JP3977786B2 - Multicast network, multicast transfer route calculation method, multicast transfer route calculation program, and recording medium recording the program - Google Patents

Description

  The present invention relates to multicast communication in which information is copied and transferred to each end point in a node where the route is divided among routes connecting the start point serving as the information distribution source and the end point serving as the information distribution destination. In particular, the present invention relates to a technique for obtaining an optimal multicast transfer path that connects a given start point and one or more end points.

  Multicast communication is attracting attention as a method for delivering moving images and audio to a large number of users over a computer network. In this communication method, information is copied at a portion where the route is divided among routes connecting the start point of the route and one or more selected end points, and the information is delivered to each end point. When information is delivered to a specific number of end points using unicast communication that performs one-to-one communication with the start point, it is necessary to prepare information for the start point by the number of end points. On the other hand, the amount of information in the network is reduced by using multicast communication.

  In multicast communication, a specific number of end points are managed in a management unit called a multicast group, and one transfer path is set for the multicast group. This transfer path is set so as to connect all the end points belonging to the multicast group from the start point. A user who wants to acquire information transferred to a certain multicast group may join the multicast group. For this reason, a transfer route changes according to a user's participation situation.

  A forwarding route in multicast communication is determined using an index called a metric given to a link. The metric is determined according to the network administrator's network design policy. The algorithm for performing the route calculation is also selected according to the design policy. There are many types of algorithms. Typical examples are an algorithm that minimizes the sum of metrics from the start point to the end point of a route, and an algorithm that minimizes the sum of metrics attached to the links that make up the route. There is. The present invention belongs to the latter algorithm.

  There are also two types of algorithms for minimizing the sum of the metrics attached to the links constituting the route. One is an algorithm that searches for a route having the smallest total metric amount of routes among all the routes in the network, and is called a minimum tree search algorithm. The other is an algorithm that searches for a route having the smallest total metric amount among routes that pass through a specific node in the network. Such an algorithm is called a Steiner tree calculation algorithm, and such a path is called a Steiner tree. A Steiner tree calculation algorithm is mainly used for multicast route calculation. Although the minimum tree calculation algorithm can perform path calculation at high speed, it is proved that the Steiner tree calculation algorithm is very difficult to solve in a finite time. For this reason, many algorithms for realizing a value close to the total metric value realized by the Steiner tree within a finite time have been proposed.

  Examples of Steiner tree calculation algorithms include those shown in Non-Patent Documents 1 and 2 below. The algorithm shown in Non-Patent Document 1 is known as a high-speed Steiner tree calculation algorithm. The algorithm described in Non-Patent Document 2 is a scheduler tree calculation algorithm, but is an algorithm for calculating a route in which a delay required to reach the route from the start point to the end point is limited.

  Comparing both algorithms in terms of the degree of reduction of the total metric of the route, the algorithm of Non-Patent Document 2 becomes more effective than the algorithm of Non-Patent Document 1 as the delay restriction between the start point and the end point is removed. However, since the method of Non-Patent Document 2 has a very long calculation time, it is difficult to apply it to an application that requires a solution in a short time such as route calculation. Here, attention is paid to the algorithm of Non-Patent Document 1.

An outline of the operation of the system introduced in Non-Patent Document 1 will be described. In Non-Patent Document 1, the following procedure is executed to calculate a Steiner tree.
1. A node set D including the start point and all the end points is defined, and a route having the smallest total metric is searched for among the routes connecting the nodes existing in D.
2. A fictitious mesh-like network is constructed with the searched route as a branch and a node in D as a point. The branch metric is 1. This is the total metric of the path connecting the nodes existing in D found in (1).
3.2. The minimum tree is searched for the network configured by. As described above, since the minimum tree calculation algorithm operates at high speed, this operation is completed within a finite time.
4.3. A route in the real network corresponding to the total metric minimum route selected in (2) is used as the calculation result.

  By using this technology for route calculation in the network, it becomes possible to determine the flow of traffic according to the design policy determined by the network administrator, such as an increase in the amount of accommodated traffic.

L. Kou, G. Markowsky, and L. Berman, "A fast Algorithm for Steiner Tree", Acta Informatica. Pp.141-145, 1981 Q. Zhu et al., "Asource-based algorithm for delay-constrained minimum-cost multicasting"

  The technique introduced in Non-Patent Document 1 has the following problems.

  Although the technique introduced in Non-Patent Document 1 calculates an approximate solution of Steiner tree at high speed, there is room for improvement as a reduction degree of the total metric. This is because there is a problem in the process of searching for the total metric minimum path connecting all the nodes on the hypothetical network.

  When calculating the total metric minimum path, the metric assigned to the node on the fictitious network is not changed in the process of determining the path. For this reason, even when a node that has already been selected as a part of the route exists in the vicinity of the real network, the route set from the neighboring sender and end point is adopted as the calculation result. In this way, since the routes that can be selected are limited, the cost reduction effect is very insufficient.

  The present invention has been made in view of the above points, and an object of the present invention is to improve the calculation speed of a multicast transfer route and reduce the total metric of the entire route.

  According to the first aspect of the present invention, multicast transfer that copies information and forwards it to each end point in a node where the route is divided among routes connecting the start point that is the information distribution source and the end point that is the information distribution destination In a multicast network where each means is provided in each node, a transfer route calculation means for calculating a multicast transfer route connecting each given start point and one or more end points, and requesting the transfer route calculation means to calculate a multicast transfer route And a transfer route setting means for setting a multicast transfer route based on the calculation result, the transfer route calculating means for each of the one or more end points from all other nodes in the network to the end point For searching the shortest metric route and the shortest from the start point to each end point of the multicast forwarding route A means to compare the metric routes and select the route to one of the end points with the smallest metric, and to investigate the shortest metric route from each node on the selected route to each end point not included in the route And further selecting a route having the smallest metric, and repeating this until the routes to all the end points are selected (Claim 1).

  The searching means stores, as a table, information on the node at the base point, the shortest metric value, and the next node after the base node when passing through the path, with respect to the shortest metric path having all the other nodes as base points. It is preferable that the repeating means includes a means and selects a route with reference to a table of the means for storing.

  The repeating means scans each node on the selected route in order from the end point of the route to the base point, and is smaller than or equal to the shortest metric route to the end point already calculated for a certain end point. If there is a path of the metric value, it is desirable to select it (Claim 3).

  According to a second aspect of the present invention, in the multicast transfer route calculation method for calculating a route connecting a starting point as a distribution source of information and one or more end points as a distribution destination of the information, each of the one or more end points And searching for the shortest metric route from all other nodes in the network to its end point, and comparing the shortest metric route from the start point of the multicast forwarding route to each end point, any one end point having the smallest metric Selecting the route that leads to the node, and examining the shortest metric route from each node of the selected route to each end point not included in the route, further selecting the route with the smallest metric, and selecting this for all end points A multicast forwarding route calculation method characterized by including a step of repeating until a route is selected until It is (claim 4).

  In the searching step, for the shortest metric path having all the other nodes as base points, the base node, the shortest metric value, and information on the next node after the base point node when passing through the path are stored as a table. In the repeating step, it is desirable to select a route with reference to this table (claim 5).

  In the repeating step, each node on the selected route is scanned in order from the end point of the route toward the base point, and is smaller than or equal to the shortest metric route to the end point already calculated for a certain end point. If there is a path of the metric value, it is desirable to select it (Claim 4).

  According to a third aspect of the present invention, there is provided a multicast transfer route calculation program for causing a computer to execute the above multicast transfer route calculation method.

  According to the fourth aspect of the present invention, the computer has a function of searching for a route having the smallest total metric among routes set from other points in the network toward the end point for each end point. As a calculation result, a function for recording the search result for each node with respect to all the nodes in the network, the information about the next node after the base node, the shortest metric value and the shortest metric path when the search result is passed. Compare the function that detects the shortest metric path from the determined node to each end point, the function that stores the metric and base point of the shortest metric path that was found, and the shortest path that was investigated for each end point. The function to add the shortest metric route to the calculation result and the route set for each end point from the node selected as the calculation result. The function that stores the metric value of the route with the smallest lick and the information of the node selected as the calculation result that is the base point of the route is compared with the metric value stored for each end point, and the metric is the shortest A function to find a route, a function to select the discovered route as a part of the calculation result, a function to scan a node on the route from the end point to the start point, and Scan the nodes on the route selected as the calculation result for the shortest metric route connecting from the node to the end point not selected as part of the route, and the shortest to the end point of the multicast forwarding route not selected as part of the calculation result A function for examining the metric path by referring to the information area in which the shortest metric path from all the nodes to each end point is described, and recorded for each end point A function for comparing the short metric information with the metric information of the investigated route, and when the metric of the investigated route is smaller than the recorded shortest metric information, the recorded shortest metric information is overwritten with the metric of the investigated route. In addition, a function that overwrites the base point of the investigated route with the information part of the node selected as the calculation result that becomes the base point of the route, and the shortest metric information recorded for each end point after the end of scanning between the end points Compare and search for the end point with the smallest metric from the selected route and the shortest metric route from the selected forwarding route associated with the found end point and set for that end point A function to newly select as a part of the calculation result and the selected route from the end point to the start point of the route in the same way as the above-mentioned operation To scan and search for the shortest metric path to an endpoint that has not yet been selected, and to repeat these operations until there are no endpoints on an unselected multicast path A multicast transfer route calculation program is provided (claim 8).

  The present invention further provides a computer-readable recording medium in which the multicast transfer path calculation program according to the third or fourth aspect of the present invention is recorded (claim 9).

  According to the present invention, a Steiner tree that maintains high accuracy in a short time by using a system having a route calculation node that includes a route calculation algorithm that takes into account the upper limit value of a delay that occurs between a start point and an end point. An approximate solution of Further, by shortening the route calculation time compared to the conventional method, the time required for providing the service can be shortened. Thereby, it becomes possible to provide a service quickly to a user.

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram for explaining the outline of the present invention. Each node in the multicast network is equipped with a multicast transfer device 10, and copies information at a node where the route is divided among the routes connecting the starting point that is the information distribution source and one or more end points that are the information distribution destinations. Forward to each end point. In addition, any node in the multicast network includes a multicast transfer path calculation device 20 that calculates a multicast transfer path that connects a given start point and a plurality of end points, and the same node or another node A multicast transfer route setting device 30 that requests the multicast transfer route calculation device 20 to calculate the multicast transfer route and sets the multicast transfer route based on the calculation result. The calculation of the multicast transfer path is performed by the Steiner tree calculation algorithm.

  Each multicast transfer apparatus 10 in the network collects network measurement information such as delay and cost information incurred in the network and the remaining bandwidth of each link for each direction in which data flows, and notifies the multicast transfer path calculation apparatus 20 of the collected data. . Then, when it becomes necessary to set the transfer path of data to be transferred by multicast, the multicast transfer path setting device 30 and the multicast transfer route calculation device 20 execute the setting of the data transfer route according to the processing described later. The

  Here, the multicast transfer device 10, the multicast transfer route calculation device 20, and the multicast transfer route setting device 30 will be described as being provided in separate nodes, but these devices can also be provided in one node.

  When it is necessary to set a multicast transfer route, the multicast transfer route setting device 30 requests the multicast transfer route calculation device 20 to calculate the transfer route. The multicast transfer route calculation device 20 calculates a transfer route based on the collected information, and notifies the multicast transfer route setting device 30 of the result. The multicast transfer path setting device 30 receives the calculation result and sets a multicast transfer path for data.

Network measurement information collection has already been proposed by OSPF (Open
Shortest Path First-Traffic Engineering) and IS-IS-TE (Intermediate
System-Intermediate system-traffic Engineering) is used by extending and using a route calculation protocol with a function for exchanging network measurement information between adjacent nodes. The collected network information is stored in a storage medium.

  Next, details of the multicast transfer route calculation device 20 and the multicast transfer route setting device 30 will be described.

  FIG. 2 is a block diagram illustrating a configuration example of the multicast transfer route calculation apparatus 20. The multicast transfer path calculation device 20 includes an information management unit 21 that manages network measurement information related to delays and metrics generated in nodes in the network and links connecting the nodes, a path calculation unit 22 that calculates transfer paths, and transmission / reception And a packet processing unit 23 for processing packets to be processed. Then, the packet processing unit 23 receives the network measurement information and the route calculation request managed by the information management unit 21, and transmits the calculation result of the transfer route calculated by the route calculation unit 22 to the multicast transfer route setting device 30. Do.

  The information management unit 21 includes a routing protocol module 211 for processing an information exchange protocol used in routing protocols such as OSPF and IS-IS used for collecting traffic state information, and a network topology obtained by the protocol, And a measurement information storage unit 212 for managing network measurement information such as delay and metric. The route calculation unit 22 includes a route calculation module 221 that calculates a transfer route, and a calculation result storage unit 222 that stores a calculation result. The packet processing unit 23 determines the type of the packet that has arrived, transfers the packet or sends the packet to the information management unit 21, a packet transfer table storage unit 232 that records the packet transfer destination, a network And an interface 233.

  FIG. 3 is a block diagram showing a configuration example of the multicast transfer path setting device 30. The multicast transfer path setting device 30 includes an information management unit 31 that manages information about delays and metrics generated in nodes and links in the network, a measurement unit 32 that measures delays and metrics generated by its own processing, A path setting protocol processing unit 33 that sets a path when a new data flow occurs, and a packet processing unit 34 that processes an incoming packet.

  The basic configuration of the information management unit 31 is the same as that of the information management unit 21 of the multicast transfer path calculation device 20, and includes a routing protocol module 311 and a measurement information storage unit 312. The measurement unit 32 includes a measurement module that measures information such as the state of the network interface 343 provided in the packet processing unit 34 and the processing delay of each node on the network. The packet processing unit 34 determines the type of the packet that has arrived, transfers the packet, determines whether to determine a new route setting, and the packet transfer table storage unit 342 that records the transfer destination of the packet. And a network interface 343.

  FIG. 3 also shows a configuration in which the multicast transfer route calculation device 20 is provided in the same node as the multicast transfer route setting device 30. When the devices 20 and 30 are provided in the same node, the information management units 21 and 31 and the packet processing units 23 and 34 are shared, and a route calculation unit 35 equivalent to the route calculation unit 22 is provided in the multicast transfer route setting device 30. Is provided. The route calculation unit 35 includes a route calculation module 351 that calculates a transfer route, and a calculation result storage unit 352 that stores a calculation result.

  The route setting protocol processing unit 33 receives the route setting request from the packet processing unit 34, and performs processing for transmitting the route setting request to the multicast transfer route calculating apparatus 20. The route setting protocol processing unit 33 sets a transfer route for data transfer according to the transfer route calculation result received from the multicast transfer route calculation device 20.

  When the function of the multicast transfer device 10 is provided in the same node as the multicast transfer route setting device 30, the route setting protocol processing unit 33 makes a route calculation request to an adjacent node.

  Next, operations of the multicast transfer device 10, the multicast transfer route calculation device 20, and the multicast transfer route setting device 30 will be described in detail.

  A node having the function of the multicast transfer apparatus 10 in the network always exchanges network measurement information representing the topology, delay, and metric of the network between adjacent nodes. Each node stores the network measurement information obtained by the exchange process.

  The network measurement information exchanged by a node includes not only network measurement information measured by the next node but also network measurement information measured by other nodes held by the own node. With these exchange operations, each node holds network measurement information such as connection information and delays at all nodes in the network. Then, the node having the function of the multicast transfer route setting device 30 that newly sets the transfer route requests the node having the function of the multicast transfer route calculation device 20 to calculate the route. At this time, the node having the function of the multicast transfer path calculation device 20 is sent from the network measurement information related to traffic such as the topology and delay in the network managed by the information management unit 21 and the node that has requested the path calculation. The transfer route is calculated based on the end point information.

  FIG. 4 is a flowchart showing route calculation processing in the multicast transfer route calculation apparatus 20.

  The multicast transfer route calculation device 20 receives a route calculation request from a node having the function of the multicast transfer route setting device 30, and at this time, also receives data transfer end point information from the multicast transfer route setting device 30. Thereby, in the multicast transfer route calculation device 20, the route calculation module 221 in the route calculation unit 22 performs network measurement information indicating the network topology and traffic status recorded in the measurement information storage unit 212 of the information management unit 21. Alternatively, based on such information, the metrics calculated so as to follow the network design guidelines of the network administrator are read (step S1).

  Next, for each end point of the multicast transfer route, the route calculation module 221 determines the metric of the route that realizes the shortest metric among the routes between the node determined as the transfer route calculation result and the end point under investigation, The node determined as the calculation result serving as the base point of the route is recorded in the calculation result storage unit 222. Then, using these pieces of information, the shortest metric route from all nodes on the network to the node that is the end point of the multicast transfer route is searched for each end point of the multicast transfer route. The calculated result is held as information specialized for the end point of each multicast transfer path (step S2). This shortest path calculation uses an algorithm for calculating the shortest metric path between two points in the network, and the type of algorithm is not limited.

  Next, the route calculation module 221 uses the start point of the route as a base point, compares the shortest metric route to each end point of the multicast transfer route between the end points, selects the route with the smallest metric as the calculation result, and selects the node and link Information is stored in the calculation result storage unit 222. (Step S3).

  Subsequently, the route calculation module 221 scans the selected route from the end point to the start point. At this time, the shortest metric path from the node being scanned to the end point not yet selected as a path is searched with reference to the shortest metric path information from all the nodes previously calculated to each end point. At this time, among the paths between the node determined as the transfer path calculation result, which is information associated with each end point, and the end point, the path metric that realizes the shortest metric, and the metric value of the searched path If the former is larger, the former information is overwritten with the latter information. At this time, the information of the node being scanned is recorded as the base point of the shortest metric path to the end point, which becomes the additional candidate path (step S5).

  Then, the metric information of the route realizing the shortest metric from the node already selected as the route held by each end point is compared between the end points. A route having the smallest metric is newly added as a part of the calculation result. The base point of this route is the base point described in the base point information of the shortest metric route to the end point held by each end point of the multicast transfer route (step S6).

  Thereafter, the process returns to step S5. Steps S5 and S6 are repeated until there is no end point not selected as a route (step S49).

  The route calculation unit 22 returns the result calculated in this way to the node that issued the route calculation request via the packet processing unit 23.

  In the present embodiment, OSPF-TE is used when the multicast transfer apparatus collects network measurement information such as delay. OSPF-TE is a communication protocol in which traffic information in the network such as a delay is stored in OSPF topology information exchange information which is a unicast routing protocol.

In the present embodiment, as a protocol for setting a data transfer route, a multicast MPLS (Multiple MPLS) (RSVP-TE (Resource Reservation Protocol-Traffic Engineering)) that performs explicit route designation is extended.
Protocol Label Switching) protocol is used. Multicast MPLS is an LSP (Label) compared to RSVP-TE used in normal MPLS.
Add an information element that can store the tree topology in the message that generates the Switched Path), and point-to-multipoint along the topology information
It is a technology that can establish an LSP.

  Next, a specific embodiment of the process for calculating the transfer path according to the present invention will be described.

  FIG. 5 shows a multicast network that is a target of transfer path setting, and FIGS. 6 to 12 show each stage of transfer path calculation. In these figures, the node having the function of the multicast transfer path setting device 30 is the starting point of the data transfer path, the data is transferred to the nodes of the end points 11 to 13, and the nodes A to K are intermediate nodes between the start point and the end point. It becomes. Each of these nodes has the function of the multicast transfer apparatus 10.

  In this embodiment, a multicast transfer path setting device 30, nodes A to K, and end points 11 to 13 are connected by a communication cable (link) to constitute a multicast network. Each link has two route selection indices, delay and metric, and it is recognized that the link has different delay characteristics and metric characteristics depending on the entry direction when data enters the link. The multicast transfer path setting device 30 transfers data to the end points 11 to 13 starting from itself based on the result calculated by the multicast transfer path calculation device 20. Each node collects network measurement information indicating a delay occurring in a link between the nodes by using the OSPF-TE. Then, the network measurement information is notified to the multicast transfer path calculation device 20 in advance.

  A calculation example of a multicast transfer path according to the present invention will be described with reference to FIGS.

  First, in the present invention, the shortest metric path set in the direction of each end point from all nodes in the network is calculated for each end point 1 to 3 of the multicast transfer path. For this shortest metric path calculation, Dijkstra's algorithm, which is famous as an algorithm for calculating the shortest path between two points, can be used.

  FIG. 6 shows the calculated shortest metric path. The route X is the shortest metric route to the end point 1, the route Y is the shortest metric route to the end point 2, and the route Z is the shortest metric route to the end point 3.

  Simultaneously with the shortest metric path calculation, each end point creates a table that records the shortest metrics from other nodes. The table 40 shows the shortest metric information up to the end point 11, the table 41 shows the shortest metric information up to the end point 12, and the table 42 shows the shortest metric information up to the end point 13. These tables describe the nodes in the network, the shortest metric value from the target node, and the next point of the target node when passing through the shortest metric path.

  FIG. 7 shows the initial information of the shortest metric from the determined path and the base point of the shortest metric path held by each end point, and further shows the operation of selecting a part of the calculation result first. At the start of the algorithm, the shortest metric value from all nodes to each end point calculated in FIG. 6 is referred to, and the shortest metric route from the start point of the multicast transfer route (multicast transfer route setting device 30, hereinafter referred to as “start point 30”) is determined. Explore. Then, as the shortest metric and the base point of the shortest metric path from the node on the fixed path held by each end point, the metric value of the shortest metric path from the start point 30 and the information of the start point 30 that is the base point for each end point To remember. Information 50 to 52 represents the above-described two pieces of information held by the end points 11 to 13, respectively.

  Next, from the stored information, an end point with the shortest metric value from the node on the confirmed route is selected, and a route from the start point 30 to the selected end point is selected as a part of the calculation result. In FIG. 7, the shortest metric value until the end point 11 and the end point 13 is the same “4”, but the end point 11 is selected here. Accordingly, the route 30-ADDF-11 is selected as the calculation result.

  Next, the selected route is scanned from the end point of the route to the start point. In the course of scanning, the shortest metric value to the end point not yet selected as a part of the calculation result is calculated.

  FIG. 8 shows a path scanning process. In this example, first, the end point 11 is scanned, and then scanning is performed in the order of the nodes F, D, A, and the start point 30.

  Focus on end point 11. Here, the shortest metric values from the end point 11 to the end points 12 and 13 that have not been selected as the calculation result are checked from the previously created tables 41 and 42. At this time, the metric value from the end point 11 to the end point 12 is “4”, and the metric value from the end point 11 to the end point 13 is “4”. On the other hand, the metric values managed by the end points 12 and 13 are “6” and “4”, respectively, and a value that is the same as or larger than the newly calculated metric value is stored. In this case, the information held at the end points 12 and 13 is updated. As a result, the information held by the end point 12 is updated to “4” for the shortest metric from some nodes to the end point 12 of the calculation result and “end point 11” for the base point information of the shortest metric path. Similarly, in the information held by the end point 13, the shortest metric from some nodes to the end point 13 of the calculation result is updated to “4”, and the base point information of the shortest metric path is updated to “end point 11”.

  Next, focus on node F. Here, the shortest metric values from the node F to the end points 12 and 13 that have not been selected as the calculation result are checked from the previously created tables 41 and 42. At this time, the metric value from the node F to the end point 12 is “3”, and the metric value from the node F to the node 13 is “3”. At this time, the metric values from some of the calculation results managed by the end points 12 and 13 are “4” and “4”, respectively, and values that are the same as or larger than the newly calculated metric values are stored. We will update these information. At this time, the shortest metric from some nodes of the calculation result held by the end point 12 to the end point 12 is updated to “3”, and the base point information of the shortest metric path is updated to “node F”. Similarly, the shortest metric from some nodes to the end point 13 in the calculation result held by the end point 13 is updated to “3”, and the base point information of the shortest metric path is updated to “node F”.

  Next, focus on node D. Here, the shortest metric values from the node D to the end points 12 and 13 that have not been selected as the calculation result are checked from the previously created tables 41 and 42. At this time, the metric value from the node D to the end point 12 is “4”, and the metric value from the node F to the end point 13 is “2”. At this time, the metric values from some of the calculation results managed by the end points 12 and 13 are “3” and “3”, respectively, but are the same as or larger than the metric values newly calculated only at the end point 13 Is stored, information specific to the end point 13 is updated. At this time, the shortest metric from some nodes to the end point 12 of the calculation result held by the end point 12 remains “3”, and the base point information of the shortest metric path remains “node F”. On the other hand, the shortest metric from some nodes of the calculation result held by the end point 13 to the end point 13 is updated to “2”, and the base point information of the shortest metric path is updated to “node D”.

  When attention is paid to the node A and the start point 30, a larger metric is required for the end point 12 compared to the case of extending the route from the node F, and for the end point 3, compared to the case of extending the route from the node D. . For this reason, the information held by the end points 12 and 13 is not updated.

  FIG. 9 shows the situation at the end of scanning. Here, with respect to the end point 12 and the end point 13, the values of the shortest metrics from some nodes of the calculation results to the respective end points are compared, and the end point associated with the smallest value is set as a part of the calculation path. Add to Then, a route from a part of the nodes of the calculation result described in the base point information of the shortest metric route associated with the selected end point to the end point is added as a part of the calculation result.

  In the example shown in FIG. 9, the shortest metric value associated with the end point 12 is “4”, whereas the value associated with the end point 13 is “2”. Therefore, the end point selected next as a part of the calculation result is the end point 13. At the same time, the shortest metric route D-E-13 from the node D to the end point 13 described in the base point information of the shortest metric route associated with the end point 13 is also added as a part of the calculation result.

  When the selected shortest metric path D-E-13 is added to the calculation result, the shortest metric value to the end point not yet selected as a part of the calculation result is calculated. The scan is performed from the end point toward the base point of the shortest metric path, similarly to the scan in FIG.

  FIG. 10 shows a path scanning process. In this example, the end point 13 is scanned first, and then the node E is scanned.

  Focus on node 3. Here, the shortest metric value from the end point 13 to the end point 12 not yet selected as the calculation result is checked from the table 41 created earlier. At this time, the metric value from the end point 13 to the end point 12 is “4”. On the other hand, the metric value from a part of the calculation result managed by the end point 12 is “3”. Since the newly calculated metric value is larger, the information is left as it is without being updated. At this time, the shortest metric from the partial node of the calculation result held by the end point 12 to the end point 12 is “3”, and the base point information of the shortest metric path is “node F”.

  Subsequently, attention is paid to the node E. Here, the shortest metric value from the node F to the end points 12 and 13 not yet selected as a calculation result is checked from the previously created table 41. At this time, the metric value from the node E to the end point 12 is “3”. On the other hand, the metric value from a part of the calculation result managed by the end point 12 is “3”. Since a value equal to or larger than the newly calculated metric value is stored, the information is updated. At this time, the shortest metric from some nodes to the end point 12 of the calculation result held by the end point 12 is updated to “3”, and the base point information of the shortest metric path is updated to “node E”.

  Finally, an end point 12 not yet selected as a part of the calculation result is selected as a part of the calculation result, and some nodes of the calculation result described in the base point information of the shortest metric path associated with the end point The route from to the end point is added as a part of the calculation result.

  FIG. 11 shows how a route is added. Since the route that reaches the end point 12 is recorded as the base point E, the route E-G-H-12 is added. Finally, a route as shown in FIG. 12 is output as a calculation result.

  The obtained calculation result is sent from the calculation result storage unit 222 to the packet processing module 231, packetized, and sent to the multicast transfer path setting device 30. The multicast transfer path setting device 30 that has received the calculation result sets a multicast transfer path according to the calculation result. When the function of the multicast transfer route calculation device 20 and the multicast transfer route setting device 30 exist in the same node, the transfer route is set according to the calculated transfer route, and is sent to the packet processing module 341 for processing. .

  The multicast network of the present invention can be easily realized by connecting an apparatus that performs the multicast transfer route calculation method of the present invention to an existing multicast network. It can also be easily implemented by installing the multicast transfer route calculation program of the present invention in a node computer in the network. This multicast transfer path calculation program may be recorded and traded on a computer-readable recording medium, or may be downloaded to a specific computer on a network.

The figure explaining the outline | summary of this invention. The block diagram which shows the structural example of a multicast transfer path | route calculation apparatus. The block diagram which shows the structural example of a multicast transfer path | route setting apparatus. The flowchart which shows the process of the route calculation in a multicast transmission route calculation apparatus. Multicast network for which transfer routes are set. The figure which shows the shortest metric path | route from all the nodes in the network calculated for every end point to each end point. The figure which shows the operation | movement from which the initial information of the shortest metric from the fixed path | route which each end point hold | maintains, the initial information of the base point of the shortest metric path | route, and a part of calculation result are selected first. The figure which shows the scanning process of a path | route. The figure which shows the condition at the time of completion | finish of scanning. The figure which shows the scanning process of a path | route. The figure which shows the mode of addition of a path | route. The figure which shows the calculation result of the final path | route.

Explanation of symbols

10 Multicast transfer device 20 Multicast transfer route calculation device 30 Multicast transfer route setting device 21, 31 Information management unit 211, 311 Routing protocol module 212, 312 Measurement information storage unit 22, 35 Route calculation unit 221, 351 Route calculation module 222, 352 Calculation result storage unit 23, 34 Packet processing unit 231, 341 Packet processing module 232, 342 Packet transfer table storage unit 233, 343 Network interface 32 Measurement unit 33 Path setting protocol processing unit 11, 12, 13 End point 40-42 Table 50 ~ 52 Information A ~ J Node

Claims (9)

A multicast network in which each node is provided with a multicast transfer means for copying information and transferring it to each end point in a node where the route is divided among routes connecting the start point serving as the information distribution source and the end point serving as the information distribution destination In
A transfer route calculating means for calculating a multicast transfer route connecting a given start point and one or more end points, and
A transfer route setting unit that requests the transfer route calculation unit to calculate a multicast transfer route and sets a multicast transfer route based on the calculation result; and
The transfer route calculation means includes
Means for searching for the shortest metric path from all other nodes in the network to the end point for each of the one or more end points;
Means for comparing the shortest metric route from the start point of the multicast transfer route to each end point and selecting the route to any one end point having the smallest metric;
Investigate the shortest metric route from each node on the selected route to each end point not included in the route, and further select the route with the smallest metric until all the routes to the end point are selected. A multicast network comprising: means for repeating. The searching means stores, as a table, information on the node at the base point, the shortest metric value, and the next node after the base node when passing through the path, with respect to the shortest metric path having all the other nodes as base points. Including means,
The multicast network according to claim 1, wherein the repeating unit selects a route with reference to a table of the storing unit. The repeating means sequentially scans each node on the selected route from the end point of the route toward the base point, and has a metric value smaller than or equal to the shortest metric route to the end point already calculated for the end point. 2. The multicast network according to claim 1, wherein when there is a route, the route is selected. In a multicast transfer route calculation method for calculating a route connecting a start point as a distribution source of information and one or more end points as a distribution destination of the information,
For each of the one or more endpoints, searching for the shortest metric path from all other nodes in the network to the endpoint;
Comparing the shortest metric route from the start point of the multicast forwarding route to each end point and selecting the route to any one end point with the smallest metric;
Investigate the shortest metric route from each node of the selected route to each end point not included in the route, further select the route with the smallest metric, and repeat this until the routes to all the end points are selected And a multicast forwarding route calculation method comprising the steps of: In the searching step, for the shortest metric path having all the other nodes as base points, the base node, the shortest metric value, and information on the next node after the base point node when passing through the path are stored as a table. ,
The multicast transfer route calculation method according to claim 4, wherein in the repeating step, a route is selected with reference to this table. In the repeating step, each node on the selected route is scanned in order from the end point of the route toward the base point, and a metric value smaller than or equal to the shortest metric route to the end point already calculated for the end point 5. The multicast transfer route calculation method according to claim 4, wherein when there is a route, the route is selected. A multicast transfer route calculation program for causing a computer to execute the multicast transfer route calculation method according to claim 4. On the computer,
For each end point, a function for searching for a route having the smallest total metric among routes set from other points in the network toward the end point;
A function of recording the search result for each node for all nodes in the network, information on the next node after the base node, the shortest metric value, and the base node when passing through the shortest metric path;
A function for detecting the shortest metric path from a node determined as a calculation result to each end point;
The ability to store the metric and base point of the shortest metric path found;
A function that compares the shortest route surveyed for each end point and adds the shortest metric route among them to the calculation result,
Among the routes set for each end point from the node selected as the calculation result, the metric value of the route with the smallest metric and the information of the node selected as the calculation result serving as the base point of the route Memorizing function,
A function that compares the metric values stored for each end point and finds the route with the shortest metric;
The ability to select discovered routes as part of the calculation results;
When selecting the route, a function that scans the nodes on the route from the end point to the start point;
Scans the nodes on the selected route as the calculation result for the shortest metric route from the operating node to the end point not selected as part of the route, and the end point of the multicast forwarding route not selected as part of the calculation result A function for investigating the shortest metric route to all destinations from each node by referring to the information area in which the shortest metric route is described;
A function that compares the shortest metric information recorded for each end point with the metric information of the investigated route,
When the metric of the investigated route is smaller than the recorded shortest metric information, the recorded shortest metric information is overwritten with the metric of the investigated route, and the base point of the investigated route becomes the base point of the route The ability to overwrite the information part of the selected node as a result,
After the scan is completed, the shortest metric information recorded for each end point is compared between the end points, and a function for searching for the end point with the smallest metric from the selected route,
A function that selects a shortest metric route from the selected forwarding route that is set for the end point that is associated with the found end point as a part of the calculation result;
A function that scans the selected route from the end point toward the start point of the route in the same manner as described above, and examines the shortest metric route to the end point that has not yet been selected;
A multicast transfer route calculation program for realizing the function of repeating these operations until there is no end point of the unselected multicast route. 9. A computer-readable recording medium on which the multicast transfer path calculation program according to claim 7 or 8 is recorded.

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