Patent ID: 7436796

Claim:
A cache server for assisting contents delivery from a delivery server to a mobile node, wherein the cache server is configured to perform the steps of: receiving a moving notice from the mobile node, the moving notice notifying a change of cache server which the mobile node utilizes from a previous cache server to the cache server, wherein the moving notice includes URL uniquely identifies a requested content; transmitting a request to the previous cache server, the request being needed for processing a retransmission request which the mobile node has a possibility of making, wherein the previous cache server is identified from information included in the moving notice and having been utilized before the moving by the mobile node; receiving information from the previous cache server, wherein the information is needed for processing the retransmission request; identifying the requested content identified by the URL in the moving notice, wherein the content has been requested by the mobile node; judging whether or not the cache server itself has already held the content identified by the URL; if the cache server itself has held the content, transmitting a deletion request to the previous cache server as the request needed for processing the retransmission request, wherein the deletion request is intended for deleting the content which the previous cache server has held; and as a response to the deletion request, receiving from the previous cache server information on a portion which the mobile node has received, and information on a portion which the mobile node has transmitted; wherein the data delivered to the mobile node is stream-delivery data and the transmission timing of which is determined on each frame basis, and the cache server is further configured to perform a step of: receiving, from the previous cache server, the stream-delivery data which the previous cache server has held with a higher-speed timing which differs from the transmission timing determined for the delivery of the stream-delivery data.