Abstract: A node of #B selects an ISDN line for backup in which a bulk transfer by a plurality of B channels is performed, out of a plurality of ISDN lines which can be set by a node of #A, by way of the pilot selection function on the ISDN switching network side. At this time, two nodes of #A and #B exchange both the child number of an ISDN line to be selected and the number of B channels to be transferred in bulk as user-user information in the D channel message of the ISDN line with each other, and select an ISDN line based on the information.

Abstract: In a managing router (communication device) managing a mobile node, the managing router releases an older tunnel already established so as to prevent the number of all tunnels established between the managing communication device itself and an accommodating router of a mobile node from exceeding e.g. a predetermined threshold value. Also, when the number of all tunnels presently established for all mobile nodes exceeds a predetermined threshold value, the managing router rejects a new tunnel establishment, or releases an older tunnel to establish a new tunnel. Also, by classifying the mobile nodes into a plurality of classes based on a plurality of threshold values, the establishment of the new tunnel is rejected or executed based on the threshold value corresponding to the class to which the mobile node belongs.