JPH10173663A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the transmission efficiency of a transmission path to be high, regardless of the change of the number of nodes by setting a back-off time being a time to be spent on waiting prior to re-transmission, based on a contention system to a time proportional to a specific random number. SOLUTION: A capturing means 15 captures the number of transmission nodes in a state capable of transmission in a single node 13, and transmits either the number or information indicating the capability of the generation of collision on a first communication path 11, when the number of nodes capable of transmission is equal to the number to a second communication path 14. Moreover, in the transmission node, a varying means 17 receives the information, generates a random number to be uniformly distributed to a wide value are according as the number or capability indicated by the information is larger, and sets a back-off time in proportion to the random number. Thus, a timing for operating the re-transmission of transmission information by the plural transmission nodes can be distributed widely along a time base, and capability that collision is generated again can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system for transmitting and receiving transmission information via a common communication path to which a contention system is applied.

[0002]

2. Description of the Related Art In recent years, LANs have become widespread in many business entities for the purpose of exchanging information without a public network and further promoting OA. Inexpensive and miniaturized notebook personal computers are connected to this LAN, and since this notebook personal computer is portable, the number of personal computers connected to the LAN has changed over a wide range.

[0003] In particular, wireless LANs are highly useful because there is no need to lay transmission lines, and this increases the degree of freedom in changing the number of wireless LANs. FIG. 7 is a diagram showing a configuration of a conventional wireless LAN. In FIG. 7, a plurality of nodes 81-1 to
81-n and the single main node 82 are arranged via a common wireless transmission path to which the full-duplex system is applied.

FIG. 8 is a diagram for explaining conventional communication control. FIG. 9 is an operation flowchart of a conventional communication control. In FIG. 9, parts involved in the back-off procedure described later are indicated by solid lines, and other parts are indicated by dotted lines to distinguish them, and the former will be described below first.

In this conventional example, nodes 81-1 to 81-n
(Hereinafter, for the sake of simplicity, attention will be focused on only a single node to which reference numeral “81-p” is assigned.) If there is transmission information to be transmitted (FIG. 9A), Carrier sensing is performed on the upstream line of the wireless transmission path described above (FIG. 8).
(1), FIG. 9 (2)), no carrier is detected,
In addition, when backoff is not being performed as described below, transmission information, a destination of the transmission information (hereinafter, a node to which a code “81-q” is assigned for simplicity), and a transmission source are given to the line. The packet generated with the identification information is transmitted (FIG. 8 (2), FIG. 9 (3)). Further, the node 81-p waits for reception of an ACK signal described later for a predetermined period (FIG. 8 (3)).

On the other hand, the main node 82 relays this packet to the downstream line of the radio transmission path (FIG. 8 (4)). Also, when the node 81-q constantly monitors the downstream line and receives a packet indicating the destination as its own station (FIG. 8 (5)), the node 81-q performs a predetermined process on the packet and performs such processing. An ACK signal indicating that the processing has been completed or started is transmitted to the upstream line (FIG. 8 (6)).

The node 81-p confirms that the transmission has been completed by receiving the ACK signal via the main node 82 (FIG. 8 (7)). However, when the node 81-p does not receive the ACK signal (FIG. 9 (4)),
A plurality of packets transmitted asynchronously by other nodes may have collided on the uplink. In this case, the node 81-p initially sets the contention window CW, which is a variable that takes a value in a preset value range (indicated by CWmin and CWmax), in order to secure a transmission path, and the value range The transmission of the packet is suspended for the back-off time T (FIG. 8 (8)) set as described later based on the uniform random number R from “0” to “1” and the slot time Ts (hereinafter, “8”). , "Back-off procedure") (FIGS. 8 (9) and 9 (5)).

Here, the above-mentioned back-off time T is represented by A
A plurality of nodes that failed to receive the CK signal individually
= R * (CW-1) * Ts, so that the probability of a packet colliding again is suppressed.

Further, the node 81-p sets the value of the contention window CW to CWmax using CWmin as an initial value until the number of retransmissions Nr is less than the maximum value until the ACK signal is received (FIG. 8 (7)). The backoff procedure and the transmission of the packet (FIG. 8 (10)) are repeated while sequentially updating the value to a double value within a range not exceeding (hereinafter, referred to as a contention window expansion procedure) (FIG. 9 (6)). Further, when the number of retransmissions Nr reaches the maximum value, the node 81-p discards the packet (FIG. 9 (7)).

[0010] The node 81-p also performs carrier sense during back-off at the time of each transmission, and appropriately performs a back-off procedure when a carrier is detected on the uplink line (FIG. 9 (8)). ) Is carried out, but if this carrier is not detected, the back-off time is updated to a shorter value (FIG. 9 (9)), so that the transmission is performed earlier.

[0011]

However, in the conventional example described above, while the number of operating nodes changes,
Contention window C for determining back-off time
Since the value range of W (CWmin, CWmax) is fixed, if the number increases significantly, the probability of occurrence of packet collision at the time of retransmission increases, and the source node receives the ACK signal. The average number of transmissions performed up to increases. On the other hand, when the number of nodes is significantly reduced, the possibility that a small number of nodes occupy the upstream line for a long time increases.

An object of the present invention is to provide a communication system capable of maintaining a high transmission efficiency of a transmission line regardless of a change in the number of nodes without changing a hardware configuration. Note that there is a CSMA / CD system as a communication system similar to the above-described conventional example, which is described above by a method described in, for example, JP-A-59-204345 or JP-A-59-204347. The probability that a collision will occur can be reduced.
However, in a wireless LAN, such a method requires that the transmission characteristics of the wireless transmission line fluctuate drastically according to changes in the amount of attenuation of a person's movement or an installed compartment, and the reception characteristics arriving via the wireless transmission line. Since it is difficult to reliably ascertain the operating state of the opposing node based only on the transmission information included in the wave, it was not actually applied.

[0013]

FIG. 1 is a block diagram showing the principle of the first and second aspects of the present invention. According to the first aspect of the present invention, the first communication path 1 is based on a contention method.
A plurality of nodes 12-1 to 12-N accessing a single node, a single node 13, and a second communication laid between the plurality of nodes 12-1 to 12-N and the single node 13 And a single node 13 includes a plurality of nodes 12-1 to 12-N
Acquiring means 15 for acquiring, via the second communication path 14, the number of transmission nodes ready to transmit to the first communication path 11, information indicating the number acquired by the acquiring means 15, Notification means 16 for transmitting to the second communication path 14 any one of information indicating a probability that a collision will occur in the first communication path 11 when the number of transmission nodes is equal to the number. Nodes 12-1 to 12-N are a single node 13
Is transmitted via the second communication path 14, and the larger the number or probability indicated by the information is, the wider the range is and the more uniform the distribution in the range is, the more the random number is generated. And a variable means 17 for setting a back-off time, which is a time to wait before retransmission based on the contention method, at a time proportional to.

According to a second aspect of the present invention, in the communication system according to the first aspect, the single node 13 accesses the first communication path 11 based on a contention method, As the number of transmitting nodes obtained by the above increases, a random number whose value range is wider and the distribution in the value range is uniform is generated, and a standby time is preceded by a retransmission based on the contention method in a time proportional to the random number. It is characterized by having a variable means 21 for setting a back-off time which is a power time.

FIG. 2 is a block diagram showing the principle of the present invention. According to a third aspect of the present invention, a plurality of nodes 32-1 to 32-N accessing the first communication path 31 based on a contention method, and a plurality of nodes 32-1 to 32-32
And a second communication path 33 laid between the nodes 32-1 to 32-N.
Among them, acquisition means 34 for acquiring the number of transmission nodes that can transmit to the first communication path 31 via the second communication path 33, and the number of transmission nodes obtained by the acquisition means 34 is large Generates a random number with a wider value range and a uniform distribution in the value range, and sets a back-off time, which is a time to wait before retransmission based on the contention method, at a time proportional to the random number. And a variable means 35.

According to a fourth aspect of the present invention, in the communication system according to any one of the first to third aspects,
The second communication path is also used as the first communication path. According to a fifth aspect of the present invention, in the communication system according to any one of the first to fourth aspects, the frequency of transmitting to the first communication path among the transmitting nodes is higher than that of the other nodes. The variable means included in the high transmitting node applies a value range in which both or one of the upper limit value and the lower limit value is smaller than the value range applied by the variable means included in these other nodes for generating random numbers. And

According to a sixth aspect of the present invention, in the communication system according to any one of the first to fifth aspects,
The variable means includes means for counting the number of retransmissions based on the contention method, and for setting the value range of the random number wider as the number of times is larger. The variable means of the transmitting node that is higher than the other nodes is characterized in that the ratio of expanding the range of random numbers in accordance with the number of times is set smaller than the variable means of these other nodes.

In the communication system according to the first aspect of the present invention, among the plurality of nodes 12-1 to 12-N, all of the transmitting nodes which are in a transmittable state asynchronously perform the first transmission based on the contention scheme. Since the communication path 11 is accessed, a collision may occur. However, a single node 13
In, the acquisition unit 15 acquires the number of transmission nodes that are ready to transmit. The notifying means 16 sends one of the number and information indicating the probability of occurrence of a collision in the first communication path 11 when the number of nodes capable of transmitting to the number is equal to the number to the second communication path 14. Send. In the sending node,
The variable means 17 receives the above-described information, generates a random number uniformly distributed in a wider value range as the number or probability indicated in the information increases, and sets a back-off time proportional to the random number.

Since the value that can be taken by such a random number increases with the number of transmitting nodes, the timing at which a plurality of transmitting nodes retransmit transmission information based on the contention method is widely distributed along the time axis. Therefore, the probability of occurrence of the above-described collision again decreases. Therefore, the transmission efficiency of the first communication path 11 is improved. The communication system according to the second aspect differs from the communication system according to the first aspect in that a single node 13 accesses the first communication path 11. The back-off time of 13 is set by the variable means 21 in the same manner as the plurality of nodes 12-1 to 12-N. Therefore, the transmission efficiency of the first communication path 11 is maintained without being significantly reduced.

In the communication system according to the third aspect of the present invention, the plurality of nodes 32-1 to 32-N can acquire the number of transmitting nodes via the second communication path 33.
The communication system according to the present invention differs from the communication system according to the first aspect in that the communication system according to the first aspect of the present invention includes both a control unit and a variable unit 35 for setting a back-off time based on the number.
The procedure for setting the back-off time in cooperation with the variable means 35 is the same. Therefore, the transmission efficiency of the first communication path 31 is improved as in the communication system according to the first aspect.

In a communication system according to a fourth aspect of the present invention, in the communication system according to any one of the first to third aspects, the second communication path is also used as the first communication path. . Therefore, if the transmission efficiency of the first communication path is improved by this communication system, the configuration can be simplified. In the communication system according to the fifth aspect, the first to fourth aspects are provided.
In the communication system according to any one of the transmission nodes, among the transmission nodes, the frequency of performing transmission to the first communication path, the variable means that the transmission node has a higher than other nodes, compared with other transmission nodes When generating a random number, a lower or upper limit and / or a lower range apply a small range, so that the value that the random number can take is generally smaller than the value of the random number that can be taken at another node. Therefore, as described above, in a transmitting node that transmits to the first communication path more frequently than other nodes, the probability of occurrence of a congestion state in which untransmitted transmission information is excessively accumulated is suppressed.

In a communication system according to a sixth aspect of the present invention, in the communication system according to any one of the first to fifth aspects, the variable means counts the number of retransmissions based on the contention method. The value range of the random number is set wider as the number of times increases. Further, a transmitting node that performs transmission more frequently than other nodes increases the range of random numbers at a smaller ratio than other nodes.

That is, every time the number of retransmissions increases, the timing at which a node with a high transmission frequency performs transmission has priority over other nodes, so that the accumulation of untransmitted transmission information is suppressed. You.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 3 is a diagram showing the configuration of the first to third embodiments. Hereinafter, referring to FIG.
The configuration of the first embodiment corresponding to No. 4 will be described. The difference between this embodiment and the conventional example shown in FIG.
The point is that nodes 41-1 to 41-n are provided instead of 81-n, and a main node 42 is provided instead of the main node 82.

Note that the correspondence between the present embodiment and the block diagram shown in FIG.
The nodes 41-1 to 4-4 correspond to the first and second communication paths 14, respectively.
1-n corresponds to the nodes 12-1 to 12-N and the variable means 17,
The main node 42 corresponds to the single node 13, the acquisition unit 15, the notification unit 16, and the variable unit 21. FIG. 4 is a diagram illustrating the operation of the present embodiment.

FIG. 5 is an operation flowchart of this embodiment. Hereinafter, the operation of the present embodiment will be described with reference to FIGS. The difference between this embodiment and the conventional example shown in FIG. 7 is that the nodes 41-1 to 41-n and the main node 42
Are in the procedure of communication control performed in cooperation with each other, so that description of other operations will be omitted below.

When the nodes 41-1 to 41-n are operating, the nodes 41-1 to 41-n transmit a status notification packet indicating the operation status indicating the fact and a transmission source at a predetermined cycle, thereby setting the main node. 42 is notified of the operation status (FIG. 4
(1)). Here, as shown in FIGS. 6A and 6B, the main storage (not shown) of the main node 42 includes the node 4
The operation status management table in which the individual operation statuses of 1-1 to 41-n are registered, and the value range (CWmin
, CWmax) are stored in advance. Also, the upper limit value CWmin and the lower limit value CWmax of this range are determined by the total number N of operating nodes.
Is adopted when the transmission efficiency of the wireless transmission path is maximized (for example, CWmin = 8 * N, CWmax
= 64 * N).

The main node 42 initializes the value to "0" for all the areas of the operation status management table at a predetermined cycle (FIG. 5 (1)), and the value of the interval is t.
The timer which is max is started (FIG. 5 (2)). When the main node 42 receives the status notification packet while the timer is counting time, the main node 42 analyzes the packet and stores “1” in the area corresponding to the node that is the transmission source of the packet in the operation status management table. (Fig. 5
(3)).

Each time the time t exceeds the maximum value tmax under the clocking performed in this way, the main node 42 sets the value of the operating status management table to "1" as the number of operating nodes. Is obtained (FIG. 5).
(4)). The main node 42 obtains a range corresponding to the total number N with reference to the range variable table (FIG. 5).
(5)), and sends window information indicating the range to the down line to all nodes (FIG. 4 (2), FIG. 5).
(6)).

The operating node among the nodes 41-1 to 41-n receives this window information, and if it cannot receive the ACK signal, it receives CWmin and CWma.
After setting the value range indicated by the window information in x, the backoff procedure and transmission are performed in the same manner as in the conventional example shown in FIG. Therefore, in the present embodiment, the total number of operating nodes is grasped at regular intervals, and the nodes 41-1 to 41-n
, The contention window CW optimal for the total number is set, so that the transmission efficiency of the wireless transmission path is kept high.

Hereinafter, the configuration of the second embodiment according to the third aspect of the present invention will be described with reference to FIG. The difference between the present embodiment and the first embodiment is that the main node 4
2 is not provided, and nodes 51-1 to 51-n are provided instead of the nodes 41-1 to 41-n. In addition, regarding the correspondence between the present embodiment and the block diagram shown in FIG. 2, the wireless transmission path corresponds to the first communication path 31 and the second communication path 33, and the nodes 51-1 to 51-n are the nodes. 32-1 ~
32-N, an acquisition unit 34, and a variable unit 35.

The operation of this embodiment will be described below with reference to FIG. The operation of this embodiment differs from that of the first embodiment in the form of communication and the procedure for obtaining the value range of the contention window CW. Hereinafter, these differences will be described, and description of other operations will be omitted.
The nodes 51-1 to 51-n perform end-to-end communication without passing through the main node.

In the main memory of the nodes 51-1 to 51-n, similarly to the main node in the first embodiment, an operation status management table (FIG. 6A) and a range variable table (FIG.
(2)). Also, nodes 51-1 to 51-n
Sends a status notification packet indicating the operating status and the transmission source to that effect to all other nodes on the upstream line of the wireless transmission line at a fixed period set in advance when it is operating. At the same time, the upstream line is constantly monitored to receive the status notification packet. Each of the nodes 51-1 to 51-n obtains the number of operating nodes by updating the operation status management table based on the status notification packet, and obtains the CWmin based on the number and the range variable table.
And CWmax are set, and these values are used in a back-off procedure performed when no ACK signal is received.

Therefore, in the present embodiment, the total number of operating nodes is grasped at a fixed period, and the contention window CW optimal for the total number is set for each node. Is kept high.
Hereinafter, a third embodiment corresponding to the invention described in claim 5 will be described with reference to FIGS.

The difference between the present embodiment and the first embodiment is that a simplex system is applied to the wireless transmission line in FIG. In such a configuration, since a collision may occur in the packet transmitted by the main node 42, when a collision occurs, the main node 42 also performs a back-off procedure like the other nodes. However, the value range variable table (FIG. 6 (2)) set in the main memory of the main node 42 includes an upper limit value CWmax indicating a value range of the contention window CW and a value higher than the other nodes 41-1 to 41-n. Lower limit value CWmi
Since both n are set small, the back-off time set in the main node 42 is generally shorter than those of the other nodes 41-1 to 41-n.

Therefore, these nodes 41-1 to 41-1
Packets accumulated for relaying between -n are preferentially transmitted, and the transmission efficiency of the wireless transmission path is improved. Less than,
A fourth embodiment according to the present invention will be described with reference to FIG. In the present embodiment, the main node 42 is connected to another node 41-1 in the same manner as in the third embodiment.
The same back-off procedure as that of ~ 41-n is performed, but at the time of retransmission, the contention window extension procedure (FIG. 9 (6)) is performed at a smaller ratio than other nodes. Main node 5 when retransmitting more than once
The back-off time set to 2 is the other nodes 41-1 to 4-1
Generally shorter than 1-n.

Therefore, these nodes 41-1 to 41-1
Packets accumulated for relaying between -n are preferentially transmitted, and the transmission efficiency of the wireless transmission path is improved. In addition,
In the first embodiment, the nodes 41-1 to 41-n voluntarily notify the operation status to the main node 42. However, the main node 42 may ask the operation status by polling.

In the first embodiment, the main node 42
The transmission timing of the information indicating the content range of the contention window is set to a fixed cycle, but any timing may be used as long as the number of nodes that can transmit is different from the previously counted value. Furthermore, in the first embodiment, the main node 42 has a mechanism for grasping the number and distributing the value of the contention window to the nodes 41-1 to 41-n. You may.

In each of the above-described embodiments, both the upper limit and the lower limit of the value range of the contention window CW are variable, but a configuration in which either one is variable is also applicable. In the third and fourth embodiments,
The node given priority for retransmission is the main node 42
However, if it is known that the frequency of transmission is relatively high, the node may not be relayed.

Further, in the first, third, and fourth embodiments, a plurality of transmission lines may be used as long as the main node 42 is connected to the other nodes 41-1 to 41-n. In the second embodiment, a plurality of transmission paths may be used as long as the nodes 51-1 to 51-n are connected to other nodes. Further, in each of the above-described embodiments, the information obtained by the node is information indicating the value range of the contention window, but any information may be used as long as the information determines an appropriate back-off time. However, in such a case, the node is provided with a mechanism for obtaining a value range of the contention window according to the information.

Further, in each of the above-described embodiments, the node notifies the operating status at a fixed cycle. However, except at the time of starting, the node notifies the content of the change only when the operating status changes, and A configuration in which a node or another node obtains the number of operating nodes based on the content of the change is also applicable. Further, in each of the embodiments described above,
Although the node sets the value of the contention window by updating or referring to the table set in the main memory, a configuration in which the same setting is performed by calculation is also applicable.

In each of the above embodiments, a mechanism for obtaining the number of operating nodes is provided. However, all or some of the nodes are provided with a man-machine interface, and the number of operating nodes is reduced. Is also possible to obtain the number by inputting information indicating. A ROM in which information indicating the number of operating nodes is written
When a storage device such as a storage device is loaded, a configuration in which the number of operating nodes is obtained by reading information indicating the number is also applicable.

Further, in each of the above-described embodiments, the variable criterion of the contention window is the number of active nodes. However, any information that indicates the probability of occurrence of a collision in the transmission path is any information. Is also good. Also,
In each of the above-described embodiments, the transmission path used for counting the number of operating nodes is shared with the transmission path used for communication exclusively performed, but such a transmission path may be separately provided. Good.

Further, in each of the above-described embodiments, a radio transmission path based on the CSMA / CA scheme is applied to the transmission path. However, for example, a radio transmission path based on a contention scheme such as the CSMA / CD scheme may be used. Any transmission path may be applied.

[0046]

As described above, according to the first to fourth aspects of the present invention, the transmission efficiency of the transmission line is maintained high regardless of the change in the number of nodes.

Further, in the invention according to claims 5 and 6,
The probability that a packet to be transmitted or relayed will accumulate can be reduced. Therefore, in the communication system to which these inventions are applied, the transmission path can be effectively used at low cost, and the communication quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the present invention.

FIG. 2 is a principle block diagram of the invention according to claim 3;

FIG. 3 is a diagram showing a configuration of the first to third embodiments.

FIG. 4 is a diagram showing a first embodiment.

FIG. 5 is a diagram showing a first embodiment.

FIG. 6 is a diagram showing first to third embodiments.

FIG. 7 is a diagram showing a configuration of a conventional wireless LAN.

FIG. 8 is a diagram for explaining conventional communication control.

FIG. 9 is an operation flowchart of a conventional communication control.

[Explanation of symbols]

 11, 31 First communication path 12, 32, 41, 51, 81 Node 13 Single node 14, 33 Second communication path 15, 34 Acquisition means 16 Notification means 21, 35 Variable means 42, 82 Main node

Claims (6)

[Claims] A plurality of nodes accessing a first communication path based on a contention method; a single node; and a second node laid between the plurality of nodes and the single node. A communication path, wherein the single node obtains, via the second communication path, the number of transmission nodes in a state capable of transmitting to the first communication path among the plurality of nodes. And information indicating the number obtained by the obtaining unit, and information indicating the probability that a collision will occur in the first communication path when the number of transmission nodes is equal to the number, Notification means for transmitting to the communication path of the plurality of nodes, the plurality of nodes receive the information transmitted by the single node via the second communication path, the number or probability indicated by the information Is larger, the value range is wider and its value And generating a random number having a uniform distribution, and having variable means for setting a back-off time, which is a time to wait before retransmission based on the contention method, at a time proportional to the random number. A communication system characterized by the following. 2. The communication system according to claim 1, wherein the single node has a means for accessing the first communication path based on a contention method, and a large number of transmission nodes obtained by the acquisition means. Generates a random number whose value range is wider and the distribution in the value range is more uniform, and sets a back-off time, which is a time to wait before retransmission based on the contention method, at a time proportional to the random number. A communication system, comprising: 3. A communication system comprising: a plurality of nodes accessing a first communication path based on a contention scheme; and a second communication path laid between the plurality of nodes, wherein the plurality of nodes include: Acquisition means for acquiring, via the second communication path, the number of transmission nodes that can transmit to the first communication path, among the plurality of nodes, and the number of transmission nodes obtained by the acquisition means Is larger, a value range is wider, and a random number having a uniform distribution in the value range is generated.At the time proportional to the random number, a back-off time, which is a time to wait before retransmission based on the contention method, is used. And a variable means for setting the following. 4. The communication system according to claim 1, wherein the second communication path is also used as the first communication path. 5. The communication system according to any one of claims 1 to 4, wherein, among the transmitting nodes, a transmitting node that transmits to the first communication path more frequently than other nodes. A communication system characterized in that the variable means has a lower limit and / or a lower limit that is smaller than a range applied by the variable means of the other nodes to the generation of random numbers. . 6. The communication system according to claim 1, wherein the variable means counts the number of retransmissions based on the contention method, and increases the random number range as the number of retransmissions increases. The variable means of the transmitting node, which has a means for setting wider, and which has a higher frequency of transmitting to the first communication path than the other nodes among the transmitting nodes, has a ratio of expanding the range of random numbers according to the number of times. Is set smaller than the variable means of these other nodes.