JP2001045040A - Multicast routing method, device therefor and program recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To configure a multicast tree at a low cost with less number of inquiries. SOLUTION: On the occurrence of a request of participation in multicast communication from a node (j), the node (j) transmits an inquiry along the direction of a sources along respectively with a minimum entire area tree and a shortest distance tree (S2), and a node (k) receiving the inquiry replies to the node (j) when the node (k) has already been included in a multicast tree (S5), transmits the inquiry to a succeeding node along with the minimum entire area tree or the shortest distance tree when the node (k) is not included in the multicast tree (S4), and the node (j) receiving the reply is connected to a connectable node at the minimum routing cost in both transmission source nodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for multicast routing on a network in a case where dynamically joining / leaving multicast communication occurs in a multicast communication service provided on an information communication network. The present invention relates to a program recording medium.

[0002]

2. Description of the Related Art A multicast communication service provided on an information communication network can simultaneously deliver the same information to a plurality of recipients. With the use of multicast communication, information can be simultaneously transmitted to a plurality of recipients without increasing the load on the network. In multicasting, information from a source copies information at a node serving as a branch point, and the information is transferred to a link corresponding to a node to which a receiver is connected. In addition, in the multicast service, it is dynamically generated that a participant joins / withdraws from the multicast communication, and provisions are made such that participation / withdrawal on the Internet or ATM is possible in the middle.

[0003] From the viewpoint of cost, the conventional multicast routing method includes a method of approximately creating a minimum cost tree (Steiner tree) based on the cost assigned to each link and a method of shortest path tree (Shortest path tree). Can be roughly divided into those that create Conventional dynamic multicast routing algorithms include a greedy algorithm (Greedy algorithm) that aims to dynamically create a Steiner tree dynamically based on the cost assigned to each link.
dy algorithm). In this algorithm, a node newly joining a multicast group connects to a node that can be connected at the lowest cost among existing participating nodes. It has been reported that this algorithm has a multicast tree cost (a value obtained by adding all costs of each link used for multicast communication) that is close to the optimum.
However, in the method for realizing the greedy algorithm on an actual network, a newly joining node transmits a message for inquiring the joining status of the multicast group to all other nodes, and among the participating nodes, In the wide area network, there is a problem that the number of messages increases due to connection to the closest one.

[0004] As another conventional dynamic multicast routing algorithm, there is an algorithm using a shortest path tree (Shortest path tree) which is a predetermined tree (hereinafter, referred to as pruned STP). In this algorithm, a node other than a source called a core or a rendezvous point (hereinafter, simply referred to as a core) is set in a network, the source transmits data to the core along the shortest path, and the core sends a core to each node. Is transmitted along the shortest path tree rooted at. However, it is not transmitted on a route that does not include a node participating in the multicast. In the shortest path tree, this algorithm forms a multicast tree in advance, so that it is easier to implement than the greedy algorithm and is actually realized in the system. However, the cost of the entire multicast tree is higher in the pruned SPT than in the greedy algorithm.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a purpose of the present invention is that a new participating node merely inquires a small number of other nodes,
An object of the present invention is to provide a method, an apparatus, and a program recording medium that enable multicast routing at a cost as low as the greedy algorithm.

[0006]

According to the present invention, when a connection request for multicast communication is generated from a new participating node, the new participating node moves in the direction toward the source along the minimum spanning tree and the shortest path tree, respectively. The node that has transmitted the inquiry message and received the inquiry message determines whether or not it is an existing participating node. If the result of the determination is an existing participating node, the node sends a reply message to the new participating node. Transmit, if the determination is not an existing participating node, if the query came along the minimum spanning tree, to the next node on the minimum spanning tree, if the query came along the shortest path tree, Forward the inquiry message to the next node on the shortest path tree, and check whether the new participating node Upon receiving the reply message, in the existing entry node in the source of both response messages, connected to the nodes connectable with minimum cost.

Here, the minimum spanning tree is a tree that includes all nodes and has a minimum cost when all nodes have joined the multicast group. The network is independent of participation or non-participation. Once decided, it is uniquely decided. When the shortest path tree is determined, the shortest path to the source for each node is determined, and the shortest path tree is formed as a whole. When there is only one participating node, the tree between the source nodes is minimized. A tree that becomes a cost is included as a partial tree.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a multicast service in which each node sequentially joins / leases from multicast communication. Further, it is assumed that a node that has already participated in the multicast communication does not change the information transfer path from the source to the node until the node leaves the multicast communication.

As shown in FIG. 1, a source and seven nodes # 1 to # 7 are connected by a link to form a network, and the number shown at each link indicates the cost of the link. The source and node # 1 have already joined the Matilcast group, and node # 6 is newly added.
Is connected as a new participating node. At this time, the new joining node # 6 transmits an inquiry message in the source direction along the minimum spanning tree and the shortest path tree, respectively. Here, first, attention is paid to a search path along the minimum spanning tree. For node # 6, the path in the source direction of the minimum spanning tree rooted at the source is <# 6 → #
4 → # 2 → # 1 → source>, so node # 6
Sends an inquiry message to node # 4. Since the node # 4 is not an existing participating node, the node # 2 transfers the inquiry message to the node # 2. Similarly, the node # 2 transfers the inquiry message to the node # 1. Node # 1
Is an existing participating node, the node # 1 transmits a reply message to the new participating node # 6 via the shortest path, and does not transmit an inquiry message to the source.

Similarly, the new participating node # 6 also sends an inquiry message for the search route <# 6 → # 4 → # 3 → source> along the shortest path tree. In FIG. 1, since nodes # 4 and # 3 are not existing participating nodes, node # 6
Will receive a reply message from the source. New participant node # 6 receiving these two reply messages
Is connected to node # 1 which is a node that can be connected with the minimum cost among the source node # 1 and the source of the reply message. In FIG. 1, the cost between the nodes # 6 and # 1 is 3 + 3 = 6, and the cost between the node # 6 and the source is 3 + 4 + 2 = 9.

According to the present invention, by inquiring only a limited number of nodes, the load on each node and the network can be increased even when the network scale is large or the number of existing participating nodes is small. (The load based on the inquiry) can be reduced. In addition, a minimum spanning tree and a shortest path tree are used as predetermined search paths. As described above, the minimum spanning tree is a tree having the minimum cost when all nodes have joined the multicast group. In the case where there is only one participating node, the shortest path tree includes a tree having the minimum cost as a subtree. This means that the searched nodes are searching only for nodes that are likely to form a low-cost multicast tree.

FIG. 2 shows a multicast routing control device in each node. It comprises a traffic controller 11 and a multicast routing controller 12.
The traffic control device 11 is a device that receives traffic transferred from another node and transmits the traffic to another node.
The multicast routing control device 12 determines the configuration of the multicast tree when the node participates in the multicast communication. Alternatively, when another node participates in the multicast communication, the node determines whether the other node transmits an inquiry message / reply message for determining the configuration of the multicast tree. The multicast routing control device 12 includes a message processing unit 13 and a routing determination unit 14. The message processing unit 13 is a device that determines whether an inquiry message is transferred or a reply message is transmitted to a new participating node when there is an inquiry message from another node. The routing determination unit 14 is a device that holds network configuration information and the status of participation of the node in multicast communication, and determines a route when the node newly requests participation in multicast communication.

A multicast routing method when a request for joining a multicast communication is newly issued from a node will be described below. FIG. 3 shows a flow of the multicast routing method in this case. Step S0: A request for participation in multicast communication is issued from the node j. Step S1: The routing determination unit 14 sends a transmission request to the traffic control unit 5 by directing the inquiry message toward the source along each of the minimum spanning tree and the shortest path tree.

Step S2: The traffic control unit 5 transmits an inquiry message toward the source along each of the minimum spanning tree and the shortest path tree. Step S3: The node k, which has received the inquiry message from the node j, sets the message processing unit 13
In, forward the inquiry message further or
Decide whether to send a reply message to the new participating node.

Step S4: If the node k is not included in the multicast tree, an inquiry message is transmitted toward the source along each of the minimum spanning tree and the shortest path tree. Step S5: If the node k is already included in the multicast tree, send a reply message to the new joining node.

Step S6: The node j requests the node specified by the routing determining unit 14 to connect to a node connectable at the minimum cost. Step S7: The traffic control unit 5 connects to the node. The multicast routing control device according to the present invention can also function by decoding and executing a program by a computer.

[0017]

The computer simulation shows that the multicast routing method according to the present invention described above is superior. Here, a random graph used in the evaluation of the conventional multicast routing method is used as the evaluation model. The random graph of N nodes represents a node placed on a plane, the nodes of the pair representing the link _{(u, v) P e (} u, v) the incidence of branches = (ke '/ N) βexp (−d (u, v) / Lα). Here, e 'is an average degree (average number of links connected to a certain node), and k is a parameter for determining an average distance of a node pair. L is the maximum distance that (u, v) can take, d (u, v) is the Euclidean distance between u and v, and β and α are parameters <0, β <α <1. Further, the cost of the branch (link) is calculated by the distance d (u,
v).

In this random graph model, participation and departure from multicast communication are performed. It is known that the probability of a node participating in multicast communication is given as follows. P _c (q) = γ (N−q) / (γ (N−q) + (1−γ)
q) Here, q is the number of nodes participating in the multicast communication at that time. γ (0 < γ < 1) determines the number of nodes participating in the multicast communication in the equilibrium state, and the average number of participating nodes is given by γN. FIG. 4 shows basic parameters for evaluation. The value of this parameter is a value conventionally used. The evaluation is performed by the average of the costs of the entire multicast tree calculated for each joining and leaving. In other words, joining and leaving the model with a probability P (q) and calculating the average cost of the multicast tree that occurs each time and taking the average are described in the method of the present invention, the conventional greedy algorithm, and the conventional pruning. Performed on SPT.

In this simulation, evaluation was performed for ten different networks. In addition, the number of events 20,000 of node participation / withdrawal was set to one simulation run, and up to the first number of events 2000 of the run was deleted from the evaluation to eliminate the influence of the initial state. FIG. 5 shows the cost when each algorithm is applied under different average number of participating nodes. This cost is normalized by the cost of the greedy algorithm. This is a case where the number of nodes is 20. As can be seen from this figure, the method of the present invention has almost the same cost as the greedy algorithm. On the other hand, it can be seen that the pruning SPT has a higher cost than the method of the present invention.

As described above, according to the present invention, since the inquiry is not made to all nodes, the number of messages does not increase. Also, a search with the minimum spanning tree is used to find the node with the lowest cost when all nodes have joined, and a search with the shortest path tree is used to find a node with the lowest cost when only one node has joined. By choosing one, a low-cost multicast tree of the same kind as the conventional method of approximating the minimum cost tree can be obtained as shown in the simulation.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a multicast routing method according to the present invention on a network.

FIG. 2 is a block diagram showing a functional configuration of an embodiment of the multicast routing control device according to the present invention.

FIG. 3 is a flowchart showing an example of an operation procedure of the apparatus shown in FIG. 2;

FIG. 4 is a diagram showing parameter values used in an evaluation simulation.

FIG. 5 is a diagram showing a result of an evaluation simulation.

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Claims (3)

[Claims] 1. A multicast routing method capable of dynamically providing a multicast service when nodes joining or leaving a multicast communication occur sequentially on a communication network. When a connection request is generated, the process of transmitting an inquiry message from the new joining node to the source along the minimum spanning tree and the shortest path tree, respectively, and the node receiving the inquiry message makes itself the existing joining node. A step of determining whether or not there is, and a step of transmitting a reply message to the new participating node if the result of the determination is that the node is an existing participating node; If it comes along a tree, on its minimum spanning tree Transferring the inquiry message to the next node, and if the inquiry comes along the shortest path tree, transferring the inquiry message to the next node on the shortest path tree; and Receiving a reply message from any one of the nodes, and connecting to a node that can be connected with the least cost among the existing participating nodes that have sent the reply message. . 2. A multicast routing control device for a node capable of dynamically providing a multicast service when a node that joins or leaves the multicast communication sequentially occurs on a communication network. Means for transmitting an inquiry message in the direction toward the source along each of the minimum spanning tree and the shortest path tree when a connection request to the multicast communication is generated. Means for determining whether the node is a node; means for transmitting a reply message to the new participating node if the result of the determination is an existing participating node; and an inquiry message if the result of the determining is not an existing participating node. Where came along the minimum spanning tree Means to forward the inquiry message to the next node on the minimum spanning tree, and if the inquiry message follows the shortest path tree, to the next node on the shortest path tree; Means for receiving a reply message from any of the nodes on both of the search paths and connecting to a node that can be connected at a minimum cost among the existing participating nodes that have sent the reply message. Characteristic multicast routing control device. 3. A program to be executed by a computer of a multicast routing control device of a node capable of dynamically providing a multicast service when a node participating in or leaving a multicast communication sequentially occurs on a communication network. A recording medium in which the node accepts a connection request for multicast communication as a new joining node, and upon receiving the connection request, an inquiry message in a direction toward the source along the minimum spanning tree and the shortest path tree, respectively. , A process of receiving an inquiry message received from another node, a process of determining whether or not itself is an existing participating node when receiving an inquiry message. If there is a new participating node Sending an answer message; and if the determination result is not an existing participating node, identifying whether the inquiry message came along the minimum spanning tree or the shortest path tree. If it is identified as having come, the process of transferring the inquiry message to the next node on the minimum spanning tree, and if it is identified that it has come along the shortest path tree, the process proceeds to the next node on the shortest path tree. A process of transferring the inquiry message, a process of receiving a reply message received from any of the nodes on the both search routes in a state where the node has made a connection request as a new participating node, and a process of receiving the above two reply messages And a process of connecting to a node that can be connected with the lowest cost among the existing participating nodes that have sent both reply messages, and A recording medium recording a program to be executed.