A telephone switching system comprises a plurality of switching nodes interconnected by a call-switching network. The switching nodes are also linked by a host network to one or more hosts that exercise supervisory control over the nodes. The hosts communicate directly with one or more of the nodes, termed 'switching nodes', by means of virtual connections over the host network. The other switching nodes, termed 'slave nodes', are assigned to host nodes. The hosts communicate indirectly with the slave nodes by way of switching nodes to which they are assigned. Communications between a host and a slave node thus comprise messages: (a) over the host network between the slave node and the switching node to which the slave node is assigned and (b) by way of a virtual connection, between the switching node and the host.