Communication system using route setup procedure

Abstract: A communication system using a network route establishing technique for a network having a plurality of nodes (11 to 18) connected through links (21 to 31), in which a route search message is delivered simultaneously in a plurality of directions from a sender node (11) through a network route to a destination node, and a confirmation is delivered from the destination through the network route back to the sender node, and accordingly, a network route is established. The communication system includes a device for detecting, at a node (13) through which a search message is to be transmitted, a possibility of a transmission of the search message beyond the node (13), a device for delivering a cancel message in the direction from which the search message has been transmitted, and a device for releasing the network route engaged by the search message, based on the delivered cancel message.

Description: The present invention relates to a communication system using a technique of establishing a network route. The system according to the present invention can be used for a network having a plurality of nodes connected through links and used in a telephone communication or a data communication system. In general, a network is constituted by a plurality of nodes connected each other through a plurality of links, communicatable terminal devices connected to the nodes, and a center station connected to the nodes through control links. The state of each of the nodes or the links is monitored by the center station, and the most suitable network route is established based on the results of the monitoring. As one method of establishing a network route by exchanging messages between two nodes, and distributing the processings of the search for a detour route to the nodes in a network, where a failure occurs in the network, a flooding technique is used. In the flooding technique, information is transmitted simultaneously in a plurality of directions. In the above-described system using a center station which monitors the state of each of the nodes and the links, the control signals are concentrated at the center station, and thus, in a complicated network having a large capacity, the length of time required for establishing a route is increased, which causes a problem in such a system. In the system using the flooding technique, problems arise in that it is difficult to deal with a situation wherein a failure occurs in a node or failures occur in a plurality of links. Reference is made to the article "Performance models for Noahnet" of Parulkar et al., Computer Communications Review, vol. 18, no. 4, August 1988, New York, US, pages 262-273, in which flood stopping messages are delivered in all directions after a flooding message is received by a destination. This causes unnecessary messages to be transmitted around within the network, which requires waiting for the disappearance of the first time messages in the network after the first time flooding before the start of the second flooding for searching other routes. Therefore, in the case where the floodings are repeated many times, a considerable length of time is needed for restoring all the faults. US-A-4,914,571 discloses a computer network in which a LOCATE search dynamically locates resources (e.g. logical units (LUs)) and transaction program and files associated with (LUs) in the computer network so that a session can be established between the origin and the destination of the search. In a network which includes end nodes associated with server nodes, a resource contained in any node is located by a requesting node. The requesting node initiates a search of the resources residing within itself. If the resource does not reside in the requesting node, the server node searches the resources known to the server node that reside anywhere in the network. If the resource is not known by the server node, it searches all resources that reside in its associated end nodes. If the resource does not reside in the associated end nodes, either a request is sent to a central directory if one exists or a search of all resources in the network is made. The present invention may be implemented according to preferred embodiments to provide an improved communication system using a network route establishing technique in which the control processes are distributed to the nodes, to thereby avoid a concentration of same at a center station, an engaged but unused route is released by a cancel message, so that the route is quickly established, and thus the utilization efficiency of the network is enhanced. With the present invention, it is also possible to provide an improved communication system using a network route establishing technique in which the processes in response to a plurality of simultaneous requirements for an establishment of routes can be carried out satisfactorily. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 illustrates a delivery of a search message and a return of a confirmation message, as in a prior art; Fig. 2 shows a communication system according to an embodiment of the present invention; Figs. 3 to 6 show communication systems according to four other embodiments of the present invention, respectively; Figs. 7 to 10 show communication systems not according to the present invention but included for descriptive purposes; Fig. 11 shows an example of the structure of a node in the communication system according to the embodiments of the present invention; Figs. 12A to 12D show an example of a flow chart of the processing of the search message in the system according to the embodiments of the present invention, whereas Fig. 12E is a corresponding flow chart for a system that is not in accordance with the invention. Fig. 13 shows an example of a flow chart of the processing in a node which delivers a search message; Fig. 14 shows an example of a flow chart of the processing in a node which receives a search message; Fig. 15 shows an example of a flow chart of the processing in a node which relays a search message; and Fig. 16 shows a communication system not according to the present invention. Before describing the preferred embodiments of the present invention, the operations of a delivery of a search message and a return of a confirmation message in a prior art will be explained with reference to Fig. 1. As shown in Fig. 1, the network is constituted by a plurality of nodes 11, 12, 13, 14, 15, 16, 17, and 18, and a plurality of links 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, and 31 by which the concerned nodes are connected, respectively. In the network shown in Fig. 1, search messages are delivered from, for example, node 11, in a plurality of directions simultaneously to reach a destination node, for example, the node 18. Upon receiving the search message, the destination node 18 returns a confirmation message to the node 11, and consequently, a network route from the node 11, through a link 27, a node 17, and a link 29 to the node 18, is established. A communication system using a network route establishing technique according to an embodiment of the present invention is shown in Fig. 2. The network to which the communication system using the network route establishing technique of Fig. 2 is applied is constituted by a plurality of nodes 11 to 18, and a plurality of links 21 to 31 by which the concerned nodes are connected, respectively. In the system of Fig. 2, one of the search messages delivered from the node 11 is propagated through a link 21, a node 12, and a link 22 toward the node 13. In the system of Fig. 2, with regard to the node 13, if the search message reaching the node 13 cannot be further propagated beyond the node 13, a cancel message is sent back from the node 13, and the network route engaged by the search message is cancelled by the returned cancel message. A communication system according to another embodiment of the present invention is shown in Fig. 3. The network to which the communication system of Fig. 3 is applied is the same as in the case of Fig. 2. In the system of Fig. 3, with regard to the node 12, if all of the cancel messages are returned to the node 12 through all of the links through which the search messages are delivered, a cancel message is delivered from the node 12 in the direction from which the search message has been received. A communication system according to another embodiment of the present invention is shown in Fig. 4. The network to which the communication system of Fig. 4 is applied is the same as in the case of Fig. 2. In the system of Fig. 4, with regard to the node 14, if a vacant line does not become available at the node 14, a cancel message is delivered in the direction from which the search message has been transmitted, and the route engaged by the search message is released by this cancel message. A communication system according to another embodiment of the present invention is shown in Fig. 5. The network to which the communication system of Fig. 5 is applied is the same as in the case of Fig. 2. In the system of Fig. 5, with regard to the node 16, if the number of nodes through which the search message has been transmitted becomes more than a predetermined number of nodes, a cancel message is delivered in the direction from which the search message has been transmitted, and the route engaged by the search message is released by this cancel message. In the system of Fig. 5, it is possible to vary the above-mentioned predetermined number of nodes. A communication system according to another embodiment of the present invention is shown in Fig. 6. The network to which the communication system of Fig. 6 is applied is the same as in the case of Fig. 2. In the system of Fig. 6, with regard to the node 17, if the same search message has already arrived through a different route, a cancel message is delivered in the direction from which the search message has been transmitted, and the route engaged by the search message is released by this cancel message. A communication system according to another embodiment is shown in Fig. 7. The network to which the communication system of Fig. 7 is applied is the same as in the case of Fig. 2. In the system of Fig. 7 which is not in accordance with the invention, with regard to the node 17, if a search message through a different route has passed by the node 17, a subsequently arrived search message is held in the node 17. When an establishing or a release of a route to be secured by the previously transmitted search message is carried out, the search message held in the node 17 is read from the node 17, and the read search message is delivered. Another communication system not according to the present invention is shown in Fig. 8. The network to which the communication system of Fig. 8 is applied is the same as in the case of Fig. 2. In the system of Fig. 8, with regard to the node 17, if the search message delivered through a different route has passed by the node 17, a subsequently arrived search message is held in the node 17 in the waiting state, and this waiting state of the held search message is informed to the node 11 from which the held search message has been transmitted. A communication system not according to the present invention is shown in Fig. 9. The network to which the communication system of Fig. 9 is applied is the same as in the case of Fig. 2. In the system of Fig. 9, with regard to the node 17, if the search message delivered through a different route has passed by the node 17, the length of time for which a subsequently arrived search message is held in the node 17 is limited to a preselected length of time, and upon an expiration of the preselected time, the subsequently arrived search message is cancelled. In the system of Fig. 9, the measurement of the elapsed time can be carried out either in the node 17 in which the search message is held or in the node 11 in which the detection of a failure is carried out. Another communication system that is not an embodiment of the present invention is shown in Fig. 10. The network to which the communication system of Fig. 10 is applied is the same as in the case of Fig. 2. In the system of Fig. 10, with regard to the node 17, the delivery of search messages held in node 17 is carried out in sequence in accordance with the sequence of the order of priority thereof. An example of the structure of a node in the communication system according to the embodiments of the present invention is shown in Fig. 11. The node 100 corresponds to the nodes 11 to 18 in Figs. 2 to 10. As shown in Fig. 11, a node 100 is constituted by a communication control portion 101, a message analyzing portion 102, a message processing portion 103, a message storing portion 104, a timer 105, and a message delivery portion 106. The control portion 101 controls the communications between the node 100 and the other nodes through links 2A, 2B and 2C, and carries out the extraction of messages from the other nodes and the insertion of messages to the other nodes. The messages from the other nodes include search messages and cancel messages, and the messages to the other nodes include confirmation messages, cancel messages, and wait messages. In the message analyzing portion 102, an analysis is made of the messages from the other nodes extracted by the communication control portion 101. In the message processing portion 103, predetermined various processings of the messages analyzed in the message analyzing portion 102 are carried out. The message storing portion 104, for example, a buffer storage, can store a plurality of messages, and exchange messages with the message storing portion 103. The timer 105 measures the time for which a message is held in the message storing portion or the time elapsed from a delivery of a message. The message delivery portion 106 delivers a message from the message processing portion 103 to the communication control portion 101. The operation of the node 100 of Fig. 11 will be explained in relation to the communication systems shown in Figs. 2 to 10 according to embodiments of the present invention. As in the case of Fig. 2, with regard to the node 13, when the search message from the node 11 cannot be transmitted beyond the node 13, a cancel message is delivered through the message processing portion 103 and the message delivery portion 106 in the direction from which the search message has been received, and the route engaged by the search message is released by the cancel message. As in the case of Fig. 3, with regard to the node 12, when the node 12 receives all of the cancel messages through all of the links through which the search messages have been delivered, a cancel message is delivered from node 12 in the direction from which the search message to node 12 has been transmitted. The cancel message is supplied through the message analyzing portion 102 to the message processing portion 103, and when in the message processing portion 103 determines that all of the cancel messages are received through all of the links, a cancel message is delivered through the message delivery portion 106 in the direction from which the search message has been transmitted. As in the case of Fig. 4, with regard to the node 14, when a vacant line is not available at the node 14 through which the search message is to be transmitted, a cancel message is delivered through the message delivery portion 106 in the direction from which the search message has been transmitted, and the route which has been engaged by the search message is released by the cancel message. As in the case of Fig. 5, with regard to the node 16, when the number of nodes 17, 15, and 16 through which the search message has passed, i.e., hop number, becomes more than a predetermined number at node 16, a cancel message is delivered from node 16 in the direction from which the search message has been transmitted, and the route engaged by the search message is released by the cancel message. In the message processing portion 103, the number of nodes through which the search message has been transmitted is compared with a predetermined number, and when the number of nodes through which the search message has been transmitted becomes more than a predetermined number, the cancel message is delivered through the message processing portion 103 and the message delivery portion 106 in the direction from which the search message has been transmitted, and the route engaged by the search message is released. Note, the above-mentioned predetermined number can be made variable. As in the case of Fig. 6, with regard to the node 17, when the same search message, i.e., the message having the same identifier (ID), has already reached the node 17, a cancel message is delivered in the direction from which the search message in question has been transmitted, and the route engaged by the search message in question is released by the cancel message. In the message processing portion 103, it is decided whether or not the same search message has already reached its destination, based on the identifier information, and when the decision is affirmative, a cancel message is delivered through the message processing portion 103 and the message delivery portion 106 in the direction from which the search message in question was transmitted, and the route engaged by the search message in question is released. As in the case of Fig. 7, with regard to the node 17, if the search message transmitted through a different route has already passed through node 17, the search messages subsequently arriving thereat are successively held by being stored in the message storing portion 104. When an establishment or release of the route engaged by the search message which has been transmitted is carried out, the message stored in the message storing portion 104 is delivered through the message processing portion 103 and the message delivery portion 106. As in the case of Fig. 8, with regard to the node 17, if the search message transmitted through a different route has already passed through the node 17, a search message subsequently arriving there is held by being stored in the message storing portion 104, and at the same time, a wait message indicating the waiting state is delivered through the message processing portion 103 and the message delivery portion 106 to the node 11 from which the search message in question has been transmitted. As in the case of Fig. 9, with regard to the node 17, if the search message transmitted through a different route has already passed through the node 17, the length of time for which it is stored in the message storing portion 104 is limited to a predetermined time length, and when this predetermined time length has elapsed, a message subsequently arriving there is cancelled by the operation of the message processing portion 103. The measurement of the elapse of time is carried out either in the node 17 in which the search message is stored or in the node 11 in which a failure is detected. The information in the timer 105 is used for the measurement of the elapse of time. As in the case of Fig. 10, with regard to the node 17, the search messages stored in the message storing portion 104 and the delivery of the read search message are read in the sequence of the priority thereof. It is also possible to carry out the reading and the delivery in accordance with the arrival sequence. A flow chart of an example of the processing of the search message in the system according to the embodiments of the present invention is shown in Figs. 12A to 12E. With regard to the flow chart of Fig. 12A, a decision on whether or not the number of the passed-by nodes is more than a predetermined number (S101), a decision on whether or not the same identifier message has reached (S102) its destination, a decision on whether or not a link through which the search message can be delivered exists (S103), a decision on whether or not a vacant line which can be established as a network route exists (S104), and a determination of an occurrence of time-out (S105) are carried out. With regard to the flow chart of Fig. 12B, a decision on whether or not a message having different identifier has reached (S106) its destination, a step of storing the message in the message buffer (S107), a process for delivering a wait message (S108), a step for starting the timer (S109), and a step for delivering the search message (S110) are carried out. With regard to the flow chart of Fig. 12C, a decision on whether or not all of the cancel messages have arrived through all of the links through which the search messages have transmitted (S111), a step for delivering a cancel message (S112), and a step for processing the next message (S113) are carried out. With regard to the flow chart of Fig. 12D, a step for delivering a route establishing message (S114), a step for delivering a cancel message (S115), and a step for processing the next message (S116) are carried out. With regard to the flow chart of Fig. 12E, a decision on whether or not a message is stored in the buffer storage (S117), and a step for reading a message having a higher priority from the buffer storage (S118), are carried out. The examples of the flow charts of the processes in a node which delivers a search message, in a node which receives a search message, and in a node which carries out a relaying of a search message, are shown in Figs. 13, 14, and 15, respectively. With regard to the flow chart of Fig. 13, a step for delivering a search message (S201), a step for starting the timer (S202), a decision on whether or not a route establishing message has arrived (S203), a step for establishing a route (S204), a decision on whether or not a cancel message has arrived (S205), a decision on whether or not a time out has occurred (S206), and a decision on whether or not a re-try is to be made (S207), are carried out. With regard to the flow chart of Fig. 14, a decision on whether or not a search message has arrived (S301), a decision on whether or not the arrived search message is the same as the previously arrived search message (S302), a step for delivering a route establishing message (S303), and a step for delivering a cancel message (S304), are carried out. With regard to the flow chart of Fig. 15, a decision on whether or not the message is a search message (S401), a step for processing the search message (S402), a decision on whether or not the message is a route establishing message (S403), a step for processing the route establishing message (S404), a decision on whether or not the message is a cancel message (S405), and a step for processing the cancel message (S406), are carried out. Another communication system that is not according to the present invention is shown in Fig. 16. In the system of Fig. 16, it is assumed that a failure has occurred in the node 19. In response to the occurrence of the failure in the node 19, first search messages are delivered from the node 11, simultaneously and in a plurality of directions, and second search messages are delivered from the node 14, also simultaneously and in a plurality of directions. With regard to the node 17, if a second search message has been passed-by when a first search message arrives at the node 17, this first search message is stored in a buffer storage 171 in the node 17. After the establishing or the release of a route engaged by the previously passed second search message, the first message stored in the buffer storage 171 is read from the buffer storage 171, and the read first message is delivered from the node 17. The information of the storage state of the first search message in the node 17 is transmitted as a wait message, from the node 17 to the node 11. The length of time for which the first search message is stored in buffer storage 171 is limited to a predetermined time length, and when this predetermined time length has expired, a cancel message is transmitted from the node 17 to the node 11 and the first search message is cancelled by this cancel message. The measurement of the elapse of time with regard to the predetermined time length can be carried out in the node 17, node 11, or node 14. With regard to the reading of the search messages stored in buffer storage 171 in the node 17 and the delivery of the read search message, it is possible to read the search messages in accordance with the priority sequence or the arrival sequence at the node 17.

Claims: A communication system using a network route establishing technique for a network having a plurality of nodes (11-18;100) connected through links (21-31), in which a route search message is delivered simultaneously in a plurality of directions from a node of the plurality comprising a sender node (11) through a network route to a node of the plurality comprising a destination node (18), the route search message successively engaging other nodes of the plurality which remain engaged until released by a cancel message, and a confirmation is delivered from said destination node through the network route back to said sender node, and accordingly, the network route is established, said communication system comprising, in each node (11-18;100): means for detecting (102), at each said node (100) through which a search message is to be transmitted, a possibility of the transmission of said search message beyond the said node; means for delivering (106) a cancel message from the said node (100) only in the direction from which said search message has been transmitted, in the event that the transmission of said search message beyond the said node (100) is detected not to be possible; and means for releasing (103) the network route engaged by said search message based on said delivered cancel message. A system according to claim 1, wherein the arrangement is such that, in operation, when one said node (12) of the plurality receives respective cancel messages through all links (22,23,26) along which respective search messages have been delivered from the one said node (12), a respective cancel message is delivered from the one said node (12) to the sender node (11) in the direction from which the said search message was received at the one said node (12). A system according to claim 1, wherein the arrangement is such that, in operation, when a vacant line at any said node through which a search message is to be transmitted becomes unavailable, the transmission of said search message beyond that node is detected as being impossible and the cancel message is delivered to effect the release of the route engaged by said search message. A system according to claim 1, wherein the arrangement is such that, when a search message is transmitted through a number of said nodes and the number of the nodes through which said search message is transmitted becomes more than a predetermined number at one said node (16), the cancel message is delivered from the one said node (16) to effect the release of the route engaged by said search message. A system according to claim 4, wherein said predetermined number is made variable. A system according to claim 1, wherein the arrangement is such that, in operation, when a search message is transmitted through a number of said nodes and it is detected that the same message has already arrived through another route at one said node (17), the cancel message is delivered from the one said node (17) to effect the release of the route engaged by said search message.

Inventors: CHUJO TAKAFUMI, KOMINE HIROAKI, MIYAZAKI KEIJI, OGURA TAKAO, SOEJIMA TETSUO, CHUJO, TAKAFUMI, KOMINE, HIROAKI, MIYAZAKI, KEIJI, OGURA, TAKAO, SOEJIMA, TETSUO
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: H04L12
IPC codes: H04L12