JP2705686B2 - Wireless data communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless data communication apparatus using wireless as a transmission medium, and more particularly to a wireless data communication system suitable for use in a wireless LAN (local area network) environment.

[0002]

2. Description of the Related Art A plurality of data communication apparatuses share a single wireless medium to perform frame communication of packetized data.
An example of such a method is IEEE 802.1 which is a standard specification of a wireless LAN.
Specified in 1.

In this system, a data communication device desiring transmission performs carrier detection on a wireless medium. Here, a predetermined inter-frame space IFS (Interter) is established between data communication devices that communicate on the same wireless medium.
If no carrier is detected during the frame space,
The data communication device can start transmitting. On the other hand, if a carrier is detected, wait until the carrier is interrupted,
Thereafter, if no carrier is detected during the IFS, the data communication device can begin transmission.

However, when a plurality of data communication apparatuses start transmission procedures at substantially the same time, they cannot detect each other's carriers due to processing delays in the apparatuses and delays on a wireless medium.
Frame collisions can occur. Then, when a collision occurs, the collision cannot be detected on the wireless medium, so that the wireless medium is uselessly occupied until the frame transmitted by each data communication device is interrupted.

[0005] To prevent this, a random time is waited after the IFS wait using a random number to avoid a frame collision.

[0006] IEEE 802.11 defines a central control function (Point Coordination Function) as one of the structures of a wireless data communication network. Perform medium access control by CSMA / CA method.
Data communication device with two relay functions (referred to as "base unit")
And a plurality of data communication devices not having a relay function (hereinafter referred to as "slave units"), communication of the slave units is always performed by relay of the master unit.

[0007] The relay function of the master unit receives a frame transmitted by the slave unit, temporarily stores the frame in a buffer held in the master unit, and transfers the frame to another data communication device that the slave unit desires to transmit a packet. To transfer.

For example, as shown in the left half of FIG.
In a network 230 including a master unit 210 having one relay function and a plurality of slave units 201, 202, and 203 having no relay function for performing wireless medium access control by the MA / CA method, these slave units Is always performed by the relay of the master unit 210.

From the state where the wireless medium is vacant, for example,
01, communication is started and stored in a buffer (not shown) of the base unit 210. During this time, another child device 20
In the case where 2 issues a transmission request, the parent device 210 and the child device 202 simultaneously compete for the right to use the wireless medium at the next transmission opportunity after the transmission of the child device 201 ends.

The priority of wireless medium acquisition prior to transmission is the same for master unit 210 and slave unit 202.
Has a half probability of being transmitted first. Further, when there are a plurality of slave units that are waiting to be transmitted similar to slave unit 202, the number of opportunities for master unit 210 to transmit early is reduced by the number of slave units that are waiting for transmission. During this time, master device 210 continues to receive the packets transmitted by the slave device and stores the packets in an internal buffer.

On a wired network, a data communication apparatus which does not cause a buffer overflow is realized by controlling a buffer accumulation amount using a collision detection function in a transceiver. For example, Japanese Patent Publication Sho 63
JP-A-43029 discloses a medium access control system CSMA / CD (Carrier Sense Mul) in a wired network.
By controlling the buffer accumulation amount using the collision detection function in the transceiver, which is a feature of tiple access with collection detection, a new buffer circuit that temporarily stores packets is used as a data communication method that does not cause buffer overflow. There has been proposed a configuration in which a buffer management circuit that determines the accommodability of a packet outputs an interfering signal to a transceiver when a new packet arrives in a state in which it is determined that there is no capacity to accommodate a new packet. I have.

[0012] Even in a wired network, there is a method in which a stored packet is relayed and transmitted to another terminal by a data communication device that temporarily stores the packet in a buffer. This data communication device may not be able to immediately send an incoming packet depending on the traffic condition of the medium used.

Therefore, when the capacity of the buffer for the packet arriving at the apparatus is not sufficient, the data communication apparatus generates an interference signal from the interference signal output means in the apparatus to the medium on which the packet is being transmitted. Intentionally cause a collision. Each terminal interrupts transmission by detecting occurrence of a collision. By recovering the buffer overflow of the data communication device on the network by immediately transmitting the packet to the place where the medium access from the terminal is stopped and the medium becomes free.

[0014]

SUMMARY OF THE INVENTION Conventional CSMA / CA
In the method, the inter-frame space IFS used on the same network is set to the same value in any data communication device, and the random waiting time is generated with the same probability.

For this reason, when the calls from the slaves are concentrated, the number of packets stored in the buffer of the master increases, and the chance of transmitting the stored packets from the master to the relay slave decreases. Therefore, buffer overflow (overflow) may occur. Then, the overflowing packet is lost from the network.

Further, even when a sufficient buffer capacity is secured, transmission delay due to a decrease in transmission opportunities becomes a problem.

The above-mentioned Japanese Patent Publication No. 63-43029 discloses that
A data communication method that does not cause a buffer overflow by controlling a buffer accumulation amount using a collision detection function in a transceiver has been proposed.

However, on a CSMA / CA wireless network, a collision cannot be detected because a signal level greatly differs depending on a part on a wireless medium and reception cannot be performed while transmitting.

For this reason, the method of controlling the buffer accumulation amount using the collision detection function is disclosed in
According to the method described in JP-A-43029, the number of packets stored in the master unit increases when the calls of the slave units are concentrated, and the chance of transmitting the stored packets to the slave unit as a relay destination decreases. It is not possible to solve the problems such as overflow of the generated buffer and transmission delay due to reduced transmission opportunities.

Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to increase the transmission priority in accordance with the amount of packets stored in the buffer of a wireless data communication apparatus, and An object of the present invention is to provide a wireless data communication system that avoids overflow and a decrease in transmission speed.

[0021]

In order to achieve the above object, according to the wireless data communication system of the present invention, a plurality of data communication devices share one wireless medium by a CSMA / CA access procedure and packetize the data. In a wireless data communication device that performs frame exchange of the data, connected to the wireless medium, receives a signal and extracts a received packet,
A receiving unit for detecting a free state of the wireless medium based on the presence or absence of a carrier on the wireless medium, and a destination connected to the destination by a destination inserted in the received packet;
That is, it is determined whether the transmission source of the received packet belongs to a network to which the transmission source belongs or another network capable of forwarding, and whether this destination is an undeliverable destination is determined. A packet filter for determining any of writing to the network, transfer of transmission / reception means to another network, or discarding, a buffer for temporarily storing and holding the received packet, and monitoring the amount of packets stored in the buffer. Buffer management means for variably controlling the transmission priority in accordance with the buffer capacity, and CSMA / CA control for performing wireless medium access control based on a free state of the wireless medium and a priority transmission instruction issued by the buffer management means. Means and adapts to the network accessing from data packet by CSMA / CA method A frame generating means for generating a frame, a transmitting means for transmitting the frame to the network according to an instruction of the CSMA / CA control unit.

In the present invention, the priority transmission operation is realized by shortening the wireless medium free space detection time when acquiring the wireless medium. After the end of the priority operation period, the process returns to the transmission procedure including the original wireless medium idle time.

[0023]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a configuration of one embodiment of the present invention.

In FIG. 1, reference numeral 100 denotes a wireless medium for performing CSMA / CA access control (referred to as “wireless medium”). Reference numeral 101 denotes a reception contact of the master unit with respect to the wireless medium 100, through which a frame is received from the wireless medium 100 and the wireless medium 100 is monitored for an empty state.

The receiving means 102 verifies whether the received frame is normal, and if so, extracts the packet and transfers it to the packet filter 103.
The empty state of 0 is transmitted to the CSMA / CA control means 112.

The packet filter 103 converts the packet into a format suitable for each processing system according to the destination of the packet and transfers the packet. When the destination belongs to the own network 230, the data is transferred from the contact 104 to the buffer 110. When the destination is connected to the other communication medium 140 adjacent thereto, the other communication medium 140 is transmitted from the contact 105 to the adjacent communication medium 140. To the transmission / reception means 130 for. Note that packets whose destination cannot be resolved and illegal packets due to errors or the like are discarded.

The buffer 110 stores packets to be relayed and holds them until transmission is completed.

The buffer management means 111
0, the amount of packets stored in the buffer 110 is monitored.
If the amount of packets stored in the buffer 110 exceeds a predetermined threshold with respect to the storable amount of the buffer 110, a priority transmission procedure is operated to satisfy certain conditions such as sweeping out all the packets in the buffer 110. Until the priority transmission means (procedure) is held.

The master unit can temporarily obtain the priority transmission right before the buffer 110 overflows and before the transmission delay becomes noticeable, thereby avoiding the problems of buffer overflow and transmission delay.

The CSMA / CA control means 112 receives the information on the free state of the wireless medium 100 by the receiving means 102 and transmits the information to the transmitting means 12 according to the CSMA / CA access method.
Control 1 Further, when the instruction of the priority transmission operation is received from the buffer management unit 111, the wireless medium empty detection time is shortened and the transmission unit 121 performs the priority transmission as described above.

The frame generation means 120 includes a buffer 11
The packet output from 0 is processed into a frame format suitable for the network and transferred to the transmitting means 121.

The transmitting means 121 transmits the framed packet to the wireless medium 100 with the permission of the CSMA / CA control means 112.

The transmission / reception means 130 for another adjacent communication medium 140 is interpreted as passing through the other adjacent communication medium 140, receives the packet transferred through the contact 105 from the packet filter 103 at the contact 131, and Send to the medium by the defined access means.

The packet received for the network of the wireless medium 100 is put into the buffer 110 through the contact 132, and the wireless medium 100 is accessed by the access means.
To the network.

The other adjacent communication medium 140 may be a CSMA / CA network having a different channel from that of the wireless medium 100. In this case, the transmitting / receiving means 130 for the other adjacent communication medium 140 is connected to the receiving contact 101, the receiving means 1
02, packet filter 103, contact point 104, contact point 10
5, buffer 110, buffer management means 111, CSM
This is realized by replacing the A / CA control unit 112, the frame generation unit 120, and the transmission unit 121 with the transmission / reception unit having the same configuration as the A / CA control unit 112, the connection unit 104, and the contact unit 105.

FIG. 2 is a diagram showing an example of a network realized by applying the embodiment of the present invention.

One master unit 210 having a relay function capable of accessing the wireless medium 100 performing the CSMA / CA access control, and the slave unit 20 having no relay function
1, 202, 203,... Constitute a network 230. Master device 210 can be connected to data communication device 221 in another network 240 through another adjacent communication medium 140, and performs packet filtering between the networks. Here, communication between the terminals (slaves) is always performed by relaying the master 210.

An example of transmission from the slave unit 201 to the slave unit 202 in FIG. 2 will be described with reference to FIG.

The packet transmitted from the slave unit 201 to the wireless medium 100 is taken in from the receiving contact 101 of the master unit. After the validity of the frame is confirmed by the receiving unit 102, the packet filter 103 recognizes that the destination of the packet is the slave unit 202.

The packet filter 103 has a destination (child device 2).
02) is determined to be a terminal belonging to the own network 230, and the packet is written to the buffer 110 from the contact point 104. The buffer management unit 111 detects writing to the buffer 110 and generates a transmission request. Here, if the wireless medium 100 is empty, transmission can be started immediately.
A packet is extracted from the buffer 110 and a transmission frame is generated by the frame generation means 120.

The CSMA / CA control means 112 detects the empty state of the wireless medium 100 from the receiving means 102, and if the wireless medium 100 is idle during the prescribed inter-frame space IFS time and the random waiting time, the transmitting means 121 transmits the prepared transmission frame immediately.

However, after the transmission request is generated, the other slave units 20
When the wireless medium 100 does not become idle and the master unit 210 continuously receives data, for example, when transmission of 1, 202, 203,... Continues, the number of packets written to the buffer 110 increases only. If this state continues, buffer overflow and transmission delay become remarkable. Therefore, when the accumulated packet amount exceeds a certain threshold, the buffer management unit 111 starts a priority transmission procedure. That is, the specified IF
The random wait time after the S time wait is shortened, the wireless medium acquisition is preferentially performed, and the packets stored in the buffer 110 are swept out.

FIG. 3 is a diagram showing the configuration of the second embodiment of the present invention. The configuration of this embodiment is the same as that of the first embodiment, and its operation is the same as that of the first embodiment except for the buffer 310, the buffer management unit 311, and the CSMA / CA control unit 312.

Buffer 310, buffer management means 31
1. The operation of the CSMA / CA control means 312 depends on the first
The buffer 110, the buffer management unit 111, and the CSMA / CA control unit 112 in the embodiment are different in the following points.

The buffer 310 accumulates packets to be relayed and holds them until transmission is completed. The buffer management unit 311 monitors the amount of packets stored in the buffer 310. The medium priority detection time is reduced in accordance with the increase in the amount of packets stored in the buffer 310, and the transmission priority is changed stepwise. The master unit can obtain a higher priority transmission right as the amount of packets stored in the buffer increases, thereby avoiding problems of buffer overflow and transmission delay.

The CSMA / CA control unit 312 receives the information on the free state of the wireless medium 100 from the receiving unit 102,
The transmitting unit 121 is controlled according to the SMA / CA access method. When receiving a priority transmission operation instruction from the buffer management unit 311, the wireless medium idle detection time is shortened and the transmission unit 121 performs priority transmission.

[0047]

As described above, according to the present invention,
The wireless medium vacancy detection time is shortened according to the amount of packets stored in the buffer of the master wireless data communication device. CS
Due to the nature of MA / CA, the transmission priority of the master unit whose wireless medium empty detection time has been shortened becomes higher, so that the transfer waiting packets accumulated in the buffer can be swept out. Also, according to the amount of packets to be buffered, it has a transmission priority in this method stepwise or for a certain period (for a certain period of time, a certain number of frames, or until the flushing of the packet is completed). Avoid drop. By increasing the transmission priority of the master wireless data communication device, it is possible to avoid buffer overflow and a reduction in transmission speed.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an entire network realized by the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Wireless medium for performing CSMA / CA access control 102 Receiving means 103 Packet filter 110 Buffer 111 Buffer managing means 112 CSMA / CA controlling means 120 Frame generating means 121 Transmitting means 130 Transmitting and receiving means for adjacent other communication medium 140 Other adjacent Communication media 201, 202, 203 Slave device 210 Master device 221 having relay function 221 Data communication device 310 Buffer 311 Buffer management means 312 CSMA / CA control means

Claims (3)

(57) [Claims] 1. A wireless data communication apparatus in which a plurality of data communication apparatuses share one wireless medium and exchange frames of packetized data by a CSMA / CA access procedure, wherein the plurality of data communication apparatuses are connected to the wireless medium. Receiving means for receiving a signal, extracting a received packet, and detecting an empty state of the wireless medium based on the presence or absence of a carrier on the wireless medium; and a destination connected to the destination by the destination inserted in the received packet. That is, it is determined whether the transmission source of the received packet belongs to the network to which the transmission source belongs or another network that can be transferred, and whether this destination is an undeliverable destination is determined. Packet buffer that decides whether to write to a buffer, transfer the transmitting / receiving means to another network, or discard A buffer that temporarily stores and holds the received packet; a buffer management unit that monitors an amount of packets stored in the buffer and variably controls a transmission priority according to an allowable amount of the buffer; C that performs wireless medium access control according to the free state of the wireless medium and the priority transmission instruction issued by the buffer management unit
SMA / CA control means, frame generation means for generating a frame suitable for a network to be accessed by a CSMA / CA method from data packets, and transmission means for transmitting a frame to the network in accordance with an instruction of the CSMA / CA control means. A wireless data communication system comprising: 2. The transmission method according to claim 1, wherein the buffer management unit is configured to, when the amount of packets stored in the buffer exceeds a predetermined threshold with respect to the storable amount of the buffer, increase a priority transmission instruction to increase the transmission priority. 2. The wireless data communication system according to claim 1, wherein the data is output to the CSMA / CA control means. 3. A wireless data communication apparatus in which a plurality of data communication apparatuses share one wireless medium and exchange frames of packetized data by a CSMA / CA access procedure, and accumulate packets to be relayed. The amount of packets stored in the buffer to be monitored is monitored, and when the amount of packets stored in the buffer exceeds a predetermined allowable amount according to the storable amount of the buffer, the wireless medium vacancy detection time is shortened. A transmission priority of the parent device is set higher, and control is performed such that transmission waiting packets stored in the buffer are preferentially transmitted and swept out.