Patent ID: 7024113

Claim:
In a network constituted by a plurality of packet switching systems connected through transmission lines, a route modification method for modifying a label switching pat from an old route to a new route, comprising the steps of: including in a label request for a new route an identifier indicating an old route having a sharable label; forwarding the label request from a packet switching system located on upstream side to a packet switching system located on downstream side along the new route; in the packet switching system located on the downstream side, setting the label for the old route to a double reserved state in case the new route being requested in the label request overlaps with the old route, or reserving a new label in case the new route does not overlap with the old route; notifying the packet switching system located upstream from the packet switching system located downstream about the each reserved label; forwarding a label release request explicitly specifying the old route to the packet switching system located on downstream side along the old route; and in the packet switching system, when receiving the label release request, either setting the double reserved label ;o a reserved state being reserved only for the new route in case the new route overlaps with the old route, or releasing the label for old route in case the new route does not overlap with the old route.