JPS6324737A - Method for detecting illegal access in multi-access - Google Patents

Abstract

PURPOSE:To easily detect an illegal access, by setting a numeric value different with each other obtained by performing the arithmetic processing of a station number, and a common numeric value at each slave station, as the initial value of a random number, and also, performing the arithmetic processing at a control station similarly. CONSTITUTION:The slave stations 21-27 can obtain the numeric values different with each other by performing the exclusive OR of the random number distributed from the control station 1, and the station number of said station, at each slave station. The arithmetic calculation of the exclusive OR at each slave station is performed at the control station 1 similarly for each slave station, and it is possible to confirm the currently generated random number of the slave station. Since the initial value of the slave station can be recognized by the control station by providing a random number generator used in common for each slave station, the control station can recognize the generated random number of the slave station, Therefore, when the control station generates a specified probability reference value, the control station can predict the slave station which may issue a request signal corresponding to the value. In this way, it is possible to confirm the illegal access of the slave station, by detecting the request signal from the slave station other than the slave station predicted by the control station.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to LAN (Local Area Network)
The present invention relates to a method for detecting unauthorized access in a multi-access method when satellite communication is used.

[Prior art]

In LAN and satellite communications, when an unspecified number of slave stations issue channel allocation requests at unscheduled times, a multi-access protocol is used to efficiently carry out the allocation work.

However, with conventional protocols, when a large number of slave stations transmit data buckets at the same time, bucket collisions occur and packet retransmissions occur frequently, resulting in an extremely low transmission efficiency. Ta.

In addition, there have been cases where the system has become unable to transmit data at all.

Therefore, a network is formed with one control station and multiple slave stations, and the control station generates a probability reference value, and each slave station generates a random number using a random number generator, and the random number and probability are generated in each slave station. A comparison is made with a reference value, and this is repeated from once to multiple times, gradually lowering the probability reference value while sequentially aligning the random numbers, and finally selecting and accessing one slave station. Multiple access methods are possible.

However, when such a method is adopted, it is conceivable that a specific slave station may access the terminal illegally with a high probability without calculating the random numbers.

[Purpose of the invention]

An object of the present invention is to make it possible to verify whether the access of each slave station is legitimate when the above situation occurs.

[Structure of the invention]

To this end, the present invention allocates different station numbers to the slave stations, and also delivers a common numerical value from the control station to each of the slave stations, so that each slave station can read the station number and the common numerical value. The different numerical values obtained through the arithmetic processing are used as the initial values of the generated random numbers, and the cough arithmetic processing is similarly performed at the control station.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is an explanatory diagram of the embodiment. In this embodiment, first, one control station 1 is provided and is assigned to perform tasks such as data transmission scheduling and channel allocation. 2, to 2 are n slave stations, which transmit data according to commands from the control station 1.

Now, assume LAN or satellite communication. It is also assumed that the transmission path is divided into m independent channels by frequency division, time division, or other methods. One of the channels is used for control, and the remaining channels are used for data transmission.

Now, when any of the slave stations 21 to 21 transmits data therefrom, it issues a request signal to the control station 1 for data transmission channel allocation for transmitting data to the control channel.

When the control station 1 receives this request, it allocates a channel and sends channel allocation information to the corresponding slave station through the control channel, which causes the slave station to transmit data packets to the data transmission channel. I'll do what I do.

By the way, slave station 2. When too many stations among ~2n output channel allocation request signals to the control channel, the signals collide on the control channel 2, and control station 1 cannot receive this request signal from the slave station. It disappears.

In such a case, in this embodiment, the control station 1 first outputs a certain probability reference value signal Pa (0<Pa<1), and the slave stations 21 to 2 . , a random number generator (not shown) generates different random numbers independently. In this case, of course, not all of the slave stations 27 generate random numbers, and only the slave stations desiring channel assignment generate random numbers.

Then, among the random numbers generated by each slave station, a slave station that has generated a random number with a value less than or equal to the probability reference value Pa described above is selected, and the slave station is caused to issue a channel allocation request signal. As a result, if only one slave station has issued the request signal, channel allocation is scheduled with that slave station.

However, if there are two or more slave stations that have generated random numbers with a value less than or equal to Pa, the request signals will collide, so the probability standard is that control station 1 will next Output the value and have the slave station generate a random number again.

As a result, if only one slave station generates a random number less than the probability reference value Pb, that station is caused to issue a channel allocation request signal, and channel allocation is scheduled with that station.

If there are two or more slave stations that have generated random numbers less than or equal to Pb,
An even lower probability reference value Pc (0<Pc<Pb) is output to cause the slave station to generate random numbers again.

As mentioned above, the probability standard value, which is the standard for selecting random numbers, is gradually lowered (for example, 0.5-0.25-0.125...)
By doing so, any one slave station will be selected with probability.

By the way, even if the probability standard value is lowered in this way, there are cases where one slave station generates the same random number as another slave station when request signals collide between slave stations.

Therefore, in this embodiment, in such a case, the initial values of the random number generators of each slave station are made to be different from each other, and the following method is adopted to ensure that the random numbers generated at a certain time are different from each other. .

For example, if the signal of the probability reference value set at the control station L is 3 bits for simplicity, then a different station number of 3 bits is also assigned to the slave stations 21 to 2fi in advance (Fig. 2 shows this example). In this example, there are 7 slave stations, 2 to 27.
Their station numbers were set to '0OIJ-'111J.

Then, a random number 'l0IJ as a 3-bit common numerical value is generated by a random number generator in the control station 1 and distributed to each slave station. Next, if the random number delivered from the control station 1 and the station number of each slave station are exclusive-ORed, as shown in the figure, slave stations 2I to 2. , different numerical values are obtained.

Therefore, this value is used for each slave station 2. 27 as the initial value of the random number generator, a random number is calculated and generated from the initial value and changes with time, so that the same random number will not be generated at the same time in each slave station.

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

Therefore, in this embodiment, the exclusive OR calculation for each slave station described above is similarly performed for each slave station in the control station 1, so that the currently generated random number of each slave station can be confirmed. If the control station is equipped with a random number generator common to each slave station, the initial value of each slave station is clear to the control station, and therefore the random number generated by each slave station can be known.

Therefore, when the control station generates a specific probability reference value,
Since it is possible to predict which slave station will issue a request signal in response to this, it is possible to confirm that the slave station is performing unauthorized access by detecting a request signal from a slave station other than the predicted slave station. This is possible.

〔Effect of the invention〕

As described above, according to the present invention, unauthorized access can be easily detected.

[Brief explanation 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 for each slave station. Agent Patent Attorney Tsuneaki Nagao Figure 1 (001) (010) (011) (10
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Claims (3)

[Claims] (1) A network is formed by one control station and a plurality of slave stations, and one of the slave stations is selected by comparing the probability standard value generated at the control station with the random number generated at the slave station. In the multi-access method, in which the slave stations are assigned different station numbers, a common value is delivered from the control station to each slave station, and each slave station receives the station number and the common value. The mutually different values obtained by processing the numerical values are used as the initial values of the generated random numbers,
An unauthorized access detection method characterized in that the arithmetic processing is similarly performed at a control station. (2) The unauthorized access detection method according to claim 1, wherein the station number and the common numerical value are binary numbers having the same number of bits. (3) The method for detecting unauthorized access according to claim 1, wherein the calculation process is a process of calculating an exclusive OR.