Abstract: A marker controlling the establishment of connections between local subscriber lines and inter-office links, via an associated line concentrator/distributor, comprises a link allocator, a signalization unit and a service unit. The link allocator responds to requests from a local subscriber line, transmitted via a line finder, or from a remote exchange, arriving over a common signal path, to control the line concentrator/distributor for connecting that local line to an available link or a designated link to a selected line. The signalization unit coacts with a respective two-way coupler in each link, in a time-division mode, to pick up outgoing dial pulses for transmission via the common path and to transmit switching instructions from that path to the engaged subscriber line. The service unit, communicating with both the link allocator and the signalization unit, receives and sends out information relating to possible malfunctions or alarm conditions.

Abstract: A marker at a central-office terminal, controlling the establishment of connections between local subscriber lines and inter-office links via an associated line concentrator/distributor, includes a test-signal generator connected via a two-way coupler to an outgoing branch of an engaged link, a first signal receiver connected by the coupler to an incoming branch of that link, and a second signal receiver inserted in a normally balanced phantom circuit formed by incoming and outgoing branches of a local line communicating with the link. Upon the establishment of a connection including such a link between two subscriber lines served by respective central-office terminals, an alternating test signal generated at one terminal must be detected with a predetermined minimum threshold by the first receiver but not by the second receiver of the other terminal before message transmission over this connection can be initiated.