JPH03201743A - Method for sharing clock in common in ring type lan - Google Patents

Abstract

PURPOSE:To simplify the error correction of a clock by discriminating it as the generation of a reception error in a data due to the difference between a received sequence number and an expected value in a communication station other than the communication station connecting with a basic timer so as to correct the count of the timer connecting to the station now in use in response to the difference. CONSTITUTION:A communication station 1 connecting with a basic timer 3 sends a data of a sequence number corresponding to a basic clock and increments the sequence number for each transmission. On the other hand, communication stations other than the communication station 1 connected with the basic timer 3 discriminates it as the generation of a reception data error when the expected value and the received sequence number have a difference and corrects the count of the timer connecting to the station now in use depending on the difference. Moreover, the communication station 1 to which the basic timer 3 is connected transfers an initializing frame resetting the sequence number. Then communication stations other than the communication station 1 to which the basic timer 3 is connected receive the initializing frame to reset the count of the timer connecting to the station now in use. Thus, the error correction of the clock shared in common is implemented simply and efficiently.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a ring-type LAN in which a plurality of communication stations are connected in a ring shape through a transmission path and data communication is performed between these stations.
The present invention relates to a clock sharing method in a ring type LAN used when a clock is shared between a plurality of communication stations in a local area information communication network.

"Conventional Technology" In a conventional ring-type LAN, when multiple communication stations share a clock to achieve synchronization, one clock source broadcasts the basic clock to multiple communication stations in real time in a one-to-many manner. This was done by communication.

"Problem to be solved by the invention" By the way, in the conventional ring type LAN mentioned above,
Since the clock must be transferred in real time, it is not possible to retransmit the lock due to an error.

Therefore, until now, there has been no means to efficiently correct errors, mainly to take measures against missed clocks.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a clock sharing method in a ring-type LAN that can easily and efficiently correct errors in a shared clock.

"Means for Solving the Problem" The present invention provides a ring-type LA in which a plurality of communication stations are connected in a ring shape through a transmission path and data is transferred between these stations.
In N, a timer is connected to each of the plurality of communication stations, one of the timers is used as a basic timer that generates a basic clock, and the communication station to which the basic timer is connected corresponds to the basic clock. The communication station other than the communication station to which the basic timer is connected has an expected value for the sequence number in advance, and the value of the sequence number is incremented each time it is sent. It is characterized by determining that a reception error of the data has occurred due to a difference between an expected value and the value of the received sequence number, and correcting the count value of the timer connected to the local station according to the difference. There is.

"Operation" According to this invention, the communication station to which the basic timer is connected,
Data with a sequence number corresponding to the basic clock is sent out, and the value of the sequence number is incremented each time it is sent out.

On the other hand, communication stations other than the communication station to which the basic timer is connected,
If there is a difference between the expected value and the value of the received sequence number, it is determined that a data reception error has occurred, and the count value of the timer connected to the own station is corrected according to the difference.

Further, the communication station to which the basic timer is connected transfers an initialization frame in which the sequence number has been reset.

Then, communication stations other than the communication station to which the basic timer is connected reset the count value of the timer connected to itself by receiving the initialization frame.

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

First, FIG. 2 shows an example of the configuration of a conventional ring type LAN. In this figure, 11~! 8 is a communication station that performs data communication with each other, and 2 is a communication station 1. ~1. 3. A transmission line connected in a ring shape between shielded twisted pair wires or optical fiber cables; 3. -38 are timers connected to each communication station (1) to (16), respectively.

Furthermore, timer 3. generates the basic clock and other timer 3
．． 36 can be synchronized with the basic clock by the function of the tick MAC frame, which will be described later.

In addition, each communication station 1. .about.16 are divided into several groups having the same address for each of a plurality of communication stations that require the same basic clock. For example, communication stations I3 to l in FIG.
, is treated as one group, and one address is assigned to that group. Then, the communication station 11 generates a frame from the clock-related data and transfers it to the group having that address.

At this time, the communication station 11 attaches a clock sequence number to the frame, increments the value each time, and transfers the frame. On the other hand, in the communication stations 13-l that receive the frame, timers 33-3.l connected to the own stations are used. It is assumed that the count value of is behind the count value of the timer 31 and has an expected value in advance for the above-mentioned sequence number.

Therefore, for example, when the expected value of the sequence number is "3" and the sequence number detected from the transferred frame is "3", the communication stations 13 to 15 can determine whether the lock transfer is normal or not. judge that it has been done.

In addition, if the sequence number detected from the transferred frame is "4" even though the expected value is r3J, it is determined that one data has been dropped, and the communication station l, ~15 side can correct clock errors.

Furthermore, even if only communication station l drops data within the same group, clock errors can be corrected individually.

By using the above concept, error correction of a shared clock can be easily and efficiently performed.

Next, among the MAC (media access control) frames used for ring-type LAN management, the format of the tick MAC frame used for synchronizing the above-mentioned timers is shown below.

Note that a tick refers to a timing for synchronizing the clocks of timers connected to each communication station.

SD ACFCDA SA INFOFC3ED PS
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, as well as information for distinguishing between tokens and frames. FC is a frame control (1 octet) containing information such as frame type. still,
The frame control (PC) of the tick MAC frame is 0.
It is 0H.

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.
PC, 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) indicating 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 for determining abnormalities.

Next, of the above formats, the destination address (DA) and information (INFO) fields, which are particularly relevant to the present invention, will be explained in more detail.

(a) Destination address (DA) GFAAAAAAAAAAAAA^ G-"O" indicates F and 14 A's are addresses of individual communication stations, G="l" and F-'0" indicates 14 A's. In the group address G="I" and F"l", the 14 A's are interpreted as functional addresses assigned to the network management function and the additional function, respectively.

When a functional address is used as the destination address, data is transferred to the functional unit of the communication station that has the specified functional unit.

In the case of the tick MAC frame described above, the following functional addresses are assigned.

That is, up to eight basic clocks can be defined.

Function Function Address DA Tick 0OIHC00IH Take 2 0028 COO2H Take 3
004 HC004H Tick 4 008HCOO8H Take 5 0108 C0IOH Take 6
0208 CO20H take 7 040HC
040H Take 8 080HC080H ('b) Information (INFO) The information field of the MAC frame contains information such as commands and responses (hereinafter referred to as vectors) transferred to manage the media access layer. It consists of the format shown below.

VL MI SVL SVI 5VV---3VL S
VI 5VV(i)VL is 16-bit binary,
Represents the number of octets in the vector, that is, the vector length.

0004H≦VL≦FFFFH (ii) Vl is a 2-octet vector ID divided into three fields.

ddddsssscccccccc dddd is a destination class, and contains an identifier indicating which functional unit in the destination communication station the frame is to be passed to.

5sss is the transmission source class, and contains the functional unit identifier of the communication station on the transmission side.

Further, CCCCCCCC,C contains a vector code indicating the function. Note that the tick MAC frame vector ID (V
l) is 8860H.

(iii) SVL is the subvector length. A subvector is information for adding more detailed information to a vector. However, there may be no subvectors.

Further, the subvector length is expressed in 8-bit binary as the length expressed in the number of octets of the subvector.

The length also includes SVL.

(iv) SVI is an l-octet subvector [D]. Note that the tick MAC frame subvector ID (SV
I) is 6511.

(v) S V V is a subvector value and a parameter of the subvector. Even if there is a subvector ID, there may be no subvector value. Length and format are subvector ID
Determined by Note that the subvector value (SVV) of the tick MAC frame is reset, 5equence
It is. reset is the l bit, which is used to reset the timer that is synchronized with the specified basic clock.
quence is 7 bits and is used to correct the above-mentioned clock deviation due to communication errors.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a communication station according to an embodiment of the present invention! FIG. 2 is a block diagram showing the configuration of FIG. 2. In this figure, parts corresponding to those in FIG. In FIG. 1, 4 is a LAN connection part,
Reception of signal SFT connected to transmission line 2 and transferred from other communication station I, and other communication station! control the transmission of the signal SFT to be transferred to. Reference numeral 5 denotes a data processing unit, which processes the received data DR received and decoded by the LAN connection unit 4 and the transmitted data DT to be transmitted to other communication stations 1.

Further, in the LAN connection unit 4, 6 is a receiving unit that receives the signal SFT transferred via the transmission path 2, and 7 is a receiving unit that receives the signal SF.
A decoding unit decodes the frame/token bit string F/TBA from T, and 8 is a received bit analysis unit, which constantly inspects the frame/token bit string F/TBA and determines the start and end of the frame/token bit string F/TB6, etc. Detection of the timing signal STH related to the ring priority, detection and generation of the ring priority Pr and reservation priority Rr, and output of the frame bit string FBA are performed.

Furthermore, 9 is a reception control unit, and the frame bit string F
BA 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. IO is a received data output unit that inputs the received data DR and outputs it to the data processing unit 5 based on the reception control signal RCTL output from the data processing unit 5.

In addition, 11 is a frame/token bit string F/T B
A bit delay unit 12 rewrites bits while relaying A, and inputs the transmission data DT to be transmitted and the transmission control signal TCTL output from the data processing unit 5,
A transmission data input unit 13 outputs transmission data D7 based on a transmission control signal TCTL, and 13 is a transmission control unit that generates a token bit string TBA and also outputs a transmission instruction signal TS and transmission end output from the transmission data input unit 12. By outputting the data request signal DR to the transmission data manual unit 12 based on the signal TE, the transmission data DT is
is input, a frame bit string FBA is generated and output according to the token ring protocol. The generation of this frame bit string FBA is based on the priority P of the data itself extracted from the transmission data DT and the priority of the current token or frame on the ring output from the reception bit analysis unit 8 (hereinafter referred to as ring priority). Pr), the priority Rr of reservations made based on the data priorities P, . . . in other communication stations, and the timing signal St.

Masuko, I4 is a transmission reservation unit, which inputs the larger of the reservation priority Rr and the data priority P output from the transmission control unit I3 (hereinafter expressed as max [Rr, P m]). The bit R of the reservation index of the frame/token bit string F/TBA that is passing through the bit delay unit If, which corresponds to the leftmost bit among the three priority bits,
Set. 15 is the frame/token bit string F/TBA output from the bit delay unit II and the transmission control unit I
Frame/token bit string F/T output from 3
This is a transmission selection section that selects and outputs either B or A. Note that this selection is made by the transmission control section! This is performed based on the selection signal SsaL output from 3.

Furthermore, 16 is a transmission selection section! an encoding unit that encodes the frame/token bit string F/TBA output from 5;
A transmitter 17 transmits the output signal SFT of the encoder I6 to another communication station I via the transmission path 2.

In the data processing unit 5, 18 is the received data Dl.
a tick frame detection unit that detects a tick MAC frame from l and outputs a sequence number or a reset pulse R; 19 a latch that holds the sequence number;
20 is a free run counter, and 21 is a comparator that compares the output value of the latch 19 and the value of the counter 20, and outputs a pulse P that increments the counter value by 1 if these values are different. . Note that the value of the counter 20 is cleared by the reset pulse R1.

Furthermore, 22 is a tick frame generation unit which inputs the pulse P output from the timer 3 and generates a sequence consisting of a predetermined functional address, reset-“0” and the lower 7 bits of the current count value of the timer 3. A tick MAC frame of the number is generated, and a pulse P3 is outputted to increment the value of the free run counter 23, that is, the sequence number by I. In addition, the counter 23
The value is cleared by the reset pulse R2 input from the upper layer, and at the same time, the tick frame generation unit 22 generates an initialization frame.

It is assumed that the communication stations 13 to I have tick 11, that is, the functional address is 001H.

In such a configuration, first, a timer 3 is installed in the communication station 11.
1 to pulse P, the tick frame generation unit 22 sets the function address to 001H and reset =
It generates a tick MAC frame with a sequence number consisting of "0" and the lower 7 bits of the current count value of the timer 31, and outputs a pulse P3 to increment the value of the free-run counter 23, that is, the sequence number l. .

As a result, the communication station 11 that has acquired the token circulating on the transmission path 2 has the right to transmit data on the transmission path 2, that is, the transmission right, and uses the acquired token in the frame start sequence in the transmission control unit 13. After adding a control field, an address field, an information field, a frame check sequence, and a frame end sequence, the data is output as a tick MAC frame bit string FB^ together with a selection signal SSEL.

Then, the transmission selection section 15 selects the tick MAC frame bit string FBA output from the transmission control section 13, and after encoding it in the encoding section I6, the transmission section 1
7 and is transmitted as a signal SFT.

As a result, the signal SFT is transmitted from the communication station II to the neighboring communication station 1! will be forwarded to. The communication station l receives the signal SFT transferred via the transmission path 2 at the receiving unit 6, decodes it at the decoding unit 7, and then detects the timing signal STH and determines the ring priority at the received bit analysis unit 8. Detection and generation of Pr and reservation priority R, and tick MAC
The frame bit string FB^ is output.

Furthermore, the reception control unit 9 determines whether the input tick MAC 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 11 rewrites the bits while relaying the tick MAC frame hit string FBA. Now, consider a case where communication station I has transmission data D7 to be transferred to communication station 14 with data priority P = "001". As a result, the transmission reservation section 14 controls the transmission control section 1.
max['Rr, P,] output from 3 is input, and the value "1" set to the leftmost among the 3 bits of that priority is set to the frame/token pit string passing through the bit delay section If. Set the corresponding position of bit R1 representing the F/TBA reservation index.

Since data is not being transmitted from the own station at the moment, the tick MAC frame bit string FBA output from the bit delay unit 11 is selected in the transmission selection unit I5, and after being encoded in the encoding unit 16, the transmission unit 17 and is transmitted as a signal SFT.

As a result, the signal SFT is transferred from the communication station I to the adjacent communication station I3. The communication station 13 receives the signal SFT transferred via the transmission path 2 in the receiving unit 6, decodes it in the decoding unit 7, and then detects the timing signal STM in the received bit analysis unit 8 and determines the ring priority P1. and detection and generation of reservation priority Rr, and tick MA
The C frame bit string FB is output.

Furthermore, the reception control unit 9 determines whether the input tick MAC frame bit string FBA is addressed to the own station. In this case, since the functional address is 001H, the received data DB addressed to the local station is output.

Next, the reception data output unit IO inputs the reception data DR and outputs the reception control signal RCT from the data processing unit 5.
It outputs to the data processing section 5 based on L.

Thereby, the tick frame detection unit 18 detects a tick MAC frame from the received data DR and outputs a sequence number. The sequence number is held in the latch 19, and is stored in the counter 2 in the comparator 21.
It is compared with a value of 0. At this time, the comparator 21 is
If these values are equal, pulse P1 is not output; however, if these values are different, pulse P1 is output that increments the counter value by 1, and the sequence number held in latch 19 is Incrementing is repeated until the value and the value of the counter 20 match. Since the sequence number is 7 bits, the adjustment value is l-127.
is within the range of

It should be noted that the expected value of each station is greater than the sequence value of the basic clock, that is, it is unthinkable that a larger amount of data will be received than the amount sent by the transmitter, so the adjustment value will be 0 or more.

For example, when the current expected value for the sequence number in the data processing unit 5 of the communication station 13 is "3", that is, the value of the counter 20 is "3", the sequence detected from the transferred tick MAC frame The number is "3"
If , the data was successfully transferred;
The comparator 21 does not output a pulse P, but if the sequence number detected from the transferred tick MAC frame is "4" even though the value of the counter 20 is "3", one pulse is output. Due to missing data,
Comparator 2I is the pulse P0 of the differential hand, in this case 1
outputs one pulse P1.

As a result, the timer 33 connected to the communication station 13 performs error correction on the internally generated clock by frequency-dividing the pulse P1.

Also, at the receiving station's discretion, the transmitting station may have a ring error monitor (R
EM) frame and report the occurrence of an error.

Note that the above-described tick MAC frame detection and clock error correction operations are carried out by the communication station 14 and! , the same thing is done.

Next, the data processing section 5 of the communication station 11. and timer 3.
When the reset pulse R2 is manually applied from the upper layer, the counter 23 and the timer 3. At the same time as the count value of is cleared, the function address is 0OIH, reset="l" and sequence number "o o o o o o" in the tick frame generation unit 22.

”, a tick MAC frame, ie, an initialization frame, is generated.

As a result, the communication station 1. which acquired the token circulating on the transmission path 2. obtains the transmission right and encodes the tick MAC frame in the encoding unit 16 as in the case described above, and then
Transmission part! 7 and then transmitted as a signal SFT.

As a result, the signal SFT is transmitted to the communication station 1. Communication station 1 via
Transferred to 3. The communication station 13 receives the signal SFT transferred via the transmission path 2 at the receiving section 6 and sends it to the decoding section 7.
After decoding, the received bit analysis unit 8 detects the timing signal STN, detects and generates the ring priority Pr and the reservation priority R, and outputs the tick MAC frame bit string FB.

Further, the reception control unit 9 determines whether the input tick MAC frame □ bit string FBA is addressed to the own station. In this case, since the functional address is 001H, the received data DR addressed to the local station is output.

Next, the reception data output unit IO inputs the reception data DR and receives the reception control signal RcT output from the data processing unit 5.
It outputs to the data processing section 5 based on L.

Thereby, the tick frame detection unit I8 detects a tick MAC frame, that is, an initialization frame, from the received data DR, and outputs a reset pulse R1. The values of both the counter 20 and the timer 33 are cleared by the reset pulse R2.

Note that the above-described operations of detecting a tick MAC frame and clearing the values of the counter 20 and timer 3 are performed in the communication stations 14 and 15 in the same manner.

As explained above, tick M regarding the basic clock
When an AC frame is transferred and a transfer error occurs, the receiving station outputs a pulse corresponding to the transfer error, so a general-purpose programmable timer can be directly connected to the communication station. Also, is the timer itself a communication station? It is also possible to incorporate this.

Therefore, even when running application software on other devices connected to a communication station, the tick MAC
Frame transfer is performed automatically by application software simply by setting timers such as basic clock intervals.

Also, in the communication station that has received the tick MAC frame, clock errors can be efficiently corrected simply by having the timer 3 divide the pulse P1 output from the data processing section 5.

As a result, the LAN existing in each communication station appears to be transparent, and each communication station can operate as if it were directly sharing one timer, without distinguishing between an external clock and an internal clock.

Further, in the embodiment described above, an example was shown in which the timer 3 is configured by hardware, but it may also be implemented by software. In this case, parameters are set to perform the same operation as described above.

"Effects of the Invention" As explained above, according to the present invention, there is an effect that clock error correction can be easily and efficiently performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a communication station (2) according to an embodiment of the present invention, and FIG. 2 is a conventional token ring type LAN.
FIG. 2 is a block diagram showing an example of the configuration. Science department, 18... Tick frame detection section, 19
...Latch, 20.23 ...Counter, 21 ...Comparator, 22 ...Tick frame generation unit.

Claims (1)

[Claims] In a ring type LAN in which a plurality of communication stations are connected in a ring shape through a transmission path and data is transferred between these stations, a timer is connected to each of the plurality of communication stations, and a timer is connected to each of the plurality of communication stations, , one of them is a basic timer that generates a basic clock, and the communication station to which the basic timer is connected sends data with a sequence number corresponding to the basic clock, and changes the value of the sequence number every time it is sent. A communication station other than the communication station to which the basic timer is connected has an expected value for the sequence number in advance, and receives the data based on the difference between the expected value and the received value of the sequence number. A clock sharing method in a ring type LAN, characterized in that it is determined that an error has occurred and the count value of the timer connected to the local station is corrected according to the difference.