Abstract: A method of and apparatus for controlling a data transfer by a transfer deliverer node from a terminal equipment belonging to the transfer deliverer node to another node, in a network system having a plurality of nodes connected to a public switched network and a plurality of terminal equipments connectable to a corresponding node.

Abstract: In a network system in which a line switching unit and the other line switching unit are connected with each other via communication lines and backup lines, and nodes which are connected with both the line switching units, respectively are adapted to communicate with each other via either one of the communication lines and backup lines and both line switching units, a line switching system wherein a network control unit is connected with the line switching units, said network control unit having, in a table, information on connecting mates of said communication and backup lines an information on a plurality of groups of communication lines each grouped based upon the former information, the network control unit being adapted to select a relevant group based upon the group information when a failure occurs in the communication lines for issuing an instruction for collectively switching a plurality of communication lines belonged to the group, whereby said line switching unit which has received the instruction