Abstract:
Access points for supporting wireless communications, a packet transmission device, and terminals for handing-over between service areas are provided. An existing terminal is provided with respect to this access point for performing a Quality of Source (QoS) guarantee. Accordingly, when a new terminal is handed over to be engaged in wireless communications with this access point, the priority of the packet associated with the existing terminal and/or new terminal is changed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wireless communications system provided with a hand-over (automatic change-over of an access point with respect to a terminal) for engaging in wireless communications with an access point. Then, the present invention relates to a technology for guaranteeing QoS (quality of service) in this kind of wireless communications system. 
     2. Description of the Related Art 
     This kind of wireless communications system allows a terminal to move between service areas of an access point. 
     Then, when the terminal moves from a service area of the access point to a service area of the next access point, the connection of the terminal is automatically changed over (handed over) to the next access point. 
     That is, in this kind of wireless communications system, the terminal has a hand-over function. 
     Furthermore, as seen from the next access point, this terminal which has moved to its own service area is a new terminal. Here, when no existing terminal which is already connected to this access point is present, no malfunction is caused even when the new terminal is connected to this access point. 
     However, when there is an existing terminal which is already connected to the next access point, some malfunctions may be caused in the wireless communications in a competition between the existing terminal and new terminal. 
     Hereinafter, this point will be explained by citing an example.  FIG. 8  is a schematic view of a conventional wireless communications system. 
     In the wireless communications system shown in  FIG. 8 , there are two terminals; a terminal  1  and a terminal  2 . 
     At present, terminal  1  exists in the service area of access point  3  to be connected therewith. Furthermore, terminal  2  exists in the service area of access point  4  to be connected therewith. 
     An access point  3  and terminal  1 , and access point  4  and terminal  2  are connected by a link having a transmission bandwidth of 10 Mbps. To terminal  1  and terminal  2 , packets  6  and  7  of the image data (MPEG 2: 6 Mbps) with the same priority (here, the priority is “medium”) are transmitted. 
     Furthermore, packet transmission device  5  has an access point  3  and an access point  4  under the control of the device. Packet transmission device  5  and access point  3 , and packet transmission device  5  and access point  4  are connected by a communications line of 100 Mbps. Furthermore, for guaranteeing QoS, either or all of packet transmission device  5 , access point  3 , and access point  4  are provided with QoS guarantee means which is configured of a scheduler, a shaper, and a queue. With the QoS guarantee means, the priority of the packet which flows through the wireless communications system shown in  FIG. 8  is controlled. 
     Furthermore, the “packet transmission device  5 ” described here has various forms such as a gateway (including a home gateway), a router, a switch or a board which serves as a major function. However, any form will do. 
     Then, in the condition shown in  FIG. 8 , only communications less than the transmission bandwidth is provided with respect to any of the terminals. Consequently, both terminal  1  and terminal  2  can receive communications without any malfunction at all. 
     SUMMARY OF THE INVENTION 
     However, referring to  FIGS. 8-9 , when the user having terminal  1  walks in a direction of an arrow NI to be distant from a service area of access point  3 , the user comes close to a service area of access point  4 . 
     At this time, as seen from access point  4 , terminal  2  is an existing terminal which is already connected and terminal  1  is a new terminal which newly comes into the service area of access point  4 . 
     Here, as shown in  FIG. 9 , the transmission of packet  6  to terminal  1  and the transmission of packet  7  to terminal  2  have the same priority. 
     Here, in the prior art, in a case where the priority of these terminals  1  and  2  connected to access point  4  are completely the same, the two terminals  1  and  2  are fairly handled. 
     However, access point  4  has only the transmission bandwidth of 10 Mbps. As a consequence, in response to impartiality, a transmission bandwidth of 5 Mbps is allocated to each of terminals  1  and  2 . 
     Under these circumstances, the transmission bandwidth (5 Mbps) is lacking as compared with the transmission capacity (6 Mbps) both in terminal  1  and terminal  2  with the result that both packets  6  and  7  are lost. That is, disorder is generated in the image received by terminal  1  and terminal  2 , so that the transmission quality is deteriorated. 
     In particular, from the viewpoint of the user of terminal  2 , the quality of the received image is suddenly deteriorated only with an approach of the user of terminal  1  despite the fact that the user has done nothing, so that the user cannot help dissatisfying. 
     Furthermore, a case of distributing an image has been explained. In a case of an object which can be transmitted in packets, the same problem as described above is present in any data. 
     Therefore, an object of the present invention is to provide a wireless communications system which can suppress, as much as possible, a disadvantage resulting from a hand-over of the terminal. 
     The wireless communications system according to a first aspect of the present invention includes, a plurality of access points for supporting wireless communications in a service area, a transmission device connected to upstream sides of the access points and controlling the access points, a plurality of terminals including an existing terminal which is already engaged in wireless communications with a point included in the access points and a new terminal different from the existing terminal, and a priority changing unit, wherein the terminals are formed in a manner movable between the service areas of the access points and have a hand-over function at the time of movement between the service areas, and wherein the priority changing unit, when the new terminal is handed over to be engaged in wireless communications with the point, changes one or both of the priorities of the packets associated with the existing terminal and the priorities of the packets associated with the new terminal. 
     In this configuration, the priority changing unit appropriately changes the priority of the existing and/or the new terminals, so that the priority of the packet can be mediated and the disadvantage resulting from the hand-over at the terminal can be eliminated. 
     In the wireless communications system according to a second aspect of the present invention, the priority changing unit changes the priority so that the packet priority associated with the new terminal becomes lower than the packet priority associated with the existing terminal. 
     With such a configuration, a priority is given to a packet associated with the existing terminal which is not associated with the hand-over, so that actual fairness can be improved. 
     That is, with respect to the new terminal which has been handed over, the allocated transmission bandwidth is suppressed. A user of the new terminal can know in advance that his or her own action may bring about a competition even by acting in this manner, so that they have little dissatisfaction. Furthermore, a user of the existing terminal has no dissatisfaction because the communications quality is not suddenly deteriorated. 
     In the wireless communications system according to a third aspect of the present invention, the priority changing unit changes the priority in accordance with the change rules which are stipulated in advance. 
     With this structure, a soft mediation is enabled in addition to classification such as new and existing terminals. For example, for each terminal, a priority is determined. Even with a new terminal, the communications quality can be secured in priority for each of the terminals. 
     The wireless communications system according to a fourth aspect of the present invention comprises a bandwidth measurement unit for measuring a bandwidth usage condition with respect to the point. When a sufficient free bandwidth is available, priority change with the priority changing unit is omitted. 
     With this structure, an unnecessary priority change is eliminated thereby making an attempt of simplifying the processing and heightening the speed. 
     The wireless communications system according to a fifth aspect of the present invention comprises change notification unit for notifying a change in priority with respect to a terminal associated with a packet which is changed so that the priority is lowered. 
     With this structure, a user of the terminal whose priority is lowered can accept notification of the priority change, a condition ceases to exist in which the communications quality is suddenly lowered so that dissatisfaction can be alleviated. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a wireless communications system according to an embodiment of the present invention. 
         FIG. 2(   a ) and  FIG. 2(   b ) are illustrative views of the same header structure. 
         FIG. 3  is a flowchart showing a processing of changing the priority. 
         FIG. 4  depicts a specific example of the wireless communications system. 
         FIG. 5  depicts a specific instance of the wireless communications system. 
         FIG. 6  depicts a specific instance of the wireless communications system. 
         FIG. 7  depicts a specific instance of the wireless communications system. 
         FIG. 8  is a schematic view showing a conventional wireless communications system. 
         FIG. 9  depicts a specific example of the conventional wireless communications system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, referring to the drawings, embodiments of the present invention will be explained. Furthermore, constituent elements identical to  FIG. 8  and  FIG. 9  showing a conventional structure are denoted by the same reference numerals. An explanation thereof is omitted. 
     First, by using  FIG. 1 , constituent elements of the wireless communications system according to the embodiment will be explained. An example shown in  FIG. 1  is engaged in communications identical to  FIG. 8  and  FIG. 9  showing the prior art. 
     In the embodiment, as compared with  FIG. 8 , a bandwidth measurement unit  10  and  11 , priority changing unit  12 , change rules memory unit  13  and change notification unit  14  are added. The bandwidth measurement unit  10  and  11 , priority changing unit  12 , change rules memory unit  13  and change notification unit  14  may be provided at any location as long as the bandwidth measurement unit  10  and  11 , priority changing unit  12 , change rules memory unit  13  and change notification unit  14  can engage communications with this wireless communications unit from their respective locations. Furthermore, the priority changing unit  12  is required. However, the bandwidth measurement unit  10  and  11 , the change rules memory unit  13 , and the change notification unit  14  can be omitted. 
     Furthermore, the bandwidth measurement unit  10  recognize the whole transmission bandwidth of access point  3  while unit  10  measures the current usage condition with respect to access point  3 . As a consequence, when a new bandwidth request is made, it is measured as to whether a sufficient free bandwidth exists. 
     The bandwidth measurement unit  11  performs the same processing as bandwidth measurement unit  10  with respect to access point  4 . 
     The provision of the bandwidth measurement unit  10  and  11  eliminates any unnecessary priority changes thereby simplifying the processing and heightening the speed of data transmission. The bandwidth measurement unit  10  and  11  are provided at access points  3  and  4  as shown in the drawings so as to report the measurement results to the packet transmission device  5 . The packet transmission device  5  may control package access points  3  and  4 . 
     The priority changing unit  12  has an existing terminal which is already engaged in wireless communications with either of access points  3  and  4 . At the same time, when a new terminal which is different from this existing terminal is handed over to be engaged in wireless communications with this access point, one or both of the priorities are changed among the packets associated with the existing terminal and the packets associated with the new terminal. In addition, a detailed operation will be explained later by using  FIG. 3 . 
     The change rules memory unit  13  stores the predefined change rules in order to change the priority. The change rules memory unit  13  is typically configured as one area of a device such as a hard disk, a memory and the like. Then, the priority changing unit  12  changes the priority by referring to the change rules of the change rules memory unit  13  when required. 
     The change rules might be such that a priority is given to the existing terminal rather than the new terminal. Otherwise, according to the rules a priority is given to the new terminal rather than to the existing terminal. 
     However, when a priority is given to the existing terminal rather than to the new terminal, a user of the new terminal can know in advance that competition is generated by his or her own action with the result that dissatisfaction is small, and a user of the existing terminal has no dissatisfaction because of the absence of an abrupt deterioration in communications quality, which is favorable. 
     Furthermore, when the priority is determined for each of the terminals as these change rules, the communications quality can be secured in priority even with the new terminal, so that soft mediation is enabled. For example, a case is considered in which a high priority is given at all times with respect to a terminal for working, and a case in which the terminal for playing is given no priority depending upon the condition, and a case in which whereby the priority of the terminal used by an executive is held at a high level. 
     In addition, the change rules may be described in a simple program language having a control structure such as if statements, while statements and the like. At this time, a parser or the like for interpreting this program language or the like is provided in the different unit from the priority change unit  12  itself or in a different unit which operates in cooperation with the priority change unit  12 . 
     The change notification unit  14  notifies the priority change to the terminal associated with the packet which is changed to lower the priority. 
     When the change notification unit  14  is provided, a previous notice of the priority change is sent to the user of the terminal whose priority is lowered prior to the priority change with the result that a condition ceases to exist in which the communications quality is suddenly deteriorated so that dissatisfaction of the user can be alleviated. 
       FIGS. 2(   a ) and  2 ( b ) show an example of a header structure of the packet. Here, an example of the IP packet is shown. 
     For example, the IPv4 has a header structure as shown in  FIG. 2(   a ). The priority is written in the TOS (Type of Service) field. 
     Furthermore, the IPv6 has a header structure shown in  FIG. 2(   b ). The priority is written in the TC (Traffic Class) field. 
     In accordance with the priority of these fields, the packet is transmitted, so that the QoS guarantee is performed. Of course, what is shown in the drawings is simply an illustration of an example. When the priority information can be stored in the packet, the present invention can be applied in a similar manner. For example, the priority is stored in the priority information of the VLAN tag of the MAC layer, and this can be changed. 
     Next, referring to  FIG. 3 , the priority change process will be explained. Of course, this processing is performed for each access point. 
     Furthermore, first, at step  1 , the priority changing unit  12  checks whether or not the hand-over is generated in the service area of the access point. When the hand-over is not generated, there is no need for the priority change. Consequently, the process returns to step  1 . 
     When the hand-over is generated, it is assumed that competition for connection is generated in the existing terminal and new terminal which is already connected. Consequently, the process moves to step  2 . 
     At step  2 , when the bandwidth measurement unit  10  and  11  exist, the process moves to step  3 . Without the bandwidth measurement unit  10  and  11 , step  3  is skipped to move to step  4 . 
     At step  3 , it is measured whether a sufficient free bandwidth exists with respect to the corresponding access point by using the bandwidth measurement unit  10  and  11 . 
     When a sufficient surplus free bandwidth is available, the priority change is omitted and the process returns to step  1 . Consequently, wasteful processing is eliminated so that a increased speed in processing is advanced. 
     When no sufficient free bandwidth exists, the process moves to step  4 . 
     At step  4 , the priority changing unit  12  investigates whether or not the change notification unit  14  exists and effective change rules are described. When the investigation result is affirmative, the priority changing unit  12  changes the priority in accordance with the change rules (step  5 ). Then, the process moves to step  7 . 
     When the investigation result is negative, the priority is given to the existing terminal and the priority of the packet associated with the new terminal is lowered (step  6 ), and the process moves to step  7 . 
     At step  7 , the priority changing unit  12  investigates whether or not the change notification unit  14  exists. When the change notification unit  14  exists, the change notification unit  14  is used to notify the change to the terminal at which the priority is changed in an unfavorable manner (step  8 ). When no change notification unit  14  exists, no notification of a change is given. 
     Furthermore, steps  7  and  8  may be performed before steps  5  and  6 . 
     Next, various cases will be explained by using  FIG. 4  through  FIG. 7 . 
     (Case 1) 
     First, the case shown in  FIG. 4  is a case in which the priority with respect to the new terminal is lowered by step  6  of  FIG. 3 . 
     When the new terminal enters into the service area of the access point  4  in the condition of  FIG. 1 , the condition shown in  FIG. 4  is provided. At this time, as shown in  FIG. 4 , the priority changing unit  12  changes the priority of the packet  6  to the terminal  1  from “medium” to “low.” 
     Consequently, the packet  7  (the priority remaining “medium”) to terminal  2  provided with a relatively high priority is given priority in transmission. As a result, the terminal  2  can secure the bandwidth of 6 Mbps as it is. 
     On the other hand, since terminal  1  is new, only the bandwidth of 4 Mbps is allocated, and the quality received by terminal  1  is deteriorated. This results from movement of the user of terminal  1  himself, so that the user of terminal  1  can accept the condition. 
     Furthermore, it is desirable to notify terminal  1  in advance of the fact that priority is changed by providing the change notification unit  14 . 
     (Case 2) 
     Next, the case of  FIG. 5  will be explained. In this case, it is described that the change rules unit  13  is effective, terminal  1  gives a very high priority to change rules memory unit  13 , and terminal  2  may change the priority depending upon the condition. Then, the condition identical to  FIG. 4  results in a condition shown in  FIG. 5 . 
     That is, in step  5  of  FIG. 5 , the priority changing unit  12  gives a priority to the new terminal  1 , and no priority is given to the existing terminal  2 . As a consequence, as shown in  FIG. 5 , a condition that reverses the condition shown in  FIG. 4  is generated. 
     (Case 3) 
     Next, the case of  FIG. 6  will be explained. In this case, bandwidth measurement unit  10  and  11  are effective, and the process moves from step  2  to step  3 . Furthermore, this is a case in which despite the generation of the hand-over, a sufficient free bandwidth exists and the priority changing unit  12  returns the processing from step  3  to step  1 . 
     As shown in  FIG. 6 , in this case, since the terminal  1  uses 1 Mbps and the terminal  2  uses 6 Mbps, only 7 Mbps can be used for the sake of convenience. At this time, since a sufficient free bandwidth exists after the hand-over, priority changing unit  12  omits the priority change, so that the priorities of packet  6  and packet  7  both remain “medium.” 
     (Case 4) 
     Furthermore, there is a case as shown in  FIG. 7 . This consequence is the same as  FIG. 6 . Before terminal  1  is handed over to access point  4 , a condition identical to that of  FIG. 1  exists. When terminal  2  continues connection, it is scheduled that the process moves to a condition as shown in  FIG. 4  or  FIG. 5 . 
     However, in the case shown in  FIG. 7 , terminal  2  terminates communications immediately after terminal  1  is handed over to access point  4 . At this time, the priority changing unit  12  is moved from step  3  in  FIG. 3  to step  1 , so that the priority is not changed. Consequently, new terminal  1  can be engaged in wireless communications free from the complete change of the priority of the packet before and after the hand-over. 
     According to the present embodiment, the priority changing unit  12  can mediate the priority of the packet and can suppress a disadvantage resulting from a hand-over of the terminal by appropriately changing the priority of the existing terminal and new terminal. 
     Furthermore, a high priority is given to the packet associated with the existing terminal and not associated with the hand-over so that actual fairness can be improved. 
     Furthermore, a soft mediation can be mediated with the change rules of the priority. 
     Furthermore, the processing can be heightened in speed by eliminating the unnecessary priority change. 
     Furthermore, dissatisfaction can be alleviated with a notification of the priority change. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.