US20070160074A1 - Terminal capable of substituting for control station - Google Patents

Terminal capable of substituting for control station Download PDF

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Publication number
US20070160074A1
US20070160074A1 US10/589,240 US58924005A US2007160074A1 US 20070160074 A1 US20070160074 A1 US 20070160074A1 US 58924005 A US58924005 A US 58924005A US 2007160074 A1 US2007160074 A1 US 2007160074A1
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United States
Prior art keywords
frame
terminal
control
substitute
control station
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Abandoned
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US10/589,240
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English (en)
Inventor
Tsuyoshi Yamaguchi
Shinichiro Ohmi
Go Kuroda
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Panasonic Corp
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Individual
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Publication of US20070160074A1 publication Critical patent/US20070160074A1/en
Assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. reassignment MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KURODA, GO, OHMI, SHINICHIRO, YAMAGUCHI, TSUYOSHI
Assigned to PANASONIC CORPORATION reassignment PANASONIC CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Priority to US12/967,496 priority Critical patent/US8565258B2/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H04L12/403—Bus networks with centralised control, e.g. polling

Definitions

  • the present invention relates to a terminal whose opportunity to access a communication medium is controlled by a control station, and more particularly, to a terminal capable of substituting for a control station.
  • a communication system which utilizes media having a problem with communication quality is provided with a control station for controlling media access of other station(s) in order to utilize media as efficiently as possible.
  • the other station is regarded as a controlled station, i.e., the control station and the controlled station have a master-slave relationship.
  • a central control type communication system protocol which can improve the efficiency of the entire communication system has been developed.
  • the efficiency of media access in the communication system is significantly influenced by communication quality of a control station and a controlled station which depends on, for example, a physical positional relationship therebetween.
  • Patent Publication 1 discloses a terminal which operates in a control station mode and in a controlled station mode (two operational forms) and can select the operational forms.
  • the terminal detects the operating modes of surrounding terminals after being powered on, and when there is no detected terminal which is activated as a control station, operates as a control station.
  • Patent Publication 2 proposes a concept that a control station transfers its information to a controlled station (another station) during operation, and when the control station is suddenly disconnected from a network, the controlled station quickly replaces the control station to maintain network quality (Patent Publication 2).
  • a control station in which the reliability of transmission characteristics varies significantly depending on a physical positional relationship between stations, the location of a control station has a significant influence on the transmission efficiency of the whole network. Therefore, unless a control station is determined, taking into consideration the location on a network of connection of a terminal, the performance of a terminal, or the like, there is a possibility that the communication quality is significantly impaired upon replacement.
  • a terminal which operates as a control station is often designed to be connected to a location suitable for control of a network, taking the importance of the function thereof into consideration. Also, it is often that a control station is capable of recovering itself quickly if it is disconnected from a network for some reason. Therefore, when a control station is disconnected from a communication system, in general it is not always satisfactory to replace the control station with a new one. It is often satisfactory that the original control station returns to a media access control.
  • a first object of the present invention is to provide a terminal having a guaranteeing mechanism such that, when an operating control station is disconnected from a communication system for some reason, media access of the communication system can be prevented from falling into an inefficient situation for a long time, without sudden replacement with a new control station.
  • a second object of the present invention is to provide a terminal having a mechanism such that, when a control station which has been disconnected from a communication system is recovered, a media access control is returned to the original control station.
  • a third object of the present invention is to a terminal which can maintain the communication quality of a whole communication system using a simple mechanism against temporary disconnection of a control station.
  • the present invention provides a terminal whose opportunity to access a communication medium is controlled in accordance with a control frame issued from a control station connected to a network, comprises a control frame detection portion of detecting the control frame issued from the control station, a control frame memory portion of storing control information contained in the control frame, a substitute frame issuance determination portion of determining to issue a substitute frame when the control frame detection portion does not detect the control frame until a predetermined first time period is elapsed, and a substitute frame issuance portion of creating a frame which is the same as or equivalent to the control frame, as the substitute frame, based on the control information stored in the control frame memory portion when the substitute frame issuance determination portion determines to issue the substitute frame, and issuing the created substitute frame.
  • control frame memory portion may store the control frame only when the control frame has a change.
  • the substitute frame issuance portion may transmit a refusal response frame indicating that a request which is transmitted from another terminal and should be responded to by the control station is refused, during issuance of the substitute frame periodically.
  • the substitute frame issuance portion may not respond to a request which is transmitted from another terminal and should be responded to by the control station, during issuance of the substitute frame periodically.
  • the substitute frame issuance portion may stop issuing the substitute frame during issuance of the substitute frame periodically, if receiving a frame from the control station.
  • the substitute frame issuance portion may determine whether or not a frame is received from the control station until a predetermined second time period is elapsed.
  • the terminal may further comprise a control station mode portion of causing the terminal to operate as a control station when the substitute frame issuance portion determines that a frame is not received from the control station until the predetermined second time period is elapsed.
  • control station mode portion may collect information required as a control station from another terminal.
  • control station mode portion may issue a reset signal to collect information required as a control station from another terminal.
  • the terminal may try to access the communication medium in accordance with control information contained in a previously received control frame.
  • the substitute frame issuance portion may compete for a right to access the communication medium before issuing the substitute frame, and when acquiring the access right, issues the substitute frame.
  • a candidate terminal which issues the substitute frame may be designated by the control station.
  • the candidate terminal may be given a priority.
  • a terminal having a higher priority may have a higher probability of acquiring the access right in the access right competition for issuance of the substitute frame.
  • a candidate terminal which issues the substitute frame may be designated by the control station.
  • the terminal may further comprise a candidate terminal designation recognition portion of recognizing whether or not the control station designates the terminal as the candidate terminal.
  • the substitute frame issuance determination portion may determine whether or not to issue the substitute frame, assuming that a time period which is shorter than a first time period in a terminal which is not designated as the candidate terminal, is the first time period.
  • the candidate terminal may be given a priority.
  • the substitute frame issuance determination portion may use a first time period having a length corresponding to the priority to determine whether or not to issue the substitute frame.
  • the candidate terminal may be designated by the control station based on information about a communication state of a terminal in the network.
  • the designation of the terminal as a candidate terminal may be released.
  • an identifier for the control station may be described in the control frame.
  • the terminal may operate as the control station when an identifier for the terminal is described in the substitute frame.
  • the present invention also provides a method executed in a terminal whose opportunity to access a communication medium is controlled in accordance with a control frame issued from a control station connected to a network, comprising detecting the control frame issued from the control station, storing control information contained in the control frame, determining to issue a substitute frame when the control frame is not detected until a predetermined first time period is elapsed, creating a frame which is the same as or equivalent to the control frame, as the substitute frame, based on the stored control information when it is determined to issue the substitute frame, and issuing the created substitute frame.
  • the present invention also provides a program executed in a terminal whose opportunity to access a communication medium is controlled in accordance with a control frame issued from a control station connected to a network, comprising detecting the control frame issued from the control station, storing control information contained in the control frame, determining to issue a substitute frame when the control frame is not detected until a predetermined first time period is elapsed, creating a frame which is the same as or equivalent to the control frame, as the substitute frame, based on the stored control information when it is determined to issue the substitute frame, and issuing the created substitute frame.
  • the present invention also provides a computer-readable recording medium storing a program executed in a terminal whose opportunity to access a communication medium is controlled in accordance with a control frame issued from a control station connected to a network.
  • the program comprises detecting the control frame issued from the control station, storing control information contained in the control frame, determining to issue a substitute frame when the control frame is not detected until a predetermined first time period is elapsed, creating a frame which is the same as or equivalent to the control frame, as the substitute frame, based on the stored control information when it is determined to issue the substitute frame, and issuing the created substitute frame.
  • a terminal which issues a substitute frame transmits a refusal response frame in response to are quest which is transmitted from another terminal and should be responded to by a control station, or does not respond to it. Therefore, the terminal which issues a substitute frame does not necessarily require a function as a control station. Note that the terminal which issues a substitute frame is provided with a function as a control station so as to prepare a situation that a control station would not be recovered. It is useful to previously designate such a terminal as a candidate terminal which issues a substitute frame.
  • a terminal having a simple mechanism and capable of maintaining communication quality of an entire communication system is provided, thereby making it possible to minimize a decrease in communication quality in a communication system.
  • FIG. 1 is a diagram schematically showing a structure of a whole communication system 1 according to a first embodiment of the present invention.
  • FIG. 2 is a timing chart for explaining an exemplary operation in the communication system of FIG. 1 .
  • FIG. 3 is a block diagram showing a hardware structure of a terminal 100 which functions as a controlled station.
  • FIG. 4 is a block diagram showing a functional structure of the terminal 100 which is executing a substitution control program.
  • FIG. 5 is a flowchart showing an operation of the terminal 100 when the substitution control program is executed.
  • FIG. 6 is a diagram showing a portion of a communication system 2 according to a second embodiment of the present invention.
  • FIG. 7 is a flowchart showing an operation of a terminal 200 when newly participating in the communication system 2 .
  • FIG. 8 is a flowchart showing an operation of a control station.
  • FIG. 9 is a flowchart showing an exemplary operation of a control station.
  • FIG. 10 is a diagram showing an exemplary form of a frame when informing control required information.
  • FIG. 11 is a timing chart showing a flow of a terminal m issuing a substitute frame, assuming that a terminal p is disconnected from the communication system 2 .
  • FIG. 12 is a block diagram showing a functional structure of the terminal 200 of the second embodiment when the substitution control program is executed.
  • FIG. 13 is a flowchart showing an operation of the terminal 200 when a substitution control program is executed.
  • FIG. 14 is a diagram showing transmission slots for a substitute frame which depend on priorities of candidate terminals.
  • FIG. 15 is a block diagram shows a functional structure of a terminal 300 of a third embodiment according to the present invention when executing a substitution control program.
  • FIG. 16 is a diagram showing an exemplary format of a control frame (substitute frame).
  • FIG. 17 is a diagram showing another exemplary format of a control frame (substitute frame).
  • FIG. 18 is a diagram showing a band which is allocated for frame transmission.
  • FIG. 19 is a flowchart showing an operation of a terminal which is issuing a substitute frame periodically.
  • FIG. 20 is a flowchart showing an operation of a terminal which was a control station, when it is connected again to and recovered in a communication system.
  • FIG. 21 is a flowchart showing an operation of a terminal after detecting that a control station is disconnected from a communication system and determining that the terminal will function as a control station.
  • FIG. 22 is a diagram showing a whole structure of a system in which a terminal of the present invention is applied to high-speed power line communication.
  • FIG. 1 is a diagram schematically showing a structure of a whole communication system 1 according to a first embodiment of the present invention.
  • the communication system 1 comprises a control station and a controlled station which is under a control of the control station.
  • a terminal A is a control station which issues a signal for controlling an opportunity of media access by a terminal which participates in the communication system 1 (hereinafter referred to as a control frame).
  • Terminals B, C and D are controlled stations.
  • the control frame is also called a beacon. Note that the number of terminals in the present invention is not limited to that which is shown in FIG. 1 .
  • the terminals may be communicated with one another via wireless communication, wired communication or high-speed power line communication.
  • a network to which the terminals are connected is not particularly limited.
  • the control station A periodically issues a control frame containing control information and informs the controlled terminals of the control frame.
  • control information contained in the control frame a time when media access is permitted and a time interval are described for each controlled station or each transmission queue of controlled stations.
  • the control information further contains a start time of a time period during which a media access right is acquired by competition, information for controlling media access for the time period during which a media access right is acquired by competition, and the like.
  • the controlled stations B, C and D store contents of a control frame every time the control frame is received. Note that the contents of the control frame may be stored only when the contents of the control frame include a change.
  • a controlled station capable of operating as a control station creates a substitute frame using control information which is stored since a control frame had been received, and performs media access competition for transmission of the substitute frame. When winning the competition, the controlled station starts transmitting the substitute frame periodically.
  • a terminal which transmits a substitute frame periodically is referred to as a substitution control station.
  • the substitute frame contains the control information which is contained in the received control frame, without modification, so that the substitute frame is the same as the control frame.
  • the substitute frame contains information equivalent to the control information which is contained in the received control frame, so that the substitute frame is equivalent to the control frame.
  • Information contained in the substitute frame is considered to inherit the control information which is contained in the control frame, for example, when the substitute frame is completely the same as the control frame; when the substitute frame contains at least the control information contained in the control frame; when the information contained in the substitute frame is compatible with the control information contained in the control frame.
  • the substitute frame may contain other information, such as, for example, a flag which informs that the frame is a substitute frame, a terminal identifier of a substitution control station, or the like.
  • FIG. 2 is a timing chart for explaining an exemplary operation in the communication system of FIG. 1 .
  • the exemplary operation in the communication system of FIG. 1 will be described with reference to FIG. 2 .
  • a vertically downward direction is assumed to be the positive direction of a time axis.
  • the control station A is assumed to transmit a control frame 21 .
  • the control frame 21 transmitted at time T 21 is received by the controlled stations B, C and D.
  • the controlled stations B, C and D store control information contained in the received control frame.
  • the control station A is disconnected from the communication system 1 . Thereby, thereafter, the control station A no longer issues a control frame.
  • each terminal has a guaranteeing function such that when no control frame can be detected for the TIME_BC_WAIT time 22 , the terminal operates in accordance with a latest control frame among those which have been received.
  • the controlled station C wins a competition process performed from time T 23 to time T 24 .
  • the controlled station C issues a substitute frame 24 .
  • the controlled stations B and D execute media access in accordance with the substitute frame 24 issued by the controlled station C.
  • FIG. 3 is a block diagram showing a hardware structure of a terminal 100 which functions as a controlled station.
  • the terminal 100 is, for example, any of the controlled stations B, C and D.
  • the terminal 100 comprises a central processing device 101 , a frame transmission/reception access processing device 102 , an auxiliary memory device 103 , and a main memory device 104 .
  • a control station can also function as a controlled station, and therefore, a terminal which functions as a control station has a hardware structure similar to that of FIG. 3 .
  • the frame transmission/reception access processing device 102 is an interface between a communication medium and the terminal 100 , and modulates a frame to be transmitted and demodulates a received frame.
  • the frame transmission/reception access processing device 102 mainly executes processes in lower layers, such as a physical layer, an MAC layer and the like.
  • the auxiliary memory device 103 is a memory device, such as a ROM, a RAM, a hard disk, an optical disc or the like.
  • the auxiliary memory device 103 stores firmware or software which is executed in the central processing device 101 .
  • the auxiliary memory device 103 stores a substitution control program for causing the terminal 100 to execute an operation of the present invention.
  • the substitution control program may be either firmware or software.
  • the auxiliary memory device 103 optionally stores information which is provided by the central processing device 101 .
  • the main memory device 104 is a RAM or the like and stores a program or information in accordance with an instruction from the central processing device 101 .
  • the central processing device 101 executes a predetermined process, and causes the main memory device 104 to read firmware or software stored in the auxiliary memory device 103 and executes the firmware or software.
  • the central processing device 101 also causes the frame transmission/reception access processing device 102 to transmit/receive a frame.
  • the central processing device 101 controls operations of the entire terminal 100 .
  • the central processing device 101 causes the auxiliary memory device 103 and/or the main memory device 104 to store information required for processing.
  • FIG. 4 is a block diagram showing a functional structure of the terminal 100 which is executing the substitution control program.
  • the terminal 100 comprises a frame transmission/reception portion 105 , a control frame detection portion 106 , a control frame memory portion 107 , a substitute frame issuance determination portion 108 , and a substitute frame issuance portion 109 .
  • the frame transmission/reception portion 105 transmits/receives a frame to/from a communication medium.
  • the frame transmission/reception portion 105 transfers a received frame to the control frame detection portion 106 and the substitute frame issuance portion 109 .
  • the control frame detection portion 106 determines whether or not a frame received by the frame transmission/reception portion 105 is a control frame. When the frame received by the frame transmission/reception portion 105 is a control frame, the control frame detection portion 106 causes the control frame memory portion 107 to store the whole control frame or control information described in the control frame.
  • the control frame memory portion 107 stores the control information described in the control frame transferred from the control frame detection portion 106 .
  • the substitute frame issuance determination portion 108 determines whether or not the current control station is disconnected from the communication system 1 , thereby determining whether or not to issue a substitute frame. For example, when the control frame detection portion 106 does not detect a control frame for a predetermined first time period (e.g., TIME_BC_WAIT time), the substitute frame issuance determination portion 108 determines that the current control station is disconnected from the communication system 1 , thereby determining to issue a substitute frame.
  • a predetermined first time period e.g., TIME_BC_WAIT time
  • the substitute frame issuance determination portion 108 counts the number of frames after receiving a control frame.
  • the substitute frame issuance determination portion 108 determines that the current control station is disconnected from the communication system 1 , thereby determining to issue a substitute frame.
  • a time period until the number of received frames exceeds the predetermined value is the first time period. Note that the first time period is not limited to that described above and may be any time period during which it can be determined whether or not a control section is disconnected from the communication system 1 .
  • the substitute frame issuance portion 109 When the substitute frame issuance determination portion 108 determines to issue a substitute frame, the substitute frame issuance portion 109 creates a frame which is the same as or equivalent to a control frame issued by a control station, as a substitute frame, based on the control information stored in the control frame memory portion 107 .
  • the substitute frame issuance portion 109 executes a competition process for accessing a communication medium, via the frame transmission/reception portion 105 in accordance with a procedure predetermined in the communication system 1 , such as a CSMA/CA scheme or the like.
  • a right to access a communication medium is obtained as a result of the competition process, the substitute frame issuance portion 109 creates and issues a substitute frame and causes the frame transmission/reception portion 105 to transmit the substitute frame to the communication medium.
  • FIG. 5 is a flowchart showing an operation of the terminal 100 when the substitution control program is executed.
  • the operation of the terminal 100 when the substitution control program is executed will be described with reference to FIG. 5 .
  • main bodies of operation of steps in FIG. 5 are associated with the blocks of FIG. 4 .
  • the terminal 100 which executes the substitution control program employs the hardware of FIG. 3 to execute the procedure of FIG. 5 . Therefore, the main bodies of operations of the steps in FIG. 5 can be replaced with the central processing device 101 , the frame transmission/reception access processing device 102 , the auxiliary memory device 103 , and the main memory device 104 when implemented by hardware. This replacement is obvious to those skilled in the art and will not be explained.
  • the operation of FIG. 5 is started by frame reception of the terminal 100 as a trigger. Initially, the control frame detection portion 106 determines whether or not the received frame is a control frame (step S 101 ). When the received frame is a control frame, the terminal 100 goes to an operation of step S 102 . On the other hand, when the received frame is not a control frame, the terminal 100 goes to an operation of step S 104 .
  • step S 102 the control frame detection portion 106 compares the previously received control frame and the currently received control frame to determine whether or not the currently received control frame includes a change. Note that when an identifier which indicates that a change is made or a change has been made is provided in a control frame, the control frame detection portion 106 may determine, based on the identifier, whether or not the control frame includes a change. When the currently received control frame does not include a change, the terminal 100 goes to the operation of step S 104 . On the other hand, when the currently received control frame includes a change, the control frame detection portion 106 causes the control frame memory portion 107 to store control information described in the currently received control frame (step S 103 ).
  • control frame detection portion 106 may not determine whether or not there is a change between control frames and may cause the control frame memory portion 107 to invariably store control information described in a newly received control frame.
  • the present invention is not limited to the operation of FIG. 5 as long as latest control information is stored in the control frame memory portion 107 .
  • step S 104 the substitute frame issuance determination portion 108 determines whether or not the first time period is elapsed from reception of an immediately previous control frame.
  • the terminal 100 becomes ready to receive a frame (step S 109 ).
  • the terminal 100 starts an operation from step S 101 .
  • the terminal 100 goes to an operation of step S 105 . Note that the determination of step S 104 is always performed, and when the first time period is elapsed from reception of an immediately previous control frame, the terminal 100 performs an interrupt process to execute operations of steps S 105 to S 108 no matter whether or not a frame is received.
  • step S 105 the substitute frame issuance portion 109 executes a competition process for accessing a communication medium in accordance with a procedure predetermined in the communication system 1 (step S 105 ).
  • the substitute frame issuance portion 109 determines, based on a result of the competition, whether or not a right to access the communication medium is acquired (step S 106 ).
  • the terminal 100 goes to the operation of step S 109 .
  • the substitute frame issuance portion 109 creates a substitute frame which is the same as or equivalent to the immediately previous control frame, based on the control information stored in the control frame memory portion 107 (step S 107 ).
  • the substitute frame issuance portion 109 causes the frame transmission/reception portion 105 to transmit the created substitute frame at predetermined time intervals (typically, time intervals at which a control frame is transmitted), i.e., issues a substitute frame periodically (step S 108 ). Although it is herein assumed that the substitute frame issuance portion 109 creates a substitute frame after the competition process, the competition process may be executed after the substitute frame is created.
  • a terminal which functions as a controlled station stores control information contained in a latest control frame.
  • the terminal When detecting that a control station is disconnected from a communication system, the terminal creates a substitute frame based on the stored control information and issues the substitute frame periodically. Therefore, even if a control station is disconnected from a communication system, a substitute frame is continued to be periodically issued in place of a control frame on the communication system. Therefore, media access is guaranteed on the communication system without suddenly exchanging with a new control station. As a result, it is possible to avoid a situation that the absence of a control station causes media access to be inefficient for a long time on the communication system. Further, in the first embodiment, communication quality of a whole communication system can be maintained by a considerably simple process, i.e., storing control information and issuing a substitute frame. Thus, the present invention is practically very useful.
  • the operation of the terminal 100 of the first embodiment of the present invention is implemented by executing the substitution control program.
  • the terminal 10 may be constructed by implementing the functional blocks of FIG. 4 using dedicated hardware, each of the functional blocks executing the operation of FIG. 5 .
  • the dedicated hardware may be incorporated in the central processing device 101 or the frame transmission/reception access processing device 102 , or alternatively may be incorporated in other portions of the terminal 100 .
  • a terminal according to a second embodiment of the present invention is assumed to function both as a control station and as a controlled station.
  • a terminal which tries to newly participate in a communication system determines whether to operate as a control station or as a controlled station before participating in the communication system.
  • FIG. 6 is a diagram showing a portion of a communication system 2 of the second embodiment.
  • the communication system 2 of the second embodiment is provided with a security management device 2 a .
  • the security management device 2 a authenticates a terminal 200 which tries to participate in a communication system and manages a cryptographic key for a link between terminals or a cryptographic key for a whole communication system.
  • the security management device 2 a may be provided in a control station which issues a control frame.
  • a user interface station 2 c which has a user interface which imparts a certain input means to a user, is connected to the communication system 2 .
  • the user interface station 2 c may be implemented by a device other than the terminal 200 capable of participating in the communication system 2 or by the terminal 200 .
  • the terminal 200 and the security management device 2 a are connected to each other via a communication medium 2 b .
  • a whole structure of the communication system 2 is similar to that of the first embodiment, and therefore, FIG. 1 is referenced.
  • FIG. 7 is a flowchart showing an operation of the terminal 200 when newly participating in the communication system 2 .
  • the operation of the terminal 200 when newly participating in the communication system 2 will be described with reference to FIG. 7 .
  • a hardware structure of the terminal 200 is similar to that of the first embodiment, and therefore, FIG. 3 is referenced.
  • the operation of FIG. 7 may be implemented by the central processing device 101 executing a program stored in the auxiliary memory device 103 , or by dedicated hardware.
  • the terminal 200 executes a terminal startup process (step S 201 ).
  • the terminal 200 executes carrier sense (step S 202 ).
  • the terminal 200 determines whether or not a control frame is detected (step S 203 ).
  • step S 203 when a control frame is detected, a control station is already present, and therefore, the terminal 200 communicates with the security management device 2 a to execute an authentication process for participating in the communication system 2 (step S 204 ).
  • a terminal which can participate in the communication system 2 should be explicitly permitted for participation. Therefore, the user utilizes the user interface station 2 c to input fixed information (serial code) for specifying a terminal which the user wants to participate in the communication system 2 .
  • the information is imparted to the security management device 2 a .
  • the security management device 2 a accumulates the information.
  • the terminal 200 which wants to participate in the communication system 2 informs the security management device 2 a of a request for participation along with a serial code thereof.
  • the security management device 2 a checks the serial code. When it can be confirmed that the terminal 200 is permitted for participation by the user, the security management device 2 a informs the terminal 200 of information about the cryptographic key, i.e., informs the terminal 200 which wants to participate in the communication system 2 of authentication/permission. On the other hand, when the informed serial code cannot be found among the accumulated serial codes, the security management device 2 a refuses participation of the terminal 200 which wants to participate in the communication system 2 .
  • a process for authenticating participation of a new entrant terminal is not limited to the example described above. For example, a new entrant terminal may be authenticated for precipitation only when a button or the like is provided in a user interface station and an authentication request can be received during a certain valid time period from the time when the button is pressed down.
  • step S 203 when a control frame is not detected, the terminal 200 determines whether or not a TIME_INT_WAIT time is elapsed (step S 205 ).
  • the TIME_INT_WAIT time is a predetermined transmission time interval of a control frame.
  • the terminal 200 returns to the operation of step S 202 .
  • the terminal 200 goes to an operation of step S 206 which is a process in which the terminal 200 itself is started up as a control station.
  • step S 206 the terminal 200 requests a station which is only one that has a function (BSSID manager) of permitting issuance of an ID of a communication system (hereinafter referred to as a BSSID) for the user, for issuance of a BSSID, in order to obtain the BSSID.
  • An effective time during which permission of BSSID issuance can be requested is a TIME_BSSID_WAIT time.
  • the BSSID manager function may be possessed by the user interface station 2 c .
  • the BSSID manager executes management for causing a BSSID to be only one that is effective on a time axis in a logical communication system which is desired by the user.
  • the BSSID manager permits issuance of a BSSID unless an effective BSSID is present at the time of the request.
  • step S 207 the terminal 200 determines whether or not issuance of a BSSID is permitted.
  • the terminal 200 sets the BSSID by itself or is informed of issuance of the BBSID by the BSSID manager, to use the BSSID to start issuance of a control frame (step S 209 ).
  • step S 207 when it is determined that issuance of a BSSID is not permitted, the terminal 200 determines whether or not the TIME_BSSID_WAIT time is elapsed (step S 208 ). When the TIME_BSSID_WAIT time is not elapsed, the terminal 200 returns to the operation of step S 206 and requests for issuance of a BSSID. On the other hand, when the TIME_BSSID_WAIT time is elapsed, the terminal 200 stops the operation (step S 210 ). Note that the process of FIG. 7 may be repeated a plurality of times.
  • the communication system is started up.
  • the control station of the second embodiment previously selects a candidate terminal which transmits a substitute frame, and gives a priority to the candidate terminal.
  • FIG. 8 is a flowchart showing an operation of a control station. Hereinafter, the operation of the control station will be described with reference to FIG. 8 .
  • the control station selects a candidate terminal which issues a substitute frame (step S 301 ).
  • a criterion for selecting a candidate is not particularly limited.
  • a terminal which has a location or performance suitable as a control station may be selected as a candidate terminal, or a terminal which is previously registered may be selected as a candidate terminal.
  • the control station may collect information about a communication state of each terminal as statistical information, and based on the collected statistical information, may select a candidate terminal.
  • the control station gives a priority to the candidate terminal (step S 302 ).
  • a criterion for giving a priority is not particularly limited. For example, a priority is given, depending on the processing performance of a terminal, or may be randomly given without considering the processing performance.
  • the control station may inform of a priority which is stored in a dedicated frame or is described in a control frame.
  • control station transmits control required information and a priority to the candidate terminal and informs that the terminal is a candidate terminal (step S 303 ).
  • control required information refers to information which is required to operate as a control station.
  • Control information contained in a control frame is a portion of control required information.
  • FIG. 9 is a flowchart showing an exemplary operation of a control station. Hereinafter, an example of selection of a candidate terminal will be described with reference to FIG. 9 .
  • a terminal which is currently operating as a control station is indicated by m.
  • the terminal m which is a control station selects a terminal p which is most appropriate to a control station, other than the terminal m, based on communication quality information of a communication system (step S 401 ).
  • the communication quality information refers to information which indicates communication quality of a terminal on a communication system.
  • control required information includes information about a reserved band requested by each station in a communication system and a request station, information for identifying a port in use or a transmission queue, and information about a traffic situation of a communication system.
  • FIG. 10 is a diagram showing an exemplary form of a frame when informing control required information.
  • the frame includes a frame header 7001 and a frame body 7002 .
  • the frame body 7002 includes a field 7003 and a field 7004 .
  • the field 7003 is a field in which, when a band guarantee request is made by a terminal in a communication system containing a control station in order to transmit specific stream contents, the control station accepts the request, and there is a link whose band is guaranteed, information about the band is described.
  • the field 7004 is a field in which information (index) about traffic (congestion level) of a whole communication system is described.
  • the field 7003 includes a field 7005 , a field 7006 , and a field 7007 .
  • the field 7005 is a field which indicates an MAC address of a request station which requests for band allocation in a link guaranteed with a band.
  • the field 7006 is a field which indicates information (stream ID) for specifying a transmission queue of the request station.
  • the field 7007 is a field which indicates information about a band for which a request is accepted. Note that a minimum band, an average band, a maximum band, a delay limit, a jitter limit, or the like may be described in the field 7007 .
  • the data body 7002 includes a plurality of fields 7003 .
  • the terminal m as a control station requests all terminals in the communication system 2 for release of designation as a candidate terminal (step S 403 ). Note that it may be defined that when one terminal in the communication system 2 is designated as a candidate terminal and other terminals are informed of control required information, the designation of the one terminal as a candidate terminal may be released.
  • the terminal m which is a control station determines whether or not to change control stations by transferring the function of a control station to the terminal p (step S 404 ).
  • a criterion for determining whether or not to change control stations is not particularly limited. For example, when the terminal p receives a signal from other terminals better than from the terminal m, the terminal m determines to change control stations.
  • the terminal m which is a control station designates the terminal p as a candidate terminal for a control station (step S 405 ).
  • the terminal m which is a control station transmits control required information to the terminal p, an intention to designate the terminal p as a candidate terminal may be described in the control required information.
  • the designation of the one terminal as a candidate terminal is released.
  • the terminal m which is the control station executes a process for causing the terminal p to become a control station in place of the terminal m (step S 406 ).
  • the terminal p which is a new control station creates a control frame or controls media access in response to requests from other terminals, based on control required information imparted from the terminal m.
  • step S 406 the terminal m sets itself to be a candidate terminal (step S 407 ).
  • a candidate terminal may be determined based on whether or not to change control stations.
  • FIG. 11 is a timing chart showing a flow of the terminal m issuing a substitute frame, assuming that the terminal p is disconnected from the communication system 2 .
  • the controlled terminal of the second embodiment stores control information contained in a control frame issued by a control station as does the controlled terminal of the first embodiment.
  • the terminal p which is a control station issues a control frame 31 , and thereafter, is disconnected from the communication system 2 without issuing a next control frame.
  • TIME_NOMINATE_WAIT time (first time period) 32 is elapsed from a time of detection of the control frame 31 issued by the terminal p
  • the terminal m which is a candidate terminal recognizes that the control station is disconnected from the communication system 2 .
  • a TIME_INIT_WAIT time (first time period) 35 is elapsed from the time of detection of the control frame 31
  • a non-candidate terminal recognizes that the control station is disconnected from the communication system 2 .
  • the TIME_INIT_WAIT time is longer than the TIME_NOMINATE_WAIT time.
  • a first time period which is used by a terminal designated as a candidate terminal is shorter than a first time period which is used by a terminal not designated as a candidate terminal.
  • the first time period may be defined using the number of frames counted, as in the first embodiment.
  • the terminal m When recognizing that the control station is disconnected from the communication system 2 , the terminal m uses the stored control information to create a substitute frame and executes a competition process 33 for communication medium so as to issue the substitute frame.
  • the terminal m transmits a substitute frame 34 .
  • FIG. 12 is a block diagram showing a functional structure of the terminal 200 of the second embodiment when the substitution control program is executed.
  • the terminal 200 comprises a frame transmission/reception portion 205 , a control frame detection portion 206 , a control frame memory portion 207 , a substitute frame issuance determination portion 208 , a substitute frame issuance portion 209 , and a candidate terminal designation recognition portion 210 .
  • the frame transmission/reception portion 205 transmits/receives a frame to/from a communication medium.
  • the frame transmission/reception portion 205 transfers the received frame to the control frame detection portion 106 , the candidate terminal designation recognition portion 210 , and the substitute frame issuance portion 209 .
  • the control frame detection portion 206 has a function similar to that of the control frame detection portion 106 of the first embodiment.
  • the control frame memory portion 207 has a function similar to that of the control frame memory portion 107 of the first embodiment.
  • the candidate terminal designation recognition portion 210 recognizes whether or not the terminal 200 is designated as a candidate terminal by a control station. When terminal 200 is designated as a candidate terminal, the candidate terminal designation recognition portion 210 memorizes the designation as a candidate terminal and a priority thereof.
  • the substitute frame issuance determination portion 208 references contents stored in the candidate terminal designation recognition portion 210 to determine whether or not the terminal 200 is designated as a candidate terminal.
  • the substitute frame issuance determination portion 208 determines whether or not a current control station is disconnected from the communication system 1 , thereby determining whether or not to issue a substitute frame.
  • a method for determining whether or not to issue a substitute frame is similar to that of the substitute frame issuance determination portion 108 in the first embodiment.
  • the substitute frame issuance portion 209 When it is determined that the substitute frame issuance determination portion 208 should issue a substitute frame, the substitute frame issuance portion 209 creates a frame which is the same as or equivalent to a control frame issued by the control station, as a substitute frame, based on control information stored in the control frame memory portion 207 . Note that the substitute frame issuance portion 209 may create a substitute frame using control required information which has been previously received from the control station.
  • FIG. 13 is a flowchart showing an operation of the terminal 200 when the substitution control program is executed.
  • the operation of the terminal 200 when the substitution control program is executed will be described with reference to FIG. 13 .
  • Note that a main body of the operation of FIG. 13 is similar to that of the first embodiment.
  • FIG. 13 The operation of FIG. 13 is started by frame reception by the terminal 200 as a trigger. Operations of steps S 501 to S 503 are similar to steps S 101 to S 103 are similar to those of the first embodiment.
  • step S 504 the substitute frame issuance determination portion 208 determines whether or not the terminal 200 is designated as a candidate terminal with reference to the candidate terminal designation recognition portion 210 .
  • the substitute frame issuance determination portion 208 recognizes a priority as a candidate terminal (step S 505 ).
  • step S 506 the substitute frame issuance determination portion 208 determines whether or not the control station is disconnected from the communication system based on whether or not the terminal 200 is a candidate terminal (step S 504 ) and the priority recognized in step S 505 (step S 506 ). Note that the determination of step S 506 is always performed, and when it is determined that the control station is disconnected from the communication system 2 , the terminal 200 performs an interrupt process to execute operations of steps S 507 to S 510 no matter whether or not a frame is received.
  • a candidate terminal determines that a control station is disconnected from a communication system.
  • the first time period is such that if a control frame is not received during this period, it is determined that the control station is disconnected.
  • a terminal other than the candidate terminal determines that the control station is disconnected from the communication system.
  • the candidate terminal transmits a substitute frame with a higher probability than that of a terminal(s) other than the candidate terminal.
  • the length of the first time period may be changed, depending on the priority. Specifically, the first time period in a candidate terminal having a high priority may be set to be shorter than the first time period of a candidate terminal having a low priority. In this case, a candidate terminal having a high priority transmits a substitute frame with a high probability.
  • step S 506 when determining that the control station is not disconnected, the terminal 200 becomes ready to receive a signal (step S 511 ).
  • step S 511 When receiving a new frame, the operation of step S 501 and thereafter are started.
  • step S 506 when the control station is disconnected, the substitute frame issuance portion 209 executes a competition process for access to a communication medium (step S 507 ). Note that a candidate terminal having a higher priority may acquire an access right with a higher probability in the competition process of step S 507 .
  • FIG. 14 is a diagram showing transmission slots for a substitute frame which depend on the priorities of candidate terminals.
  • slots S 31 , S 32 , . . . , S 3 n for transmitting a substitute frame are allocated successively, depending on the priority, from time T 31 when the absence of a control station is determined.
  • the slot S 30 for transmitting a substitute frame is allocated at an end for a terminal which is not in formed of a priority.
  • a candidate terminal transmits a substitute frame using a slot allocated depending on the priority.
  • a candidate terminal having a higher priority acquires an access right with a higher probability and can issue a substitute frame earlier.
  • collision of substitute frames can be reliably avoided, and even when the information of a priority or the like is incomplete, a substitute frame can be transmitted.
  • the scheme includes a method of specifying only a single terminal having a highest priority and issuing a substitute frame from a dedicated slot.
  • a terminal which is given a higher priority can be caused to acquire an access right to transmit a substitute frame, with a higher probability. For example, time is divided into unit intervals in each of which is required for frame detection on media. Such a unit is here called a slot. A random number is calculated where its maximum is a predetermined number of slots (here called a contention window). Transmission is performed after waiting until a time corresponding to the calculated number of slots is elapsed (a general access control). In this case, if a terminal having a higher priority has a smaller width of the contention window, the probability of acquisition of an access right to transmit a substitute frame can be increased.
  • the substitute frame issuance portion 209 determines whether or not an access right to transmit a substitute frame is acquired as a result of a competition process (step S 508 ). When the access right is not acquired, the terminal 200 goes to an operation of step S 511 . On the other hand, when the access right is acquired, the substitute frame issuance portion 209 creates a substitute frame which is the same as or equivalent to an immediately previous control frame, based on control information stored in the control frame memory portion 207 (step S 509 ). The substitute frame issuance portion 209 causes the frame transmission/reception portion 205 to transmit the created substitute frame at predetermined time intervals (typically, time intervals at which a control frame is transmitted) to issue a substitute frame periodically (step S 510 ). Although it is herein assumed that the substitute frame issuance portion 209 creates a substitute frame after a competition process, the competition process may be executed after the substitute frame is created.
  • a terminal which functions as a controlled station stores control information contained in a latest control frame.
  • a control station previously selects a candidate terminal which issues a substitute frame and gives a priority thereto.
  • the terminal which functions as a controlled station determines whether or not the control station is disconnected from a communication system, based on the presence or absence of designation of a candidate terminal and the priority.
  • the terminal which functions as a controlled station creates a substitute frame based on the stored control information and issues the substitute frame periodically. Therefore, even when the control station is disconnected, a substitute frame is periodically issued instead of a control station on the communication system. Therefore, media access is guaranteed on the communication system without suddenly exchanging with a new control station.
  • the candidate terminal may only memorize that it is a candidate terminal and may not be given a priority.
  • a competition process is executed so as to obtain an opportunity to issue a substitute frame.
  • a terminal may issue a substitute frame immediately after determining that a control station is disconnected from a communication system.
  • a terminal may issue a substitute frame with timing with which a control frame is originally transmitted.
  • a station which stores a state of a communication system in a non-volatile ROM flash ROM
  • the non-volatile ROM may be any memory device which can hold information after being powered off.
  • the non-volatile ROM stores an index capable of identifying a station which is authenticated by a security manager to be able to participate in the communication system; an index capable of identifying a control station in the communication system; an index capable of identifying a station having the security manager function; and the like.
  • information written in the non-volatile ROM of a station having the system backup function is utilized to recover the communication system.
  • the information written in the non-volatile ROM is used in selection of a control station and a security manager when a station in the communication system is started up again. Also in the authentication task of the security management device 2 a in step S 204 , the information written in the non-volatile ROM is utilized. Specifically, the security management device 2 a performs authentication based on the information written in the non-volatile ROM without the user's reconfirmation.
  • a terminal having such a non-volatile ROM may be a terminal having the BSSID manager function.
  • each terminal starts up either as a control station or as a controlled station.
  • the communication system may include a terminal which starts up only as a control station and a terminal which starts up only as a controlled station.
  • a hardware structure of a terminal of the third embodiment is similar to that of the first embodiment, and therefore, FIG. 3 is referenced.
  • FIG. 15 is a block diagram showing a functional structure of a terminal 300 of the third embodiment when executing a substitution control program.
  • the terminal 300 comprises a frame transmission/reception portion 310 , an operating mode management portion 320 , a controlled station mode portion 330 , and a control station mode portion 340 .
  • the frame transmission/reception portion 310 is an interface to a communication medium. When receiving a frame, the frame transmission/reception portion 310 transfers the frame to the operating mode management portion 320 .
  • the operating mode management portion 320 manages whether or not the operating mode of the terminal 300 is a control station mode or a controlled station mode. When a terminal is operating, one of the modes is selected.
  • the controlled station mode portion 330 and the control station mode portion 340 are connected to the operating mode management portion 320 .
  • the terminal 300 uses the controlled station mode portion 330 or the control station mode portion 340 in accordance with the operating mode managed by the operating mode management portion 320 .
  • the controlled station mode portion 330 comprises a control frame detection portion 331 , a control frame memory portion 332 , a substitute frame issuance determination section 333 , and a substitute frame issuance portion 334 .
  • the operating mode management portion 320 transfers a frame from the frame transmission/reception portion 310 to the control frame detection portion 331 .
  • the control frame detection portion 331 determines whether or not the frame from the operating mode management portion 320 is a control frame, and when it is a control frame, causes the control frame memory portion 332 to store information (control information) contained in the control frame.
  • the control frame memory portion 332 stores the control information. Note that, as in the first embodiment, only control information contained in a latest control frame may be stored in the control frame memory portion 332 .
  • the substitute frame issuance determination section 333 starts up a timer (not shown) every time a control frame is detected, to monitor intervals at which a control station issues a control frame.
  • the substitute frame issuance determination section 333 monitors the control frame interval to determine the presence or absence of a control frame which is expected to be issued for a predetermined time period.
  • the substitute frame issuance determination section 333 determines that the control station is disconnected from the communication system.
  • the substitute frame issuance determination portion 333 may comprise a mechanism which starts up a counter for monitoring the number of received frames and resets the counter every time a control frame is detected. In this case, when the counter reaches its maximum count, the substitute frame issuance determination portion 333 determines that the control station is disconnected from a communication system.
  • the predetermined time period or the maximum value of the counter is a first time period.
  • the substitute frame issuance portion 334 When the substitute frame issuance determination section 333 determines that the control station is disconnected from the communication system, the substitute frame issuance portion 334 creates a substitute frame using the control information stored in the control frame memory portion 332 and executes a competition process via the operating mode management portion 320 and the frame transmission/reception portion 310 . When acquiring an access right, the substitute frame issuance portion 334 transfers a substitute frame to the operating mode management portion 320 , which in turn transmits the substitute frame via the frame transmission/reception portion 310 to a communication medium. Thereafter, the substitute frame issuance portion 334 issues the substitute frame periodically.
  • the substitute frame issuance portion 334 determines whether or not the frame is a frame from a terminal which is a control station. When the frame is a frame from a terminal which is a control station, the substitute frame issuance portion 334 stops transmitting the substitute frame. When a time for waiting for recovery of a control station (second time period) is elapsed, the substitute frame issuance portion 334 instructs the operating mode management portion 320 to switch the mode so that the terminal 300 operates as a control station. In response to this, the operating mode management portion 320 switches the operating mode.
  • the control station mode portion 340 comprises an access control portion 341 for scheduling media access of a terminal in a communication network, which is a key function of a control station, and a substitute station management portion 342 . Note that the substitute station management portion 342 may not be included.
  • the access control portion 341 collects a frame issuance request from other terminal(s) operating in the controlled station mode in the communication system, and a frame issuance request in the terminal 300 and allocates a transmission resource of a communication medium to the other terminal(s) or the terminal 300 in a time-division or frequency-division manner. Information about the allocation of the transmission resource is stored as scheduling information in a control frame.
  • the access control portion 341 issues the control frame periodically.
  • Such a centralized media access control can prevent collision of frames on a network in media in which collision detection is difficult, thereby, for example, making it possible to guarantee transmission quality required for the network without reducing the use efficiency of the media.
  • the substitute station management portion 342 previously sets and manages a candidate terminal which issues a substitute frame.
  • a method for selecting a candidate terminal is similar to that of the second embodiment.
  • a memory portion 350 is a non-volatile memory device which is connected to the access control portion 341 .
  • the memory portion 350 stores a request for acquisition of a transmission resource from a terminal on a network, and information about updating of scheduling information, such as allocation, change and erase of a transmission band depending on a state of a transmission channel.
  • the memory portion 350 does not lose the stored information even when the power source of the terminal 300 is suddenly interrupted. Therefore, when a terminal which has been disconnected from a communication system is recovered and started up as a control station, the terminal can reference to the information stored in the memory portion 350 to obtain information required as a control station. Note that the memory portion 350 may not be provided.
  • the terminal A operates as a control terminal while the terminals B, C and D operate as controlled terminals in the communication system.
  • the terminal A issues a control frame periodically.
  • access scheduling information about access to a communication medium is described.
  • the terminals B, C and D access the communication medium in accordance with the access scheduling information described in the control frame.
  • FIG. 16 is a diagram showing an exemplary format of a control frame (substitute frame).
  • the control frame comprises a frame header 40 , an access scheduling information field 41 , and a field 43 .
  • the frame header 40 is provided to all frames issued in the communication system.
  • the frame header 40 includes an identifier for a destination or sender terminal of a frame, a frame type, encryption information, and the like.
  • the access scheduling information field 41 includes access scheduling information 42 which is scheduled by the access control portion 341 .
  • the access scheduling information 42 is composed of designation of a terminal, a data stream, a transmission resource request, an access protocol (priority assignment by time division or frequency division, a competition-based access scheme in compliance with the CSMA/CA scheme, etc.).
  • the access scheduling information field 41 is composed of the access scheduling information 42 of each data stream, for example.
  • the field 43 includes an identifier for a terminal which has executed access scheduling. It is herein assumed that the terminal A is a control station. Therefore, the field 43 stores an identifier for the control station A.
  • a format of a substitute frame is as shown in FIG. 16 , and information stored in the substitute frame is the same as that of a control frame. Therefore, the field 43 of the substitute frame stores the identifier for the terminal A without modification.
  • the control frame issued by the control station A is received by a controlled station.
  • the frame transmission/reception portion 310 of the controlled station transfers the received control frame to the operating mode management portion 320 .
  • the operating mode of the controlled station is the controlled station mode, and therefore, the operating mode management portion 320 transfers the received control frame to the control frame detection portion 331 .
  • the control information contained in the control frame (in the example of FIG. 16 , the information described in the frame header 40 , information described in the access scheduling information field 41 , and information described in the field 43 ) is stored in the control frame memory portion 332 . Note that past control information may be overwritten in the storing process.
  • the substitute frame issuance determination section 333 starts up a timer (not shown) and determines whether or not the control station is disconnected from the communication system.
  • a time for the determination is preferably set to be slightly longer than the control frame issuance interval.
  • FIG. 17 is a diagram showing another exemplary format of a control frame (substitute frame).
  • a control frame (substitute frame) comprises a frame header 40 , a substitute frame flag 52 , and an access scheduling information field 41 .
  • the frame header 40 and the access scheduling information field 41 of the substitute frame are completely the same as the frame header 40 and the access scheduling information field 41 of the control frame.
  • the control frame and the substitute frame are different from each other only in information stored in the substitute frame flag 52 . Therefore, when the format of FIG. 17 is used, the substitute frame is considered to be equivalent to the control frame.
  • the frame header 40 is assumed to include a source address 51 .
  • the source address is also contained in the frame header of the control frame.
  • the source address of the control frame is an identifier for the terminal A.
  • the source address of the frame header of the substitute frame is the same as the source address contained in the frame header of the control frame. In other words, a terminal which transmits the substitute frame is other than the terminal A, however, the source address contained in the substitute frame is the identifier for the terminal A.
  • the substitute frame flag 52 is false when the frame is a control frame and true when the frame is a substitute frame. Note that only a substitute frame may include a substitute frame flag while a control frame may not include a substitute frame flag.
  • the terminal 300 may determine an opportunity to access to the communication medium several times based on the control information stored in the control frame memory portion 332 .
  • the terminal 300 may comprise a means for trying to access to a communication medium in accordance with control information contained in the previously received control frame even if a control frame cannot be received. Such a means can guarantee media access even when a control frame is normally issued, however, is not normally received due to a fluctuation in a transmission channel or the like.
  • the substitute frame issuance determination section 333 determines to issue a substitute frame.
  • a procedure for issuing a substitute frame may be the procedure of the first embodiment, or alternatively, a procedure in which a candidate terminal has a priority to issue a substitute frame as in the second embodiment.
  • the substitute frame issuance portion 334 references latest control information from the control frame memory portion 332 to create a substitute frame.
  • the substitute frame issuance portion 334 transfers the created substitute frame to the frame transmission/reception portion 310 .
  • the frame transmission/reception portion 310 executes a competition process in accordance with a predetermined procedure, and when win the competition, transmits a substitute frame.
  • the competition process is executed by, for example, random backoff based on carrier sense.
  • FIG. 18 is a diagram showing a band which is allocated for frame transmission.
  • a control frame slot 61 is allocated for each system cycle.
  • the control frame slot 61 is a band in which only a control frame is issued.
  • a substitute frame slot 62 is allocated.
  • a substitute frame is issued by random backoff based on carrier sense.
  • a band 63 is for data communication.
  • the controlled station mode portion 330 of the terminal 300 may be provided with the candidate terminal designation recognition portion 210 as in the second embodiment.
  • the substitute frame issuance determination section 333 may determine whether or not a control station is disconnected from a communication system, based on whether or not the terminal is a candidate terminal, and the priority, as in the second embodiment.
  • the substitute frame issuance portion 334 may execute a competition process based on the priority.
  • the frame transmission/reception portion 310 returns a result (success or failure) of issuance of a substitute frame via the operating mode management portion 320 to the substitute frame issuance portion 334 .
  • a result uccess or failure
  • the frame transmission/reception portion 310 returns the failure of issuance of a substitute frame to the substitute frame issuance portion 334 without transmitting a substitute frame.
  • the substitute frame issuance portion 334 stops issuance of a substitute frame. Thereby, a sequence for issuance of a substitute frame is ended.
  • the substitute frame issuance portion 334 continues to issue a substitute frame in accordance with transmission frame cycles for a predetermined time TIME_TENT or a predetermined number of times CNT_TENT.
  • the predetermined time TIME_TENT or a time period corresponding to the predetermined number of times CNT_TENT is a second time period.
  • an identifier for the terminal A which is a control station is described in the field 43 of a substitute frame thus issued.
  • An identifier for a terminal which issues the substitute frame is not described in the field 43 .
  • an identifier for a substitute frame is described in the frame header 40 of the substitute frame. Therefore, if the terminal A which was a control station is subsequently recovered, it can be recognized that a frame transmitted at control frame cycles is a substitute frame.
  • the substitute frame flag 52 describes whether or not the frame is a substitute frame. Therefore, a terminal which receives a substitute frame can recognize whether the frame is a substitute frame or a control frame, by referencing the substitute frame flag 52 .
  • the frame is a substitute frame, it may be defined that a terminal which receives a substitute frame does not request for a control station.
  • a terminal which issues a substitute frame periodically issues a frame which is the same as or equivalent to a control frame, and does not operate as a control station.
  • the terminal which issues a substitute frame does not execute band allocation or the like. Therefore, the terminal which issues a substitute frame cannot accept another terminal's request for allocation of a transmission resource. Therefore, the terminal which issues a substitute frame refuses all requests from the other terminals, and creates a refusal response frame indicating refusal of the request and returns the frame to the other terminal. Note that the terminal which issues a substitute frame may ignore all requests and may not return a response.
  • a function of the terminal which issues a substitute frame is executed in the controlled station mode portion 330 , and therefore, the terminal which issues a substitute frame cannot still be said to be a control station.
  • a control station is considered to have various functions, such as acceptance of a new terminal onto a network (authentication, attribution, security setting, etc.).
  • the terminal which issues a substitute frame issues a refusal response frame to all request frames directed to a control station.
  • the terminal which issues a substitute frame detects a frame transmitted from the terminal A which was a control station while being operating as a substitute control station, the terminal which issues a substitute frame determines that the terminal A is recovered as a control station and stops issuing a substitute frame.
  • FIG. 19 is a flowchart showing an operation of a terminal which is issuing a substitute frame periodically.
  • the operation of the terminal which is issuing a substitute frame periodically will be described with reference to FIG. 19 .
  • the substitute frame issuance portion 334 is issuing a substitute frame periodically.
  • the substitute frame issuance portion 334 determines whether or not a predetermined wait time for recovery of a control station (second time period) is elapsed (step S 601 ). Specifically, the substitute frame issuance portion 334 determines whether or not a timer which is set to be TIME_TENT is expired or a counter which is set to be CNT_TENT is expired. Note that the second time period may be longer or shorter than or the same as the first time period.
  • the substitute frame issuance portion 334 determines whether or not a frame is received (step S 604 ). When a frame is not received, the substitute frame issuance portion 334 returns to the operation of step S 601 . On the other hand, when a frame is received, the substitute frame issuance portion 334 goes to an operation of step S 605 .
  • step S 605 the substitute frame issuance portion 334 determines whether or not the received frame is a frame which is from a control station which has been determined to be disconnected.
  • the substitute frame issuance portion 334 transmits a refusal response frame in response to the received frame, or ignores or does not respond to the received frame (step S 608 ), and returns to the operation of step S 601 .
  • the substitute frame issuance portion 334 goes to an operation of step S 606 .
  • step S 606 the substitute frame issuance portion 334 stops issuing a substitute frame. This is because it is recognized that the control station is recovered in the communication system. Thereafter, the substitute frame issuance portion 334 requests the operating mode management portion 320 to operate in a controlled station mode (step S 607 ), and ends the process.
  • the substitute frame issuance portion 334 collects information required for the terminal 300 to operate as a control station (control required information) from another terminal (step S 602 ). Specifically, in step S 602 , when information stored in the control frame memory portion 332 is not sufficient for an operation as a control terminal, the substitute frame issuance portion 334 transmits a request for required information to another terminal, and collects information contained in a frame returned from the other terminal to obtain information required for an operation as a control station. Note that the substitute frame issuance portion 334 may transmit a reset signal to a network and collect a control request from another terminal to collect information required as a control station.
  • the substitute frame issuance portion 334 requests the operating mode management portion 320 to operate in the control station mode (step S 603 ), and ends the process.
  • a terminal which issues a substitute frame uses the field 43 of a control frame as an identifier for itself.
  • the terminal which issues a substitute frame uses the source address 51 of the frame header 40 in a control frame as an identifier for itself.
  • step S 602 may be executed either before or after the process of step S 603 .
  • the required information may be collected after issuance of a control frame. Therefore, when the information required as a control station cannot be sufficiently obtained from the control information stored in the control frame memory portion 332 , the terminal which issues a substitute frame transmits an inquiry to another terminal in the communication system while issuing a control frame, to collect the required information. Thereby, network quality is maintained.
  • the terminal which issues a substitute frame may transmits an inquiry to another terminal in the communication system using contents of a substitute frame to collect latest required information. Note that the terminal which issues a substitute frame may continue to refuse a control request until sufficient information is collected.
  • FIG. 20 is a flowchart showing an operation of a terminal which was a control station and is thereafter connected again to and recovered in a communication system.
  • the terminal which was a control station and is thereafter is connected again to and recovered in a communication system, will be described with reference to FIG. 20 .
  • the terminal which was a control station is represented by a terminal A.
  • the terminal A starts up in the controlled station mode (step S 701 ).
  • the terminal A receives a substitute (or control) frame (step S 702 ). Note that, in a situation that the second time period is elapsed and therefore a terminal which issues a substitute frame operates as a control station, the terminal A receives a control frame rather than a substitute frame.
  • the terminal A determines whether or not a terminal which performs scheduling of band allocation is set to be the terminal A in the received substitute (or control) frame (step S 703 ). Specifically, when the control frame has a formant of FIG. 16 , the terminal A references the field 43 of the substitute frame to determine whether or not a terminal which performs scheduling is the terminal A. Note that when the control frame has the formant of FIG. 17 , the terminal A references of the source address 51 of the frame header 40 to determine whether or not a terminal which performs scheduling is the terminal A.
  • step S 703 when a terminal which performs scheduling is assumed to be the terminal A, the terminal A operates in the control station mode since the frame received in step S 702 is a substitute frame (step S 705 ).
  • step S 703 when it is determined in step S 703 that the terminal which performs scheduling is not the terminal A, the terminal A operates in the controlled station mode since the frame received in step S 702 is a control frame which is issued by a new control station (step S 704 ).
  • the terminal A may transmit a particular frame for informing of recovery in the communication system, to a terminal which is operating in the substitute control station, rather than transmitting a control frame.
  • the terminal A When operating in the control station mode, the terminal A may issue a control frame by utilizing a band, such as a control frame slot allocated for a control frame or the like. Thereby, it is easier to determine that a terminal which is issuing a substitute frame receives a control frame from a control station in steps S 604 and S 605 .
  • a band such as a control frame slot allocated for a control frame or the like.
  • the terminal A When operating in the control station mode, the terminal A stores the received substitute frame into the control frame memory portion 332 . When operating in the control station mode, the terminal A may reconstruct a control frame using the substitute frame stored in the control frame memory portion 332 .
  • the substitute frame is constructed based on a control frame previously used, and therefore, may not store control information which is suitable for a latest situation.
  • the control information stored in the substitute frame is only a portion of information required for an operation as a control station. For example, usually, detailed information about requirement for a transmission resource for performing rescheduling of media access, and information about a terminal participating in a network (information about authentication, performance or the like) are not described in a control frame. Therefore, the terminal A collects information from other terminal(s) to obtain control information required as a control station.
  • a terminal which operates as a control station uses an empty transmission band to obtain required information from a terminal on the communication system.
  • an identifier for a terminal which manages band reservation information for achieve QoS must be described in a substitute frame which is a duplicate of a control frame. Therefore, a terminal which operates as a control station issues a confirmation frame for confirming band reservation information, to a terminal which has the identifier, thereby collecting information about band requirement.
  • a terminal which operates as a control station communicates a terminal which performs authentication management to obtain authentication information, thereby confirming a terminal which participates in the communication system.
  • the terminal which operates as a control station transmits an inquiry to a terminal in the communication system to collect required information.
  • the terminal which operates as a control station may refuse reception of a control request until all required information is obtained.
  • the terminal which issues a substitute frame when receiving a frame from an original control station during the second time period, the terminal which issues a substitute frame periodically stops issuance of a substitute frame and operates in the controlled station mode. Therefore, a media access control by the original control station can be recovered. As a result, an efficient media access control can be achieved.
  • the terminal which issues a substitute frame periodically transmits a refusal response frame or does not respond to a request from terminals other than an original control station during the second time period. Therefore, a state when the control station was disconnected is maintained until the control station is recovered. Therefore, when the control station is recovered, a post-recovery process can be smoothly performed.
  • a terminal which transmits a substitute frame subsequently operates as a control station, thereby eliminating a situation that a control station is absent.
  • a terminal which becomes a control station since an original control station is not recovered collects information to obtain information required as a control station if information required for a media access control is insufficient. Therefore, it is possible to avoid a situation that media access is inefficient for a long time in the communication system.
  • a control station may inform a candidate terminal of control required information or may inform each terminal of control required information by multi-broadcasting.
  • a controlled station causes the control frame memory portion 332 to store control required information.
  • the controlled station detects that the control station is disconnected from the communication system since the first time period is elapsed and determines that it will functions as a control station since the second time period is elapsed, the controlled station starts an operation shown in FIG. 21 . For example, after the determination of step S 601 in FIG. 19 is affirmative, the operation of FIG. 21 is started.
  • FIG. 21 is a flowchart showing an operation of a terminal after detecting that a control station is disconnected from the communication system and determining that the terminal will function as a control station.
  • the terminal determines whether or not the terminal has been informed of latest control required information (step S 801 ). For example, it is assumed that, when control required information includes an item which has not been updated, an identifier for the item which has not been updated is store in a control frame, which is in turn transmitted by a control station. In this case, the terminal determines whether or not there is an item which has not been updated, based on the recorded control information. When there is not an item which has not been updated, the terminal determines that the informing of latest control required information has been completed.
  • the terminal When the informing of latest control required information has been completed, the terminal creates a control frame based on the received control required information and starts operating as a control terminal (step S 802 ). On the other hand, when the informing of latest control required information has not been completed, the terminal starts an operation as a control station after collecting required information as in step S 602 of the third embodiment of FIG. 19 (step S 803 ). Note that, when the latest control required information has been partly received in step S 803 , the terminal may start an operation as a control station using the partly received control required information.
  • LSI integrated circuit
  • the functional blocks may be mounted on one chip, or a part or the whole of the functional blocks may be mounted on one chip.
  • LSI may be called IC, system LSI, super LSI or ultra LSI, depending on the packaging density.
  • the integrated circuit is not limited to LSI.
  • the integrated circuit may be achieved by a dedicated circuit or a general-purpose processor.
  • an FPGA Field Programmable Gate Array
  • the functional blocks may be packaged using such a technology. A biotechnology may be applicable.
  • FIG. 22 is a diagram showing a whole structure of a system in which a terminal of the present invention is applied to high-speed power line communication.
  • the terminal of the present invention provides an interface between a multimedia apparatus (e.g., a digital television (DTV), a personal computer (PC), a DVD recorder, etc.) and a power line.
  • a multimedia apparatus e.g., a digital television (DTV), a personal computer (PC), a DVD recorder, etc.
  • An interface between the multimedia apparatus and the terminal of the present invention may be an IEEE1394 interface, a USB interface, an Ethernet(R) interface or the like.
  • a communication network system which transmits digital data, such as multimedia data or the like, via a power line with high speed, is constructed.
  • a power line which is already provided in home, offices and the like can be used as a network line without newly introducing a network cable, such as a conventional wired LAN. Therefore, the present invention is considerably useful in terms of cost and simplicity of installation.
  • the terminal of the present invention serves as an adaptor which converts a signal interface of an existing multimedia apparatus to an interface of power line communication.
  • the terminal of the present invention may be incorporated into a multimedia apparatus, such as a personal computer, a DVD recorder, a digital television, a home server system or the like.
  • a multimedia apparatus such as a personal computer, a DVD recorder, a digital television, a home server system or the like.
  • data transfer between apparatuses can be achieved via a power source cable of the multimedia apparatus.
  • a line for connecting the adaptor and the power line, an IEEE1394 cable, a USB cable, and an Ethernet (R) cable are not required, thereby simplifying wiring.
  • a communication network system which uses a power line can be connected via a router and/or a hub to the Internet, a wireless LAN, and a conventional wired cable LAN, thereby extending a LAN system in which the communication network system of the present invention is used without any problem.
  • Communication data transferred via a power line may be intercepted by an apparatus directly connected to the power line, but is free from an eaves drop problem with wireless LAN. Therefore, the power line transmission scheme is effective in terms of security. Further, data transferred on a power line may be protected by IPSec of an IP protocol, encryption of the contents themselves, other DRM schemes, or the like.
  • a control station is provided as a particular terminal distinguished from a semi-fixed terminal having a general function, in the high-speed power line communication, if taking into consideration coexistence of adjacent access systems, provision of a gateway/router function, positional characteristics of a power line, expected characteristics of a vender, and the like. Therefore, when a semi-fixed control station is used, indiscriminately changing of control stations would lead to a situation that communication quality is not guaranteed. Therefore, a system of the present invention is practically very useful, in which, when a control station is disconnected from a communication system, another terminal issues a substitute frame, and thereafter, if a control station is recovered, issuance of a control frame is inherited to the recovered control station.
  • the terminal of the present invention may be used as a home electrical product which is a communication module having a communication function.
  • a home network communication system situations, such as the power source of a control station which have an important influence on a whole communication system is abruptly shut down, a connecting point of a control station and a communication medium is removed, and the like, are readily expected.
  • the present invention provides a substitute control station which issues a substitute frame to keep a communication process effective. Therefore, there is a possibility that the present invention provides a means for optimizing communication quality of a communication system, and further, solving an adjacent network interference problem and an adjacent channel interference problem.
  • the terminal of the present invention can avoid a situation that a communication system falls into an inefficient state for a long time, and is useful in communication fields, such as wireless communication, power line communication and the like.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Small-Scale Networks (AREA)
US10/589,240 2004-03-01 2005-02-28 Terminal capable of substituting for control station Abandoned US20070160074A1 (en)

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EP (1) EP1721426B1 (fr)
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US20110176469A1 (en) * 2010-01-21 2011-07-21 Ki Hyung Kim LoWMob and DLoWMob SYSTEM
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CN1926825A (zh) 2007-03-07
JP2007525874A (ja) 2007-09-06
EP1721426B1 (fr) 2013-01-02
JP5438810B2 (ja) 2014-03-12
JP5143097B2 (ja) 2013-02-13
KR101072072B1 (ko) 2011-10-10
JP2013009429A (ja) 2013-01-10
KR20060127169A (ko) 2006-12-11
WO2005083952A1 (fr) 2005-09-09
JP4393517B2 (ja) 2010-01-06
US20110161490A1 (en) 2011-06-30
CN1926825B (zh) 2011-01-19
JP2009296636A (ja) 2009-12-17
US8565258B2 (en) 2013-10-22
EP1721426A1 (fr) 2006-11-15

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