JPH0620202B2 - Multi-access method - Google Patents

Description

The present invention relates to a method of detecting unauthorized access in a multi-access method when using a LAN (local area network) or satellite communication.

[Prior art]

There is a multi-access protocol as an arrangement for efficiently performing the assignment work when an unspecified number of slave stations issue a channel assignment request at an undefined time in LAN or satellite communication.

However, the conventional protocol has a problem in that when a large number of slave stations transmit data packets at the same time, packet collisions occur, packet retransmissions frequently occur, and transmission efficiency is extremely reduced.

Further, there are cases where transmission cannot be performed at all.

Therefore, a network is formed by one control station and a plurality of slave stations, a probability reference value is generated in that control station, and a random number is generated by a random number generator in each slave station,
The random number is compared with the probability reference value, and this is repeated from once to multiple times by gradually changing the random number while gradually decreasing the probability reference value, and finally selecting one child station. A multi-access method of accessing by accessing is possible.

However, when such a method is adopted, it is conceivable that a specific slave station illegally accesses with high probability without calculating a random number.

[Object of the Invention]

An object of the present invention is to be able to verify whether or not the access of each slave station is valid when the above situation occurs.

[Structure of Invention]

To this end, the present invention performs data transmission by receiving one control station and one data transmission channel assigned from the plurality of data transmission channels by the control station via the control channel. A plurality of slave stations, wherein one or more slave stations requesting allocation of a data transmission channel among the slave stations generate random numbers different from each other, and generate random numbers through the control channel; It is taken in by the control station, a probability reference value is generated in the control station, and this is compared with the random number. Request the allocation of the data transmission channel by using the numerical value obtained by performing the arithmetic processing of the station number and the common numerical value in each slave station as the initial value of the random number. Until the slave station is narrowed down to one in which the probability reference value and the random number have a specific relationship, the probability reference value is sequentially changed, and the random number generation in the slave station is started and changed from the initial value. In addition, the above calculation is also performed in the control station so that the random number generated in each slave station is constantly monitored from the initial value, and a channel for specific data transmission is selected for one slave station narrowed down by the above comparison. A slave station that is illegally accessed is detected by comparing the monitor random number generated through the control station with the random number generated by each slave station and assigned through the control channel.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is an explanatory view of the embodiment. In the present embodiment, first, one control station 1 is provided to perform data transmission scheduling, channel assignment work, and the like. 2 _{1 to} 2 _n are n slave stations, which transmit data in response to a command from the control station 1.

Now, assume LAN and satellite communication. Further, it is assumed that the transmission path is divided into m independent channels by frequency division, time division, or another method. Then, one of the channels is used for control, and the remaining channels are used for data transmission.

When any of the slave stations 2 _{1 to} 2 _n transmits data from the slave station 2 _{1 to} 2 _n , a request signal for data transmission channel allocation for transmitting data to the control channel is sent to the control station 1. put out. Then, when the control station 1 receives this request, it performs channel allocation, and to that effect, channel allocation information is sent to the corresponding slave station through the control channel, whereby the specific data transmission channel to which the slave station is allocated is transmitted. To send data packets to.

By the way, when a very large number of the slave stations 2 _{1 to} 2 _n output a channel allocation request signal to the control channel, the signals collide with each other on the control channel, and the control station 1 receives the signal from the slave station. The request signal cannot be received.

Therefore, in such a case, in the present embodiment, the control station 1 first outputs a certain probability reference value signal Pa (0 <Pa <1), and the slave stations 2 ₁ to 2 _n each independently generate a different random number. It was generated from a generator (not shown). In this case, naturally, not all of the slave stations 2 ₁ to 2 _n generate random numbers, and only the slave stations desiring channel allocation generate random numbers.

Then, among the random numbers generated by each slave station, a slave station that generates a random number having a value equal to or less than the above-mentioned probability reference value Pa is selected, and the slave station is made to issue a channel allocation request signal. As a result, when there is only one slave station which has issued the request signal, channel allocation is scheduled with the slave station.

However, when there are two or more slave stations that have generated random numbers with a value of Pa or less, the request signals collide with each other, so that the probability reference value of Pb (0 <Pb <Pa) is next in the control station 1. To generate a random number again in the slave station.

As a result, when there is only one slave station that has generated a random number equal to or smaller than the probability reference value Pb, the station is caused to issue a channel allocation request signal and the channel allocation is scheduled with that station.

If there are two or more slave stations that generated random numbers less than Pb,
By issuing a lower probability reference value Pc (0 <Pc <Pb),
Generate a random number again in the slave station.

As described above, by gradually decreasing the probability reference value serving as a reference for selecting a random number (for example, 0.5 → 0.25 → 0.125 ...), any one of the slave stations is stochastically selected.

By the way, even if the probability reference value is lowered in this way, there may be a case where a certain slave station generates the same random number as another slave station while the request signals collide with each other.

Therefore, in this embodiment, in such a case, the following method is adopted so that the initial values of the random number generators of the respective slave stations are different from each other so that the random numbers generated at a certain time are always different from each other. .

For example, if the signal of the probability reference value set in the control station 1 is 3 bits for simplicity, the slave stations 2 ₁ to 2 _n also have 3 bits.
Assign station numbers with different bits in advance. FIG. 2 shows this example, and the slave stations are 7 stations 2 ₁ to 2 ₇ , and their station numbers are “001” to “111”.

Then, the random number generator in the control station 1 generates a random number “101” as a common 3-bit numerical value and delivers it to each slave station. Next, if the exclusive OR of the random number delivered from the control station 1 and the station number of the station is taken in each slave station, as shown in the figure, the slave stations 2 ₁ to 2 ₇ are different from each other. The numerical value is obtained.

Therefore, by setting this value as the initial value of the random number generator of the slave station 2 ₁ to 2 _7, occurs is calculated random numbers from the initial value, so we continue to change with time, the same in each slave station The same random number will not be generated at the time.

However, even in the above case, it is conceivable that any one of the slave stations will generate a random number with an illegally high probability without calculating the random number.

Therefore, in the present embodiment, the arithmetic operation of the exclusive OR in each of the slave stations described above is similarly performed in the control station 1 for each slave station starting from the above initial value, and the operation of each slave station starting from the above initial value is performed. The current generated random number can be confirmed. If the control station is equipped with a common random number generator for each slave station, the initial value of each slave station is clear by the control station.
It is possible to know the random number generated by each slave station.

Therefore, when the control station generates a certain probability reference value,
In response to this, it is possible to predict which slave station will output the request signal, so by detecting the request signal from a slave station other than the predicted slave station, confirm that the slave station is making unauthorized access. Can be done.

〔The invention's effect〕

From the above, according to the present invention, it becomes possible to easily detect an unauthorized access.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of random number initial value setting of each slave station.

Claims (3)

[Claims] Claim: What is claimed is: 1. A control station, and a plurality of data transmission channels, each of which receives one data transmission channel from a plurality of data transmission channels by the control station via the control channel. A slave station, wherein one or more slave stations requesting allocation of a data transmission channel among the slave stations generate mutually different random numbers, and the random numbers are generated through the control channel to the control station. The control station generates a probability reference value and compares it with the random number.At this time, a different station number is assigned to each slave station in advance, and a common numerical value from the control station is assigned to each slave station. A mobile station that has requested the allocation of the data transmission channel by using the numerical value obtained by calculating the station number and the common numerical value by each slave station as an initial value of the random number Until the probability reference value and the random number are narrowed down to one having a specific relationship, the probability reference value is sequentially changed, and the random number generation in the slave station is started and changed from the initial value. The random number generated in each slave station is constantly monitored from the initial value by performing the calculation also in the control station, and a specific data transmission channel is selected as the control channel for one slave station narrowed down by the comparison. A multi-access method in which a slave station that makes an unauthorized access is detected by comparing the monitor random number generated through the control station with the random number generated through each slave station. 2. The station number and the common numerical value are binary numbers having the same number of bits.
The multi-access method described in the section. 3. The multi-access method according to claim 1, wherein the arithmetic processing is processing for taking an exclusive OR.