JPH03201746A - Priority setting method in token ring type lan - Google Patents

Abstract

PURPOSE:To simplify the priority setting by discriminating it that the station now in use revises a 1st priority when the 1st priority in the recovered token is equal to a 3rd priority stored in a communication station. CONSTITUTION:When communication stations 11-14 reserve data transfer, a bit corresponding to the priority of a data in the station now in use is set in N-bit of 2nd priority in a token or a frame transferred in a transmission line 2 is set. Moreover, when the communication stations 11-14 revise the 1st priority, the bit of the 1st priority of the frame or the token transferred the same as the bit of the 3rd priority stored in a storage means is set/reset. Furthermore, the communication stations 11-14 discriminates it that the station now in use revises the 1st priority depending on the 1st priority of the recovered token equal to the 3rd priority stored in the storage means. Thus, the priority is simply set.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a token ring type LAN (local area information The present invention relates to a priority setting method in a token ring LAN, which is used when setting priorities in a communication network.

“Conventional technology.

In a conventional token ring type LAN, a concept of priority is used to preferentially transfer important data.

This priority includes the current priority of tokens or frames being transferred on a ring-shaped transmission path (hereinafter referred to as ring priority Pr), and the priority of data held within the communication station ( There is a reservation priority Rr used for reserving data transfer according to the data priorities P and I.

Both of these priorities have eight levels, and access control (AC
) is represented by a 3-bit value, ie, "OOO" to "111".

F Problems to be Solved by the Invention J By the way, in the conventional token ring type LAN described above, the priority setting method has the following drawbacks.

(a) Since the priority may be changed multiple times within the own station, both the ring priority P changed by the own station and the previous priority must be placed on the stack within the own station.

(b) To make a reservation, compare the current reservation priority R of the transferred token or frame with the data priority P of your own station, and select when the data priority Pm of your own station is high. , the value of the reservation priority R1 of the token or frame must be rewritten.

This invention was made in view of the above-mentioned circumstances, and is a token ring type LA that can easily set priorities.
The purpose of this paper is to provide a priority setting method in N.

``Means for Solving the Problems'' This invention provides a first priority indicating the current priority of tokens or frames transferred on a transmission path, and a communication station transmits data according to the priority of data within its own station. a second priority used for making a transfer reservation; and a third priority stored in a station that changed the first priority in order to store the change in the first priority. The priority level is represented by N bits and has (N+1) levels in which the priority is indicated by the position of each bit, and the N bits are allocated for the first and second priorities in the format of the token and the frame, The priority is determined based on the first bit set from the most significant bit of the first to third priorities, and the N bits of the second priority of the transferred token or frame are determined. Of these,
The data transfer is reserved by setting a bit corresponding to the priority of data within the local station, and the first priority of the transferred token or frame and the third priority stored in the communication station are set. The first priority is changed by setting/resetting the same bit as the priority of the token, and the first priority of the collected token is the same as the third priority stored in the communication station. The present invention is characterized in that it is determined that the own station has changed the first priority based on the fact that the priority is equal.

According to the present invention, in order for a communication station to make a reservation for data transfer, it selects one of the N bits of the second priority of the transferred token or frame that corresponds to the priority of the data within its own station. Set the bit.

In addition, in order for the communication station to change the first priority, it sets/sets the same bit of the first priority of the transferred token or frame and the third priority stored in the storage means.
Reset.

Further, the communication station determines that the first priority of the collected token is equal to the third priority stored in the storage means, so that the communication station has changed the first priority.

"Embodiment" Before describing an embodiment of the present invention, the basic idea for solving the above-mentioned problem will be explained.

First, the priority is not expressed by a value, but by allocating a predetermined number of bits for the ring priority P and reservation priority R1 in the format of the token and frame, and changing the ring priority P and making reservations. Among those multiple bits, reservation priority R,,f)
or is expressed by setting a bit corresponding to data priority P0 within the local station. Note that changing the ring priority Pr sets/resets the corresponding hit. For example, if 3 bits are assigned to priority, each priority will be as shown below.

Priority o: Oo o...■ Priority 1:001...■ Priority 2:01X...■ Priority 3: IXX...■ However, this means that X may be 1 or O.

Furthermore, the concept of a bitmap is introduced, and the previous priority is left as a history in the bits to the right of the bits set to "I" in (1) and (2), that is, in the X part.

For example, both the ring priority P and the reservation priority R of a frame transferred to a certain communication station A are "001".
”, and the data priority of own station A is P.

If the priority is 2, this communication station A sets the reservation priority Rr to "011" and transfers the frame.

Then, communication station B, which is the source of the frame, sets the ring priority P of the recovered frame, the reservation priority R, and the own station B.
, whichever is larger (hereinafter referred to as max[Rr, P j), and the data priority P0 in
When x[Rr, Pyu] is greater than the ring priority Pr, the bit of the ring priority P corresponding to the priority of max[Rr+P+++] is set. Now, assuming that data priority P is priority I, ll1a has [
Since the priority of Rr and P- is priority 2, this communication station B generates a token with the ring priority Pr set to "011".

Note that the bits set by the local station must be stored in a register within the local station as a bit map, but there is no need to store them on a stack as in the conventional case.

Furthermore, when making a reservation, the own station with the reservation priority R, does not compare the reservation priority Rr of the transferred token or frame with the data priority P1 of the own station, as in the past. It is sufficient to set the bit corresponding to the data priority Pyu unconditionally.

In addition, by not providing a bit corresponding to the lowest priority (corresponds when all bits are 0), there is an advantage that reservation of the lowest priority can be prevented and one bit can be omitted.

By adopting the concept explained above, priorities can be easily set.

Next, the respective formats of the token and frame used in this invention are shown below.

(a) Token format SD ACHD Here, SD is a starting delimiter (1 octet) that indicates the start of a token, and AC has information regarding transmission rights and information for transmission reservation, and is used to distinguish between tokens and frames. ED is an ending delimiter (1 octet) indicating the end of the token.

(b) Frame format SD ACFCDA SA INFOFCS ED F
S Here, SD is a starting delimiter (1 octet) indicating the start of a frame, and AC has information such as frame priority and reception of reservations from other communication stations,
Access control (1 octet) also includes information for distinguishing between tokens and frames, and FC is frame control (1 octet) that includes information on frame type.

In addition, DA and SA are the destination address and source address (2 octets) that contain information about the destination and source address of the data, respectively, and INFO is the data part to be transmitted, which is 0 to 136 in one frame. This is information that can transfer octets of data.

Additionally, the FCS is a frame test sequence (2 octets). This information is used to test whether information has been dropped or changed during frame transfer.
FC, DA, SA, and INF excluding the start frame sequence and end frame sequence among frames
The part O is the object of inspection.

In addition, ED is an ending delimiter (1 octet) that indicates the end of the frame, and FS is a frame status (1 octet) that holds information such as whether the frame has been read or not and is used to determine abnormalities. .

Next, among the above-mentioned token and frame formats, access control (AC') is particularly relevant to this invention.
and frame control (FC) will be explained in more detail.

(a) Access control (AC) P 3P 2 P 1T M R3R2R1(')
p+ (i=1 to 3) is a priority index bit and indicates the ring priority P of a token or frame.

Here, a specific example of the priority index will be shown.

P 3P 2 F 000: Ring priority (0) 00 l: Ring priority (1) 0 1 h,: Ring priority (2) I hzhl
: Ring priority (3) In the above case, there are four levels of priority, and the lowest priority is "000". Data with the lowest priority can be divided into a plurality of frames and transferred continuously with one token acquisition, but data (frames) with other priorities cannot be divided and transferred.

However, a frame with a high priority can interrupt the divided transfer, and the divided transfer is temporarily interrupted, the high priority frame is transferred, and the continuation of the divided transfer is transferred again.

In addition, high priority is P3. P2. Corresponding to each bit of P l, the highest priority is P3=1. MSB side,
That is, when looking at the bits from the leftmost bit (P3) side, the priority level is the bit that becomes l for the first time.

In addition, a high-priority reservation indicator (described later) for the token or frame currently being transferred is
If the agreement is made, the transmitting communication station has ring priority P.
A token or frame with a high r value is issued, but in this case, an “I” is placed further to the left of the priority pit row before the change.
Therefore, the priority index h+, h2 mentioned above
In this section, the priority before the change can be kept as a history.

Then, when the transfer of the higher priority frame is finished,
The station that manipulated the priority removes the manipulated bit, returns it to the priority token of the part of the history, and releases the token. If there is no history, a token with priority O is issued.

(ii) T is the token bit, 0 for token;
It is 1 in the frame.

(Mountain) M is a monitor bit used to check to prevent frames or tokens with a priority higher than O from continuing to circulate on the ring.

(iv) R+ (i = 1 to 3) is a reservation index bit indicating reservation priority Rr.

Here, a specific example of the reservation index will be shown.

R3R2R3 000: No reservation 00 l: Reservation priority (1) 01'X: Reservation priority (2) IXX ・Reservation priority (3) However, this means that X may be either I or 0.

Note that a communication station that has data with a high priority sets a bit corresponding to the priority among the reserved bits in order to acquire the right to issue the next frame. The communication station that retrieved the frame then checks the reservation index bits of that frame and sets the corresponding priority (the leftmost bit set among the three bits) to the corresponding bit of the ring priority Pr. issue a token.

Further, similarly to the ring priority PT, the reservation priority Rr is determined on the MSB side, that is, on the leftmost ring (R3) side.

Therefore, even if multiple bits are set in the reservation index, the leftmost bit is significant and the other bits are ignored.

(b) Frame control (FC) F, Fo Dr Dns Dne SD3 SD2 S
DI) PL (i = 1.2) is a frame indicator bit, "00" indicates ~fAc (media access control) frame of information for managing and maintaining the network, and "Ol" indicates upper layer LLC. (Logical link control) frame, “IX” indicates that it is undefined.

(ii) Df is "0" indicating a non-divided frame, and "I" indicating a divided frame.

(iii) Dns and Dne are "00" for the undivided frame, "01" for the first frame of the divided frame, and "10" for the first frame of the divided frame.
"" indicates the end frame of the divided frame, and "II" indicates the intermediate frame of the divided frame.

(iv) SD□ (i=1 to 3)) indicates data priority P, when Df=0. Data priority P. indicates the priority of the data itself, not the ring priority indicator for the actual transfer on the ring.

The ring priority Pr is such that when data is transferred on the ring, data with a higher priority than the priority index of a token is transferred with the priority Pr of that token. For this reason, the priority of the data is not correctly communicated to the other party. Therefore, by giving the priority of the data itself to the data priority P, the priority of the data can be conveyed to the transfer destination.

Furthermore, the data priorities P and n are the ring priorities P and n described above.
, and reservation priority R1, there are four types, “100
” is the most popular.

On the other hand, SD+(i=1 to 3)) indicates the division sequence number when Df=1. This is to check whether or not the divided frames are omitted during divided transfer.The first frame is "000" and 1
The number is increased by increments, and when it reaches "111", it returns to "000".

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a token ring type LAN according to an embodiment of the present invention. are communication stations that perform data communication with each other, and 2 is a transmission line such as a shielded twisted pair wire or an optical fiber cable that connects the communication stations 1 and 1° in a ring shape.

Here, a block diagram of the configuration of the communication station 1 is shown in FIG.

In FIG. 2, 3 is a LAN connection unit, which is connected to the transmission line 2 and is used to receive the loquat signal SFT transferred from another communication station 1 and to receive the loquat signal SFT from other communication stations! control the transmission of the signal Syr to be transferred to. 4 is a data processing unit, which processes the received data DR received and decoded by the LAN connection unit 3, and processes the received data DR received by the LAN connection unit 3, and processes the received data DR received by the LAN connection unit 3, and
and processing of transmission data DT to be transmitted.

Further, in the LAN connection unit 3, 5 is a receiving unit that receives the signal SFT transferred via the transmission path 2, 6 is a decoding unit that decodes the frame/token bit string F/TBA from the signal SFT, and 7 is a receiving unit. This is a bit analysis unit that constantly inspects the frame/token bit string F/TBA and detects the timing signal Sll regarding the start/end etc. of the frame/token bit string F/TB8, detects the ring priority Pr and the reservation priority R1, and It generates and outputs a frame bit string FBA.

Now, 8 is a reception control section, which controls the frame bit string FB.
A is input, it is determined whether this frame bit string FBA is addressed to the local station, and the received data DR addressed to the local station is output. Reference numeral 9 denotes a received data output section which inputs the received data DR and outputs it to the data processing section 4 based on a reception control signal RCTL output from the data processing section 4.

In addition, 10 is a frame/token bit string F/TBA
A bit delay unit that rewrites bits while relaying l! 12 is a transmission control unit, which inputs the transmission data DT to be transmitted and the transmission control signal TCTL outputted from the data processing unit 4, and outputs the transmission data DT based on the transmission control signal TCTL; While generating the token bit string TBA, the transmission data input unit 1
By outputting a data request signal DR to the transmission data input section 11 based on the transmission instruction signal TS and transmission end signal TE output from the transmission data input section 11, the transmission data D1 is input, a frame bit string FBA is generated, and a token is generated. Output according to the ring protocol. This frame bit string FBA is generated based on the data priority P extracted from the transmission data Dr, the ring priority Pr output from the reception bit analysis section 7, the reservation priority R, and the timing signal STM. .

13 is a transmission reservation unit which inputs max[Rr, PmE output from the transmission control unit I2, and selects the bit delay 110 that corresponds to the leftmost bit among the 3 bits of priority. Frame/token bit string F/
Set bit RI of the reservation index of T EA. I4
is a transmission selection section that selects and outputs either the frame/token bit string F/TEA outputted from the bit delay section 10 or the frame/token bit string F/TEA outputted from the transmission control section 12. Note that this selection is performed using a selection signal S SE output from the transmission control unit I2.
Based on L.

Further, 15 is an encoding unit that encodes the frame/token bit string F/TEA output from the transmission selection unit 14;
16 is a transmitter that transmits the output signal SFT of the encoder 15 to another communication station (2) via the transmission path 2;

In such a configuration, first, communication station II has data priority P. A case where data of = "001" is transferred to the communication station 13 will be explained.

Communication station 1. If the ring priority Pr of the token received by the receiving unit 5, detected and generated through the decoding unit 6 and the received hit analysis unit 7 is lower than the priority “001”, that token is acquired.

As a result, the communication station I obtains the right to transmit data to the transmission path 2, that is, the transmission right, and changes the obtained token to a frame start sequence in the transmission control unit 12,
Furthermore, after adding a control field, an address field, an information field, a frame check sequence, and a frame end sequence, it is output as a frame bit string FB^ together with a selection signal SSEL. At this time, frame access control (AC) and frame control (F
C) is expressed as follows. Note that "-" means that the bits are not changed. The same applies hereinafter.

00110000...(AC) 01000001...(FC) Then, the frame bit string FBA output from the transmission control unit I2 is selected in the transmission selection unit 14, and after being encoded in the encoding unit I5, the transmission unit 16 via signal S
Sent as FT.

As a result, the signal SFT is transferred from the communication station I to the adjacent communication station 12. The communication station I2 receives the signal SFT transferred via the transmission path 2 in the receiving unit 5, decodes it in the decoding unit 6, and then detects the timing signal STH in the received bit analysis unit 7, and determines the ring priority Pr and The reception control unit 8 detects and generates the reservation priority Rr and outputs the frame bit string FBA.Furthermore, the reception control unit 8 determines whether the input frame bit string FBA is addressed to the own station. In this case, since it is not addressed to the local station, the received data DT is not output.

Next, the bit delay unit IO rewrites the bits while relaying the frame bit string FBA.

Communications station now! , has data priority P. Consider a case where there is transmission data D1 to be transferred to communication station l with = "001". As a result, the transmission reservation unit 13 can control the bit delay unit l.
At bit R1 of the reservation index of the frame bit string FBA that is passing through
Of the three priority bits of Rr and Pff1F, bit manipulation is performed at the position of the bit corresponding to the value "1" set to the leftmost side.

Now, the reservation priority is Rr-"OOO" and the data priority Pffi is "001", so of the three bits mentioned above, the rightmost bit is operated, and the reservation index of the frame bit string FBA is The value "■" is set to the rightmost bit of bit R1, and as a result, reservation priority Rr="00"
1'' bit string. Here, a specific example of access control (AC) of the frame bit string FBA is shown below.

1 ・ ・ ・ (AC) Then, since the local station is not transmitting data at the moment, the frame bit string FB^ output from the bit delay unit 10 is selected in the transmission selection unit 14, and encoded in the encoding unit 15. After that, it is transmitted via the transmitter 16 as a signal SFT.

Thereby, the signal SFT is transferred from the communication station I2 to the adjacent communication station 13. The communication station 13 receives the signal SFT transferred via the transmission path 2 in the receiving unit 5, decodes it in the decoding unit 6, and then detects the timing signal STM in the received bit analysis unit 7, and determines the ring priority Pr and The reception control unit 8 detects and generates the reservation priority Rr and outputs the frame bit string FBA.Furthermore, the reception control unit 8 determines whether the input frame bit string FBA is addressed to the own station. In this case, since the data is addressed to the local station, the received data DR addressed to the local station is output. Next, the received data output unit 9 inputs the received data DR and outputs it to the data processing unit 4 based on the reception control signal RCTL output from the data processing unit 4.

Next, the bit delay section! 0 rewrites the bits while relaying the frame bit string FBA.

Now, consider a case where the communication station 13 has transmission data Dr to be transferred to the communication station l with data priority P and = "010". As a result, the transmission reservation unit 13
l1la output from the transmission control unit 12 at bit R0 of the reservation index of the frame bit string FBA that is passing 0.
Then, among the three priority bits of [Rr, P,], a bit operation is performed at the bit position corresponding to the value "1" set to the leftmost side.

Now, since the reservation priority Rr="001" and the data priority P1="010", among the three bits mentioned above,
The center bit is manipulated, and the value “■” is set in the center bit of the reservation index bit Rt of the frame bit string FBA.
is set, resulting in a bit string with reservation priority R, ,=“011”. Here, frame bit string F B
A specific example of A's access control m(AC) is shown below.

1 I . After that, it is transmitted from the transmission path 2 via the transmitter 16.

Note that the operation of the communication station 14 is the same as that of the communication station 1. Since it is the same as
The explanation will be omitted.

Next, the communication station 11 detects and generates the ring priority Pr and the reservation priority R1 from the signal SFT transferred via the transmission path 2.

Then, the transmission control unit I2 of the communication station II receives the value of the ring priority Pr, in this case, the priority “000”, and the value of the reservation priority Rr, the priority “011” from the reception bit storage unit 7. Be notified. Incidentally, now, the communication station 11 has data priority P,=
Consider a case where only transmission data DT of "000" exists.

Therefore, among reservation priority R, data priority P, and ring priority Pr, the value of reservation priority Rt is the largest, so the transmission system @ section 12 of communication station 1□ performs access control (A
A bit corresponding to the value of the reservation priority Rr is set in the ring priority index of C), and a token bit string TBA in which all the bits of the reservation index are replaced with 0 is generated and output. Here, a specific example of the access control all (AC) of the token bit string TBA is shown below.

01110000...(AC) At this time, the transmission control unit 12 selects the bit corresponding to the changed priority among the bits of the changed priority P (3-bit configuration) stored in the changed priority register. set. In the present case, ring priority P1=“0!I”.

Next, when a new token bit string TB^ is generated, the token bit string TBA is decoded into a signal SFA as in the case of frame transfer described above, and the communication station 1
from there to the communication stations 12 and 13.

Furthermore, communication station 1. It is assumed that no high-priority reservations are made.

Then, the communication station I detects and generates the ring priority P1 and the reservation priority R from the token transferred via the transmission path 2.

Next, the value of the ring priority Pr from the received bit analysis unit 7 is sent to the transmission control unit 12 of the communication station l, in this case, the value of the ring priority “Priority”
011'', the value of the reservation priority R, and the priority ``000''.Currently, the communication station l.

Consider a case where only transmission data Dτ with data priority Pm=“010” exists in .

Therefore, among the reservation priority Rr, the data priority P, and the ring priority P, the respective values of the ring priority P, r and the data priority P are equal, that is, the ring priority P, or the data priority Priority P. Since it is not larger than communication station 1
3 gets that token.

As a result, the communication station I3 obtains a transmitting unit, changes the acquired token into a frame start sequence in the transmission control unit I2, and further changes the control field, address field, information field, frame check nook, and frame end sequence. After n additions, it is output as a frame bit string FBA together with a 0 selection signal SSEL.

As a result, the frame bit string FBA output from the transmission control unit I2 is selected in the transmission selection unit 14, encoded in the encoding unit 5, and then transmitted as a signal SFT from the transmission path 2 via the transmission unit 16. . Here, a specific example of access control (AC) of the frame bit string FB^ will be shown below. At this time, the reservation index bits of the frame bit string FBA are all replaced with O in order to know the latest reservation status. However, in this case, no reservations have been made, so no changes will be made.

10000...(AC) As a result, the signal SFT is transferred from the communication station 13 to the adjacent communication station 14.

Then, after this signal SFT is transferred from the communication station l to the communication station I2, which is the transmission destination, through the communication station I, the operation in which the signal SFT is collected by the communication station l, which is the transmission source, is described in the above-mentioned frame transfer. Since this is the same as in the case of , the explanation thereof will be omitted. It is assumed that no reservation is made in any of the communication stations 1 during this frame transfer.

Next, the communication station 13 detects and generates a ring priority Pr and a reservation priority Rt from the token transferred via the transmission path 2.

Then, the transmission control unit 12 of the communication station I3 is notified by the received bit analysis unit 7 of the value of the ring priority Pr, in this case, the priority “011”, the value of the reservation priority R1, and the priority “000”. be done. Now, the communication station 13 has data priority P,...
, = "000" is present.

Therefore, among the reservation priority Rr, the data priority Pm, and the ring priority P, the value of the ring priority Pr is the largest, so the transmission control unit 12 of the communication station 13
4 is used as is to generate and output a token bit string T EA in which the bit corresponding to the data priority P□ is set in the access control (AC) reservation index bit. Here, a specific example of access control (AC) of the token bit string TBA is shown below.

01100000...(AC) Next, when a new token bit string TB^ is generated,
The token bit string TBA is decoded and sent to the communication station 13 as a signal SFT, as in the case of frame transfer described above.
from there to the communication stations 14 and 11. Furthermore, communication station I
4, it is assumed that high-priority reservations are not made.

Then, the communication station 11 detects and generates the ring priority Pr and the reservation priority R1 from the token transferred via the transmission path 2.

Next, the transmission control unit 12 of the communication station 11 receives the value of the ring priority P, in this case, the priority “011”, the value of the reservation priority R, and the priority "000"
will be notified. Now, communication station l has data priority P0-
Consider a case where only transmission data DT of "000" exists. Further, the change priority P8 is "011".

Therefore, among the data priorities P, , the most significant bit position where the value "1" is set and the change priority P.

Since the positions of the similar bit positions of P are the same, the communication station determines that it has changed the ring priority Pr, and first changes the ring priority Pr corresponding to the bit position of the changed priority P. and reset the change priority P8 bit.

As a result, ring priority Pr="001", reservation priority R,="000", data priority p,="000",
After the change priority Px becomes "00bi" and the communication station I performs the same operation as the communication station I3 described above, the communication station ■1 again
Returning to , at this time as well, the same operation as described above is performed in the communication station 11 .

As a result, the transmission control unit I2 determines the new ring priority P
Compare r with reservation priority R1 and data priority P1. In this case, all of these have priority "000", so a token bit string TBA having access control 7 (AC) shown below is generated and output.

00100000...(AC) Note that the subsequent operations are the same as those described above, so the explanation thereof will be omitted.

Flowcharts of the operations when the communication station I receives a frame and a token are shown in FIGS. 3 and 4, respectively.

"Effects of the Invention" As explained above, according to the present invention, it is possible to easily set priorities.

[Brief explanation of drawings]

FIG. 1 shows a token ring type L according to an embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of communication station 1, FIG. 3 is a flowchart showing the operation when communication station l receives a frame, and FIG. 4 is a block diagram showing the configuration of communication station 1. 3 is a flowchart showing the operation when a token is received. 1... Communication station, 2... Transmission line, 3...
...LAN connection section, 4...data processing section,
5... Receiving section, 6... Decoding section, 7...
... Reception bit solution Fr section, 8 ... Reception control section, 9 ... Reception data output section, 10 ...
・Bit delay section, II...Transmission data manual section,
12... Transmission control unit, 13... Transmission reservation unit, I4... Transmission selection unit, 15...
Encoding section, 16...Transmission section.

Claims (1)

[Claims] In order for a communication station to reserve data transfer according to the first priority indicating the current priority of a token or frame transferred on a transmission path and the priority of data within its own station. The second priority to be used and the third priority stored in the station that changed the first priority in order to store the change in the first priority are each expressed by N bits, and each The priority level is set to (N+1) levels in which the priority level is indicated by the bit position, and the N bits are allocated for the first and second priorities in the format of the token and the frame, and the first to third The priority is determined based on the bit that is set first in terms of the most significant bit of the priority, and among the N bits of the second priority of the transferred token or the frame, the The data transfer is reserved by setting a bit corresponding to the priority of the data, and the first priority of the transferred token or the frame and the third priority stored in the communication station are set. The first priority is changed by setting/resetting the same bit of the communication station, and the first priority of the collected token is equal to the third priority stored in the communication station. A priority setting method in a token ring type LAN, characterized in that it is determined that a station has changed the first priority.