JPH0964888A - Data communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the data communication equipment with an excellent communication efficiency in which collision of data is less by calculating and utilizing a medium reservation time. SOLUTION: The data communication equipment is made up of a radio LAN adaptor 36, a host computer 38, and an antenna 26 or the like. A data communication time from the data communication equipment to an external communication equipment and a data communication time from the external communication equipment to the data communication equipment conducted after data communication are calculated by a medium reservation time and the calculated medium reservation time is informed to the external communication equipment. Since the medium reservation time is reserved by this processing, the data communication efficiency is improved and data collision is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication device, and more particularly to a data communication device used in a local area network.

[0002]

2. Description of the Related Art CSMA / CA (Carrier Sense Multip)
le Access / Collision Avoidance) and CSMA / CD
(Carrier Sense Multiple Access / Collision Detect)
Is a medium access protocol used in the currently widely used local area networks.
In these protocols, it is considered that the medium access right of the terminals on the local area network is imparted to each terminal fairly.

IEEE 802.11 standard proposal (IEEE802.11
Wireless Access Method and Physical Layer Specifi
CS proposed in cations March 10. 1993)
Communication between a plurality of wireless terminals in the MA / CA system is performed as follows.

For example, referring to FIG. 7, wireless terminals A to
Assume an environment in which four wireless terminals (communication devices) of D exist. In wireless local area networks, there is a limit to the reach of transmission data of each terminal. In the figure, the communicable range of the wireless terminal A is shown by a frame 18, and the communicable range of the wireless terminal B is shown by a frame 19. That is, in the figure, the terminals with which the wireless terminal A can communicate are wireless terminals B and C, and the terminals with which the wireless terminal B can communicate are wireless terminals A and D. That is, the wireless terminals B and C cannot communicate with each other, and similarly, the wireless terminals A and D cannot communicate with each other.

In the environment as shown in FIG. 7, a procedure when the wireless terminal A transmits a data frame (a frame including data to be transmitted; the same applies hereinafter) to the wireless terminal B will be described.

Referring to FIG. 8, at time t0, wireless terminal A sends a request frame (hereinafter referred to as "RTS frame") to wireless terminals B and C within communicable range 18 of wireless terminal A. What is RTS? "Request-To Send"
Is an abbreviation for. ). The RTS frame is a frame transmitted to acquire the medium access right.
The RTS frame includes the address of the wireless terminal (here, wireless terminal B) to which the data of wireless terminal A is transmitted, and the data length of the data frame to be transmitted after the medium access right is acquired.

At time t1, the RTS frame transmitted from the terminal A is received by the terminals B and C. At this time, the terminal B and the terminal C compare the address of the destination terminal included in the received RTS frame with the own address of each terminal. If the comparison results match, the terminal reads the data length of the data frame to be received from the received RTS frame. The read data length is used to transmit a transmission enable response frame (hereinafter referred to as “CTS frame”. CTS is an abbreviation for “Clear-To Send”) to terminals within a communicable range.

On the other hand, if the comparison result of the destination address and the own address does not match, the terminal receives the received RT.
Based on the data length of the data frame recorded in the S frame, data transmission to a medium for transmitting information (here, a space for transmitting radio waves) is postponed. This avoids another data frame communication, that is, a data frame collision, while a data frame is being communicated on the medium.

For example, in FIG. 8, terminal B has time t.
Assuming that the comparison result of the destination address of the RTS frame received in 1 and its own address is the same, the time t
2, the CTS frame is transmitted to the terminal A and the terminal D existing in the communicable range 19.

On the other hand, since the terminal C receiving the RTS frame at the time t1 has determined that the comparison result of the destination address and its own address do not match, the time 106 from the time t1 to the time t7 is data. No transmission is done.

The terminal (here, terminal A) transmitting data is C
After receiving the TS frame, the data frame is transmitted. When the transmission of the data frame is completed, the terminal which received the data frame receives the confirmation frame (hereinafter referred to as “A
CK frame ". ACK is "Acknowledgme
abbreviation of "nt".) to the sending terminal.

In FIG. 8, terminal A at time t4.
Is transmitting a data frame (DATA) to terminal B. At time t5, the data frame transmission is completed. At time t6, the terminal B sends A to the terminal A
Sending a CK frame. Terminal A at time t7
Has received an ACK frame.

A wireless terminal that has received a CTS frame and has not transmitted an RTS frame is a CT
The data transmission is stopped for the time corresponding to the data length recorded in the S frame. This avoids data collisions on the medium.

In FIG. 8, the terminal D receives the CTS frame at time t3. Here, terminal D is RT
Since it is not the terminal that has transmitted the S frame, data communication is not performed during the time 108 from time t3 to time t7.

That is, the RTS frame or the CTS frame is a frame transmitted to notify the terminal on the wireless local area network that the medium access right has been acquired or is trying to acquire the medium access right.

When the terminal transmitting the RTS frame receives the CTS frame, it is considered that the terminal transmitting the RTS frame has acquired the medium access right. The data frame is transmitted after the medium access right is acquired.

(1) When the terminal that has transmitted the RTS frame cannot receive the CTS frame,
(2) When the terminal that transmits the RTS frame receives an RTS frame from another terminal, (3) When the terminal that receives the RTS frame further receives an RTS frame from another terminal before transmitting the CTS frame , It is considered that a plurality of accesses collide on one communication medium. In such a case, the terminal that has detected the collision interrupts the process and restarts the transmission procedure from the beginning.

[0018]

However, in the above data communication environment, (1) communication efficiency is poor,
(2) There is a problem that data collisions on the medium occur relatively frequently.

The above problems are caused by the following reasons. (1) Reason for poor communication efficiency The exchange of the RTS frame and the CTS frame described above prevents the occurrence of collision during data frame transmission, but at the same time, becomes an overhead accompanying the transfer of the data frame,
It reduces the data transfer efficiency.

In data communication in a local area network, in addition to one-way data transmission from one terminal to the other terminal, for example, after data transmission from one terminal to the other terminal, the other terminal is transmitted. There is a case where bidirectional data transmission is performed as a series of processes, such as data being transmitted from one terminal to another terminal.

In such a case, as shown in FIG. 9, from the time t8 after the data transmission processing from the terminal A to the terminal B shown in FIG. 8 is performed from the time t0 to the time t7. At time t15, this time, the terminal B transmits the RTS frame to the terminal A, the terminal A transmits the CTS frame to the terminal B, the terminal B transmits the data frame to the terminal A, and the terminal The ACK frame is transmitted from A to terminal B. That is, the terminal C cannot perform transmission from the time t1 to the time t7 and the time t11 to t15, and the terminal D transmits the time t3.
From time t7 to time t7 and from time t9 to time t15, transmission cannot be performed.

Further, at time t7 in FIG. 9, after the end of the data communication from the terminal A to the terminal B, the other terminals (terminals C and D) acquire the access right until time t8, during which the terminal B keeps the terminal A Reply data cannot be sent to.

(2) Reasons why data collisions often occur Transmission delay between terminals (time t0 to t1, t2 to t3, etc.)
Thus, while the RTS frame or the CTS frame is being transmitted in the medium, another terminal may issue the RTS frame or the CTS frame, or two or more terminals may issue the RTS frame or the CTS frame at the same time. In such a case, data collision in the medium occurs. In FIG. 9, there is a possibility that a collision will occur between times t0 to t3 and t8 to t11.

Also, in the CSMA / CD protocol, there is no handshake procedure such as RTS frame and CTS frame, but since the medium access right is impartially given to all terminals, at the time of transmission of each data frame. There was a possibility that a data frame collision would occur.

The present invention has been made to solve the above problems, and an object of the present invention is to improve communication efficiency in a data communication device and reduce data collision.

[0026]

In order to solve the above problems, the data communication apparatus according to the first aspect is performed after the data communication time from the data communication apparatus to the external communication apparatus and after the data communication. It is provided with calculating means for calculating a communication time of data from the external communication device to the data communication device as a medium reservation time, and notifying means for notifying the external communication device of the calculated medium reservation time.

A data communication device according to a second aspect is the data communication device according to the first aspect, wherein data communication from an external communication device to the data communication device is data transmission from the data communication device to the external communication device. The calculation means further calculates a medium reservation time on the basis of the determination result of the determination means.

A data communication device according to a third aspect is the data communication device according to the second aspect, and transmits a flag indicating succession of the medium access right to the external communication device based on the determination result of the determination means. It further comprises a transmitting means for performing.

[0029]

DETAILED DESCRIPTION OF THE INVENTION One of the embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

In order to explain the embodiment of the present invention, communication between terminals performed in the environment shown in FIG. 7 is assumed. As described above, in the communication environment, the wireless terminals A to D exist, the wireless terminals A and C are within the communicable range 18 of the wireless terminal A, and the wireless terminals B are within the communicable range 19 of the wireless terminal B. Has terminals A and D.

In the present embodiment, CSMA /
Although a wireless local area network using the CA protocol is adopted, the present invention can be implemented regardless of the environment of wired communication or wireless communication, and the protocol is CSMA / C.
It is not limited to A.

FIG. 2 is a block diagram showing one device configuration of the terminal of FIG. Referring to the figure, the terminal comprises a host computer 38 and a wireless LAN (abbreviation of local area network) adapter 36.

The wireless LAN adapter 36 is a program memory 28 that stores software and communication protocols.
And a microcontroller 20 that executes software stored in the program memory 28, and a data memory 3 in which the microcontroller 20 temporarily holds data.
2, a host interface 30 for exchanging information with the host computer 38, a wireless interface 22 for serializing and parallelizing data, and wireless communication with other terminals in the wireless local area network. It is composed of a wireless transceiver 24 for performing and an antenna 26 connected to the wireless transceiver 24.

The program memory 28, the host interface 30, the data memory 32, the microcontroller 20, and the wireless interface 22 are connected by a local bus 34.

The wireless interface 22 has a function of serializing the transmission data written in the data memory 32 by the microcontroller 20 and sending it to the wireless transceiver 24.
It has a function of parallelizing the received data from another terminal in the wireless local area network input from the wireless transceiver 24 and writing it in the data memory 32.

FIG. 3 is a block diagram showing the configuration of software included in the terminal. Referring to the figure, the software is composed of host computer software 100 installed in host computer 38 and LAN adapter software 110 installed in wireless LAN adapter 36.

Host computer software 100
Is a network layer protocol processing unit 46 for performing higher-level communication protocol processing such as packet delivery confirmation and retransmission, operating system software 44 for performing various operations of the terminal, and operating system software 44 for the wireless LAN adapter 36. Device driver software 42 for writing transmission data and reading reception data, and application software (application program) 4 for using the communication service of the network layer protocol processing unit 46.
8 and.

Software 1 for wireless LAN adapter
Reference numeral 10 includes a medium access protocol processing unit 40 that performs transmission / reception processing of data using the medium access protocol, which is a feature of the terminal in the embodiment of the present invention.

FIG. 5 is a diagram for explaining the format of a frame transmitted and received by the wireless terminal shown in FIG.

Referring to the figure, (a) shows a transmission request frame (RTS frame), (b) shows a transmission enable response frame (CTS frame), and (c) shows a data frame.

Referring to FIG. 5A, the RTS frame includes an octet 120b for recording the medium reservation time and a destination MA.
Octet 120d for recording the C (Media Access Control) address (address of the destination terminal).

Referring to FIG. 5B, the CTS frame includes an octet 121b for recording the medium reservation time.

Referring to FIG. 5C, the data frame has a portion 122d for recording the data body and an octet 12 for recording the MAC address of the data transmission destination.
2c and a portion 122e for recording an INH flag indicating succession of medium access right to the destination terminal.

The terminal receiving the data frame in which the INH flag is set can continue to use the medium for the time reserved by the terminal transmitting the data.

FIG. 1 is a flow chart showing a data transmission process performed by the terminal shown in FIG. Referring to the figure, if the data transmission process is started in step S200, it is determined in step S202 whether or not a medium reservation is made by another terminal. Step S20
The data transmission process is on standby until it is determined to be NO in 2.

In step S204, it is determined whether it is expected to receive response data from the communication destination terminal after the data transmission.

Here, when it is predicted that the response is received from the communication destination terminal, for example, when the terminal sends data requesting the transfer of the data file to the communication destination terminal,
There may be a case where it is expected that data for confirmation will be received from the communication destination after communication. These are predicted based on the processing by the application protocol.

If YES in step S204, in step S208 the data to be transmitted (first
Octet 120b for recording the medium reservation time of the RTS frame of FIG. 5A, where the time required for transmitting the data of the received data (second data) by the response is set as the medium reservation time. Recorded in. After that, the RTS frame is transmitted to the terminals within the communication range.

In step S212, it is determined whether a data collision has occurred. If NO in step S212 (if the CTS frame is normally received from the communication destination terminal), in step S216, the process illustrated in FIG.
The INH flag is set in the portion 122e for recording the INH flag of the data frame shown in (c). Thereafter, the data frame is transmitted. Step S216
The time required to transmit the data frame in step S2 is
It corresponds to the time required to transmit the first data set in 08.

In step S218, a response data frame is received from the terminal that transmitted the data. The time required for this reception corresponds to the time set as the time required for the communication of the second data in step S208. That is, the time required for transmitting and receiving the data frame in steps S216 and S218 is set as the medium reservation time in step S208.

When the processing in step S218 ends,
In step S220, the data transmission process ends.

On the other hand, if NO at step S204,
In step S206, the time required for transmitting the data frame to the destination terminal is set as the medium reservation time. After the medium reservation time is recorded in the octet 120b which records the medium reservation time of the RTS frame shown in FIG. 5A, the RTS frame is transmitted to the external terminal.

In step S210, it is determined whether data collision has occurred. If NO in step S210, in step S214, the place 122e for recording the INH flag of the data frame shown in FIG. 5C.
INH flag is cleared. The data frame with the INH flag cleared is transmitted to the communication destination terminal. Here, the time required for data frame transmission in step S214 corresponds to the time set as the medium reservation time in step S206.

When the processing in step S214 ends,
In step S220, the data transmission procedure ends.

If YES is determined in step S212 or S210, step S is performed.
At 222, it is determined whether the number of data transmission attempts exceeds the number of retransmissions. Here, the number of retransmissions is a numerical value indicating the limit of the number of times of retrying transmission when data transmission fails.

If NO in step S222, the processes from step S202 are repeated.

On the other hand, if YES in step S222, the device user is notified that communication has not been performed, and then the data transmission procedure ends in step S220.

FIG. 4 is a flow chart showing a process when the terminal shown in FIG. 2 receives data.

Referring to the figure, if the data receiving process is started in step S230, the destination MAC address in the RTS frame received in step S232 is compared with the address of the own terminal, and the data transmission is performed by itself. It is determined whether or not it has been performed for the terminal.

If YES in step S232, the medium reservation time is read from the medium reservation time recording octet 120b stored in the RTS frame received in step S234, and the read medium reservation time is CTS.
Octet for recording medium reservation time in frame (Fig. 5
It is recorded in 121b) in (b). The CTS frame in which the medium reservation time is recorded is transmitted to the terminals within the communicable area.

In step S236, it is determined whether data collision has occurred. NO in step S236
If so, in step S238, the subsequently transmitted data frame is received.

In step S240, it is determined whether or not there is a response data frame to be transmitted corresponding to the data frame received.

If YES in step S240, it is determined whether or not the INH flag recorded in the data frame received in step S242 is set.

If YES in step S242, it is determined in step S244 whether a data frame of response data can be transmitted within the medium reservation time.

If YES in step S244, a response data frame is transmitted in step S246, and the processing from step S232 is repeated.

Note that YES in step S236, or
If NO in step S240, S242 or S244, the process from step S232 is repeated.

If NO in step S232, it is determined in step S250 whether an RTS frame for another terminal has been received. This determination is made when the comparison result between the destination MAC address in the received RTS frame and the own address does not match.

If YES in step S250, a time (medium access time) for suspending or delaying access from the medium reservation time recorded in the RTS frame received in step S254 is set. During the medium access time, the terminal cannot communicate with the external terminal.

After the processing in step S254, the processing from step S232 is repeated.

If NO in step S250, it is determined in step S252 whether or not a CTS frame has been received by another terminal. CTS for other terminals
The fact that the frame was received means that the terminal is RTS.
CT alone even though no frame is transmitted
It is determined by the reception of the S frame.

If YES in step S252, the time (medium access time) during which the terminal cannot communicate with other terminals from the medium reservation time recorded in the CTS frame received in step S256. Is set.

When the processing in step S256 ends,
The process from step S232 is repeated.

If NO in step S252, the processes from step S232 are repeated.

That is, data exchange between the communication devices in this embodiment is performed as follows.

Referring to FIG. 6, at time t0, terminal A
When the terminal B transmits the data for which the response from the terminal B is expected, when the medium reservation time in the RTS frame transmitted at time t0 in advance, the data (the first data ) And the data from the terminal B to the terminal A (second data)
Is recorded as the medium reservation time. The RTS frame is transmitted to all terminals existing in the area where data can be transmitted.

At time t1, the terminals B and C are
The RTS frame transmitted from the terminal A is received. Here, in the terminal C, by comparing the MAC addresses, R
Since the MAC address recorded in the TS frame and the MAC address of the own terminal do not match, during the medium reservation time recorded in the RTS frame (time t1 to t
In 7), transmission / reception of data is stopped.

On the other hand, in the terminal B, since the MAC address recorded in the RTS frame and the MAC address of its own terminal match, all the terminals existing in the communicable area of the terminal B at the time t2. Send a CTS frame.

Here, since the terminal D does not match the MAC address recorded in the received CTS frame with the MAC address of its own terminal, during the medium reservation time recorded in the CTS frame (from time t3 onward). At t7), transmission / reception of data is stopped.

On the other hand, terminal A, which has received the CTS frame from terminal B, transmits the data frame at time t4. Here, the INH flag in the data frame is set.

At time t5, terminal B receives all data frames from terminal A. Here, the terminal B confirms that the INH flag is set in the data frame and that the data assembly and transmission are completed within the reserved time, and the time t6 is reached.
At, the data frame of the response is transmitted to the terminal A. At time t7, terminal A receives the data frame of the response from terminal B, and the communication processing ends.

When terminal A transmits to terminal B data for which no response from terminal B is expected, the conventional processing shown in FIG. 8 is performed. However, for simplification of the procedure, transmission and reception of the ACK frame will be omitted.

That is, in the prior art, when data is transmitted from terminal B to terminal A after data is transmitted from terminal A to terminal B as shown in FIG. Although it was necessary to exchange the RTS frame and the CTS frame before transmitting each data frame, according to the implementation of the present invention, a combination of the RTS frame and the CTS frame as shown in FIG. It is possible to realize bidirectional data exchange between the terminal A and the terminal B. As a result, the data communication time can be reduced and the communication efficiency of the communication system can be improved.

In the communication of the response data frame, transmission / reception of the RTS frame and the CTS frame can be omitted, and only the terminal receiving the INH flag has the medium access right, so that the collision of data in this portion is eliminated. be able to.

In particular, the present invention relates to the second data after the first data reception.
This is effective when the time required to generate the data is smaller than the overhead related to the data transmission. Further, the reservation and succession of the medium access right are not unlimitedly performed, but the transmission data and the response data thereof are limited, so that it is possible to restrict the particular terminal from extremely holding the medium access right.

[0085]

That is, according to the invention described in claim 1, the communication time of data from the data communication device to the external communication device and the communication of data from the external communication device to the data communication device after the data communication. Time is calculated as the medium reservation time, and the calculated medium reservation time is notified to the external communication device, so that the data communication efficiency can be improved.

According to the invention of claim 2, claim 1
In addition to the effect of the invention described in, the medium reservation time is calculated after determining whether the data communication from the external communication device to the data communication device is performed after the data communication from the data communication device to the external communication device. Therefore, the data communication efficiency can be further improved.

According to the invention of claim 3, claim 2
In addition to the effect of the invention described in (3), the medium access right is determined based on the determination result of whether the data communication from the external communication device to the data communication device is performed after the data communication from the data communication device to the external communication device. Since the flag indicating succession to is transmitted to the external communication device, communication efficiency is further improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing a data transmission process performed by a communication device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a device configuration of a communication device according to one of the embodiments of the present invention.

FIG. 3 is a block diagram showing a configuration of software included in the communication device of FIG.

4 is a flowchart showing a data reception process in the communication device shown in FIG.

5 is a diagram showing a specific configuration of a frame transmitted and received between the communication devices shown in FIG.

FIG. 6 is a diagram for explaining communication processing performed between the terminals shown in FIG.

FIG. 7 is a diagram showing a specific example of a communication environment when there are a plurality of terminals.

FIG. 8 is a diagram for explaining a data communication process performed between a plurality of terminals in the related art.

FIG. 9 is a diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 20 Microcontroller 22 Wireless Interface 24 Wireless Transceiver 26 Antenna 28 Program Memory 30 Host Interface 32 Data Memory 36 Wireless LAN Adapter 38 Host Computer 40 Media Access Protocol Processor 42 Device Driver 44 Operating System 46 Network Layer Protocol Processor 48 Application Software

Claims (3)

[Claims] 1. A data communication device that communicates with an external communication device, the communication time of data from the data communication device to the external communication device, and the external communication device performed after the data communication. A data communication device comprising: a calculating unit that calculates a communication time of data from the device to the data communication device as a medium reservation time; and a notifying unit that notifies the external communication device of the calculated medium reservation time. 2. A determination means for determining whether or not data communication from the external communication device to the data communication device is performed after data communication from the data communication device to the external communication device, The data communication device according to claim 1, wherein the calculating unit calculates the medium reservation time based on the determination result of the determining unit. 3. The data communication device according to claim 2, further comprising a transmission unit that transmits a flag indicating succession of the medium access right to the external communication device based on the determination result of the determination unit.