Assigning and updating dynamically through asynchronous communication non unique second identifiers to a plurality of stations for isochronous data communication

CROSS REFERENCE TO RELATED APPLICATION

0001The present application is related to copending U.S. patent application Serial No. 08/843,597 filed on April 16, 1997 assigned to the same assignee of the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

0002The present invention relates to a communication network, and more particularly, to a communication network capable of establishing asynchronous data communication not requiring real time properties and isochronous data communication requiring the real time properties.

Description of the Background Art

0003Examples of a conventional loop communication network include one disclosed in "JP-A-9-289518". Fig. 29 is a block diagram showing the structure of the loop communication network. In Fig. 29, a plurality of stations (four stations 29₁ to 29₄ are illustrated) are connected so as to be capable of communicating with each other by a loop-shaped transmission path 295. Identifiers which are not overlapped with each other (hereinafter referred to as actual IDs) are fixedly assigned to the stations 29₁ to 29₄, respectively. The station 29₁ of the four stations 29₁ to 29₄ functions as a master station, and the other stations 29₂ to 29₄ function as slave stations (which may, in some cases, be hereinafter referred to as the master station 29₁ and the slave stations 29₂ to 29₄).

0004The procedure for communication in the communication network will be described.

0005The master station 29₁ holds a table 296 for managing a transmission bandwidth. The master station 29₁ generates a token packet in which a station to be a source of transmission of data (hereinafter referred to as a sending station) and a station to be a destination of transmission of the data (hereinafter referred to as a receiving station) are designated using actual IDs (hereinafter referred to as a sending station ID and a receiving station ID) in accordance with contents described in the table 296, and sends out the token packet to the transmission path 295. It is assumed that the station 29₄ and the station 29₃ are designated as the sending station and the receiving station. The token packet returns to the master station 29₁ upon circulating around the loop-shaped transmission path 295. The master station 29₁ deletes the returned token packet. When the token packet circulating around the transmission path 295 arrives, each of the slave stations 29₂ to 29₄ branches the token packet into two token packets, to receive one branched token packet, while sending out the other branched token packet to the transmission path 295 on the downstream side. Each of the slave stations 29₂ to 29₄ judges whether or not the sending station ID or the receiving station ID of the accepted token packet identifies with the actual ID of the slave station. The slave station 29₄ judges that data transmission is enable because the sending station ID and the actual ID of the slave station identify with each other. Further, the slave station 29₃ judges that data receiving is enable because the receiving station ID and the actual ID of the slave station identify with each other.

0006The slave station 29₄ sends out, when it holds a data packet to be transmitted immediately after judging that data transmission is enable, the data packet to the transmission path 295. The data packet is transmitted so as to succeed the token packet when it is sent out to the loop-shaped transmission path 295, and returns to the sending station (the slave station 29₄) upon circulating around the transmission path 295. The slave station 29₄ deletes the returned data packet.

0007The master station 29₁ controls a switch (not shown) when the token packet and the data packet arrive from the transmission path 295 on the upstream side, to send out only the data packet of the two types of arrived packets to the transmission path 295 on the downstream side. Fig. 29 illustrates the data packet immediately after the master station 29₁ controls the switch.

0008The slave station 29₃ receives, when it judges that data receiving is enable, the data packet arriving within a predetermined time period elapsed since it received the token packet.

0009In the communication network, point to point communication can be established between the sending station and the receiving station which are designated by the token packet. Further, the master station 29₁ sends out the token packet at predetermined time intervals in accordance with contents described in the table 296 for managing the transmission bandwidth in the communication network. When isochronous data is communicated between the sending station and the receiving station, therefore, the real time transfer of the isochronous data are reserved if the transmission bandwidth is ensured on the table 296.

0010In the communication network shown in Fig. 29, a first method in which the master station 29₁ sets a plurality of receiving station IDs in the token packet in order to establish communication between one station and a plurality of stations (which is referred to as multicast communication, and broadcast communication particularly in the case of communication between one station and all stations) is considered. Since the token packet generally has a fixed length, the number of receiving station IDs which can be set has a limit. If the number of stations which are accommodated in the communication network is increased, it is possible to anticipate the problem that multicast communication cannot be ensured. Next, a second method in which special IDs for multicast communication are provided in addition to actual IDs is considered. That is, it is assumed that a special ID (for example, #1) is assigned to a combination of the slave stations 29₂ and 29₃, for example, in Fig. 29. If the special ID ; #1 is set to the receiving station ID of the token packet, therefore, the master station 29₁ can designate the plurality of stations (the slave stations 29₂ and 29₃) as receiving stations. However, an attempt to apply the second method to ensure multicast communication requires the number of special IDs corresponding to combinations of all the stations. If the number of stations accommodated in the communication network is increased, the data length of the IDs is increased. Therefore, it is possible to anticipate a first problem that the special ID cannot, in some cases, be set in the token packet having a fixed length. Further, the master station 29₁ must manage not only the actual ID but also the special ID, whose management becomes difficult.

0011In the communication network shown in Fig. 29, the master station 29₁ sends out the token packet in which the sending station and the receiving station are designated to the transmission path 295. However, the station 29 designated as a sending station by the token packet does not necessarily hold transmission data. That is, each of the stations 29 sends out nothing to the transmission path 295 when it does not hold a data packet to be transmitted immediately after judging that data can be transmitted. As a result, there is a second problem that an unnecessary token packet may be transmitted in the communication network.

0012In not only the communication network shown in Fig. 29 but also a general communication network, actual IDs are managed by a network administrator and should not identify with the actual ID of the other station 29. In the communication network, however, a new station 29 may be added, and the existing station 29 may be withdrawn. Therefore, there is a third problem that it is difficult for the network administrator to manage actual IDs. Such a problem has been conventionally pointed out. A method of automatically setting actual IDs is disclosed in "JP-A-4-88737". However, a communication network disclosed in the publication differs from a communication network disclosed in the present application in that it does not consider communication relating to isochronous data.

SUMMARY OF THE INVENTION

0013Therefore, a first object of the present invention is to provide a communication network capable of ensuring point to point communication and communication between one station and a plurality of stations without significantly increasing the number of IDs respectively assigned to the stations. A second object is to provide a communication network in which an unnecessary token packet need not be sent out. A third object is to provide a communication network capable of automatically setting actual IDs at the time of starting stations in order to simplify the management of the actual IDs.

0014In order to attain the above-mentioned three objects, the present invention has the following aspects.

0015A first aspect is directed to a communication network in which a plurality of stations are connected to each other by a loop-shaped transmission path, any one of the plurality of stations functioning as a master station, and asynchronous data communication relating to asynchronous data not requiring real time properties and isochronous data communication relating to isochronous data requiring the real time properties can be established, wherein first identifiers which are used at the time of the asynchronous data communication and are not overlapped with each other are respectively fixedly assigned to the stations, second identifiers which are used at the time of the isochronous data communication and may be overlapped with each other are assigned to the stations as required, the master station sends out to the transmission path for each predetermined time period a token packet for isochronous data in which a station transmitting the isochronous data (hereinafter referred to as a sending station) and a station receiving the isochronous data (hereinafter referred to as a receiving station) are designated using the second identifiers when the isochronous data communication should be established, so that a plurality of stations receiving the isochronous data can be designated, and the sending station transmits, when the token packet for isochronous data is transmitted through the transmission path, the isochronous data to be transmitted to the receiving stations, so that the isochronous data communication is started.

0016According to the first aspect, the isochronous data communication is started on the basis of the token packet for isochronous data in which the receiving stations are designated using the second identifiers. The second identifiers may be assigned to the stations as required and also be overlapped with each other, so that it is possible to easily ensure multicast communication of the isochronous data.

0017A second aspect is characterized in that in the first aspect, the second identifiers are assigned to the stations establishing the isochronous data communication by the asynchronous data communication.

0018According to the second aspect, the second identifiers are set by the asynchronous data communication. Therefore, it becomes easy to add a new station to the stations receiving the same isochronous data (a broadcast group) by the multicast communication and withdraw the station, which has already belonged to the broadcast group, from the group.

0019A third aspect is characterized in that in the second aspect, when the isochronous data transmitted by the sending station is received by the plurality of receiving stations in the isochronous data communication, the only one receiving station of the plurality of receiving stations sends out to the transmission path a response signal for controlling the transmission of the isochronous data by the sending station and/or reporting the acknowledgment of the isochronous data communication by the receiving station.

0020According to the third aspect, the only one receiving station in the broadcast group sends out the response signal to the transmission path. Therefore, no signal collision occurs on the transmission path.

0021A fourth aspect is characterized in that in the third aspect, the only one receiving station is set by the asynchronous data communication.

0022According to the fourth aspect, the only one receiving station is set by the asynchronous data communication. Therefore, it becomes easy to change the different receiving stations in the broadcast group into the only one receiving station.

0023A fifth aspect is characterized in that in the second aspect, when the isochronous data transmitted by the sending station is received by the plurality of receiving stations in the isochronous data communication, the plurality of receiving stations respectively send out to the transmission path response signals for controlling the transmission of the isochronous data by the sending station and/or reporting the acknowledgment of the isochronous data communication by the receiving stations, and the sending station receives only the response signal sent out from the only one receiving station of the plurality of receiving stations.

0024According to the fifth aspect, only the response signal sent out from the only one receiving station of the response signals sent out from the plurality of receiving stations is transmitted to the sending station. Therefore, no signal collision occurs on the transmission path.

0025A sixth aspect is directed to a communication network in which a plurality of stations are connected to each other by a loop-shaped transmission path, any one of the plurality of stations functioning as a master station, and asynchronous data communication relating to asynchronous data not requiring real time properties and isochronous data communication relating to isochronous data requiring the real time properties can be established, wherein actual IDs which are used at the time of the asynchronous data communication and are not overlapped with each other are respectively fixedly assigned to the stations, the master station sends out to the transmission path an inquiry token packet for inquiring whether or not each of the stations has a communication request of the asynchronous data, each of the stations sends out, provided that it holds the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data when it receives the inquiry token packet transmitted through the transmission path, the communication request of the asynchronous data and the actual ID of the station to be the destination of transmission to the transmission path using a slot previously assigned to each of the stations, the master station sends out to the transmission path a token packet for asynchronous data in which a station to be a source of transmission of the asynchronous data (hereinafter referred to as a sending station) and a station to be a destination of transmission of the asynchronous data (hereinafter referred to as a receiving station) are designated using the actual IDs on the basis of the communication request of the asynchronous data and the actual ID of the station to be the destination of transmission which are transmitted through the transmission path, and the station which sends out the communication request of the asynchronous data transmits, when the token packet for asynchronous data in which the station is designated as a sending station is transmitted through the transmission path, the asynchronous data to be transmitted to the receiving station, so that the asynchronous data communication is started.

0026According to the sixth aspect, the master station can recognize the stations which establish the asynchronous data communication of the stations accommodated in the network using the communication request sent out on the basis of the inquiry token packet. Consequently, the master station can efficiently send out the token packet for asynchronous data without sending out an unnecessary token packet for asynchronous data. Moreover, the master station sends out the token packet for asynchronous data to the station having the communication request, so that it can fairly send out the token packet for asynchronous data.

0027A seventh aspect is characterized in that in the sixth aspect, each of the stations further sends out the actual ID of the station which is a source of transmission of the asynchronous data when it receives the inquiry token packet transmitted through the transmission path.

0028According to the seventh aspect, the master station can recognize the actual ID of the station transmitting the asynchronous data, so that it can send out the token packet for asynchronous data more efficiently.

0029An eighth aspect is characterized in that in the seventh aspect, each of the stations further sends out information representing the amount and/or the priority of the asynchronous data when it receives the inquiry token packet transmitted through the transmission path.

0030According to the eighth aspect, the master station can recognize the amount and/or the priority of the asynchronous data which are sent out by the station transmitting the asynchronous data, so that it can send out the efficient token packet for asynchronous data corresponding to the amount and/or the priority.

0031A ninth aspect is characterized in that in the eighth aspect, the master station further sends out to the transmission path an identification signal for each of the stations to identify the slot after sending out the inquiry token packet.

0032According to the ninth aspect, each of the stations can easily identify the slot using the identification signal sent out by the master station.

0033A tenth aspect is characterized in that in the ninth aspect, the sending station sends out, provided that the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data are set in its inner by an equipment connected to the external thereof when it receives the inquiry token packet transmitted through the transmission path to the inner, the communication request of the asynchronous data and the actual ID of the station to be the destination of transmission to the transmission path using the slot, and the asynchronous data corresponding to one packet and the actual ID of a source of transmission of the asynchronous data which are transmitted through the transmission path from the sending station are stored in the receiving station and then read out by the equipment connected to the external thereof.

0034According to the tenth aspect, the sending station can send out the communication request when the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data are set in the inner by the equipment connected to the outside thereof. After the asynchronous data corresponding to one packet stored in the receiving station, the equipment can read out the asynchronous data.

0035An eleventh aspect is characterized in that in the sixth aspect, each of the plurality of stations belongs to any one of a plurality of predetermined groups, the master station sends out the inquiry token packet to the transmission path for each of the groups, each of the stations receives the inquiry token packet transmitted through the transmission path, and sends out, provided that it holds the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data when the token packet is for the group to which the station belongs, the communication request of the asynchronous data and the actual ID of the station to be the destination of transmission to the transmission path using a slot previously assigned to each of the stations, the master station sends out to the transmission path a token packet for asynchronous data in which the sending station and the receiving station are designated using the actual IDs on the basis of the communication request of the asynchronous data and the actual ID of the station to be the destination of transmission which are transmitted through the transmission path for each of the groups, and the station which sends out the communication request of the asynchronous data transmits, when the token packet for asynchronous data in which the station is designated as the sending station is transmitted through the transmission path, the asynchronous data to be transmitted to the receiving station, so that the asynchronous data communication is started.

0036According to the eleventh aspect, the plurality of stations are divided into groups. Therefore, the master station can send out the token packet for asynchronous data more efficiently.

0037A twelfth aspect is characterized in that in the eleventh aspect, the master station sends out, next time it sends out the inquiry token packet to the certain group of the plurality of groups, the inquiry token packet to the other group.

0038According to the twelfth aspect, the master station can fairly send out the inquiry token packet for each group.

0039A thirteenth aspect is characterized in that in the twelfth aspect, each of the stations receives the inquiry token packet transmitted through the transmission path, and further sends out, when the token packet is for the group to which the station belongs, the actual ID of the station to be a source of transmission of the asynchronous data.

0040According to the thirteenth aspect, the master station can recognize the actual ID of the station transmitting the asynchronous data, so that it can send out the token packet for asynchronous data more efficiently.

0041A fourteenth aspect is characterized in that in the thirteenth aspect, each of the stations receives the inquiry token packet transmitted through the transmission path, and further sends out, when the token packet is for the group to which the station belongs, information representing the amount and/or the priority of the asynchronous data.

0042According to the fourteenth aspect, the master station can recognize the amount and/or the priority of the asynchronous data which are sent out by the station transmitting the asynchronous data, so that it can send out the efficient token packet for asynchronous data corresponding to the amount and/or the priority.

0043A fifteenth aspect is characterized in that in the fourteenth aspect, the master station further sends out to the transmission path an identification signal for each of the stations to identify the slot after sending out the inquiry token packet.

0044According to the fifteenth aspect, each of the stations can easily identify the slot using the identification signal sent out by the master station.

0045A sixteenth aspect is characterized in that in the fifteenth aspect, the sending station receives the inquiry token packet transmitted through the transmission path to its inner, and sends out, provided that the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data are set in the inner by an equipment connected to the external thereof when the token packet is for the group to which the station belongs, a transmission request of the asynchronous data and the actual ID of the station to be the destination of transmission to the transmission path using the slot, and the asynchronous data corresponding to one packet and the actual ID of a source of transmission of the asynchronous data which are transmitted through the transmission path from the sending station are stored in the receiving station and then are read out by the equipment connected to the external thereof.

0046According to the sixteenth aspect, the sending station can send out the communication request when the asynchronous data and the actual ID of the station to be a destination of transmission of the asynchronous data are set in the inner by the equipment connected to the external thereof. After the asynchronous data corresponding to one packet stored in the receiving station, the equipment can read out the asynchronous data.

0047In a communication network in which a plurality of stations are connected to each other by a loop-shaped transmission path, any one of the plurality of stations functioning as a master station, the stations other than the master station functioning as slave stations, and asynchronous data communication relating to asynchronous data not requiring real time properties and isochronous data communication relating to isochronous data requiring the real time properties can be established, a seventeenth aspect is directed to a method of setting actual IDs which are used at the time of the asynchronous data communication and are not overlapped with each other, wherein the slave stations are respectively initially assigned initial IDs which are common at least among the slave stations and further respectively comprise switches for switching between connection and disconnection of the transmission path, the master station sends out to the transmission path a token packet for switching which can be received by the slave stations having the initial IDs, and then sends out to the transmission path an actual ID setting command for respectively setting the actual IDs which differ from each other in the slave stations, each of the slave stations disconnects the transmission path using the switch when it receives the token packet for switching from the master station in a case where it has the initial ID, not to transmit a receiving signal to the station positioned on the downstream side of the slave station on the transmission path, each of the slave stations sets, when it receives through the transmission path the actual ID setting command from the master station in a case where it has the initial ID, the actual ID on the basis of the received command, and each of the slave stations connects the transmission path using the switch when the actual ID is set therein, to transmit to the station positioned on the downstream side of the slave station on the transmission path the subsequent token packet for switching transmitted through the transmission path from the master station, so that the actual IDs are successively set in the slave stations, starting in the slave station positioned on the downstream side of the master station and nearest thereto.

0048According to the seventeenth aspect, the actual ID is automatically set in each of the stations. Therefore, it becomes easy to manage the actual IDs.

0049An eighteenth aspect is characterized in that in the seventeenth aspect, each of the slave stations transmits, after the actual ID is set therein, an actual ID setting acknowledgment indicating that the actual ID is set to the master station.

0050According to the eighteenth aspect, the master station can recognize that the actual ID is correctly set in the slave station using the actual ID setting acknowledgment.

0051A nineteenth aspect is characterized in that in the seventeenth aspect, each of the stations synchronizes an internal clock with a clock of the master station by receiving the token packet for switching sent out by the master station for each predetermined time period and transmitted through the transmission path.

0052A twentieth aspect is characterized in that in the eighteenth aspect, each of the stations synchronizes an internal clock with a clock of the master station by receiving the token packet for switching sent out by the master station for each predetermined time period and transmitted through the transmission path.

0053According to the nineteenth and twentieth aspects, each of the slave stations can easily synchronize the internal clock with the clock of the master station using the token packet for switching.

0054The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0055<ul id="ul0001" list-style="none" compact="compact"><li>Figs. 1 to 3 are diagrams for explaining the procedure for point to point communication in a communication network;</li><li>Fig. 4 illustrates the structure of a communication network according to a first embodiment of the present invention;</li><li>Fig. 5 is a diagram showing an actual ID and an ID for isochronous data which are set in each of stations 1₁ to 1₄ shown in Fig. 4;</li><li>Fig. 6 is a timing chart of two types of token packets (for isochronous data and for asynchronous data) used in the communication network shown in Fig. 4;</li><li>Fig. 7 illustrates the structure of a communication network according to a second embodiment of the present invention;</li><li>Fig. 8 illustrates the structures of ID holding portions 19₁ to 19₄ in stations 1₁ to 1₄ shown in Fig. 7;</li><li>Fig. 9 is a timing chart of signals sent out and received by each of stations 1₁ to 1₄ in a communication network according to a third embodiment of the present invention;</li><li>Fig. 10 illustrates the structure of a communication network according to a fourth embodiment of the present invention;</li><li>Fig. 11 is a block diagram showing the structures of a token packet sending/analysis executing device 16 and a switch 18, in a master station 1₁ shown in Fig. 10;</li><li>Fig. 12 is a block diagram showing the structures of analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄ in slave nations 1₂ to 1₄ shown in Fig. 10;</li><li>Fig. 13 is a diagram showing on a time base packets transmitted on a transmission path 15 in the communication network shown in Fig. 10;</li><li>Fig. 14 is a flow chart showing the procedure that the master station 1₁ sends out a token packet shown in Fig. 10;</li><li>Fig. 15 illustrates the structure of a communication network according to a fifth embodiment of the present invention;</li><li>Fig. 16 is a flow chart showing the procedure that a master station 1₁ sends out a token packet shown in Fig. 15;</li><li>Fig. 17 illustrates on a time base an inquiry token packet 131 and identification signals 171 which are transmitted on a transmission path 15 in a communication network according to a sixth embodiment;</li><li>Fig. 18 is a block diagram showing the other structures of a token packet sending/analysis executing device 16 and a switch 18₁ in a master station 1₁ and analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄ in slave stations 1₂ to 1₄;</li><li>Fig. 19 illustrates the structure of a communication network according to an eighth embodiment of the present invention;</li><li>Figs. 20 to 27 are diagrams for explaining the procedure for automatically setting an actual ID in each station 1 in the communication network shown in Fig. 19;</li><li>Fig. 28 is a block diagram showing the structures of a token packet sending/analysis executing device 16 and a switch 18₁ in a master station 1₁ shown in Fig. 19 and the structures of analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄ in slave stations 1₂ to 1₄ shown in Fig. 19; and</li><li>Fig. 29 illustrates the structure of a conventional communication network.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0056Although the procedure for point to point communication in a communication network will be first summarized with reference to Figs. 1 to 3, the details of the procedure for communication should be referred to because it is disclosed in copending U.S. patent application Serial No. 08/843,597 filed on April 16, 1997 and assigned to the same assignee of the present application. In Figs. 1 to 3, a plurality of stations (four stations 1₁ to 1₄ are illustrated) are connected so as to be capable of communicating with each other by a loop-shaped transmission path 15. Identifiers (hereinafter referred to as actual IDs) #a to #d which are not overlapped with each other are fixedly assigned to the stations 1₁ to 1₄. The station 1₁ functions as a master station, and the other stations 1₂ to 1₄ function as slave stations (which may, in some cases, be hereinafter referred to as the master station 1₁ and the slave stations 1₂ to 1₄). The master station 1₁ comprises a token packet sending/analysis executing device 16 and a switch 18₁. The slave stations 1₂ to 1₄ comprise analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄.

0057The procedure for data communication in the communication network constructed as described above will be described below. At the time of the initial state of the communication network, the stations 1₁ to 1₄ connect the switches 18₁ to 18₄ to terminals A, to connect the transmission path 15 (see Fig. 1).

0058The master station 1₁ then produces a token packet 21 in which a station to be a source of transmission of data (hereinafter referred to as a sending station) and a station to be a destination of transmission of the data (hereinafter referred to as a receiving station) are designated using the actual IDs in accordance with contents described in a table 16₁ held so as to manage a transmission bandwidth in the token packet sending/analysis executing device 16. The master station 1₁ connects the switch 18₁ to a terminal B, to disconnect the transmission path 15 immediately after producing the token packet 21, and sends out the token packet 21 to the transmission path 15 on the downstream side through the switch 18₁ from the token packet sending/analysis executing device 16 (see Fig. 2).

0059As shown in Fig. 2, the switches 18₂ to 18₄ in the slave stations 1₂ to 1₄ are connected to the terminals A. Therefore, the slave stations 1₂ to 1₄ branch the token packet 21 arriving from the transmission path 15 on the upstream side into two token packets 21 in portions of the terminals A of the switches 18₂ to 18₄. One branched token packet 21 is received and analyzed by the analysis executing devices 17₂ to 17₄. On the other hand, the other branched token packet 21 is sent out to the transmission path 15 on the downstream side of the slave stations 1₂ to 1₄. Accordingly, the token packet 21 sent out from the master station 1₁ circulates around the transmission path 15 while being received by the slave stations 1₂ to 1₄ positioned on the transmission path 15, and returns to the master station 1₁. The master station 1₁ receives and analyzes the returned token packet 21, and then deletes the token packet 21, and connects the switch 18₁ to the terminal A, to connect the transmission path 15.

0060The token packet sending/analysis executing device 16 and each of the analysis executing devices 17₂ to 17₄ analyzes the received token packet 21, to judge whether or not the actual ID of the sending station or the actual ID of the receiving station which is designated by the token packet identifies with the actual ID of the station. When it is assumed that an actual ID ; #c and an actual ID ; #b are set as the actual ID of the sending station and the actual ID of the receiving station, the slave station 1₃ judges that data transmission is enable because the actual IDs of the sending station and the slave station identify with each other, and the slave station 1₂ judges that data receiving is enable because the actual IDs of the receiving station and the slave station identify with each other.

0061The slave station 1₃ connects, when it holds a data packet 31 to be transmitted immediately after judging that data transmission is enable, the switch 18₃ to the terminal B to disconnect the transmission path 15 as shown in Fig. 3 after an elapse of a predetermined time period since the token packet was received, and sends out the data packet 31 to the transmission path 15 on the downstream side. The data packet 31 circulates around the transmission path 15 when the slave station 1₃ switches the switch 18₃. The slave station 1₂ receives, when it judges that data receiving is enable, the data packet 31 arriving from the upstream side on the transmission path 15 within a predetermined time period since the token packet 21 was received. Further, the slave station 1₃ deletes, when the data packet 31 sent out by itself returns upon circulating around the transmission path 15, the data packet 31, and connects the switch 18₃ to the terminal A to connect the transmission path 15. Consequently, the communication network enters the same state as that shown in Fig. 1, so that the same procedure for communication as that described above with reference to Figs. 1 to 3 is repeated again.

0062In the communication network, therefore, point to point communication can be established between the sending station and the receiving station which are designated using the actual IDs included in the token packet. Further, the master station 1₁ sends out the token packet 21 at predetermined time intervals in accordance with the contents described in the table 16₁ for managing the transmission bandwidth in the communication network. The master station 1₁ ensures the transmission bandwidth on the table 16₁ when isochronous data is communicated between the sending station and the receiving station. Consequently, the real time properties of the isochronous data (data requiring strict time management such as AV (Audio Video) data) are ensured.

0063As described in the foregoing, in the communication network shown in Figs. 1 to 3, there are some problems. For example, it is difficult to ensure communication between one station and a plurality of stations (multicast communication). The applicant of the present application discloses communication networks according to first to eighth embodiments described below in order to solve the problems.

(First Embodiment)

0064Fig. 4 illustrates the structure of a communication network according to a first embodiment of the present invention. The communication network shown in Fig. 4 has approximately the same structure as that shown in Figs. 1 to 3. Therefore, in Fig. 4, the same reference numerals are assigned to structures corresponding to the structures shown in Figs. 1 to 3 and hence, the description thereof is not repeated. Stations 1₁ to 1₄ shown in Fig. 4 are the same as the stations shown in Figs. 1 to 3 in that actual IDs ; #a to #d are respectively fixedly assigned thereto, and differ from the stations shown in Figs. 1 to 3 in that IDs for isochronous data are dynamically assigned thereto. The actual IDs are used for not only asynchronous data communication but also isochronous data point to point communication in the communication network shown in Figs. 1 to 3. However, attention must be given to the fact that the actual IDs are used only in the case of asynchronous data communication in the first embodiment. On the other hand the IDs for isochronous data are used in the case of isochronous data communication because a plurality of IDs for isochronous data can be set with respect to one station and overlapped values can be set in a plurality of stations. Further, the stations 1₁ to 1₄ comprise ID holding portions 19₁ to 19₄ each capable of storing a plurality of IDs for isochronous data.

0065Fig. 5 is a diagram showing an actual ID and an ID for isochronous data which are set in each of the stations 1₁ to 1₄ shown in Fig. 4. As described above, the actual IDs in the respective stations 1₁, 1₂, 1₃ and 1₄ shall be "#a", "#b", "#c" and "#d". The actual IDs are thus inherent in the stations, and are not overlapped with each other. In the stations 1₁, 1₂, 1₃ and 1₄, one or more IDs for isochronous data are respectively set in addition to the actual IDs in the ID holding portions 19₁, 19₂, 19₃ and 19₄. It is assumed that the IDs for isochronous data in the stations 1₁, 1₂, 1₃ and 1₄ are set to "#1", "#2", "#3" and "#3". The same ID for isochronous data "#3" is thus set in the slave station 1₃ and the slave station 1₄, so that the slave stations form a broadcast group.

0066Description is now made of the procedure for data communication in the communication network constructed as described above. For example, when isochronous data is transmitted from the master station 1₁ to the slave station 1₂, the master station 1₁ sends out a token packet for isochronous data 41 in which the master station 1₁ and the slave station 1₂ serving as a sending station and a receiving station (as described above) are designated using the IDs for isochronous data "#1" and "#2". In this case, the above-mentioned normal point to point communication is established and hence, the detailed description thereof is omitted.

0067For example, even when isochronous data is transmitted from the slave station 1₂ to the slave stations 1₃ and 1₄, the procedure for data communication as shown in Figs. 1 to 3 is basically carried out. That is, the master station 1₁ produces a token packet for isochronous data 41 in which the slave station 1₂ and the slave stations 1₃ and 1₄ serving as a sending station and receiving stations are designated using the IDs for isochronous data "#2" and "#3" in accordance with contents described in the table 16₁ held so as to manage the transmission bandwidth in the token packet sending/analysis executing device 16, and sends out the token packet 41 to the transmission path 15 on the downstream side (operations at this time are the same as those in the case of the master station 1₁ described using Fig. 2). As apparent from the foregoing, the slave station 1₂ sends out an isochronous data packet 42 to the transmission path 15 using the token packet for isochronous data 41. According to the token packet for isochronous data 41, the slave stations 1₃ and 1₄ are designated as receiving stations using the ID for isochronous data "#3", so that the slave stations 1₃ and 1₄ perform the above-mentioned operations, to receive the isochronous data packet 42. A sending station can thus transmit the same isochronous data to a plurality of receiving stations belonging to a broadcast group, thereby multicast communication (communication to a plurality of nodes) can be established.

0068In the stations 1₁ to 1₄, one or more IDs for isochronous data are respectively held in the ID holding portions 19₁ to 19₄. IDs for isochronous data having the same value are set in the stations 1 other than the sending station, thereby broadcast communication of the isochronous data can be established.

0069In the first embodiment, each of the stations 1 holds one or more IDs for isochronous data which can be set to arbitrary values in addition to the actual ID. A plurality of stations in which IDs for isochronous data having overlapped values are set form a broadcast group, to receive the same isochronous data. In the first embodiment, the IDs for isochronous data are thus overlapped with each other, so that the plurality of stations can be designated as receiving stations. Consequently, the communication network according to the first embodiment can ensure multicast communication and broadcast communication between one station and a plurality of stations, provided that a token packet includes one ID for isochronous data.

0070Fig. 6 is a timing chart of two types of token packets (for isochronous data and for asynchronous data) used in the communication network shown in Fig. 4. As shown in Fig. 6, the master station 1₁ sends out a token packet for isochronous data 41 or a token packet for asynchronous data 43 for each predetermined time period. In this example, the master station 1₁ continuously sends out m (m is an integer of one or more) token packets for isochronous data 41 onto the transmission path 15, and then sends out one token packet for asynchronous data 43 onto the transmission path 15. The master station 1₁ repeats the series of operations for sending out the token packets. Each of the stations 1₁ to 1₄ can judge the two types of token packets 41 and 43. Specifically, the two types of token packets 41 and 43 include packet type information in addition to actual IDs for designating a sending station and a receiving station (as described above). The packet type information indicates whether the token packet is for isochronous data communication or for asynchronous data communication. Each of the stations 1₁ to 1₄ judges whether the token packet is for isochronous data communication (the token packet 41) or for asynchronous data communication (the token packet 43) on the basis of the packet type information of the received token packet. Each of the stations 1₁ to 1₄ executes, when it receives the token packet for isochronous data 41, analysis as to whether the IDs for isochronous data set in the ID holding portion 19 in the station identify with the IDs for isochronous data of the sending station and the receiving station, to establish the above-mentioned isochronous data communication. Further, each of the stations 1₁ to 1₄ executes, when it receives the token packet for asynchronous data 43, analysis as to whether the actual ID fixedly assigned to the station identifies with the actual IDs of the sending station and the receiving station, to establish the asynchronous data communication.

0071By the asynchronous data communication, the IDs for isochronous data in the ID holding portions 19₁ to 19₄ in the stations 1₁ to 1₄ are rewritten. This rewriting makes it easily feasible to start and terminate the transmission in the case of isochronous data point to point communication, to add the station to the broadcast group and to withdraw the station from the broadcast group in the case of multicast communication. In the communication network according to the first embodiment, the IDs for isochronous data can be thus dynamically rewritten as required, so that multicast communication (and broadcast communication) can be ensured without requiring IDs for isochronous data corresponding to combinations of all the stations.

(Second Embodiment)

0072Fig. 7 illustrates the structure of a communication network according to a second embodiment of the present invention. The communication network shown in Fig. 7 has approximately the same structure as the communication network according to the first embodiment. Therefore, in Fig. 7, the same reference numerals are assigned to structures corresponding to the structures shown in Figs. 1 to 3 and Fig. 4 and hence, the description thereof is not repeated. Description is now made of the procedure for data communication in the communication network according to the second embodiment mainly with respect to the difference from the first embodiment.

0073In the initial state of the communication network, IDs for isochronous data are not set in ID holding portions 19₁ to 19₄ in stations 1₁ to 1₄. The master station 1₁ sends out a token packet for isochronous data 41 or a token packet for asynchronous data 43 onto a transmission path 15 for each predetermined time period, as shown in Fig. 6. However, isochronous data communication is not established, and only asynchronous data communication is established. In the master station 1₁, the IDs for isochronous data are set in the ID holding portions 19₁ to 19₄ by the asynchronous data communication using the token packet for asynchronous data 43 in order to start point to point communication of isochronous data or multicast communication of isochronous data (see the first embodiment). The master station 1₁ designates the only one station 1 of the plurality of stations 1 in which the same ID for isochronous data is set, that is, the plurality of stations 1 belonging to a broadcast group as a group leader at the time of setting the IDs for isochronous data. The master station 1₁ designates the station 1 in which the ID for isochronous data is set as a group leader even in the case of isochronous data point to point communication. Although isochronous data point to point communication is established at the beginning, the transition to multicast communication may occur by thereafter rewriting the ID for isochronous data (as described above). In the point to point communication of isochronous data and the multicast communication of isochronous data, the station 1 which is a group leader of the stations 1 receiving isochronous data sends out a response signal 71 immediately before the data packet 42, immediately after the data packet 42, both immediately before and immediately after the data packet 42, as shown in Fig. 7. The station 1 which is not a group leader of the stations 1 receiving the isochronous data (a broadcast group) does not send out the response signal 71. The only one station 1 to be a group leader in the broadcast group sends out the response signal 71 immediately before the data packet 42 is sent out, to control the sending of the data packet 42 from a sending station. Consequently, the sending station can wait for the sending of the data packet, so that it can also correspond with data communication at a variable bit rate (hereinafter referred to as VBR). Further, the station 1 sends out the response signal 71 immediately after the data packet, so that the normal acknowledgment of the data communication is confirmed. Since the only one station in the broadcast group sends out the response signal 71, no signal collision occurs on the transmission path 15.

0074The only one station 1 to be a group leader thus exists in the broadcast group, and only the group leader outputs the response signal 71, thereby making it possible to establish reliable data communication corresponding to a VBR and causing no signal collision on the transmission path 15.

0075Fig. 8 illustrates the structures of the ID holding portions 19₁ to 19₄ in the stations 1₁ to 1₄ shown in Fig. 7. In Fig. 8, the ID holding portions 19₁ to 19₄ include fields holding IDs for isochronous data in the stations 1₁ to 1₄ and the set conditions of the group leader.

0076In the initial state of the communication network, the IDs for isochronous data are not also assigned to the stations 1₁ to 1₄, so that any of the stations 1₁ to 1₄ cannot be a group leader. In order to indicate such situations, "NOTHING" is set as the ID for isochronous data, and "NO" is further set as the set conditions of the group leader in each of the ID holding portions 19₁ to 19₄. Under such situations, the master station 1₁ sends out the token packet for isochronous data 41 or the token packet for asynchronous data 43 to the transmission path 15 for each predetermined time period, as shown in Fig. 6. However, isochronous data communication is not established, and only asynchronous data communication is established. In the master station 1₁, IDs for isochronous data are set in the respective ID holding portions 19₁ to 19₄ and a group leader is further set by the asynchronous data communication using the token packet for asynchronous data 43 in order to start point to point communication of isochronous data or multicast communication of isochronous data. By setting the ID for isochronous data and the group leader using the asynchronous data communication, "XX" is set as the ID for isochronous data in the ID holding portions 19 in the plurality of stations 1, and "YES" is further set as the set conditions of the group leader in the ID holding portion 19 in the only one station 1 of the plurality of stations 1 in which the same ID for isochronous data is set, for example. Consequently, only the station 1 set as the group leader can send out the above-mentioned response signal 71 to the transmission path 15.

0077By the asynchronous data communication, the ID for isochronous data and the set conditions of the group leader are thus rewritten in the ID holding portion 19, thereby making it easy to add each of the stations 1₁ to 1₄ to the broadcast group and withdraw each of the stations from the broadcast group as well as to change the group leader in the broadcast group.

0078In the above-mentioned second embodiment, description was made of the situations where the ID for isochronous data and the group leader are simultaneously rewritten in the ID holding portions 19 in the plurality of stations 1. However, the ID for isochronous data and the group leader may be separately rewritten in the ID holding portions 19 in the plurality of stations 1, in which case the same effect as described above is obtained. Further, it is also easily feasible to change the station 1 in which the group leader has been set once into the other station 1.

(Third Embodiment)

0079Fig. 9 is a timing chart of signals sent out and received by each of stations 1₁ to 1₄ in a communication network according to a third embodiment of the present invention. In Fig. 9, a square portion indicted by a solid line represents the timing of sending out each signal, and a square portion indicated by a dotted line represents the timing of receiving each signal. Further, the structure of the communication network according to the present embodiment is the same as the structure of the communication network according to the second embodiment. In the present embodiment, therefore, the same reference numerals are respectively assigned to structures corresponding to those in the second embodiment and hence, the description thereof is not repeated.

0080In Fig. 9, a master station 1₁ sends out a token packet for isochronous data 41 to a transmission path 15 at predetermined timing in the same manner as described above. The token packet for isochronous data 41 is received by slave stations 1₂ to 1₄ with delays corresponding to the positional relationships among the slave stations 1₂ to 1₄ on the transmission path 15 on the basis of the time when the master station 1₁ sends out the token packet, and is then received by the master station 1₁ with a delay 91 corresponding to one circulation around the transmission path 15. A response signal 71 sent out by each of the stations 1₁ to 1₄ also circulates around the transmission path 15, and returns to each of the stations 1₁ to 1₄ sending out the response signal 71 when a time period corresponding to the delay 91 has elapsed. More specifically, each of the stations 1₁ to 1₄ disconnects the transmission path 15 by switching control of a switch in the station, to send out the response signal 71 to the transmission path 15 as described above. Each of the stations 1₁ to 1₄ receives the response signal 71 sent out by itself when the time period corresponding to the delay 91 which corresponds to one circulation around the transmission path 15 has elapsed. Immediately after each of the stations 1₁ to 1₄ receives the response signal 71 sent out by itself, a state where the transmission path 15 is disconnected is returned to a state where it is connected by switching control of the switch.

0081It is assumed that the master station 1₁ and the slave stations 1₂ and 1₄ belong the same broadcast group, and the slave station 1₃ transmits isochronous data to the broadcast group. First, a response signal 71₁ sent out by the master station 1₁ is transmitted to the slave station 1₂ through the transmission path 15. At the timing at which the response signal 71₁ sent out from the master station 1₁ arrives at the slave station 1₂, the slave station 1₂ disconnects the transmission path 15 by switching control of the switch because it is a receiving station, to receive and at the same time send out a response signal 71₂ sent out by itself to the transmission path 15 on the downstream side. Therefore, the response signal 71₁ sent out by the master station 1₁ is transmitted only to the slave station 1₂, and is deleted by the slave station 1₂. That is, the response signal 71₁ is not transmitted to the transmission path 15 on the downstream side of the slave station 1₂. However, the slave station 1₂ sends out the response signal 71₂ sent out by itself, and the response signal 71₂ is transmitted to the slave station 1₃. The slave station 1₃ which is a sending station receives the response signal 71₂ and at the same time, passes the response signal 71₂ to the transmission path 15 on the downstream side, and then the response signal 71₂ is transmitted to the slave station 1₄. The slave station 1₄ is operated similarly to the slave station 1₂ because it is also a receiving station, so that the response signal 71₂ which arrived is received without being transmitted to the transmission path 15 on the downstream side and is deleted. Further, the slave station 1₄ sends out a response signal 71₄ sent out by itself to the transmission path 15 on the downstream side. The response signal 71₄ is also received by the master station 1₁ which is a receiving station and is deleted. As a result, even when all the stations 1 belonging to the broadcast group (the master station 1₁ and the slave stations 1₂ and 1₄ in this description) send out the response signals to the transmission path 15, no signal collision occurs on the transmission path 15. To the sending station 1 transmitting the data packet 42 (the slave station 1₃ in this description), only the response signal sent out by the station 1 positioned on the upstream side of the sending station 1 and nearest thereto (the slave station 1₂ in this description) of the stations 1 belonging to the broadcast group is transmitted.

0082The slave station 1₂ which is a sending station receives the response signal 71₂ and at the same time, passes the response signal 71₂, and then switches the switch 18₂ in the slave station to disconnect the transmission path 15, and sends out the data packet 42 to the transmission path 15 on the downstream side. The data packet 42 is received by all the stations 1 belonging to the broadcast group (the slave station 1₄, the master station 1₁, and the slave station 1₂ in this order in this description) as described above.

0083In the third embodiment, all the stations 1 belonging to the broadcast group thus send out the response signals 71, unlike the second embodiment. However, the only one response signal 71 of the plurality of response signals sent out is received by the sending station, so that no signal collision occurs on the transmission path 15. This also makes it possible to establish data communication corresponding to a VBR and high is reliability, as in the second embodiment.

(Fourth Embodiment)

0084Fig. 10 illustrates the structure of a communication network according to a fourth embodiment of the present invention. The communication network shown in Fig. 10 has approximately the same structure as that shown in Figs. 1 to 3. Therefore, in Fig. 10, the same reference numerals are assigned to structures corresponding to the structures shown in Figs. 1 to 3 and hence, the description thereof is not repeated. That is, a master station 1, shown in Fig. 10 comprises a table 16₁, whose illustration is omitted, similarly to that shown in Figs. 1 to 3.

0085Fig. 11 is a block diagram showing the structures of a token packet sending/analysis executing device 16 and a switch 18₁ in the master station 1₁ shown in Fig. 10. Fig. 12 is a block diagram showing the structures of analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄ in slave stations 1₂ to 1₄ shown in Fig. 10. In Figs. 11 and 12, each of the token packet sending/analysis executing device 16 and the analysis executing devices 17₂ to 17₄ comprises a sending and receiving control portion 111, a transmission buffer 112, a receiving buffer 113, a packet detecting portion 114, and a communication request packet output portion 115. Further, in Fig. 11, the token packet sending/analysis executing device 16 further comprises a token packet output portion 116. As apparent from comparison between Figs. 11 and 12, the difference between the master station 1₁ and the slave stations 1₂ to 1₄ is the presence or absence of the token packet output portion 116 and the table 16₁.

0086Fig. 13 is a diagram showing on a time base packets transmitted on a transmission path 15 in the communication network shown in Fig. 10. In Fig. 13, an inquiry token packet 131, a token packet for asynchronous data 132, a token packet for isochronous data 133, a packet for asynchronous data 134, a packet for isochronous data 135, and a communication request packet (not shown) are transmitted to the transmission path 15 shown in Fig. 10. The token packet for asynchronous data 132 and the packet for asynchronous data 134 as well as the token packet for isochronous data 133 and the packet for isochronous data 135 are used in the case of asynchronous data communication and isochronous data communication described in the first embodiment and hence, the description thereof is simplified. The inquiry token packet 131 is a token packet for collecting communication requests of the respective stations 1, and a transmission bandwidth immediately after the inquiry token packet 131 is previously divided into a plurality of slots 136. Each of the stations 1 shown in Fig. 10 is previously assigned any one of the plurality of slots 136. Each of the stations 1 sends out the communication request packet to the slot assigned to itself.

0087The procedure for data communication in the communication network constructed as described above will be described.

0088The switch 18₁ in the master station 1₁ (see Fig. 11) and the switches 18₂ to 18₄ in the slave stations 1₂ to 1₄ (see Fig. 12) are in a state where the transmission path 15 is connected (on the side of terminals A) when the stations send out no packets. The switch 18₁ in the master station 1₁ and the switches 18₂ to 18₄ in the slave stations 1₂ to 1₄ disconnect the transmission path 15 (on the side of terminals B) only when the stations send out the packets (the packets other than the communication request packet), and connect the transmission path 15 again (on the side of the terminals A) immediately after packets which sent out by the station returns upon circulating around the transmission path 15. The basic operations are the same as those described in the first embodiment. As to the communication request packet, the stations 1₁ to 1₄ immediately return the switches 18₁ to 18₄, after sending out the communication request packet.

0089The token packet output portion 116 in the master station 1₁ sends out to the transmission path 15 the token packet for asynchronous data 132 for establishing asynchronous data communication, the token packet for isochronous data 135 for establishing isochronous data communication, or the inquiry token packet 131 for each predetermined time period. Examples of a sequence of sending of tokens from the master station 1₁ include a sequence for isochronous data communication and a sequence for asynchronous data communication. In the sequence for isochronous data communication, the token packet for isochronous data 135 is sent out. On the other hand, in the sequence for asynchronous data communication, the token packet for asynchronous data 132 or the inquiry token packet 131 is sent out.

0090In the case of the sequence for asynchronous data communication, the sending and receiving control portion 111 in the master station 1₁ (see Fig. 11) connects the switch 18₁ to the terminal B to disconnect the transmission path 15, and then sends out the produced inquiry token packet 131 (see Fig. 13) to the transmission path 15 from the token packet output portion 116. In each of the stations 1₁ to 1₄, the inquiry token packet 131 transmitted from the transmission path 15 on the upstream side is detected by the packet detecting portion 114. The sending and receiving control portion 111 in each of the stations 1₁ to 1₄ sends out, when the inquiry token packet 131 is detected, and when a communication request of asynchronous data to be transmitted is stored in the transmission buffer 112 in the station, a communication request packet representing the communication request of the asynchronous data from the communication request packet output portion 115 to the transmission path 15 on the downstream side using the slot for a communication request 136 previously assigned to the station. On the other hand, the sending and receiving control portion 111 in each of the stations 1₁ to 1₄ performs nothing or sends out, even when the inquiry token packet 131 is detected, and when a communication request of asynchronous data to be transmitted is not stored in the transmission buffer 112 in the station, a packet not representing the communication request of the asynchronous data to the transmission path 15 on the downstream side.

0091The packet detecting portion 114 in the master station 1₁ detects that the inquiry token packet 131 returns upon circulating around the transmission path 15, and detects and analyzes the communication request packet transmitted immediately after the inquiry token packet 131. Consequently, the master station 1₁ can receive the communication request packets in the stations 1 which are sent out to a plurality of slots for a communication request 136, and successively sends out, when there exits a station 1 which has sent a communication request, the token packet for asynchronous data 132 in which the station 1 which has sent a communication request is designated as a sending station to the transmission path 15 on the downstream side in the subsequent sequence for asynchronous data communication. The station 1 which has sent a communication request can send out asynchronous data stored in the transmission buffer 112 in the station using the token packet for asynchronous data 132. The master station 1₁ sends out, after finishing outputting the token packets for asynchronous data 132 corresponding to all the stations 1 which has sent the communication request, the inquiry token packet 131 again. By repeating the foregoing operations, asynchronous data communication between the stations is established.

0092Fig. 14 is a flow chart showing the procedure for sending of the token packets from the master station 1₁ shown in Fig. 10. The master station 1₁ judges whether or not a sequence to be currently established is a sequence for asynchronous data communication (step S141). In the case of the sequence for asynchronous data communication, there exists no station 1 which has sent the communication request in the initial state (step S143), so that the master station 1₁ sends out the inquiry token packet 131 to the transmission path 15 on the downstream side in the above-mentioned procedure (step S145). Consequently, the master station 1₁ can receive communication request packets in the stations 1 which are sent out to the slots for a communication request 136 in the above-mentioned procedure. The master station 1₁ sends out, when there exits a station 1 sending out the communication request packet, the token packet for asynchronous data 132 in which the station 1 is designated as a sending station to the transmission path 15 in the subsequent sequence for asynchronous data communication (step S144). The master station 1₁ sends out, when it finishes sending out the token packet for asynchronous data 132 in each of the stations 1 sending out the communication request packets, the inquiry token packet 131 again in the subsequent sequence for asynchronous data communication (step S145). The master station 1₁ sends out the token packet for isochronous data 133 when a sequence to be currently established is not the sequence for asynchronous data communication in the step S141 (step S142). The master station 1₁ repeats the procedure in the steps S141 to S145 described above. The master station 1₁ sends out the inquiry token packet 131, the token packet for asynchronous data 132, or the token packet for isochronous data 133 for each predetermined time period, as described above.

0093Each of the stations 1 thus outputs the communication request packet to the assigned slot for a communication request 136, provided that it holds asynchronous data to be transmitted in response to the inquiry token packet 131 sent out by the master station 1₁. The master station 1₁ sends out the token packet for asynchronous data 132 in which the station 1 sending out the communication request packet is designated as a sending station in the subsequent sequence for asynchronous data communication. Consequently, the master station 1₁ need not send out an unnecessary token packet for asynchronous data 132, and can reliably send out a token packet for asynchronous data in which the station 1 holding asynchronous data to be transmitted is designated as a sending station. This makes it possible to establish fair and efficient asynchronous data communication between the stations 1.

0094Each of the stations 1₁ to 1₄ designates an actual ID of the station 1 which should receive asynchronous data using the communication request packet sent out, making it possible for the master station 1₁ to send out the token packet for asynchronous data 132 in which the station 1 designated by the actual ID is designated as a receiving station. Simultaneously, each of the stations 1₁ to 1₄ sends out an actual ID of the station when it sends out the communication request packet, also making it possible for the master station 1₁ to easily send out the token packet for asynchronous data 132.

0095Furthermore, if information representing the amount of asynchronous data to be sent out and/or the priority of the asynchronous data to be sent out is added to the communication request packet sent out by each of the stations 1₁ to 1₄, the master station 1₁ can send out the token packet for asynchronous data 132 corresponding to the amount and/or the priority held by each of the stations 1₁ to 1₄.

(Fifth Embodiment)

0096Fig. 15 illustrates the structure of a communication network according to a fifth embodiment of the present invention. The communication network according to the present embodiment has approximately the same structure as the communication network according to the fourth embodiment. Therefore, in the structure shown in Fig. 15, the same reference numerals are assigned to structures corresponding to the structures shown in Fig. 10 and hence, the description thereof is not repeated. That is, a master station 1₁ shown in Fig. 15 comprises a table 16₁, whose illustration is omitted, similarly to that shown in each of Figs. 1 to 3, and a token packet sending/analysis executing device 161 in the master station has the same structure as that shown in Fig. 11. Slave stations 1₂ to 1₄ shown in Fig. 15 have the same structures as those shown in Fig. 12. Packets transmitted on a transmission path 15 in the communication network according to the fifth embodiment is the same as those shown in Fig. 13 if they are illustrated on a time base and hence, Fig. 13 will be incorporated in the following description.

0097The significant difference between the fifth embodiment and the fourth embodiment is that all the stations 1₁ to 1₄ are classified into a plurality of groups. More specifically, each of the stations 1₁ to 1₄ belongs to only one group, and is assigned a group ID for identifying the group to which the station itself belongs. In Fig. 15, it is assumed that the stations 1₁ and 1₂ belong to a group A (a group ID ; #A), and the stations 1₃ and 1₄ belong to a group B (a group ID ; #B).

0098The procedure of data communication in the communication network constructed as described above will be described. The procedure for data communication in the communication network according to the fifth embodiment is partially the same as the above-mentioned procedure for data communication in the communication network according to the fourth embodiment. Description is now made mainly with respect to the difference between them.

0099In the case of a sequence for asynchronous data communication, the master station 1₁ sends out a produced inquiry token packet 131 (see Fig. 13) to the transmission path 15. A group ID ; #A is set in the inquiry token packet 131 currently sent out. The stations 1₁ to 1₄ detect the inquiry token packet 131 transmitted from the transmission path 15. However, only the stations 1₁ and 1₂ receive, because the group ID designated by the currently detected inquiry token packet and the group ID of the stations identify with each other, the token packet. Each of the stations 1₁ and 1₂ sends out, provided that it receives the inquiry token packet 131, and it holds a communication request of asynchronous data to be transmitted, a communication request packet including the communication request of the asynchronous data and an actual ID of a station 1 which is a destination of transmission of the asynchronous data to the transmission path 15 using a slot 136 for a communication request packet assigned to the station (see Fig. 13).

0100The master station 1₁ detects that the inquiry token packet 131 returns upon circulating around the transmission path 15, and receives a communication request packet transmitted immediately after the inquiry token packet 131. The master station 1₁ successively sends out, provided that there exists a station 1 which has sent out a communication request of asynchronous data, a token packet for asynchronous data 132 in which a sending station and a receiving station are designated using actual IDs of the station 1 which has sent out the communication request of the asynchronous data and the station 1 which is a destination of transmission of the asynchronous data to the transmission pate 15 in the subsequent sequence for asynchronous data communication. The station 1 which has sent the communication request can send out the asynchronous data held therein in response to the token packet for asynchronous data 132. The master station 1₁ sends out token packets for asynchronous data 132 corresponding to all the stations 1 which has sent out communication requests.

0101In the subsequent sequence for asynchronous data, the master station 1₁ sends out a newly produced inquiry token packet 131 (see Fig. 13) to the transmission path 15. A group ID ; #B is set in the inquiry token packet 131 currently sent out. The stations 1₁ to 1₄ detect the inquiry token packet 131 transmitted from the transmission path 15. However, only the stations 1₃ and 1₄ receive, because the group ID designated by the currently detected inquiry token packet and the group ID of the stations identify with each other, the token packet. Each of the stations 1₃ and 1₄ sends out, provided that it receives the inquiry token packet 131, and it holds a communication request of asynchronous data to be transmitted, a communication request packet including the communication request of the asynchronous data and an actual ID of a station 1 which is a destination of transmission of the asynchronous data to the transmission path 15 using a slot for a communication request 136 assigned to the station (see Fig. 13). The subsequent procedure for communication is the same as that described above and hence, the description thereof is not repeated. The master station 1₁ repeats the foregoing operations, whereby asynchronous data communication is performed.

0102Fig. 16 is a flow chart showing the procedure that the master station 1₁ sends out the token packets shown in Fig. 15. The master station 1₁ judges whether or not a sequence to be currently established is a sequence for asynchronous data communication (step S161). In the initial state of the sequence for asynchronous data communication, there exists no station 1 which has sent out a communication request (step S163), so that the master station 1₁ sends out the inquiry token packet 131 in which the group ID ; #A is designated to the transmission path 15 (step S165), and then changes the group ID to be designated by an inquiry token packet 131 to be subsequently sent out into #B (step S166). Consequently, the master station 1₁ can receive communication request packets transmitted from the stations belonging to the group A (the stations 1₁ and 1₂) in the above-mentioned procedure. The master station 1₁ sends out, when there exits a station 1 which has sent out the communication request packet, the token packet for asynchronous data 132 in which a sending station and a receiving station are designated to the transmission path 15 in the subsequent sequence for asynchronous data communication (step S164). The master station 1₁ belongs to the group A, and sends out, when it finishes sending out the token packet for asynchronous data 132 in each of the stations 1 which have sent out communication request packets (step S163), the inquiry token packet 131 in which the group ID ; #B is designated to the transmission path 15 (step S165). The designated group ID is changed every time when the inquiry token packet is sent out. Consequently, asynchronous data communication is established fairly for each group. The master station 1₁ sends out the token packet for isochronous data 133 when a sequence to be currently established is not the sequence for asynchronous data communication in the step S161 (step S162). The master station 1₁ repeats the procedure in the steps S161 to S166 as described above. The master station 1₁ sends out the inquiry token packet 131, the token packet for asynchronous data 132, or the token packet for isochronous data 133 for each predetermined time period, as described above.

0103Each of the stations 1₁ to 1₄ can easily send out, in sending out the communication request packet, the token packet for asynchronous data 132 if it sends out an actual ID of the station together with the communication request packet because the master station 1₁ can easily designate a sending station.

0104If information representing the amount of asynchronous data to be sent out and/or the priority of the asynchronous data to be sent out is added to the communication request packet sent out by each of the stations 1₁ to 1₄, the master station 1₁ can send out the token packet for asynchronous data 132 corresponding to the amount and/or the priority held by each of the stations 1₁ to 1₄.

(Sixth Embodiment)

0105A communication network according to a sixth embodiment has approximately the same structure as the communication network according to the fourth or fifth embodiment (see Fig. 10 or 15). In the above-mentioned fourth or fifth embodiment, the master station 1₁ merely sends out an inquiry token packet 131, as shown in Fig. 13. In the sixth embodiment, however, a master station 1₁ sends out an identification signal in order that each of stations 1 can easily identify the above-mentioned slot 136 after an inquiry token packet 131. Fig. 17 illustrates on a time base the inquiry token packet 131 and identification signals 171 which are transmitted on a transmission path 15 in the communication network according to the sixth embodiment. In Fig. 17, each of the identification signals 171 is sent out from the master station 1₁ so as to represent the head of each of slots 136 subsequently to the inquiry token packet 131. Consequently, each of the stations 1 detects, when it detects the inquiry token packet 131, the identification signals 171 succeeding the inquiry token packet 131, so that a communication request packet (as described above) can be easily inserted into the slot 136 assigned to the station. Further, the master station 1₁ also detects the identification signals 171 succeeding the inquiry token packet circulating around the transmission path 15, to recognize the communication request packet.

0106In the foregoing description, each of the identification signals 171 shall be sent out to the transmission path 15 so as to represent the head of each of the slots 136. However, it may represent the end of the slot for a communication request 136, in which case the same effect is obtained.

0107Although in the above-mentioned sixth embodiment, description was made of a communication network which is constituted by one loop, the sixth embodiment is also applicable in a communication network which is constituted by a plurality of loops.

(Seventh Embodiment)

0108In the fourth embodiment, description was made of the structures of the token packet sending/analysis executing device 16 and the switch 18, in the master station 1₁ and the analysis executing devices 17₂ to 17₄ and the switches 18₂ to 18₄ in the slave stations 1₂ to 1₄ with reference to Figs. 11 and 12. Fig. 18 is a block diagram showing the other structures of a token packet sending/analysis executing device 16 and a switch 18₁ in a master station 1₁ and analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄ in slave stations 1₂ to 1₄. In Fig. 18, the token packet sending/analysis executing device 16 comprises a sending and receiving control portion 181, a transmission buffer 182, a receiving buffer 183, a packet detecting portion 184, a communication request packet output portion 185, a token packet output portion 186, a register for a destination of transmission 187, and a register for a source of transmission 188. Each of the analysis executing devices 17₂ to 17₄ in the slave stations 1₂ to 1₄ differ from the token packet sending/analysis executing device 16 in the master station 1₁ in that it does not comprise the token packet output portion 186 and a table 16₁. In Fig. 18, structures corresponding to the structures shown in Figs. 11 and 12 are assigned difference reference numerals and the same names and hence, the description thereof is not repeated.

0109In transmitting asynchronous data, an equipments 1820 connected to the outside of the token packet sending/analysis executing device 16 or the analysis executing devices 17₂ to 17₄ write asynchronous data to be transmitted to the transmission buffer 182 and write an actual ID of a station to be a destination of transmission of the asynchronous data in the register for a destination of transmission 187. The sending and receiving control portion 181 in each of the stations sends out, after the asynchronous data to be transmitted and the actual ID of the station to be the destination of transmission start to be stored in the transmission buffer 182 and the register for a destination of transmission 187, a communication request packet to a transmission path 15 through the switch 18 in the station from the communication request packet output portion 186 in response to an inquiry token packet sent out by the master station 1₁. Thereafter, the station 1 sends out the asynchronous data stored in the transmission buffer 182 to the transmission path 15 through the switch 18 in the station using a token packet for asynchronous data which is sent out by the master station 1₁ and in which the station is designated as a sending station.

0110Furthermore, the asynchronous data is received by a token packet for asynchronous data which is sent out by the master station 1₁ and in which the station is designated as a receiving station. The asynchronous data received by each of the stations is held once in the receiving buffer 183. When asynchronous data corresponding to one packet is held in the receiving buffer 183, an actual ID of a station transmitting the asynchronous data (a sending station) is stored in the register for a source of transmission 188. The equipment 1820 connected to the receiving station can read out, after the asynchronous data corresponding to one packet and the actual ID of the sending station are stored in the receiving buffer 183 and the register for a source of transmission 188, the received asynchronous data and the actual ID of the sending station.

0111In transmitting asynchronous data, the asynchronous data is thus stored in the transmission buffer 182, and an actual ID of a station which should receive the data (a receiving station) is stored in the register for a destination of transmission 187, after which each of the sending stations responds to the inquiry token packet sent out by the master station 1₁. On the other hand, in receiving asynchronous data, the equipment 1820 can read out, when the received asynchronous data corresponding to one packet is stored in the receiving buffer 183, and the actual ID of the station which is a source of transmission of the data (a sending station) is stored in the register for a source of transmission 188, the asynchronous data and the actual ID. Consequently, it is possible to transmit the asynchronous data to each of the stations 1 and receive the asynchronous data from the station 1.

(Eighth Embodiment)

0112Fig. 19 illustrates the structure of a communication network according to an eighth embodiment of the present invention. In Fig. 19, a plurality of stations (four stations 1₁ to 1₄ are illustrated) are connected so as to be capable of communicating with each other by a loop-shaped transmission path 15. Further, the station 1₁ functions as a master station, and the other stations 1₂ to 1₄ function as slave stations (which are hereinafter referred to as the master station 1₁ and the slave stations 1₂ to 1₄). The master station 1₁ comprises a token packet sending/analysis executing device 16 and a switch 18₁. The slave stations 1₂ to 1₄ comprise analysis executing devices 17₂ to 17₄ and switches 18₂ to 18₄. The procedure for automatically setting an actual ID in each of the stations 1 accommodated in the network in the communication network constructed as above will be described with reference to Figs. 20 to 28.

0113First, Fig. 20 illustrates the initial state such as the time of turning on the power supply of the communication network according to the present embodiment. In the initial state, "0x3E" is set as initial IDs in the stations 1₁ to 1₄, and the switches 18₁ to 18₄ are further connected to terminals A, respectively. The initial IDs are identifiers which are common among the stations 1 in the communication network. The common initial ID need not be necessarily set in the master station 1₁, and an actual ID (for example, "0x00") may be set from the beginning, unlike the other slave stations 1₂ to 1₄.

0114The master station 1₁ first produces a token packet for switching using the token packet sending/analysis executing device 16, and sends out the token packet to a transmission path 15 upon connecting the switch 18₁ to a terminal B. In the token packet for switching, a station to be a source of transmission of data (a sending station) and a station to be a destination of transmission of the data (a receiving station) are designated using the initial ID ("0x3E"). Therefore, the station 1 having the initial ID on the transmission path 15 connects the switch 18 (switches 18₁ to 18₄ in all the stations 1₁ to 1₄ in this description) to the terminal B in an attempt to transmit a data packet, as shown in Fig. 21. The process is hereinafter referred to as a switching process. The master station 1₁ must connect, when it is assigned the actual ID from the beginning, the switch 18₁ in the station to the terminal B after sending the token packet for switching and receiving the sent token packet which circulated.

0115By the switching process, the master station 1₁ sends out an actual ID setting command 221 to the transmission path 15 as one type of data packet as shown in Fig. 22 while the switches 18₁ to 18₄ in all the stations 1₁ to 1₄ are connected to the terminals B. The actual ID setting command 221 is sent out in order to set the actual ID of a receiving station to "0x01". Since all the stations 1₁ to 1₄ on the transmission path 15 are designated as receiving stations, and all the switches 18₁ to 18₄ are connected to the terminals B, the actual ID setting command currently sent out is received only by the slave station 1₂ which is a station subsequent to the master station 1₁, not to be transmitted to the stations 1 on the downstream side of the slave station 1₂. Consequently, only the slave station 1₂ performs processing conforming to the received actual ID setting command 221, so that "0x01"is fixedly set therein as an actual ID (see Fig. 22). A process as shown in Fig. 22 is hereinafter referred to as an actual ID setting command sending process. The station 1 in which the switch 18 is connected to the terminal B using the current token packet for switching (all the stations 1₁ to 1₄ in this description) connects the switch 18 to the terminal A after an elapse of a predetermined time period.

0116The master station 1₁ sends out the actual ID setting command 221, and then judges whether or not the actual ID setting command 221 returns again upon circulating around the transmission path 15. Since the actual ID setting command is not transmitted to the stations 1 on the downstream side of the slave station 1₂, it is not returned to the master station 1₁. The master station 1₁ considers, when the actual ID setting command 221 sent out by itself does not return within a predetermined time period, that the actual ID setting command 221 is received by any one of the slave stations 1₂ to 1₄, and waits for an actual ID setting acknowledgment transmitted from the slave station 1. In the case, the master station 1₁ designates a sending station using the actual ID ("0x01") and sends out a token packet for asynchronous data in which the master station 1₁ is designated as a receiving station to the transmission path 15 in order that the slave station 1 in which the actual ID is set can transmit the actual ID setting acknowledgment. In the token packet for asynchronous data, when the master station 1₁ has an initial ID ("0x3E") which is common to those of the slave stations 1₂ to 1₄, the master station 1₁ may be designated as a receiving station using the common initial ID. On the other hand, when the master station 1₁ has an actual ID from the beginning, the master station 1₁ may be designated as a receiving station using the actual ID ("0x00").

0117The slave station 1₂ in which the actual ID ("0x01") is set sends out, when data transmission is enable by a token packet for asynchronous data, an actual ID setting acknowledgment indicating that the actual ID is correctly set as a data packet. The actual ID setting acknowledgment is received by the station 1 having an initial ID "0x3E" or an actual ID "0x00". Although the actual ID setting acknowledgment is also received, when the master station 1₁ has the common initial ID, by the other slave station 1 having the initial ID (the slave stations 1₃ and 1₄ at the present time point), the contents thereof exert no adverse effect because they are interpreted only by the master station 1₁. When the master station 1₁ receives the actual ID setting acknowledgment from the slave station 1₂ as described above, it is recognized that the actual ID "0x01"is correctly set in any one of the slave stations 1. This process is hereinafter referred to as an actual ID confirmation process. The master station 1₁ recognizes, when it does not receive the actual ID setting acknowledgment, that the actual ID is not correctly set in any of the slave stations 1. In this case, the above-mentioned switching process to the actual ID confirmation process are repeated in the communication network.

0118When the master station 1₁ receives the above-mentioned actual ID setting acknowledgment, the subsequent switching process is carried out in the communication network. The master station 1₁ first determines an actual ID to be currently set. The actual ID to be currently set is so selected as not to be overlapped with the actual ID previously set ("0x01"). For example, the master station 1₁ increments the actual ID previously set, to select the actual ID to be currently set. By following this selecting method, the actual ID to be subsequently set is "0x02".

0119The master station 1₁ produces the same token packet for switching as described above, and sends out the produced token packet to the transmission path 15 after selecting the actual ID. Also in the current token packet for switching, both a sending station and a receiving station are designated using the initial ID ("0x3E"). Therefore, the switch 18 in the station 1 having the initial ID (the switches 18₁, 18₃ and 18₄ in the stations 1₁, 1₃ and 1₄ in this description) on the transmission path 15 is connected to the terminal B, as shown in Fig. 23. The switch 18₂ in the station 1₂ remains connected to the terminal A because the actual ID is set therein.

0120While the switches 18₁, 18₃ and 18₄ in the stations 1₁, 1₃ and 1₄ are connected to the terminals B by the switching process, the master station 1₁ sends out the actual ID setting command 221 to the transmission path 15, as shown in Fig. 24. The current actual ID setting command 221 is sent out in order to set an actual ID of a predetermined receiving station to "0x02". Since the stations 1₁, 1₃ and 1₄ on the transmission path 15 are designated as receiving stations, and the switch 18₂ is connected to the terminal A, the actual ID setting command 221 currently sent out is received only by the slave station 1₃ through the slave station 1₂, not to be transmitted to the stations 1 on the downstream side of the slave station 1₃. Consequently, only the slave station 1₃ performs processing conforming to the received actual ID setting command 221, so that "0x02" is fixedly set therein as an actual ID (see Fig. 24). The station 1 in which the internal switch 18 is connected to the terminal B using the current token packet for switching (the stations 1₁, 1₃ and 1₄ in this description) connects the switch 18 to the terminal A after an elapse of a predetermined time period.

0121The master station 1₁ judges whether or not the actual ID setting command sent out by itself returns upon circulating around the transmission path 15. Since the current actual ID setting command does not return, however, the master station 1₁ waits for the actual ID setting acknowledgment transmitted from the slave station 1 receiving the actual ID setting command. In the case, the master station 1₁ designates a sending station using the actual ID ("0x02") in order that the slave station 1 in which the actual ID is currently set can transmit the actual ID setting acknowledgment, and sends out to the transmission path 15 the token packet for asynchronous data in which the master station 1₁ is designated as a receiving station.

0122The slave station 1₃ in which the actual ID ("0x02") is set sends out, when data transmission is enable by the token packet for asynchronous data, the actual ID setting acknowledgment as a data packet. The actual ID setting acknowledgment is received and interpreted only by the master station 1₁ as described above, so that it is recognized that the actual ID "0x02" is correctly set in any one of the slave stations 1 (an actual ID confirmation process). When the master station 1₁ does not receive the actual ID setting acknowledgment as described above, the above-mentioned switching process to the actual ID confirmation process are repeated in the communication network.

0123When the master station 1₁ receives the above-mentioned actual ID setting acknowledgment, the subsequent switching process to the actual ID confirmation process are carried out in the communication network. The master station 1₁ first determines an actual ID to be currently set. The actual ID to be currently set is so selected as not to be overlapped with the actual IDs ("0x01" and "0x02") previously set. The master station 1₁ increments the actual ID "0x02" previously set, for example, to select an actual ID "0x03" to be currently set. As apparent from the foregoing, the actual ID "0x03" is fixedly set in the slave station 1₄.

0124When the master station 1₁ receives the above-mentioned actual ID setting acknowledgment, the subsequent switching process to the actual ID confirmation process are carried out in the communication network. The master station 1₁ first determines an actual ID to be currently set. The actual ID to be currently set is so selected as not to be overlapped with the actual IDs ("0x01", "0x02" and "0x03") previously set. For example, the master station 1₁ increments the actual ID "0x03" previously set, to select an actual ID "0x04" to be currently set.

0125The master station 1₁ produces the same token packet for switching as described above, and sends out the produced token packet to the transmission path 15 after selecting the actual ID to be currently set. Also in the current token packet for switching, both a sending station and a receiving station are designated using an initial ID ("0x3E"). Therefore, the switch 18 in the station 1 having the initial ID (the switch 18₁ in the station 1₁ in this description) on the transmission path 15 is connected to the terminal B, as shown in Fig. 25. The switches 18₂ to 18₄ in the stations 1₂ to 1₄ remain connected to the terminals A because the actual IDs are set therein.

0126While the switch 18₁ in the station 1₁ is connected to the terminal B by the switching process, the master station 1₁ sends out the actual ID setting command 221 to the transmission path 15, as shown in Fig. 26. The actual ID setting command 221 is sent out in order to set an actual ID of a predetermined receiving station to "0x04". Since the station 1₁ on the transmission path 15 is designated as a receiving station, and the switches 18₂ to 18₄ are connected to the terminals A, the actual ID setting command 221 currently sent out is received only by the master station 1₁ through the slave stations 1₂ to 1₄. Consequently, only the master station 1₁ performs processing conforming to the received actual ID setting command 221, so that "0x04" is fixedly set therein as an actual ID (see Fig. 26). The station 1 in which the switch 18 is connected to the terminal B using the current token packet for switching (the station 1₁ in this description) connects the switch 18 to the terminal A after an elapse of a predetermined time period.

0127The master station 1₁ judges whether or not the actual ID setting command 221 sent out by itself is returned upon circulating around the transmission path 15. The master station 1₁ recognizes that the actual IDs are fixedly set in all the stations 1 accommodated in the communication network because the current actual ID setting command 221 returns, to complete the setting of the actual IDs (see Fig. 27). In the communication network, isochronous data communication or the like described in the first embodiment, for example, will be thereafter established.

0128As described in the foregoing, if the token packet for switching and the actual ID setting command are repeatedly transmitted, it is possible to automatically set the actual IDs in the stations from the station subsequent to the master station 1₁ to the station on the downstream side (the slave stations 1₂, 1₃ and 1₄ and the master station 1₁ in this order).

0129Fig. 28 is a block diagram showing the structures of the token packet sending/analysis executing device 16 and the switch 18₁ in the master station 1₁ shown in Fig. 19 and the structures of the analysis executing devices 17₂ to 17₄ and the switches 18₂ to 18₄ in the slave stations 1₂ to 1₄ shown in Fig. 19. The token packet sending/analysis executing device 16 differs from the analysis executing devices 17₂ to 17₄ in that it has a function of sending out token packets. It will be previously noted that the function of sending out token packets is not illustrated in Fig. 28.

0130In Fig. 28, each of the token packet sending/analysis executing device 16 and the analysis executing devices 17₂ to 17₄ comprises a storage device 281, a sending and receiving control portion 282, and a packet detecting portion 283. Although the storage device 281 initially stores an initial ID ("0x3E"), it stores an actual ID fed by the master station 1₁ through the above-mentioned setting of actual IDs. The packet detecting portion 283 detects a special pattern included in a token packet (a token packet for switching, for example) sent out for each predetermined time period from the master station 1₁, and detects an actual ID setting command. The sending and receiving control portion 282 in the station receives an actual ID setting command and transmits an actual ID setting acknowledgment while a clock of the station is synchronized with a clock of the master station 1₁ on the basis of the special pattern detected by the packet detecting portion 283. This establishes the synchronization between clocks of all the stations 1₁ to 1₄ and a clock of the communication network.

0131Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.