Patent ID: 7400601
Filing Date: 2008-07-15
Classification: H04L,H04W

Abstract:
1. A mobile communication system comprising: a multicast router which receives an information signal addressed to a predetermined multicast group transmitted from a transmitter and which makes a copy of the received information signal and distributes it to a network downstream thereof when a mobile terminal belonging to the multicast group is present downstream of the multicast router; a data link layer switch which receives the information signal distributed from the multicast router and which distributes a copy of the received information signal only to a multicast distribution path in which a mobile terminal belonging to the multicast group is present; a radio base station which is connected to the data link layer switch and which distributes the information signal distributed by the data link layer switch to a radio network downstream thereof; and a mobile terminal which receives the information signal distributed by the radio base station, the mobile terminal comprising: station switching detection means which detects that the radio base station connected to the mobile terminal itself has been switched; router switching detection means which detects that the multicast router connected to the mobile terminal itself has been switched; establishment request transmission means which transmits a path establishing request for requesting at least the data link layer switch to establish a multicast distribution path for distributing the information signal to the radio base station connected to the mobile terminal itself; withdrawal request transmission means which transmits a withdrawal request for requesting at least the multicast router to withdraw from the multicast group to which the mobile terminal itself belongs; and transmission control means which transmits a first instruction signal for instructing the establishment request transmission means to transmit the path establishing request and a second instruction signal for instructing the withdrawal request transmission means to transmit the withdrawal request, depending on the detection by the station switching detection means, wherein: when the station switching detection means detects the switching of the radio base station but the router switching detection means does not detect the switching of the multicast router, the transmission control means sequentially outputs the first instruction signal, the second instruction signal, and the first instruction signal again; and when the station switching detection means detects the switching of the radio base station and the router switching detection means detects the switching of the multicast router, the transmission control means outputs the first instruction signal to transmit the path establishing request to a first multicast router which is the multicast router connected to the mobile terminal after the switching of the multicast router and thereafter outputs the second instruction signal to transmit the withdrawal request to a second multicast router which is the multicast router connected to the mobile terminal before the switching of the multicast router.