JP3043192B2 - Token simultaneous acquisition prevention method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a token simultaneous acquisition prevention system, and more particularly, to a token passing system in which a plurality of stations having duplicate station numbers try to join a line at the same time due to an error or other factors. It relates to a token simultaneous acquisition prevention system.

[0002]

2. Description of the Related Art Conventionally, in a system in which a plurality of devices such as a computer and a controller are connected to one network to perform communication by a packet switching system, network management is performed by individual stations (network terminal exchanges). .

In such a system, when data is transmitted and received between stations, the transmitting station first obtains the transmission right, sets the destination station address to the destination station address of the transmission frame, and sends the transmission frame to the network. I do. Each station checks the destination station address of the transmission frame on the network, and fetches data when the destination station address matches the station number of the own station.

In such systems, for example, LAN
2. Description of the Related Art A token passing network system in which control information for acquiring a transmission right called a token, which is widely used in a (Local Area Network), is transmitted in a transmission path is well known.

In this token passing type network system, at the time of token acquisition processing after power-on, the station monitoring number is determined for each station using its own station number as a parameter, and the station number is determined. Causes a difference in line monitoring time for each station due to the difference in
A method for preventing the simultaneous acquisition of tokens by a plurality of stations by this is known (patent pending).

[0006]

Normally, the station number is set by software or hardware. However, in each case, the same station number is erroneously set to a plurality of stations because it is manually performed. Sometimes.

As described above, if the same station number is set for a plurality of stations, the line monitoring time is determined using the own station number as a parameter for each station so that the tokens are not simultaneously obtained for the plurality of stations. Even in this case, if a plurality of stations having the same station number are started up at the same time, the line monitoring times of the plurality of stations become the same, so that a plurality of stations may acquire a token at the same time. When a plurality of stations acquire the token at the same time as described above, the right to transmit data is given to the plurality of stations at the same time, and the data is simultaneously transmitted from the respective stations to the network. As a result, an abnormality such as data collision occurs on the network.

[0008] As described above, the above-mentioned problem caused by the duplication of the station number is not only difficult to find, but also causes the network not to function properly and becomes a serious obstacle to the entire system.

An object of the present invention is to provide a token simultaneous acquisition prevention system in which even when a plurality of stations having overlapping station numbers are started up at the same time, a plurality of stations do not simultaneously acquire a token.

[0010]

According to the present invention, the dummy means adds or does not add a dummy frame to the token frame transmitted after the line monitoring ends based on the value of the random number by the random number element. . And
Even if a plurality of stations whose station numbers are duplicated due to errors or other factors are started up at the same time, a shift occurs in the line monitoring start timing depending on the presence or absence of the dummy frame added to the token frame. As a result, the station that first recognizes the presence of another station in the line interrupts the token acquisition process. This prevents simultaneous acquisition of tokens by stations having overlapping station numbers. For example, a value of a timer included in each station is used as the random number element.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows two stations 0a and 0b in which the same station number “0” is set in duplicate, and another station number “N”.
The timers a, b, and n included in a total of three stations of the station N for which (0 <N) are set are shown. Timers a, b,
And n each use an arbitrary bit, for example, an 8-bit or 16-bit timer. These timers a, b, or n correspond to station 0a, station 0b, or station N, respectively.
Are started when the power is turned on by turning on the power, and time counting is started, and “1” is repeated by the system clock, and the value is sequentially increased. The system clocks of the stations 0a, 0b, or N do not oscillate at exactly the same cycle, and therefore, even if they are started simultaneously, the values of the timers a, b, and n differ with the passage of time. Therefore, the LSB (least significant bit) of each of the timers a, b, or n that repeats the value of “1” and “0” every clock does not always become “1” or “0” at the same time. It can be considered that one often becomes “1” and the other becomes “0” during time measurement.

FIG. 2 is a time chart showing the operation when two stations 0a and 0b with the same station number "0" set in duplicate and another station N, a total of three stations, start up at the same time. The operations of the station 0a, the station 0b, and the station N are shown from the top of the figure. In this example, the LSBs of the internal timers a, b, and n described above are used as random number elements.

In FIG. 1, when the power is turned on, the time t0
Thus, the three stations 0a, 0b, and N start up at the same time. At this time, each station first calculates and sets the line monitoring time by a predetermined formula based on the station number of the own station. As a result, the same line monitoring time T1-0 is set in the station 0a and the station 0b, and the station 0a and the station 0 are set in the station N.
A line monitoring time T1-N different from b is set. In the above calculation formula, it is assumed that the line monitoring time becomes longer as the station number becomes larger. Therefore, T1-0 <T1-N.

The line monitoring time T1 set here
−0 and T1-N are the primary monitoring times,
After the elapse of the next monitoring time, a second line monitoring time T2-0 for further confirmation is set in advance for the three stations 0a, 0b, and N.

Next, at the same time as the rise, that is, at time t0, each station starts the internal timers a, b, and n, respectively. As described above, each line monitoring time is T1
Since −0 <T1-N, the station 0a whose station number is duplicated
After the line monitoring time T1-0, both the stations 0b and 0b send out a claim-token frame (token request frame) on the line before the station N. At this time, the stations 0a and 0b refer to the internal timers a and b, respectively,
If SB is “0”, no dummy frame is added and LS
When B is "1", a dummy frame is added.

FIG. 2 shows that the LSB of the internal timer a of the station 0a is "0" at the time t1 after the elapse of the line monitoring time T1-0, so that the station 0a receives a Clam-Token frame from which no dummy frame is added. 21 is transmitted, while the LSB of the internal timer b of the station 0b is "1". Therefore, the station 0b outputs a frame 24 to which the dummy frame 25 is added in the Claim-To
This indicates that the data has been transmitted as a ken frame 26.

At this time, the station N receives its own line monitoring time T1.
Since −N> T1-0, the line is still being monitored, and therefore, the Cla transmitted from both stations 0a, 0b
By receiving the im-Token frame 21 or 26, it recognizes that another station already exists on the line, interrupts the token acquisition process at time t2, and returns to the line monitoring state by the line monitoring time T1-N again. .

On the other hand, the station 0a is a Claim-Token
After the frame 21 is sent out on the line, when the second line monitoring state is entered, the station 0b's Claim-Toke
Since the n frame 26 is received from the middle (that is, from the dummy frame 25), the existence of the station 0b cannot be recognized because the n frame 26 cannot be received as an effective frame. Therefore, next, every time the secondary line monitoring time T2-0 elapses, the claim-token frames 22, 23 for confirmation are checked.
Are sequentially transmitted on the transmission path.

On the other hand, the station 0b also has a C
After the transmission of the laim-Token frame 26 is completed, the second
At time t3 at the time of entering the next line monitoring state, the presence of the station 0a cannot be recognized because the frame 21 transmitted by the station 0a has passed and is not already on the line. Therefore, the second
The line monitoring state is maintained for the next line monitoring time T2-0.

By the way, Claim- transmitted by the station 0a
Since the Token frame 21 has no dummy frame and the Clam-Token frame 26 transmitted by the station 0b has the dummy frame 25 added thereto, the dummy line 25 is added to the start time of the secondary line monitoring after the transmission of both stations is completed. A time difference corresponding to the frame length occurs.

In other words, the start of the secondary line monitoring by the station 0a starts at the station 0b by the amount that the dummy frame is not added to the transmitted claim-token frame 21.
It is starting earlier. Accordingly, the line monitoring period T2-0 ends earlier than the station 0b. Therefore, station 0
Before b ends the line monitoring state at time T2-0, station 0
The second claim-token frame 22 for confirmation is sent out from a.

The station 0b receives the Cl transmitted from the station 0a.
Upon receiving the aim-Token frame 22, it recognizes that there is already another station on the line, stops participating in the network, and returns to the primary line monitoring state at time T1-0.

As described above, in this embodiment, even if a plurality of stations having the same station number exist in the stations started up at the same time, only one of the stations obtains the token. Therefore, it is possible to prevent occurrence of an abnormal occurrence of simultaneous token acquisition.

In the present embodiment, when the primary line monitoring time ends, the internal timers a and
Although the LSB of b is different between “0” and “1”, there is no problem even if they are the same. That is, even if the internal timers a and b are started simultaneously, an error gradually occurs, and the LSBs of the timers a and b become different bit values while repeating the second line monitoring. There is no difference in that one station will add a dummy frame to the Claim-Token frame, and only the other station that has not added the dummy frame will acquire a token.

Although the value of the LSB of the internal timer is used as a random number, the present invention is not limited to this, and any circuit that generates a different value can be used.

[0026]

As described in detail above, according to the present invention,
Even if there are multiple stations with the same station number among the stations started up at the same time, it is possible to prevent the failure of simultaneous acquisition of tokens by those stations, and maintain and control the network smoothly and normally. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a timer for each station according to an embodiment of the present invention.

FIG. 2 is a time chart illustrating an operation of each station in the embodiment.

[Explanation of symbols]

a, b, n counters 21, 22, 23, 24 Token request frame 25 Dummy frame 26 Token request frame with dummy frame added

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-226741 (JP, A) JP-A-3-23735 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/28

Claims (2)

(57) [Claims] 1. A random number element, and dummy means for adding a dummy frame to a token frame transmitted after completion of line monitoring according to a random number value of the random number element or not adding a dummy frame according to a random number value. When a plurality of stations having the same station number are simultaneously activated, a delay occurs in the line monitoring time depending on the presence or absence of the dummy frame added to the token frame, and the tokens generated by the plurality of stations having the same station number are duplicated. A token simultaneous acquisition prevention method characterized by preventing simultaneous acquisition. 2. The token simultaneous acquisition prevention method according to claim 1, wherein said random number element is a timer value in a station.