Method for controlling cleardown operations in communications switching systems

摘要

In communications switching systems which use digital time division multiplex switching and have a time-space-time division switching arrangement, incorrect cleardown of connections is intended to be prevented when cleardown signals associated with a connection which has already been cleared down are received and the time slots now occupied for a new connection are identical to those which were present during the connection which has just been cleared down. An additional connection number which is assigned to the connection-characterising data is recorded for each connection in a centrally disposed time slot memory. This is supplied by a counter which is incremented with every connection stimulus. This connection number is forwarded to the group controllers and stored there so that it is contained in cleardown signals whose content is compared by a comparator during cleardown operations with the content of the time slot memory. Connections in the space division switching stage are cleared down only when the comparator supplies a delete command when correspondence is identified. The connection number ensures that the connection codes differ from one another even if the time slots and connection end points are identical. This ensures that the content of a cleardown signal always differs from the existing data for a new connection.