JP5950201B2 - Communications system - Google Patents

Description

  The present invention relates to a communication system in which a plurality of communication terminals transmit and receive transmission signals.

  In a local area network (LAN), an access control method called carrier sense multiple access (CSMA) is adopted so that a plurality of communication terminals share a transmission medium. In addition, when some communication terminals do not share the transmission medium, for example, when a plurality of communication terminals communicate via a repeater, it is not possible to detect the carrier of the transmission signal transmitted by the other communication terminal, Transmission signals collide with high probability in the repeater.

  Also, in wireless LAN using radio waves as a transmission medium, access control called RTS / CTS method is used to prevent the occurrence of “hidden terminal problem” in which packets are collided when communication terminals that do not reach radio waves simultaneously transmit data. A method may be adopted. For example, it is assumed that there is a communication terminal C in which the communication terminal A wants to transmit data to the communication terminal B, but there are obstacles and the radio wave of the communication terminal A does not reach. Before transmitting data, the communication terminal A transmits an RTS (request to send) packet to the communication terminal B which is a transmission partner. The communication terminal B that has received the RTS packet returns a CTS (clear to send) packet to the communication terminal A. Since the communication terminal C receives the radio wave from the communication terminal B, the communication terminal C postpones the transmission of data when the CTS packet is intercepted. Thereby, collision of packets transmitted from the communication terminals A and C that are hidden terminals can be avoided.

  However, if the communication terminal C transmits an RTS packet between the time when the communication terminal A starts transmitting the RTS packet and the time when the communication terminal B starts returning the CTS packet, the communication terminal A transmits it. There is a possibility that the RTS packet being transmitted and the RTS packet transmitted by the communication terminal C collide.

  On the other hand, in the conventional example described in Patent Document 1, the difference between the packet interval of the communication station with the higher priority and the packet interval of the lower communication station is determined, and the reception of the CTS packet is completed after the RTS packet transmission is started. It is set to be longer than required time. Even if the RTS packet is transmitted first from the communication station that is the hidden terminal for itself, the local station with the lower priority order can receive the CTS packet in response to this, so the collision is correctly performed. It can be avoided.

JP 2006-41627 A

  However, in the conventional example described in Patent Document 1, since the priority is set only for the communication station (communication terminal), when it is desired to prioritize the type of data included in the transmission signal, There is a problem in that transmission of a communication station with a higher priority is given priority, and a delay (data transmission delay) of a communication station with a lower priority is increased. In addition, as a case where priority is given to the type of data, for example, there is a case where it is desired to increase the priority of video or audio data in order to suppress the delay time compared to the control command.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce transmission packet loss due to collision while suppressing delay of data set with high priority in communication between hidden terminals.

In the communication system of the present invention, a plurality of communication terminals transmit and receive a transmission packet via a transmission medium by a carrier detection multiple access control method, and the communication terminal of the transmission source When the transmission request packet is transmitted to the communication terminal, and the communication terminal of the transmission destination receives the transmission request packet, it returns a reception preparation completion packet to the communication terminal of the transmission source, and the communication terminal of the transmission source A communication system that transmits a data packet including the data to the destination communication terminal when receiving a reception preparation completion packet, wherein each communication terminal has a terminal priority set in the communication terminal, and Data priority set for each data type, packet transmission interval and maximum back-off time set according to packet transmission priority Storing, counting the packet transmission interval from the time when transmission of the data packet is completed, counting a backoff time randomly generated within the maximum backoff time following the packet transmission interval, and the backoff time The packet transmission priority is set higher as the data priority is higher, and when the data priority is equal, the packet transmission priority is set higher as the terminal priority is higher. The packet transmission interval is set to a minimum value when the packet transmission priority is the highest, and when the packet transmission priority is the second highest, the minimum value, the maximum backoff time, and the transmission request packet are set. The packet length and the short packet interval are set to be equal to or longer than the total time.

  In this communication system, comprising a repeater for relaying the data packet transmitted from the communication terminal of the transmission source to the communication terminal of the transmission destination, the repeater, the terminal priority including its own priority, Preferably, the data priority, the packet transmission interval, and the maximum backoff time are stored, and the priority of the repeater is set to the highest priority among the terminal priorities.

  In this communication system, it is preferable that the terminal priority is set higher as the number of transmissions of the data packet per unit time increases.

  In this communication system, it is preferable that the terminal priority is set higher as the number of transmissions per unit time of the data packet including data having the higher data priority increases.

  In this communication system, the packet transmission interval and the maximum back-off time stored in each communication terminal are determined by a relay that relays the data packet transmitted from the communication terminal as a transmission source to the communication terminal as a transmission destination. It is preferable to set the value according to the presence or absence.

  In this communication system, each of the communication terminals includes a determination unit that determines whether or not the repeater is present, and the packet transmission interval and the maximum back-off time may be changed based on a determination result of the determination unit. preferable.

  In this communication system, it is preferable that the determination unit determines that the repeater is present when the repeater receives a packet periodically broadcast.

  In this communication system, the specific communication terminal of the plurality of communication terminals has a determination unit that determines whether or not the repeater exists, and based on a determination result of the determination unit, the packet transmission interval and the A packet for changing the maximum back-off time and notifying the determination result is transmitted to each communication terminal except the specific communication terminal, and each communication terminal excluding the specific communication terminal transmits the packet. It is preferable to change the packet transmission interval and the maximum back-off time based on the determination result received and acquired.

  In this communication system, when there are a plurality of repeaters, each communication terminal is configured to transmit the packet transmission interval according to which segment of the plurality of segments delimited by the plurality of repeaters. Preferably, the maximum backoff time is changed.

  In the communication system of the present invention, the frame transmission interval and the back-off time are set according to both the terminal priority and the data priority. Therefore, in the communication between hidden terminals, the delay of data having a high data priority is suppressed. However, there is an effect that transmission packet loss due to collision can be reduced.

1 is a system configuration diagram showing an embodiment (intercom system for collective housing) of a communication system according to the present invention. (a), (b) is a time chart for operation description same as the above.

  Hereinafter, an embodiment in which the technical idea of the present invention is applied to an intercom system for a housing complex will be described in detail. However, the communication system to which the technical idea of the present invention can be applied is not limited to the apartment house intercom system, but can be applied to a communication system other than the apartment house intercom system. The transmission medium is not limited to a communication line made of a metal conductor, and may be a wireless medium such as a radio wave.

  As shown in FIG. 1, the intercom system for an apartment building of this embodiment includes a common terminal (lobby interphone) C installed at the common entrance (lobby) of the apartment house, and a dwelling unit installed in each unit of the apartment house. A terminal A, a trunk line control terminal B, and a repeater E are included. Note that both the dwelling unit terminal A and the main line control terminal B correspond to communication terminals in the present invention.

  The plurality of dwelling unit terminals A and the lobby intercom C are connected via a trunk line control terminal B through a communication path. The communication path includes a shared trunk LC connecting the lobby intercom C and the trunk control terminal B, a main trunk LA having one end connected to the trunk control terminal B and the other end terminated with a terminator (not shown), A plurality of secondary trunk lines LB1, LB2,..., LBn added to the main trunk line LA, and a plurality of dwelling unit lines LD branched from the secondary trunk line LBi (i = 1, 2,..., N) by the branching device D. It consists of. The communication path is composed of a balanced two-wire communication cable.

  The lobby intercom C is an imaging device that captures an image of a visitor, a microphone and a speaker, a numeric keypad or touch panel for the visitor to input the dwelling unit number of the visited residence, a transmission unit that transmits voice and video through a communication path, and the like It has. In the lobby intercom C, when the ten key switch or the touch panel is operated and the operation input of the dwelling unit number of any dwelling unit is received, the packet storing the dwelling unit number in the data field and the visitor image (video) captured by the imaging device. A packet storing information) in the data field is transmitted (packet transmission) from the transmission section to the address of the trunk control terminal B via the shared trunk line LC.

  The main line control terminal B stores the correspondence between the address assigned to the dwelling unit terminal A of each dwelling unit and the dwelling unit number of the dwelling unit. The trunk line control terminal B compares the dwelling unit number stored in the data field of the packet received from the lobby interphone C with the corresponding relationship, converts it into an address, stores the address in the destination address field, and stores the address in the lobby intercom A packet storing a call command for notifying a call from C in the data field and a packet storing the video information in the data field are sent to the main line LA.

  The dwelling unit A includes a control unit 1, a transmission processing unit 2, a call processing unit 3, a microphone 4, a speaker 5, an A / D converter 6, a D / A converter 7, a video processing unit 8, a display unit 9, and an operation input. The reception unit 10 is provided. The sound collected by the microphone 4 is converted into an electrical signal (voice signal), and the analog voice signal (speech voice signal) output from the microphone 4 is converted into a digital voice signal (speech) by the A / D converter 6. Voice data) and input to the call processing unit 3. Further, a digital voice signal (received voice data) output from the call processing unit 3 is converted into an analog voice signal (received voice signal) by the D / A converter 7. An analog received voice signal output from the D / A converter 7 is input to the speaker 5, and a voice (received voice) is generated from the speaker 5.

  The call processing unit 3 includes a voice switch, an echo canceller, and the like, and performs signal processing on the received voice signal input from the transmission processing unit 2 and the transmission voice signal input from the A / D converter 6 to perform howling and The echo is suppressed to realize a good hands-free call. The transmitted voice signal processed by the call processing unit 3 is output to the transmission processing unit 2.

  The display unit 9 includes a display device such as a liquid crystal display or an organic EL display, and a drive circuit that drives the display device to display an image (none is shown). The video processing unit 8 reconstructs the original video from the video signal (video data) output from the transmission processing unit 2 and causes the display unit 9 to display the reconstructed video.

  The control unit 1 includes hardware such as a CPU and a memory, and various programs (software) executed by the CPU. The operation input accepting unit 10 has an input device such as a touch panel or a push button switch, accepts various operation inputs by operating the input device, and outputs an operation signal corresponding to each operation input to the control unit 1. To do. For example, a response button (not shown) is provided on the front of the housing of the dwelling unit terminal A. When this response button is pressed, an operation input is received by the operation input receiving unit 10 and a response operation signal is output. Is done. When an operation signal is input from the operation input receiving unit 10, the control unit 1 executes processing (described later) according to each operation signal.

  The transmission processing unit 2 performs packet transmission with the trunk line control terminal B and other dwelling unit terminals A via a communication path. The transmission processing unit 2 divides the control signal (control data) created by the control unit 1 to create a packet (control packet), and the transmission voice signal (transmission voice data) also created by the call processing unit 3. ) To create a packet (voice packet). However, the control packet and the voice packet mean a packet (data packet) in which the divided control data and voice data are stored in the data field.

  Further, the transmission processing unit 2 encodes the control packet and the voice packet, converts (modulates) the encoded bit string into an electric signal, and sends the electric signal to the dwelling unit LD. The transmission processing unit 2 converts (demodulates) an electric signal flowing through the dwelling unit line LD into a bit string and decodes a packet (voice packet, control packet, video packet) from the demodulated bit string. The transmission processing unit 2 discards the packet if the address of the decrypted packet does not match its own address (address of the dwelling unit A), and if the address matches, it is included in the data field of the packet. Decrypt the data. If the decoded data is video data (video signal), it is output to the video processing unit 8, if it is control data (control signal), it is output to the control unit 1, and if it is audio data (audio signal), a call is made. It is output to the processing unit 3.

  The repeater E includes a pair of connection terminals 30 and 31, a modem unit 32, a relay processing unit 33, receiving units 34 and 35, transmitting units 36 and 37, and the like. One connection terminal 30 is connected to the main trunk line LA on the trunk control terminal B side (hereinafter referred to as the upstream side), and the other connection terminal 31 is connected to the main terminal on the terminator side (hereinafter referred to as the downstream side). Main line LA is connected. The relay processing unit 33 rewrites the transmission source address of the communication signal received from the upstream main line LA with its own address, sends (relays) it to the downstream main line LA, and receives from the downstream main line LA. The transmission source address of the communication signal is rewritten from its own address to the address of the trunk line control terminal B or the upstream dwelling unit terminal A, and transmitted (relayed) to the upstream trunk line LA. The modem 32 digitally demodulates the communication signal received at the receiving end Rx and outputs the demodulated signal to the relay processing unit 33, and transmits the communication signal obtained by digitally modulating the packet output from the relay processing unit 33 from the transmitting end Tx. The receiving units 34 and 37 are each composed of an amplifier inserted between the connection terminals 30 and 31 and the receiving end Rx of the modulation / demodulation unit 32. The transmission units 35 and 36 are respectively connected to the connection terminals 30 and 31 and the modulation / demodulation unit 32. It consists of an amplifier inserted between the transmitting end Tx. That is, the communication signal flowing in from the upstream connection terminal 30 is received (amplified) by the receiving unit 34, relayed by the modem unit 32 and the relay processing unit 33, and then transmitted (amplified) by the transmitting unit 36 and then downstream Is sent from the connection terminal 31 on the side. Similarly, a communication signal flowing in from the downstream connection terminal 31 is received (amplified) by the receiving unit 37, relayed by the modem unit 32 and the relay processing unit 33, and then transmitted (amplified) by the transmitting unit 35. It is sent from the connection terminal 30 on the upstream side.

  Thus, since the communication signal flowing in the main line LA is relayed by the repeater E, transmission loss and the like are improved. Therefore, the length of the main line LA is increased as compared with the case where the repeater E is not used. Or the number of system expansion devices F that can be connected to the main line LA can be increased. Further, the repeater E in the present embodiment is miniaturized by sharing the modem unit 32 on the upstream side and the downstream side, and can be easily installed in a narrow place.

  Next, an intercom call performed between the dwelling unit terminal A and the lobby intercom C will be described. In the lobby intercom C, when a visitor receives an operation input of a dwelling unit number of any dwelling unit by operating a numeric keypad or a touch panel, the packet storing the dwelling unit number in the data field and the visitor imaged by the imaging device A packet storing video (video data) in the data field is transmitted (packet transmission) from the transmission unit to the address of the trunk control terminal B via the shared trunk line LC. The main line control terminal B sends a control packet storing a call command for notifying the call from the lobby intercom C in the data field and a video packet storing the video data in the data field to the main line LA.

  In the dwelling unit terminal A installed in the dwelling unit with the dwelling unit number, when the transmission processing unit 2 receives the control packet and the video packet through the main trunk line LA, the sub trunk line LBi, and the dwelling unit line LD, it is stored in the data field of the control packet. The paging command (control signal) being output is output to the control unit 1, and the video data stored in the data field of the video packet is output to the video processing unit 8. When receiving the call command, the control unit 1 causes the speaker 5 to ring. The video processing unit 8 processes the video signal received from the transmission processing unit 2 and causes the display unit 9 to display the video of the visitor. Then, when the resident who has heard the ringing tone confirms the video of the visitor displayed on the display unit 9 of the dwelling unit A and operates the response button, the operation input accepting unit 10 responds to the operation input of the response button. An operation signal is output. The control unit 1 that has received the operation signal activates the call processing unit 3, and the audio signal (speech audio signal) output from the microphone 4 is packet-transmitted from the transmission processing unit 2. As a result, a resident of the dwelling unit and a visitor can make an interphone call using the dwelling unit terminal A and the lobby intercom C.

  Then, when the response button of the dwelling unit terminal A is pressed during the interphone call and an operation signal is output from the operation input receiving unit 10 to the control unit 1, the control unit 1 transmits the call processing unit 3, the video processing unit 8, and the transmission. The processing unit 2 is stopped and the intercom call ends. However, even when the response button is not pressed, the control unit 1 switches the call processing unit 3, the video processing unit 8 and the transmission processing unit 2 when a predetermined time (for example, several minutes) has elapsed since the start of the call. Stop and end the intercom call. When the called dwelling unit A exists on the downstream side of the repeater E, the repeater E relays packet transmission between the lobby intercom C and the dwelling unit A. Further, in this embodiment, intercom calls can be performed between the dwelling unit terminals A of different dwelling units via the main line control terminal B, but basically, the same procedure as that for the intercom call with the lobby intercom C is performed. Therefore, the description is omitted.

  By the way, in this embodiment, a plurality of communication terminals (dwelling unit terminal A, trunk line control terminal B, repeater E) share a communication path (main trunk line LA and secondary trunk line LBi). Therefore, in order to avoid collision of transmission signals (packets), each communication terminal performs packet transmission by the carrier detection multiple access control method. From the viewpoint of the main line control terminal B, the repeater E corresponds to the same communication terminal as the dwelling unit terminal A, and the dwelling unit A connected to the downstream side of the repeater E and the communication path are connected to the main line without going through the repeater E. It is regarded as a segment different from the segment (network) of the dwelling unit terminal A group connected to the control terminal B. Therefore, the communication terminals (dwelling unit terminal A and main line control terminal B) belonging to the upstream segment (referred to as the first segment) of the repeater E and the downstream segment (referred to as the second segment) of the repeater E. Are likely to become “hidden terminals” (however, the repeater E belongs to both segments). Therefore, in order to deal with the “hidden terminal problem” described in the prior art, each communication terminal adopts the RTS / CTS method as an access control method.

  Next, consider a case where an intercom call is performed between the dwelling unit terminal A belonging to the second segment and the lobby intercom C. When audio data and video data are transmitted from the lobby intercom C to the dwelling unit terminal A, the main line control terminal B transmits the RTS packet to the repeater E, and receives the CTS packet returned from the repeater E. A data packet including data is transmitted to the relay E. Then, the repeater E transmits (relays) the data packet received from the main line control terminal B to the dwelling unit terminal A. On the other hand, when audio data is transmitted from the dwelling unit A to the lobby intercom C, the RTS packet is transmitted from the dwelling unit A to the repeater E, and the data including the audio data is received after receiving the CTS packet transmitted from the repeater E. The packet is transmitted to the relay E. Then, the repeater E transmits (relays) the data packet received from the dwelling unit terminal A to the main line control terminal B.

  In this case, the other dwelling unit terminal A and the main line control terminal B belonging to the first segment can receive the CTS packet transmitted from the repeater E, stop the transmission, and wait for the second segment communication. The RTS packet transmitted on the path cannot be received. For this reason, the dwelling unit terminal A and the trunk line control terminal B belonging to the first segment are in the time from when the dwelling unit A belonging to the second segment starts transmitting the RTS packet until the repeater E starts returning the CTS packet. There is a possibility of starting to transmit data packets. In particular, in a situation where the communication frequency is high, there is a possibility that RTS packets of the first segment and the second segment collide with each other in the repeater E and cause a communication error.

  Thus, as in the conventional example described in Patent Document 1, a case is considered in which priority is set for a communication terminal. For example, when the priority order of the main line control terminal B is higher than the priority order of the dwelling terminal A, the frame transmission interval (AIFS: Arbitration Inter Frame Spase) and the backoff time Tbo are both higher in the main control terminal B. It is set shorter than the terminal A. The frame transmission interval is synonymous with the packet transmission interval in the present invention.

  As shown in FIG. 2 (a), it is assumed that the trunk line control terminal B and the dwelling unit terminal A are in a transmission waiting state, and simultaneously start counting frame transmission intervals from time t0 when packet transmission of other communication terminals is completed. . In this case, the main line control terminal B completes the frame transmission interval and the back-off time Tbo counting before the dwelling terminal A, so that the RTS packet is transmitted from the main line control terminal B to the destination communication terminal (relay E). Then, the CTS packet is returned from the repeater E to the main line control terminal B. Then, the data packet is transmitted from the trunk control terminal B that has received the CTS packet to the repeater E. At this time, if the timing at which the dwelling terminal A completes the counting of the frame transmission interval AIFS and the backoff time Tbo and the transmission period of the data packet from the trunk control terminal B to the repeater E overlap, the dwelling terminal A will The packet cannot be sent. If the main line control terminal B continues to transmit the data packet, the dwelling unit terminal A cannot transmit data during that time regardless of the type of data packet.

  Therefore, in this embodiment, not only the priority (terminal priority) is set for the communication terminal, but also the priority (data priority) is set for the data to be transmitted, and the data priority is set higher than the terminal priority. Has priority. That is, when the main line control terminal B having a relatively high terminal priority and the dwelling terminal A having a relatively low terminal priority are in a transmission waiting state, the data priority of the dwelling terminal A is the main line control terminal. If it is higher than the data priority of B, the dwelling unit terminal A can be transmitted first.

  For example, in the present embodiment, the first terminal priority is set for the repeater E, the second terminal priority is set for the trunk control terminal B, and the third terminal priority is set for each dwelling terminal A. The Also, the first data priority is set for the audio packet, and the second data priority is set for the video packet. Further, a session initiation protocol (SIP) command used when starting a session of an intercom call (a call between the lobby intercom C and the dwelling unit terminal A or a call between the two dwelling unit terminals A) The 3rd data priority is set in (Request and Response). It should be noted that the fourth data priority is set for data (best effort data) such as control commands other than these. However, the data priority is also called an access category (AC), and each communication terminal classifies packets from the upper layer into the above four types of access categories AC1, AC2, AC3, and AC4, and a transmission queue for each access category. To store.

  A frame transmission interval AIFS, a minimum contention window value CWmin, and a maximum contention window value CWmax are set for each of the four classified access categories ACi (i = 1, 2, 3, 4). The back-off time Tbo is determined by multiplying a unit time Ts called a slot time by a random number consisting of an integer, as shown in Equation 1 below. However, the random number starts from the minimum contention window value CWmin, and increases in a stepwise manner with the maximum contention window value CWmax as the upper limit when retransmission due to packet loss occurs.

Tbo = Ts × Rand (1, N) ... (1)
Here, N represents an integer from CWmin to CWmax, and Ran (1, N) represents a random number (integer) generated between 1 and N.

  For example, in the communication terminal (main line control terminal B) having the highest terminal priority, the frame transmission interval AIFS of the voice packet having the first access category (AC1) is the minimum value, for example, 1 slot (1 times the slot time). Set to Further, the backoff time Tbo of the voice packet of the trunk line control terminal B is set to 1 slot (the minimum contention window value CWmin is 1) (see FIG. 2B).

  On the other hand, in the communication terminal (unit D) having the second highest terminal priority, the frame transmission interval AIFS of the voice packet with the first access category is the frame transmission interval of the voice packet of the trunk control terminal B and the backoff time Tbo. It is set to a time equal to or longer than the sum of the total and the sum of the RTS packet and the minimum waiting time interval (SIFS: Short Inter Frame Space) (see FIG. 2B).

  Further, in the trunk line control terminal B, the frame transmission interval AIFS of the video packet having the second access category (AC2) is the sum of the frame transmission interval and the back-off time Tbo of the voice packet of the dwelling unit A and the packet length of the RTS packet. The minimum waiting time interval (short packet interval) is set to a time equal to or longer than the sum of SIFS (see FIG. 2B).

  Here, as shown in FIG. 2B, it is assumed that the voice packet and the video packet are stored in the transmission queue of the trunk line control terminal B, and the voice packet is stored in the transmission queue of the dwelling unit terminal A. The trunk line control terminal B and the dwelling unit terminal A simultaneously start counting the frame transmission interval from the time t0 when the packet transmission of the other communication terminals is completed. Then, since the frame transmission interval and the backoff time Tbo corresponding to the voice packet of the trunk line control terminal B are counted up first, the trunk line control terminal B transmits the RTS packet to the communication terminal of the voice packet transmission destination. Next, since the frame transmission interval and the back-off time Tbo corresponding to the voice packet of the dwelling unit terminal A, not the video packet of the main line control terminal B, are counted up second, the dwelling unit terminal A communicates the transmission destination of the voice packet. Send an RTS packet to the terminal. Subsequently, since the frame transmission interval and backoff time Tbo corresponding to the video packet of the main line control terminal B are counted up third, the main line control terminal B transmits the RTS packet to the communication terminal of the video packet transmission destination.

  As described above, when the frame transmission interval and maximum backoff time are determined only by the terminal priority, when priority is given to each access category, transmission of communication terminals with higher terminal priority is given priority, and terminal priority is given. There is a problem that a delay of a communication terminal having a lower rank is increased. On the other hand, in this embodiment, the higher the data priority, and the higher the data priority, and the higher the terminal priority, the higher the terminal priority, the higher the frame transmission interval and the maximum backoff time depending on the packet transmission priority set. Is set. Therefore, in communication between hidden terminals, it is possible to reduce packet loss due to collision while suppressing delay of data (voice or video) having a high access category. The frame transmission interval and the maximum backoff time may be set for each segment divided by the relay E.

  In this embodiment, the frame transmission interval and the maximum back-off time of the repeater E are set to be the same as those of the trunk line control terminal B having the highest terminal priority. Therefore, when the repeater E loops and forwards a packet transmitted from another communication terminal, collision with a subsequent packet transmitted from the other communication terminal can be reduced. As a result, it is possible to avoid an increase in the transmission delay of the entire system due to an increase in the packet transfer waiting time of the relay E.

  By the way, the higher the number of data packets transmitted per unit time, the higher the terminal priority may be set for the communication terminal. That is, by setting the frame transmission interval and backoff time of the communication terminal that frequently transmits data packets to be short, it is possible to suppress a decrease in the throughput of the entire system.

  Alternatively, the higher the number of transmissions per unit time of data packets including data with higher data priority (access category), the higher the terminal priority may be set for the communication terminal. That is, by setting the frame transmission interval and the back-off time of the communication terminal that frequently transmits audio packets and video packets to be short, it is possible to suppress the delay of audio and video and improve the communication quality.

  By the way, although this embodiment presupposes the presence of the repeater E, a system configuration without the repeater E may be used. When the repeater E does not exist, for example, the terminal priority of the trunk line control terminal B is set to the first rank, and the terminal priority of the dwelling terminal A is set to the second rank. Therefore, when the repeater E is not present, the transmission waiting time (frame transmission interval and backoff time) of the dwelling unit terminal A and the trunk line control terminal B is shortened compared with the case where the repeater E is present. When the device E is not present, unnecessary reduction in throughput can be prevented. Alternatively, it is preferable to adjust the frame transmission interval and back-off time of each communication terminal according to the communication status, for example, the presence or absence of a hidden terminal.

  Here, the presence / absence of the repeater E may be set by, for example, a dip switch provided in the dwelling unit terminal A and the main line control terminal B. That is, if the dwell unit A and the main line control terminal B determine that the relay E exists from the setting of the dip switch, the frame transmission interval and the back-off time are set according to the terminal priority including the relay E and the data priority. Set. On the other hand, if the dwell unit A and the main line control terminal B determine that the repeater E does not exist from the setting of the dip switch, the frame transmission interval and the backoff are determined according to the terminal priority and the data priority not including the repeater E. Set the time.

  However, since setting by the dip switch requires setting work by a person (contractor), it is preferable that each communication terminal automatically determines whether or not the repeater E is present. For example, the repeater E periodically broadcasts (multicasts) presence notification packets. Then, the dwelling unit terminal A and the trunk line control terminal B determine that the repeater E exists if the presence notification packet is periodically received, and the repeater E does not exist unless the presence notification packet is periodically received. Judge that. Thus, if each communication terminal automatically and periodically determines the presence or absence of the repeater E, the setting work by the contractor becomes unnecessary, and the construction work can be simplified. Even if the repeater E is added or deleted after the operation starts, it can be automatically handled.

  A specific communication terminal (for example, main line control terminal B) determines the presence / absence of repeater E by receiving presence notification packets periodically transmitted (unicast) from repeater E. You may make it notify a result to another communication terminal (for example, dwelling unit terminal A). By centrally managing the presence / absence of the repeater E at the main line control terminal B in this way, the determination status of the presence / absence of the repeater E can be easily confirmed during system maintenance.

A dwelling unit terminal (communication terminal)
B Trunk line control terminal (communication terminal)
E Repeater (communication terminal)
LA trunk line (transmission medium)
LBi secondary trunk (transmission medium)
LD Sumitomo Line (transmission medium)

Claims (9)

A plurality of communication terminals transmit and receive transmission packets via a transmission medium by a carrier detection multiple access control method,
The transmission source communication terminal transmits a transmission request packet to the transmission destination communication terminal before transmitting data, and the transmission destination communication terminal transmits a reception preparation completion packet when receiving the transmission request packet. Replying to the original communication terminal, the communication terminal of the transmission source is a communication system that transmits a data packet including the data to the communication terminal of the transmission destination when the reception preparation completion packet is received,
Each of the communication terminals includes a terminal priority set for each communication terminal, a data priority set for each type of data, a packet transmission interval and a maximum set according to the packet transmission priority. The packet transmission interval is counted from the time when transmission of the data packet is completed, and the backoff time that occurs randomly within the maximum backoff time is counted following the packet transmission interval. Sending the data packet after the back-off time has been counted,
The packet transmission priority is set higher as the data priority is higher, and higher when the terminal priority is higher when the data priority is equal,
The packet transmission interval is set to a minimum value when the packet transmission priority is the highest, and when the packet transmission priority is the second highest, the minimum value and the maximum backoff time and the transmission request packet A communication system, characterized in that it is set to be equal to or longer than a total time of a packet length and a short packet interval.   A relay that relays the data packet transmitted from the communication terminal as a transmission source to the communication terminal as a transmission destination, the relay including the terminal priority including its own priority, the data priority, 2. The communication system according to claim 1, wherein the packet transmission interval and the maximum back-off time are stored, and the priority of the repeater is set to the highest priority among the terminal priorities. .   The communication system according to claim 1 or 2, wherein the terminal priority is set higher as the number of transmissions of the data packet per unit time is larger.   The said terminal priority is set to a high priority, so that there are many transmissions per unit time of the said data packet containing the data with the said high data priority. The communication system described.   The packet transmission interval and the maximum back-off time stored in each communication terminal are values according to the presence or absence of a relay that relays the data packet transmitted from the communication terminal as a transmission source to the communication terminal as a transmission destination. The communication system according to any one of claims 1 to 4, wherein the communication system is set to one of the following.   The communication terminal includes a determination unit that determines whether or not the repeater is present, and changes the packet transmission interval and the maximum back-off time based on a determination result of the determination unit. 5. The communication system according to 5.   The communication system according to claim 6, wherein the determination unit determines that the repeater is present when the repeater receives a packet periodically broadcast. The specific communication terminal of the plurality of communication terminals includes a determination unit that determines whether or not the repeater is present, and determines the packet transmission interval and the maximum back-off time based on the determination result of the determination unit. Change and send a packet for notifying the determination result to each communication terminal except the specific communication terminal,
7. The communication terminals other than the specific communication terminal change the packet transmission interval and the maximum back-off time based on the determination result obtained by receiving and acquiring the packet. Communication system.   When there are a plurality of the repeaters, each communication terminal is configured to transmit the packet transmission interval and the maximum back-off according to which segment of the plurality of segments delimited by the plurality of repeaters. The communication system according to any one of claims 5 to 8, wherein the time is changed.

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