JPH0149221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a computer network that enables simplified packet communication procedures and rapid system maintenance.

[Technical background of the invention and its problems] Recently, with the development of office automation, various switching networks have been developed. However, in this type of exchange network, data is sent as a packet, and the data communication is completed by detecting a response confirming receipt of the packet. However, if the above response is not obtained, the communication partner station may be unable to receive the packet because it is busy, or it may not be participating in the network due to the power being turned off, etc. Therefore, it is not possible to determine whether the packet is not received or not, and therefore the communication source station repeatedly retransmits the same packet. When a reception confirmation response is not obtained even after a predetermined number of packet transmissions, this is regarded as an abnormality in the destination station, and packet transmission is stopped.

In addition, with this type of abnormality detection method, only the station that accidentally sent a packet to that station can detect an abnormality, so conventionally a special monitor station is set up, and this monitor station monitors the network at regular intervals. Anomaly detection is performed for each station. However, it is uneconomical to create and provide such a special monitor station, and there is a problem in that it is not possible to deal with an abnormality until the monitor station detects the abnormality. For this reason, the above-mentioned retransmission of packets is often repeated, resulting in a decrease in network efficiency and wasteful occupation of the network.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to enable each of the stations making up the network to be aware of abnormalities such as non-participation, etc., thereby preventing packet communication. The objective is to provide a computer network that can simplify procedures and speed up system maintenance.

[Summary of the invention]

In the present invention, when a plurality of slave stations sequentially transmit packets according to a frame header generated by a master station, each slave station transmits transmission data or a dummy packet when there is no data, and the master station transmits packets within a predetermined timeout period. If the slave station is not sent, it is assumed that the slave station is not participating in the network and a proxy packet is sent.At this time, each station determines the type of the header of the communication packet and determines whether the station is connected to the network. It is designed to determine whether or not each participant is participating in the event.

〔Effect of the invention〕

Thus, according to the present invention, a station participating in the network can determine from the header of a communication packet on the transmission path whether the packet is a normal data packet or not.
Is it a frame header packet or a dummy packet?
Alternatively, it is possible to determine whether the packet is a proxy packet, and if it is a proxy packet, it can be determined that the station in that slot is not participating in the network. Therefore, if there is data to be transmitted to this non-participating station, the packet transmission can be immediately stopped, thereby simplifying the packet communication procedure. In addition, each station can detect non-participating stations, so they can quickly perform recovery work to resolve the reason for non-participating.
This has great practical effects, such as making system maintenance easier.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the computer network according to the present invention, when the transmission path is configured using coaxial cables, a plurality of stations 1 ₁ , 1 ₂ to 1 _o are connected to a bus 2 to form a bus type as shown in FIG. When the transmission line is constructed using optical fibers, it is constructed in a star configuration in which a plurality of stations 1 ₁ , 1 2 to _{1 o} are connected to a star coupler 3, as shown in FIG. Each of these stations has a function that can act as a master station, and the functions of the master station and slave stations are adjusted so that when one station becomes the master station, the remaining stations become slave stations. It has a configuration that combines the following.

Therefore, it is very important to provide reliability and real-time performance in this type of network, and this purpose is achieved in the following manner.

Real-time property means that a station that has a transmission packet can always secure the transmission right (transmission path usage right) within a certain period of time.For example, in the field of process control, etc. When implementing functions to collect data at control points, etc.
This is unparalleled performance. Incidentally, conventionally, methods such as token passing are known, but in this embodiment, implicit token passing is used.
A method called ``Passing'' is adopted.

This method sends Tokens in order, and this Token
Unlike the conventional method in which the station that holds the packet transmission right secures the right to transmit the packet, the order of packet transmission is determined in advance for multiple stations, and when the previous station completes packet transmission, the next station In this case, it is decided that the token has been passed implicitly, and the packet transmission operation starts.

Adopting this method eliminates the need to alternately switch the bus between the token sending phase and the data sending phase, as seen in conventional token passing methods, even if the basic clock for signal transmission is high. Even if the transmission path is used efficiently, the efficiency of using the transmission path will not deteriorate.

The reliability of the network is achieved by generally configuring the transmission path only with passive elements, and by making all the stations that make up the network homogeneous by having the same structure. That is,
The transmission path uses only coaxial cables and optical fibers, and has a bus-shaped or star-shaped configuration as shown in FIG. 1 or 2. Furthermore, no reproduction device (active element) called a repeater or the like is used in this transmission path. As for the stations constituting the network, all the stations have the function of becoming a master station, as described above, and only one of them is designed to selectively work as a master station. It goes without saying that the master station simultaneously functions as a master station and as a slave station.

The above is the basic outline of the computer network according to the present invention.

Figure 3 shows the frame structure of this network. Among the multiple stations that make up the network, a selectively determined master station transmits a packet called a frame header (FH), detects the completion of transmission of this frame header, and transmits a predetermined packet to multiple slave stations. In this order, the completion of packet transmission from the previous station is detected and the packets are transmitted.As will be described later, four types of packets are prepared, including the above-mentioned frame header. For example, one packet consists of a 1-byte header section, a 1-byte destination (communication destination) address section, a 1-byte source (destination: own station) address section, and a 1-byte source address section, as shown in Figure 4. data type part, data part of 0 to 2042 bytes, and 2 bytes of
It consists of a CRC code part. When the value of the header section is "0", the packet is a frame header (FH) generated by the master station.
It shows that. Further, when the value of the header part is "1", it is a proxy packet, when it is "2", it is a data packet, and when it is "3", it is a dummy packet.

Proxy packets are used when the slave station does not transmit packets for some reason, such as failure,
These packets are generated by the master station in place of the slave station when the slave station is not participating in the network due to maintenance, power off, or the like. In addition, a data packet is a packet that a slave station transmits by converting the transmission data part into a packet according to the original format, and in this case, the length of the data part varies from 0 to 100 depending on the amount of data to be transmitted.
Variable within the range of 2042 bytes. Furthermore, dummy packets are sent in place of the above-mentioned data packets when a station participating in the network does not have any data to send at that time. is minimized.

In addition, the data type distinguishes whether the packet is a priority packet or a non-priority packet, and the communication destination station compares this data type with the current processing status and determines whether to capture the communication packet. control. It goes without saying that the CRC code is used to detect data errors in communication packets.

FIG. 5 schematically shows the procedure for attempting to set up a master station for each station in this network and the procedure for transmitting packets. The operation of this network will be explained with reference to this figure.

First, the procedure for setting the master station will be explained. There are three typical cases in which the master station is set. The first is when multiple stations that make up the network turn on their power one by one and join the network one after the other, and the second is when multiple stations turn on their power at the same time and join the network. ,3
The second case is when the master station leaves the network for some reason and selects a new master station from among the remaining stations. Thus, when a plurality of stations join the network one after another, each station that joins the network detects a carrier on the transmission path. still,
This carrier detection is performed for a sufficiently longer period of time than the slot interval shown in FIG. At this time, the first station sends a frame header and attempts to set up a master station because no carrier is detected, but the stations that join from the second station onwards detect the carrier of the station that joined first, so they Becomes a station child. The first station to join the network is
After transmitting the frame header, it detects the return of the frame header within the slot period, confirms that the transmission path is normal, and then becomes the master station after confirming that no collision occurs on the frame header transmission path. . Note that the self-packet return check during the time slot period is performed by taking advantage of the fact that the transmission path is composed of passive elements, as described above, and that transmitted packets are always returned to the local station. For example, bus 2
If there is a disconnection on the transmitting side or the receiving side on the transmission path up to the star coupler 3, as a matter of course, the self-packet will not be returned.
In this case, recovery efforts include quickly turning off the power and notifying the operator of the situation.

By the way, in the second case, when multiple stations join the network at the same time,
Since there is no carrier on the transmission path, each of these stations transmits a frame header. Therefore, frame headers from these stations collide on the transmission path. The collision detection is to detect such a collision of frame headers, and thereby each station knows that there is a station other than the own station that is attempting to establish a master station.
When this collision is detected, each station repeats the procedure starting from the carrier detection after a predetermined backoff time has elapsed. The above-mentioned backoff time consists of mutually different times determined for each station, for example, the packet transmission order (slot number: N) determined in advance for each station.
Based on this, it is set as N x (certain time). Therefore, each station will try to set up a master station in order after the backoff time corresponding to its slot number has elapsed, so here, the station with the lowest time slot number will try to set up a master station first. It turns out. At this time, since the other stations have not yet started attempting to set up a master station, the station with the smaller time slot number becomes the master station. In this way, one station becomes a master station, and a plurality of stations sequentially detect the completion of packet transmission of the previous station and transmit packets according to the frame header generated by this master station.

Further, when the master station set as described above leaves the network, the frame header from the master station disappears, so each station stops transmitting packets. As a result, the carrier on the transmission path disappears for a long time, so each station that was a slave station detects the disappearance of the master station, and after the predetermined back-off time described above has elapsed, A trial will be made to set up the station. Even in this case, the station with the lowest slot number will first attempt to set up the master station, so as in the second example above, the station with the lowest slot number will become the master station, and the other stations will The station becomes a slave station again.

In this way, in this network, one of the multiple stations that make up the network becomes the master station depending on the situation of the network. At the same time as the master station is set up, the frame header is transmitted to manage the entire network. Furthermore, as mentioned above, if a carrier no longer exists on the transmission path, each station quickly attempts to set up a master station and determines the master station, making it possible to keep the period during which the master station disappears sufficiently short. can.

By the way, conventionally, the absence of a master station is determined by detecting the presence of a frame header in only one place in one frame, so if more than one frame time has not elapsed since the time when the master station was absent, the I couldn't make a judgment. However, according to this network, the absence of a master station can be determined only by the elapse of the maximum time slot interval, as will be described later, and its effectiveness is enormous.

The procedure for setting the master station has been described above. After the master station is set in this manner, each station transmits packets as follows.
When the master station transmits a frame header, each station making up the network checks the header part of the communication packet and determines that it is a frame header. This frame header is detected and a slot counter is initialized, and the counter is incremented each time a carrier is detected by packet transmission. In this case, since the slots are counted using the carrier of the communication packet, even if the packet becomes an error packet due to noise being mixed in, the slot counting operation will be performed normally. Then, based on this slot count value, the slot of the own station is determined, and the completion of the packet transmission of the previous station (temporary disappearance of the carrier) is detected, and the packet is transmitted. At this time, depending on whether or not the station has transmission data, the station assembles and transmits a packet as shown in FIG. 4 if it has transmission data, and if it does not have transmission data, the data section A 0-byte dummy packet is assembled and sent. The master station, as one station, packetizes data and transmits it to its designated slot, and when the slot counter reaches a predetermined value, it composes a frame header packet and sends it to the packet. Sending.

Furthermore, each time each station transmits a packet as described above, each station determines whether or not its own packet returns to itself within the slot period, and monitors the state of the transmission path. Needless to say, there are. If there is no return of the own packet, it is determined that an accident such as a disconnection of the transmission line has occurred.

By the way, when all the stations that make up a network participate in the network, each of the stations transmits packets in order according to the frame header generated by the master station as described above, but when the power is turned off, etc. If there is a non-participating station in the network, no packets will be transmitted from that station even if the slot becomes that station's turn. In such a case, the station following the station will not be able to increment the slot counter due to carrier detection, so there is a risk that packet communication will be interrupted. Therefore, in such a case, the master station detects the frame interval (idle period) at which the carrier is temporarily lost, and if the idle period continues for a certain period or more, the station in that slot joins the network. Assuming that the station is not participating, it sends out a proxy packet on behalf of the station. The time for this idle period detection is
It is set to be sufficiently long compared to the maximum propagation delay time between any stations in the network. As a result, after the master station sends a proxy packet,
This prevents problems such as packet collisions occurring when packets from the station with the longest propagation delay reach the master station.

When an idle period is detected in this manner and a proxy packet is transmitted from the master station, the above-mentioned dummy packet plays an effective role in the system. That is, if a dummy packet is not used, no data packet is transmitted, so it is necessary to detect the idle period and transmit a proxy packet each time. In this case, there is no problem in terms of the system, but as described above, idle period detection is performed for longer than the maximum propagation delay time of the network. For this reason, it is undeniable that the packet interval inevitably becomes longer, and the proportion of the entire frame increases. This means a decrease in network efficiency.

In this regard, if you use the dummy packet mentioned above,
Even when there is no data to be transmitted, the packet interval remains the same as normal, so it is only necessary to detect the idle period and transmit a proxy packet when the station does not participate in the network. Therefore, even if there is no data to be sent, this will not cause a decrease in network efficiency.

Thus, the packets transmitted in order as described above are checked at each station.
This check consists of determining whether the communication packet is addressed to the local station by identifying the destination address of the packet, and determining the priority by identifying the data type. If the communication packet is addressed to the own station, the communication packet is received and captured according to the above-mentioned priority and the own status. At the same time, each station identifies whether or not the communication packet is a proxy packet. If the communication packet is a proxy packet, the station corresponding to the slot is determined based on the value of the slot counter at that time. Network non-participation is detected.
It goes without saying that this determination of the proxy packet is made in accordance with the information in the header section described above. The information on non-participation in the network is used as control information for stopping data packet communication, etc., if there is data to be transmitted to that station. Therefore, it is no longer necessary to repeatedly retransmit the same data to a station that does not participate in the network based on the information that packet communication has not been established, and it is possible to greatly simplify the communication procedure.

As explained above, according to this network, a master station is set among a plurality of stations making up the network, and each station sequentially transmits data packets or dummy packets according to the frame header generated by the master station. If the slave station does not participate in the network, the master station transmits a proxy packet. and,
When transmitting these packets, each station detects the return of its own packet within its slot period, manages abnormalities in the transmission path in a distributed manner, and also detects proxy packets to simplify the transmission procedure. It's on. Furthermore, in this way, the absence of a master station is quickly detected from an abnormality in the packet interval of sequentially transmitted packets, and the master station setting is performed without delay.

Therefore, according to this network, it is possible to operate the system efficiently and improve the network efficiency. Furthermore, since each station detects the return of its own packets and monitors transmission path abnormalities, a station with a transmission path abnormality may, for example, repeat attempts to set up a master station just because the carrier is not detected. network, and there are no defects that would interfere with normal network communication. Further, by detecting this abnormality, recovery measures can be taken promptly, so that effects such as high system integrity can be achieved. Note that the check of the own packet may be performed by checking the source address, error detection based on the CRC code, etc., and the abnormality determination may also be performed, for example, by detecting abnormality three times in a row.

In addition, this system does not have a fixed number of slots, but instead assigns slot numbers to multiple stations that make up the network, and each station operates according to these slot numbers. It is possible to efficiently construct a network based on the network, and it is also possible to sufficiently cope with changes in the number of stations.

Note that the present invention is not limited to the above embodiments. For example, the number of stations that make up the network,
The structure of the packet may be determined according to the specifications.
Furthermore, the packet transmission procedure at each station is not limited to the example shown in FIG. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

The figures show one embodiment of the present invention, and FIGS. 1 and 2 respectively show the basic configuration of the network, FIG. 3 shows the frame structure, and FIG. 4 shows the basic configuration of the network.
The figure shows the structure of a packet, and FIG. 5 shows the procedure for attempting to set up a master station and the procedure for transmitting a packet. 1 ₁ , 1 ₂ ~ 1 _o ... Station, 2 ... Bus, 3 ... Star Katsupura.

Claims (1)

[Claims] 1. Consists of a master station and a plurality of slave stations that constitute a bus-type or star-type network, and each station that has joined the network sequentially sends data packets or dummy packets in a predetermined order according to the frame header generated by the master station. In a computer network in which the master station detects a timeout and transmits a proxy packet to a slave station that does not participate in the network, each station checks the header of the transmitted packet and A computer network characterized in that when a packet is the proxy packet, the station in that time slot is determined to be non-participating in the network, and at least the packet transmission procedure is controlled.