage network including a plurality of matrix stages interconnected to provide plural control paths and plural holding paths between circuits connected to opposite ends of the network, wherein each stage is divided into a plurality of separate matrix groups, wherein each matrix group includes a plurality of crosspoint relays arranged to form a matrix switch, wherein each relay includes a hold winding connection in series with contacts of the relay and includes a control winding, with the control windings of each relay being connected in the control paths, and the hold windings of each relay being connected through the series contacts in corresponding holding paths, and wherein two stages at each opposite end of the multistage network are interconnected to form two group of a plurality of individual two stage networks, each group being at opposite ends of the network; means for selectively marking circuits connected to the matrix groups in the stages at opposite ends of the network; detection means sequentially scanning the individual holding path connections to the two stage network connected to a marked circuit at one end of the multistage network and simultaneously therewith sequentially scanning the individual holding path connections to the two stage network connected to a marked circuit at the other end of the multistage network, so that the busy-free condition of the link interconnections that define separate paths through the multistage network for interconnecting the marked circuits are sequentially detected, and circuit means, responsive to the simultaneous detection of free holding path connections to each two stage networks at opposite ends of the multistage network defining a free path through the multistage network between marked circuits, for completing the interconneCtion through the multistage network including the free path.

Claim 33

A switching system as defined in claim 26 wherein said circuit means includes: a plurality of switch means, a separate switch means for each of the two stage networks in at least one of said groups of two stage networks, and wherein separate ones of said switch means are connected in series with said control path link connections to said at least one of said groups of the two stage networks, and means for applying enabling signals synchronized to said detection means to selected switch means included in control paths for interconnecting the marked circuits at a rate insufficient to permit enabling of said switch means, and when a free path is detected to apply an enabling signal to said switch means in the control path of a detected free path for a sufficient period of time to complete a connection through the network between marked circuits at opposite ends of said network.

Claim 34

A switching system as defined in claim 26 wherein said circuit means includes: a plurality of switch means, a separate switch means for each of the two stage network in at least one of said groups of two stage networks, and wherein separate ones of said switch means are connected in series with said control path connections to said at least one of said groups of the two stage networks; means for sequentially applying a first signal synchronized to said detection means to selected switch means included in control paths for interconnecting the marked circuits, and when a free path is detected for applying a continuous signal to the switch means in the control path of said detected free path, and means for applying a second signal to the switch means in said free path when a free path is detected so that said switch means in said detected free path is actuated by the simultaneous presence of said first and second signals to complete a connection between marked circuits on opposite ends of said network.