Abstract: An asynchronous transfer mode (ATM) switch (20) has plural switch ports (24) connected by respective bidirectional links (27, 28) to a switch core (22). Connected to each switch port is a corresponding row column unit (40), each row column unit managing the writing of service cells to one row of cross point units (32) and the reading of service cells from one column of cross point units. The bidirectional links between each switch port and its corresponding row column unit of the switch core carry both service cells and control cells. An interactive exchange of control cells is implemented to sequence operation of the switch core. The operations particularly dependent upon control cell generation include transmission of service cells from the switch core; transmission of pollstate control cells from the switch core; retrieval of contents of certain control registers maintained by the switch core; and synchronization procedures.

Abstract: In the connection of a number of telephone sets to a private branch exchange, control information is communicated between the telephone sets and the exchange set in such a way that a bidirected conversion unit is required. In order to provide a high degree of service at a reasonable cost the telephone sets are collected in groups which share a generally smaller number of conversion units. By way of suitable control devices and switch units in the forwarding of control information, a suitable non-occupied conversion unit can be selected.