Handover control, apparatus, base station, edge router, relay router, radio terminal apparatus, mobile communication system, and handover control method

Abstract

When a radio terminal unit 30 undergoes a handover between base stations 34, 36 , a previous edge router 40 having been connected to the radio terminal unit 30 , out of edge routers 40, 42 provided in respective base stations 34, 36 , provides an instruction to instruct a relay router 48 , under which the edge router 40 and every edge router 42 in the base station 36 as a candidate for a destination of the movement are connected, to buffer data from a correspondent node, and instructs the relay router to forward the data buffered in the relay router 48 according to the instruction, to the radio terminal unit 30 after the movement, after completion of the handover, whereby the buffered data is forwarded to the radio terminal unit 30 . This implements forwarding packet data through the optimal path to the radio terminal unit after the movement in the handover control and achieves effective utilization of network resources and reduction of handover transactions.

1 . A handover control apparatus for controlling handover of a radio terminal unit between edge routers provided in respective base stations for radio communication with radio terminal unit, said handover control apparatus comprising: 
 control means for performing such control as to buffer data from a correspondent node in a relay router under which a previous edge router having been connected to the radio terminal unit and every edge router as a candidate for a destination of the movement are connected, during the handover.    
     
     
         2 . The handover control apparatus according to  claim 1 , wherein the relay router in which the data from the correspondent node is buffered is a relay router with a minimum hop count from the radio terminal unit, out of a plurality of relay routers connected in a hierarchical structure.  
     
     
         3 . The handover control apparatus according to  claim 1  or  2 , wherein the control means puts the data buffered in the relay router, a destination address of the radio terminal unit and an identifier for identification of packet data and forwards the buffered data to said address.  
     
     
         4 . A base station for detecting handover of a radio terminal unit, said base station comprising: 
 retaining means for retaining location information about locations of an adjacent base station and every relay router connected to the adjacent base station;    determining means for determining a relay router under which a base station having been connected to the radio terminal unit and every base station as a candidate for a destination of the movement are connected, based on the location information thus retained; and    instructing means for instructing the relay router thus determined to buffer data from a correspondent node.    
     
     
         5 . The base station according to  claim 4 , wherein, for determining said relay router, said determining means determines a relay router with a minimum hop count from the radio terminal unit among relay routers under which all candidate base stations as potential destinations are connected, out of a plurality of relay routers connected in a hierarchical structure.  
     
     
         6 . The base station according to  claim 4  or  5 , wherein, after movement by handover of the radio terminal unit, said instructing means instructs the relay router determined by the determining means to forward the buffered data to the radio terminal unit after the movement.  
     
     
         7 . An edge router provided in a base station for detecting handover of a radio terminal unit and connected by radio communication to the radio terminal unit, said edge router comprising: 
 retaining means for retaining location information about locations of an adjacent edge router and every relay router connected to the adjacent edge router;    determining means for determining a relay router under which a previous edge router having been connected to the radio terminal unit and every edge router as a candidate for a destination of the movement are connected, based on the location information thus retained; and    instructing means for instructing the relay router thus determined to buffer data from a correspondent node.    
     
     
         8 . The edge router according to  claim 7 , wherein, for determining the relay router, the determining means determines a relay router with a minimum hop count from the radio terminal unit, out of a plurality of relay routers connected in a hierarchical structure.  
     
     
         9 . The edge router according to  claim 7  or  8 , wherein, after movement by handover of the radio terminal unit, said instructing means instructs the relay router determined by the determining means to forward the buffered data to the radio terminal unit after the movement.  
     
     
         10 . A relay router configured to buffer data from a correspondent node in accordance with an instruction to buffer data, given by the instructing means of the base station as set forth in one of  claims 4  to  6  or the edge router as set forth in one of  claims 7  to  9 ; in accordance with a data forwarding instruction given by the instructing means, buffer the data from the correspondent node, put the data a current address of the radio terminal unit and an identifier for identification of packet data, and forward the packet data to the current address of the radio terminal unit; after the movement of the radio terminal unit, forward the packet data to the current address of the radio terminal unit in accordance with the forwarding instruction.  
     
     
         11 . A radio terminal unit comprising: 
 memory means for memorizing an address for identifying the radio terminal unit in a relay router during handover; and    instructing means for, in order to change a forwarding address of packet data after the handover in the relay router from a previous address of the radio terminal unit to a current address of the radio terminal unit, instructing the relay router to forward packet data to the current address of the radio terminal unit.    
     
     
         12 . A radio terminal unit configured to implement radio communication with each base station and, during handover between edge routers provided in respective base stations, perform control of the handover, the radio terminal unit comprising: 
 control means for performing such control as to make a relay router under which a previous edge router having been connected to the radio terminal unit and every edge router as a candidate for a destination of the movement are connected, buffer data from a correspondent node during the handover.    
     
     
         13 . The radio terminal unit according to  claim 12 , which is configured to select and apply a relay router with a minimum hop count from the radio terminal unit, out of a plurality of relay routers connected in a hierarchical structure, as the relay router for buffering the data from the correspondent node.  
     
     
         14 . The radio terminal unit according to  claim 12  or  13 , wherein the control means makes the relay router put the data buffered in the relay router, a destination address of the radio terminal unit and an identifier for identification of packet data, and forward the buffered data to said address.  
     
     
         15 . A mobile communication system for implementing handover of a radio terminal unit between base stations, said mobile communication system comprising: 
 relay routers connected above the base stations in a hierarchical structure and configured to perform relaying of data to the base stations and buffering of data; and    edge routers provided in the respective base stations, each edge router being configured to provide an instruction to instruct a relay router under which a base station having been connected to the radio terminal unit and every base station as a candidate for a destination of the movement are connected, to buffer data from a correspondent node during the handover, and instruct the relay router to forward the data buffered in the relay router in accordance with the instruction to the radio terminal unit after the movement.    
     
     
         16 . The mobile communication system according to  claim 15 , wherein the relay router buffers packet data therein in accordance with the instruction to buffer packet data from the edge router, forwards the packet data with an identifier of data to the radio terminal unit, and forwards the packet data to a current address of the radio terminal unit in accordance with a packet data forwarding instruction of the radio terminal unit after the handover.  
     
     
         17 . The mobile communication system according to  claim 15  or  16 , wherein the radio terminal unit negotiates a buffer size of data from the correspondent node with the relay router.  
     
     
         18 . The mobile communication system according to  claim 17 , wherein the radio terminal unit notifies the relay router of information about already-received data in the radio terminal unit itself, before excess over the buffer size determined by the negotiation with the relay router.  
     
     
         19 . The mobile communication system according to  claim 17 , wherein the relay router deletes the data in chronological order from the oldest during an operation of buffering data over the buffer size determined by the negotiation.  
     
     
         20 . The mobile communication system according to  claim 18 , wherein the relay router deletes the already-received data notified of by the radio terminal unit and updates an expiration date of a buffer area allocated for the radio terminal unit.  
     
     
         21 . The mobile communication system according to  claim 18 , wherein the relay router deletes a buffer area whose expiration date has passed.  
     
     
         22 . The mobile communication system according to one of  claims 16  to  21 , wherein after the handover, the radio terminal unit notifies the relay router of information about data having already been received before the handover.  
     
     
         23 . The mobile communication system according to  claim 22 , wherein the relay router deletes the already-received data having already been received before the handover, notified of by the radio terminal unit, and forwards data except said already-received data to the radio terminal unit.  
     
     
         24 . A handover control method of controlling handover of a radio terminal unit between edge routers provided in respective base stations for radio communication with radio terminal unit, said handover control method comprising: 
 a control step of performing such control as to buffer data from a correspondent node in a relay router under which a previous edge router having been connected to the radio terminal unit and every edge router as a candidate for a destination of the movement are connected, in accordance with an instruction to buffer the data from the correspondent node.    
     
     
         25 . The handover control method according to  claim 24 , wherein a relay router with a minimum hop count from the radio terminal unit out of a plurality of relay routers connected in a hierarchical structure is applied to the relay router for buffering the data from the correspondent node.  
     
     
         26 . The handover control method according to  claim 24  or  25 , wherein said control step is to assign the data buffered in the relay router, a current address of the radio terminal unit and forward the buffered data to said address.  
     
     
         27 . The handover control method according to  claim 26 , wherein said control step is to assign the data an identifier of data on the occasion of forwarding the buffered data.  
     
     
         28 . The handover control method according to  claim 26  or  27 , wherein said control step is to conduct a negotiation about a buffer size of the data from the correspondent node in the relay router.  
     
     
         29 . The handover control method according to  claim 28 , wherein said control step is to delete the data in chronological order from the oldest during an operation of buffering the data over the buffer size determined by the negotiation.  
     
     
         30 . The handover control method according to  claim 28 , wherein said control step is to delete already-received data notified of by the radio terminal unit.  
     
     
         31 . The handover control method according to one of  claims 26  to  30 , wherein said control step is to, after the handover of the radio terminal unit, delete already-received data having already been received before the handover by the radio terminal unit, from the data buffered in the relay router and forward data except for the already-received data to the radio terminal unit.