JP2014200003A - Method and device for calculating channel of content delivery system, content delivery network, and relay node thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To deliver a plurality of threshold-secrete-sharing partial contents on different channels by utilizing by-group network encoding.SOLUTION: A first solution unit 102 finds, by a first integer programming, a solution for a maximum number of link-independent channels m leading from each delivery source node s to each delivery destination node d. A multiplex count calculation unit 103 calculates a minimum number of links F in which N-K+1 channels can be included when N channels are evenly distributed to M links. A second solution unit 104 finds, by a second integer programming, a solution for N channels leading to each delivery destination node so as to minimize an expected value for the number of delivery destination nodes at which the original content cannot be restored due to the occurrence of multiple link faults equal to or less than F-multiple link faults where a link fault occurs in all of F or less links in which N-K+1 or more channels are included, the solution being calculated by limiting the scope of application of network encoding to the partial contents in one and the group.

Description

  The present invention relates to a route calculation method and apparatus for a content distribution system, a content distribution network, and a relay node thereof, and in particular, one content is divided into a plurality of partial contents and distributed on the network, and network coding ( content distribution system route calculation method and apparatus suitable for threshold secret sharing, and content distribution network and its relay node that distribute each partial content to a plurality of distribution destination nodes through a plurality of routes while improving throughput by network coding) About.

  In Non-Patent Document 1, one content is divided into n pieces of encrypted partial content, and k (≦ n) or more pieces of partial content out of n pieces of partial content are not collected. A threshold secret sharing method is disclosed in which secret sharing is performed so that it cannot be restored.

  In Patent Documents 1 and 2, when transferring N pieces of partial content secretly held by a plurality of nodes to a delivery destination node via a network, there are more pieces of partial contents than NK due to multiple link failures. There is disclosed a method for calculating a delivery route that is lost during transfer and has a minimum probability that the original content cannot be restored at the delivery destination node.

  In Non-Patent Document 2, a relay node encodes and transfers a plurality of partial contents distributed to different distribution destination nodes into one partial content using network encoding technology, thereby effectively using a link band. A technique for achieving this is disclosed.

  In Patent Document 3, when content secretly held by a plurality of nodes is simultaneously transferred to a plurality of distribution destination nodes via a network, network coding is applied to effectively use a link band. A technique for calculating a content distribution route that reduces the expected value of the number of distribution destination nodes that cannot restore the original content due to a multilink failure is disclosed.

Japanese Patent Application No. 2012-23993 Japanese Patent Application No. 2012-45315 Japanese Patent Application No. 2012-275828

Shamir, Adi (1979), "How to share a secret", Communications of the ACM 22 (11): 612-613 R. Ahlswede, et.al., "Network information flow," IEEE Trans. Inf. Theory, vol. 46, no. 4, pp. 1204-1216, July 2000.

  Original data can be restored by collecting arbitrary K partial contents from N partial contents, but original data cannot be restored from (K-1) partial contents (K, N) N threshold value secret sharing The partial contents are distributed and distributed to the distribution source nodes on the network, and the partial contents are distributed from the distribution source node holding the partial contents to each distribution destination node to the distribution destination node that is to restore the original data.

  In (K, N) threshold secret sharing, the original content can be restored by collecting arbitrary K pieces of partial content from N pieces of partial content. When transferring to the delivery destination node via the network, the original content can be restored at the delivery destination node even if NK partial contents are lost during the transfer.

  In other words, with (K, N) threshold secret sharing, if a distribution path for partial content that can minimize the probability that N-K + 1 or more partial contents will be lost due to a multilink failure can be set, the multilink failure will cause the original. The probability that the contents cannot be restored can be minimized.

  On the other hand, if the distribution route of each partial content passes through the same link, the original content may not be able to be restored even if there are less than N-K multi-link failures when a failure occurs in the link. Therefore, in content distribution to which (K, N) threshold secret sharing is applied, each distribution route is preferably a route that does not pass through the same link (link independent route).

  However, in the prior art, when distributing partial content using multiple paths using (K, N) threshold secret sharing, the original content is restored due to multiple link failures by allowing the partial content to pass through a link independent route. It was not possible to easily calculate a route that could minimize the probability of being unable to restore.

  According to Patent Document 3, when N partial contents are distributed to each of a plurality of distribution destination nodes, network coding is applied, so that an improvement in throughput can be expected. However, there has been a technical problem that due to a multilink failure, the number of partial contents that cannot be network-decoded at the distribution destination node increases, and the expected value of the number of distribution destination nodes that cannot restore the original content increases.

  An object of the present invention is to solve the above-described problems of the prior art, use network coding, and distribute a plurality of partial contents with threshold secret sharing to different groups in a different route. By classifying and applying network coding only to partial contents belonging to the same group and different delivery destination nodes, the effective use of the link bandwidth is limited, but the original contents cannot be restored due to a multilink failure It is an object of the present invention to provide a content distribution system route calculation method and apparatus, a content distribution network, and a relay node thereof that can reduce the expected value of the number of distribution destination nodes.

  In order to achieve the above object, the present invention divides content to be distributed into N groups by (K, N) threshold secret sharing method, and each partial content is distributed from a distribution source node on the network. A route calculation device of a content distribution system that distributes to a plurality of distribution destination nodes via a plurality of routes via a relay node that applies network coding only to partial contents that belong to the same group but have different distribution destination nodes. Based on the topology of the encoding network, the maximum number m of link-independent paths from a plurality of distribution source nodes to each distribution destination node is solved by the first integer programming method, and the link independence for each distribution destination node is determined. First solving means for obtaining the minimum number M of the maximum number m of simple routes, and the minimum number of links that can include N−K + 1 routes when N routes are equally distributed to M links. Multiplex number calculation means for calculating the number of links F, and distribution that cannot restore the original content due to the occurrence of a multilink failure that causes a link failure in F or less link pairs that include N-K + 1 or more routes A second solving means for solving N routes to each delivery destination node that minimizes the expected value of the number of destination nodes by a second integer programming method, and each relay node includes When the bandwidth used for the egress link is estimated to be the sum of the maximum number of routes that pass through the egress link in each group and reach the same destination for all groups, and network encoded partial content is lost Imposed a constraint that all partial contents of the same group would be lost.

According to the content distribution system apparatus of the present invention, the following effects are achieved.
(1) When simultaneously transferring content held by threshold secret sharing at multiple nodes to multiple delivery destination nodes via the network, multiple link failures are made while using link bandwidth effectively using network coding. This makes it possible to calculate a highly reliable content distribution route that minimizes the expected value of the number of distribution destination nodes from which the original content cannot be restored.

  (2) Dividing partial content into multiple groups and applying network coding only to partial content in the same group limits the effective use of link bandwidth, but the original content is It is possible to calculate a content distribution route that reduces the expected value of the number of distribution destination nodes that cannot be restored.

  (3) When each partial content is lost, it is considered that all partial contents belonging to the same group as the partial content are lost, and the actual combination of the partial contents that are network-encoded at each relay node is taken into consideration. Therefore, it is possible to easily calculate a safe content distribution route with respect to reliability.

Moreover, according to the route calculation method of the content distribution system of the present invention, the following effects are achieved.
(4) While updating the link cost, using the minimum cost route calculation method, the content delivery route is made faster by sequentially calculating the route for delivering each partial content to each delivery destination node one by one. Can be calculated.

It is the figure which showed the network structure of the content delivery system with which this invention is applied. It is a functional block diagram of 1st Embodiment of a delivery route calculation server. It is the flowchart which showed operation | movement of one Embodiment of this invention. It is the figure which showed the modification of network topology. It is the figure which showed the application method of the network coding classified by group in each link. It is a functional block diagram of 2nd Embodiment of a delivery route calculation server. It is the flowchart which showed the setting procedure of the content delivery path | route which concerns on 2nd Embodiment. It is the flowchart which showed the calculation procedure of the initial value of link cost Cost1. It is the flowchart which showed the procedure which calculates link cost Cost1. It is the figure which showed the example of calculation of link cost typically.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a network configuration of a content distribution system to which a distribution route calculation method and apparatus according to the present invention is applied. Here, content distribution by a plurality of routes using (K, N) threshold secret sharing is performed. An example will be described.

  In the control target network, S distribution source nodes (content holding nodes) s that hold content are arranged, and N partial contents obtained by dividing one content into N in each distribution source node s Are distributed. The partial content distributed to each distribution source node s is not limited to one, and a plurality of different partial contents may be arranged. N partial contents are distributed from each of the S distribution source nodes to each of the D distribution destination nodes d.

  The partial content transmitted from each distribution source node s is distributed to each distribution destination node d via a plurality of relay nodes. Each relay node has a known network encoding function that encodes a plurality of partial contents with different destination distribution destination nodes d and combines them into one encoded partial content.

  In the present embodiment, the partial content is divided into a plurality of groups, and the application range of network coding is limited to the partial content in the same group. As a result, even if a certain partial content is lost due to a link failure, the partial content that may not be network-decoded at the distribution destination node can be limited to only the partial content that belongs to the same group as the lost partial content.

  That is, if K or more partial contents that do not belong to the group can be network-decoded at the distribution destination node, the original contents can be restored at the distribution destination node. At this time, by making the partial contents held in different nodes belong to the same group, network coding is promoted and the link band can be effectively used.

  Each distribution destination node d has a network decoding function that reproduces each partial content by decoding the encoded partial content in which a plurality of partial contents are combined into one by network encoding, and an original from at least K partial contents A content restoration function for restoring content is provided.

  The delivery route calculation server 1 determines a route for delivering N partial contents without omission from each delivery source node s to each delivery destination node d using network encoding, and notifies each delivery source node s. , Request its delivery. Each distribution source node s distributes the held partial content to each distribution destination node d through the notified distribution route.

  The number of partial contents requested for distribution from the distribution path calculation server 1 to each distribution source node s is not limited to one, and there may be a plurality of partial contents. Then, a plurality of routes corresponding to the number of partial contents are notified to the distribution source node s that distributes the plurality of partial contents. Note that the distribution route calculation server 1 recognizes partial contents distributed in each distribution source node s in advance, and each partial content is identical to a plurality of partial contents distributed in the same distribution source node. It is classified into a plurality of groups in advance so as not to belong to a group. In other words, only partial contents distributed in different distribution source nodes are allowed to be classified into the same group. When notifying the path of each partial content, the group identifier IDg to which each partial content belongs is also notified.

  In this embodiment, a distribution path is calculated that minimizes the expected value of the number of distribution destination nodes that cannot restore the original content due to a multilink failure while improving the efficiency of link band use by network coding.

[First embodiment]
FIG. 2 is a functional block diagram showing the configuration of the main part of the distribution route calculation server (computer) 1 according to the first embodiment of the present invention. Here, the configuration unnecessary for the description of the present invention is not shown. Has been.

  The topology acquisition unit 100 acquires the topology of the network. The topology transformation unit 101 transforms the acquired real topology of the network into the virtual topology shown in FIG. 4 as will be described in detail later. The first finding unit 102 finds the maximum number m of link-independent routes from each delivery source node s to each delivery destination node d by a first integer programming method to be described later, and further each of the D delivery destinations. The minimum value M is determined from the maximum number m of link-independent paths determined for the node d.

  The multiplexing number calculation unit 103 evenly distributes the N routes for transferring the N partial contents to the M links constituting the minimum cut set between the distribution source node s and the distribution destination node d. In this case, the minimum number of links F including N−K + 1 paths is calculated.

  The second solver 104 determines the original content by the occurrence of a multi-link failure below the F-multiple link failure that causes a link failure on all the F links or less that include N-K + 1 or more routes. N paths that reach each distribution destination node that minimizes the expected value of the number of distribution destination nodes that can no longer be restored are divided into parts within the same group according to the second integer programming method described later. Solve while limiting to content. The route notification unit 105 notifies the determination result of the N routes to each corresponding distribution source node s.

  Next, the operation of the present invention will be described with reference to a flowchart. FIG. 3 is a flowchart showing a content delivery route setting procedure according to an embodiment of the present invention.

  In step S1, the actual topology (Node, Link) of the network is acquired by the topology acquisition unit 101 together with the failure probability of each link. In step S2, the topology of the network is virtually deformed as shown in FIG.

  That is, one pseudo source node vs is virtually provided on the upstream side of each distribution node s and is connected to each distribution source node s by a virtual link vlink. The failure probability of each virtual link vlink is set to zero, and the capacity of each virtual link vlink is set to a value corresponding to the number of partial contents C (s) held by each connected distribution source node s. Such a network modification makes it possible to calculate a content distribution path in consideration of the partial content number C (s) held by each distribution source node s.

  In step S3, the maximum number m of link independent paths that do not include a common link from each of the S distribution source nodes s holding the partial content to each distribution destination node d is the first solving unit 102. , By solving the following first integer programming. In the first integer programming, each constant is defined as follows.

-Node: a node constituting a network-Node: a set of node nodes excluding a pseudo-originating node-d: a destination node-link: a link constituting a network-Link: a set of link links including virtual links-vs: pseudo-originating Node-vlink: Virtual link-VLink: Set of virtual links-s (vlink): Distribution source node to which the virtual link vlink is connected-Cs (vlink): Number of partial contents held by the distribution source node s (vlink) Clink: Capacity of each link link excluding virtual links-INnode: A set of links whose end point is node node-OUTnode: A set of links whose start point is node node

In this embodiment, variables are defined as follows.
Xlink: integer variable indicating the number of link independent paths that pass through link link m: number of link independent paths

  In the first integer programming method in the first solving unit 102, the constraint equations are given by the following equations (1) to (4). These are related to the path conservation rule, and equation (1) is a constraint that the total number of paths exiting from the pseudo-origin node vs is equal to the number m of link-independent paths. Equation (2) is a constraint that the number of routes entering each distribution destination node d is m. Equation (3) is a constraint that the number of routes from each distribution destination node d is zero. The expression (4) is a constraint that the number of incoming routes is the same as the outgoing route number in nodes (relay nodes) other than the pseudo origin node vs and the distribution destination node d.

  In the present embodiment, all routes must be link-independent, and a plurality of routes do not pass through each link, so the following equation (5) is given as a link-independent condition.

  Furthermore, in the present embodiment, the constraint condition on the number of partial contents held by each distribution source node s is given by the following equation (6). This is because each distribution source node s holds the number of routes passing through the virtual link vlink connecting the pseudo origin node vs and each distribution source node s, that is, the number of partial contents distributed from the distribution source node s. The condition is that the number of partial contents is not exceeded.

  Further, in this embodiment, the capacity condition of the link link is given by the following equation (7). This is a condition that the number of link-independent paths passing through each link does not exceed the link Clink.

  Here, since the objective function Obj to be maximized is the variable m, in step S3, by solving the first integer programming, the maximum number m of link-independent paths from the distribution source node is obtained for each distribution destination node. Desired. Then, all the link independent paths are specifically obtained based on the maximum number m and the variable xlink.

  On the other hand, if the maximum number of link-independent routes is m, all the N routes from each distribution source node s to each distribution destination node d are included in a certain m link set. Means that it must pass through. Therefore, when the minimum value among the maximum number m of link-independent paths obtained for each of the D distribution-destination nodes d is M, the distribution-destination node d has a maximum number of link-independent paths of M. N routes will pass through any of M links. In the present embodiment, it is considered that such N paths are distributed to M links as evenly as possible (most even in integer units) without considering the link capacity.

  In step S4, the multiplexing number calculation unit 103 calculates the minimum number of links F that can include N−K + 1 paths when N paths are evenly distributed to M links. . In other words, hi routes given by the following equation (8) are allocated to the i (= 1 to M) th link.

H is given by the following equation (9).

  The number of links F is given by the following equation (10) as the minimum number of links in which the total number of paths to be distributed is N−K + 1 or more.

  At this time, if a failure occurs in F links among the M links, the distribution destination node whose maximum number of link-independent routes is M has N routes for transferring partial contents. Of these, N-K + 1 or more routes are always obstacles. When there is no link capacity constraint, there is a possibility that more than N-K + 1 routes to a certain destination node may become a failure due to fewer than F links due to link capacity constraints. However, due to F heavy link failure, N-K + 1 or more routes will always fail. That is, even when network coding is not performed at all, N−K + 1 or more partial contents are lost due to the F-multiple link failure, and the distribution destination node d cannot restore the original contents.

  In this embodiment, assuming that the failure probability of each link is sufficiently small, only the multi-link failure below the F-multiple link failure in which the original content cannot be restored at any of the delivery destination nodes is considered. That is, consider the calculation of a distribution route that minimizes the expected value of the number of distribution destination nodes that cannot restore the original content when a multi-link failure equal to or less than the F-multiple link failure occurs.

  Therefore, in this embodiment, the second integer programming method is solved to minimize the expected value of the number of distribution destination nodes that cannot restore the original content, and each of N distributions to D distribution destination nodes. A route is calculated. At this time, the N partial contents are divided into G groups, and each relay node applies network coding only to partial contents belonging to the same group and having different delivery destination nodes. When a certain partial content is lost, it is considered that only the partial content belonging to the same group as the lost partial content to which network coding may be applied is lost at the same time.

  Therefore, in step S5 and subsequent steps, assuming that the failure probability of each link is sufficiently small, only N-K + 1 or more partial contents can be lost in consideration of only the multilink failure below the F-multiple link failure. N distribution routes that minimize the probability of occurrence of multiple link failures equal to or less than F double link failures are solved by the second integer solving unit 104 by the second integer programming method.

  In the present embodiment, constants and sets in the second integer programming method are defined as follows. In addition, since the same code | symbol as the above represents the same or equivalent part, the description is abbreviate | omitted.

-Dest: Set of delivery destination nodes-FLink: Set of combinations of F or less links that do not include virtual links-FLinkf: Set of links included in the f-th combination in FLink-Plink: Pre-given links failure probability of link-GPC g: Set of delivery routes belonging to group g (1 to G)-ng: Number of delivery routes belonging to group g (1 to G)

The variables in the second integer programming method are defined as follows.
Xlink (d, n): “1” when the n (1 to N) th route to the distribution destination node d (1 to D) passes the link link of interest, “0” when it does not pass Binary variable that is-Clink (g): Integer variable that represents the bandwidth used for link links excluding virtual links by routes belonging to group g-Yf (d, g): Delivery destination node due to multiple link failure of link combination FLink f In d (1 to D), a binary variable that is “1” when the partial content belonging to group g (1 to G) cannot be network-decoded and “0” when it can be decoded ・ Zf (d): Multiplex of link combination FLink f It is “1” when the N-K + 1 or more partial contents cannot be network-decoded at the distribution destination node d (1 to D) due to a link failure, and the original contents cannot be restored, and “0” when the contents can be restored. Binary variable

  Further, in the second integer programming, the constraint equations are given by the following equations (11) to (13). Equation (11) indicates that each of N routes passes only one of the virtual links that exit from the pseudo-originating node, that is, N routes pass through one of the virtual links that exit from the pseudo-originating node. It is a conservation law. Expression (12) is a path preservation rule that all distribution paths pass only one of the links entering the distribution destination node only once and do not pass the link exiting from the distribution destination node. Equation (13) is a path conservation rule that all routes pass through the link starting from the relay node other than the pseudo-origin node and delivery destination node d and the link starting from the end point only once, or neither. is there.

  In the present embodiment, the capacity condition of the virtual link vlink is given by the following equation (14). This is because the distribution source node s holds the number of routes passing through the virtual link vlink connecting the pseudo origin node vs and each distribution source node s, that is, the number of partial contents distributed from the distribution source node s. The condition is that the number of partial contents is not exceeded.

  If the network coding for each group is adopted, each relay node can encode a plurality of partial contents belonging to the same group and having different delivery destination nodes into one partial content and transfer it to the outgoing link. That is, a plurality of distribution paths that belong to the same group and reach different distribution destination nodes can share the outgoing link bandwidth with each other. Therefore, the bandwidth used for each link is a value obtained by calculating the maximum number of distribution routes passing through the link in each group and reaching each distribution destination node, and adding the calculated maximum number for all groups.

  FIG. 5 is a diagram schematically showing how a bandwidth is shared by a plurality of routes in the outgoing link of a relay node by network coding for each group, and the horizontal axis indicates D delivery destination nodes d. The vertical axis indicates N distribution routes.

  The distribution path 1 leading to the distribution destination node 2 belonging to the group 1 and the distribution path 1 reaching the distribution destination node 3 can share the link band with each other. Further, the distribution route 2 to the distribution destination node 1 belonging to the group 1, the distribution route 2 to the distribution destination node 2, and the distribution route 2 to the distribution destination node 3 can share a link band with each other. Furthermore, the distribution path n1 + 2 to the distribution destination node 2 belonging to the group 2 and the distribution path n1 + 2 to the distribution destination node D can share the link band with each other. Finally, the distribution route n1 + n2 to the distribution destination node 1 belonging to the group 2 and the distribution route n1 + 1 to the distribution destination node 2 can share the link band with each other.

  From the above, the bandwidth used for this link is the number of distribution routes 3 that reach the distribution destination node 3 that is the largest among the distribution routes that belong to the group 1 and reach each distribution destination node. The value is 5, which is the sum of the number of distribution routes 2 reaching the distribution destination node 2 which is the maximum among the number of distribution routes reaching the distribution destination node.

  As described above, if network coding is applied, a plurality of partial contents with different destinations can be combined into one coded partial content. Therefore, the capacity constraint of each link in the second integer programming method is as follows.

  The following equation (15) is a link capacity constraint based on network coding. The bandwidth used for each link by the partial contents belonging to each group is the maximum number of distribution paths that pass through the link and reach each distribution destination node, and the bandwidth used for each link must be less than or equal to the link capacity. .

  On the other hand, if the partial content that is network-encoded within a certain group is lost due to a link failure, the distribution destination node d may not be able to perform network decoding on all partial content belonging to the group. Therefore, when each partial content is lost, it is considered that all partial contents belonging to the same group as the partial content cannot be network-decoded at the distribution destination node. As a result, it is possible to calculate the content delivery path on the safe side with respect to reliability without considering the method of combining partial contents at the time of network coding in each relay node.

  For example, when a failure occurs in the link shown in FIG. 5, with respect to the delivery destination node 1, only the partial content 2 and the partial content n1 + n2 are lost, but the group 1 and the group to which network coding may be applied. It is assumed that all n1 + n2 partial contents belonging to 2 cannot be network-decrypted. At this time, the constraint condition in the second integer programming method is as follows.

  The following expression (17) is a condition that the partial content cannot be network-decoded at each distribution destination node due to each multi-link failure.

  The following equation (18) is a condition that the original content cannot be restored at each distribution destination node due to each multi-link failure. Note that the sign A is a positive constant having a sufficiently large value.

  An object of the present invention is a distribution destination in which N-K + 1 or more partial contents cannot be restored among N pieces of partial content due to a multi-link failure of F-fold link failure or less, and the original content cannot be restored. Since the expected value of the number of nodes is to be minimized, the objective function to be minimized is given by the following equation (19), and Xlink (d, n) obtained by solving the second integer programming method From the value, N routes to each distribution destination node d are calculated.

  Returning to FIG. 3, in step S6, the passing link of the nth route to the delivery destination node d is calculated from the value of Xlink (d, n) obtained by solving the second integer programming. The route link information of a total of N routes is notified from the route notification unit 6 to each corresponding distribution source node s. At this time, the group identifier IDg to which each partial content belongs is also notified, and each distribution source node s distributes the partial content with the group identifier IDg when distributing the partial content. As a result, each relay node can recognize the group to which each partial content belongs, so that network coding can be applied only to partial contents belonging to the same group.

  According to the present invention, when simultaneously transferring content held by threshold secret sharing at a plurality of nodes to a plurality of distribution destination nodes via a network, while effectively using a link band using network coding, It is possible to calculate a highly reliable content distribution route that minimizes the expected value of the number of distribution destination nodes that cannot restore the original content due to a multilink failure.

  Further, according to the present embodiment, although the partial content is divided into a plurality of groups and the network coding is applied only to the partial content of the same group, the effective use of the link band is limited, but the multiple link It is possible to calculate a content distribution route that reduces the expected value of the number of distribution destination nodes that cannot restore the original content due to a failure.

  Furthermore, according to the present embodiment, when each partial content is lost, it is assumed that all the partial contents belonging to the same group as the partial content are lost, so that the content of the partial content that is network-encoded at each relay node. It is possible to easily calculate a safe content distribution route with respect to reliability without considering an actual combination.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 6 is a functional block diagram showing the configuration of the main part of the distribution route calculation server (computer) 1, and illustrations of components unnecessary for the description of the present invention are omitted. In this embodiment, a content distribution route that reduces the expected value of the number of distribution destination nodes that cannot restore the original content due to a multi-link failure is sequentially set by calculating the minimum cost route while updating the cost of each link. The

  The topology acquisition unit 201 acquires the actual topology of the monitored network NW illustrated in FIG. 1 together with the failure probability of each link. The topology transformation unit 202 converts the real topology of the network NW into the virtual topology shown in FIG. 4 as in the first embodiment. The link independent path number calculation unit 203 finds the maximum number m of link independent paths from a plurality of distribution source nodes s to each distribution destination node d by integer programming described later.

  The route setting unit 204 includes a link cost updating unit 204a that updates the cost Cost l of each link l configuring the network. Then, at each stage of the sequential route calculation, while updating the cost Cost l of each link l, the calculation of the minimum cost route is repeated until the number of existing routes to each delivery destination node d becomes N. Add to delivery route. The route notification unit 205 notifies the corresponding delivery source node s of the setting results of the N minimum cost routes to the delivery destination nodes d.

  Next, the operation of this embodiment will be described with reference to a flowchart. FIG. 7 is a flowchart showing a procedure for setting a content distribution route according to the second embodiment.

  In step S20, the actual topology (Node, Link) of the network and the failure probability of each link l are acquired by the topology acquisition unit 201. In step S21, the network for calculating the content distribution route is virtually deformed as shown in FIG.

In step S22, an initial value (= 1) is set to the identifier i of the distribution destination node d. In step S23, the maximum number of link-independent paths that do not include a common link among a large number of paths from S distribution source nodes s holding partial content to the current distribution destination node d (i) m is obtained by solving the following integer programming method in the link independent path number calculation unit 203. Here, integer programming constants are defined as follows:
-Node: a node constituting a network-Node: a set of node nodes excluding a pseudo-originating node-d: a destination node-link: a link constituting a network-Link: a set of link links including virtual links-vs: pseudo-originating Node • vlink: Virtual link • VLink: Set of virtual links • s (vlink): Partial content holding node connected to virtual link vlink • Cs (vlink): Number of partial contents held by distribution source node s (vlink) -INnode: A set of links with node node as the end point-OUTnode: A set of links with node node as the start point

In this embodiment, variables are defined as follows.
X link :: An integer variable representing the number of link independent paths that pass through the link link.
M: Number of link independent routes.

  In the integer programming method in the link independent path number calculation unit 203, the constraint equations are given by the above equations (1) to (4) as in the first embodiment. These relate to the path conservation law. Also in this embodiment, since all routes must be link-independent, and a plurality of routes do not pass through each link, the above equation (5) is given as a link-independent condition. Further, the capacity condition of the virtual link vlink is given by the above equation (6).

  Here, since the objective function Obj to be maximized is the variable m, in step S23, the above integer programming is solved to obtain the maximum number m of link independent paths. The value of the maximized objective function m is the maximum number of link-independent paths to the distribution destination node d (i) this time. In step S24, an initial value of each link cost Cost l is calculated.

  In steps S25 to S29, the route setting unit 204 updates the cost Cost l of each link l constituting the network by the link cost update unit 204a until the number n of existing routes reaches N, while the pseudo-originating node vs To the current delivery destination node d (i) via each delivery source node s is sequentially calculated. At this time, the N partial contents are divided into G groups, and each relay node applies network coding only to partial contents belonging to the same group and having different delivery destination nodes. The calculation order of the minimum cost route is that the route calculation for all partial contents belonging to a certain group is performed, and then the route calculation for the partial content belonging to the next group is performed.

  That is, in step S25, the number of existing routes n is initialized (= 0). In step S26, the cost of each link is calculated. In step S27, the minimum cost path from the pseudo origin node vs to the distribution destination node d (i) is calculated based on each link cost Cost l updated in step S26. A method for updating each link cost Cost l and a method for calculating the minimum cost path will be described in detail later.

  In step S28, the calculated minimum cost route is added as an existing route, and the existing route number n is incremented. In step S29, the number of existing routes n is compared with N. If the number of routes n has not reached N, the process returns to step S26 and the above processes are repeated.

  When the number of existing routes becomes N, the identifier i of the distribution destination node d is incremented in step S30. In step S31, it is determined whether or not each of the above processes has been completed for all distribution destination nodes d. If not completed, the process returns to step S23, and the above-described processes are repeated while switching the delivery destination node d.

  When calculating the minimum cost path in step S27, it is necessary to satisfy the capacity constraint of each virtual link. In other words, if the number of distribution routes that have passed through a virtual link vlink and reach the distribution destination node d (i) reaches the capacity of the virtual link, the cost of the virtual link is increased from zero to a sufficiently large value. change.

  The cost Cost l of each link when repeatedly executing the minimum cost route calculation is the original cost among the i-1 destination nodes d for which N distribution routes have already been determined by the minimum cost route calculation. A route is obtained that minimizes the sum of the expected value of the number of distribution destination nodes that cannot restore content and the probability that N -K + 1 or more partial contents cannot be restored at this distribution destination node d (i). To be set.

  However, the bandwidth used for each link is regarded as a value obtained by calculating the maximum number of distribution paths passing through the link in each group and reaching each distribution destination node, and adding the calculated maximum number for all groups. Therefore, based on the link capacity constraint considering network coding, if the distribution route newly calculated by the minimum cost route calculation passes through a certain link, and the used bandwidth of the link exceeds the link capacity, the link Is set to a sufficiently large value.

  In addition, if partial content that is network-encoded within a group is lost due to a link failure, the distribution destination node d may not be able to perform network decoding on all partial content belonging to the group. Therefore, when the partial content to be transferred to the distribution destination node d is lost, it is considered that all partial contents belonging to the same group as the partial content transferred to the distribution destination node d are lost. As a result, it is possible to calculate a safe content distribution route with respect to reliability without considering an actual combination of partial contents to be network-encoded at each relay node.

  Next, the initial value Cost 0 of each link cost obtained in step S24 of FIG. 7 will be described. The link cost initial value Cost 0 is common to all links, and the distribution destination node that cannot restore the original content among the d-1 distribution destination nodes for which N distribution routes have already been determined. Corresponds to the expected value of the number. In other words, when the original content cannot be restored in each of the d−1 delivery destination nodes due to a certain multilink failure, the occurrence probability of the multilink failure is added to the initial value Cost 0 of the link cost.

  At that time, if a partial content to be transferred to a certain distribution destination node is lost, it is considered that all partial contents belonging to the same group transferred to the distribution destination node are lost. When N−K + 1 or more partial contents transferred to a certain distribution destination node are lost, the occurrence probability of the multilink failure is added to the initial value Cost 0 of the link cost.

  When the maximum number of link-independent routes to the distribution destination node d calculated in step S23 is m, the link cost initial value Cost 0 is calculated in consideration of the maximum m-fold link failure. At this time, assuming that the failure probability of each link is sufficiently small, if the link cost initial value Cost 0 becomes a positive value due to f (= 1 to m) heavy link failure, multiple links larger than f Disability is not considered. In step S26, N distribution routes toward the distribution destination node d are sequentially calculated while updating the cost of each link. The cost Cost l of each link l is obtained by adding the cost update value of the link l to the link cost initial value Cost 0 calculated in step S24.

  The cost update value for link l is calculated when the total number of routes included in the group group to which the already calculated n-1 distribution routes and the newly calculated nth distribution route belong is N-K + 1 or less. The probability that all the partial contents transferred to the distribution destination node d are lost when the new distribution path passes through the link l. In addition, when the total number of routes included in the group group to which the already calculated n-1 distribution routes and the newly calculated nth distribution route belong exceeds N-K + 1, new distribution routes It is assumed that N−K + 1 or more partial contents transferred to the distribution destination node d are lost by passing through the link l. However, when one partial content transferred to the distribution destination node d is lost, it is considered that all partial contents belonging to the same group transferred to the distribution destination node d are lost.

  FIG. 8 is a flowchart showing a procedure for calculating the initial value Cost 0 of each link cost executed in step S24 of FIG. Here, if the original content cannot be restored in each of d-1 destination nodes for which all distribution routes have already been determined due to a certain multilink failure, the probability of the multilink failure is the link cost. It is added to the initial value.

  In step S61, the cost Cost 0 is reset (= 0), and the link failure multiplexing number f is initialized (= 1). In step S62, a list is constructed by listing the combinations of f links. In step S63, one link combination is extracted from the list one by one, and a multi-link failure is assumed.

  In step S64, an identifier i for specifying the distribution destination node d of interest is initialized (= 1). In step S65, it is determined whether or not N−K + 1 or more partial contents reaching the distribution destination node d (i) are lost. If lost, the process proceeds to step S66, and the multilink failure probability is added to the cost Cost0.

  In step S67, the identifier i specifying the distribution destination node d of interest is updated. In step S68, the identifier i is compared with the distribution destination node number d. If i <d, the process returns to step S65, the delivery destination node d is switched, and the above processes are repeated. In step S69, it is determined whether or not all link combinations have been extracted. If not completed, the process returns to step S63, and the above processes are repeated while switching the link combination.

  Thereafter, when all the link combinations have been extracted, the process proceeds to step S70, and it is determined whether or not the cost Cost 0 is zero. If not zero, the process ends. If zero, the process proceeds to step S71. In step S71, the number of link combinations f and m are compared. If f <m, the process ends. If f <m, f is updated (f = f + 1) in step S72, and the process proceeds to step S62. Return.

  Next, the procedure for calculating the link cost Cost l executed in step S26 of FIG. 7 will be described. In this embodiment, the cost Cost l of the link l is first set to the link cost initial value Cost 0. Assuming that the newly calculated nth delivery route passes through the link l, the n-1 delivery route that has already been calculated and the route included in the group group to which the newly calculated nth delivery route belongs. When the total number is less than N-K + 1, and if all partial contents transferred to the destination node d are lost due to a certain multilink failure, the probability of occurrence of the multilink failure is the link cost Cost l. Is added.

  In addition, when the total number of routes included in the group group to which the (n-1) delivery routes already calculated and the newly calculated (n) delivery route belong exceeds N-K + 1, When N−K + 1 or more partial contents transferred to the distribution destination node d are lost, the occurrence probability of the multilink failure is added to the link cost Cost l.

  If the maximum number of link-independent routes to the distribution destination node d calculated in step S23 in FIG. 7 is m, the link cost Cost l is calculated in consideration of the maximum m-fold link failure. At this time, assuming that the failure probability of each link is sufficiently small, if the link cost Cost l increases from the link cost initial value Cost 0 due to f (= 1 to m) heavy link failure, the multiplexing is larger than f. Does not consider link failures.

  FIG. 9 is a flowchart showing a procedure for calculating the link cost Cost l. In step S81, the cost Cost l is set to an initial value, and the multiplexing number f of link failures is initialized (= 1). In step S82, combinations of f links are listed to form a list. In step S83, one link combination is extracted from the list one by one, and a multi-link failure is assumed.

  In step S84, it is determined whether or not the total number of routes included in the group group to which the already calculated n-1 delivery routes and the newly calculated nth delivery route belong is N-K + 1 or less. Is done. If the total number of paths is N−K + 1 or less, the process proceeds to step S85, and it is determined whether or not all partial contents including new partial contents are lost due to the assumed multiple link failure. If all the partial contents are lost, the process proceeds to step S87, and the multilink failure probability is added to the link cost Cost l. If all the partial contents are not lost, the process proceeds to step 88 without adding to the link cost Cost l.

  On the other hand, if the total number of paths is not less than N−K + 1, the process proceeds to step S86, and N−K + 1 of all partial contents including new partial contents are caused by the assumed multilink failure. It is determined whether or not the above partial content is lost. If N−K + 1 or more partial contents are lost, the process proceeds to step S87, and the multilink failure probability is added to the link cost Cost l. If there is a loss of less than N−K + 1 partial contents, the process proceeds to step S88 without adding to the link cost Cost l.

In step S88, it is determined whether or not all link combinations have been extracted. If not completed, the process returns to step S83, and the above processes are repeated while switching the link combination.

  Thereafter, when all the link combinations have been extracted, the process proceeds to step S89, and it is determined whether or not the link cost Cost l remains the initial value. If the initial value is not maintained, the process ends. If the initial value is maintained, the process proceeds to step S90. In step S90, the number of link combinations f and m are compared. If f <m, the process ends. If f <m, the process proceeds to step S91 to update the number of link combinations f (f = f + After 1), the process returns to step S82.

  FIG. 10 is a diagram schematically showing an example of calculating the link cost. Here, three distribution paths P1, P2, and P3 toward the distribution destination node d have already been calculated, and the distribution paths P1 and P2 , It is assumed that one group is configured, and the distribution route P3 and the fourth distribution route P4 for newly calculating a route individually constitute one group. Also assume that N−K + 1> 3.

  At this time, when calculating the fourth delivery route P4, the cost Cost l1 of the link l1 is the double link failure occurrence probability of the link l1 and the link l3 and the double link failure occurrence probability of the link l1 and the link l4. Is added to the link cost initial value. The cost Cost l2 of the link l2 is obtained by adding the product of the single link failure occurrence probability that the distribution route P3 becomes a failure and the failure probability of the link l2 to the link cost initial value. Further, the cost Cost l3 of the link l3 is obtained by adding the failure probability of the link l3 to the link cost initial value. The cost Cost l4 of the link l4 is obtained by adding the failure probability of the link l4 to the link cost initial value.

  Similarly, assuming that N−K + 1 = 3, when calculating the fourth delivery route P4, the cost Cost l1 of the link l1 is the link cost initial value of the failure probability of the link l3 and the failure probability of the link l4. Set to the value added to the value. The cost Cost l2 of the link l2 is set to a value obtained by adding the failure probability of the link l2, the failure probability of the link l3, and the failure probability of the link l4 to the link cost initial value. Further, the cost Cost l3 of the link l3 is set to a value obtained by adding the failure probability of the link l3 and the failure probability of the link l4 to the link cost initial value. The cost Cost l4 of the link l4 is also set to a value obtained by adding the failure probability of the link l3 and the failure probability of the link l4 to the link cost initial value.

  According to the present embodiment, when simultaneously transferring content held by threshold secret sharing at a plurality of nodes to a plurality of distribution destination nodes via a network, effective use of a link band is achieved by using network coding. Therefore, it is possible to calculate a highly reliable content distribution route that reduces the expected value of the number of distribution destination nodes that cannot restore the original content due to a multilink failure.

  Further, according to the present embodiment, the link cost is updated, and the route for delivering each partial content to each delivery destination node is sequentially calculated one by one using the minimum cost route calculation method. The content distribution route can be calculated at high speed.

  Furthermore, according to the present embodiment, although the partial content is divided into a plurality of groups and the network coding is applied only to the partial content in the same group, the effective use of the link band is limited, but the multiplexing is limited. It is possible to calculate a content distribution route that reduces the expected value of the number of distribution destination nodes that cannot restore the original content due to a link failure.

  Furthermore, according to the present embodiment, when each partial content is lost, it is assumed that all partial contents belonging to the same group as the partial content are lost, so that the actual content of the partial content to be network-encoded at each relay node is determined. It is possible to easily calculate a safe content distribution route with respect to reliability without considering the combination.

  DESCRIPTION OF SYMBOLS 1 ... Distribution route calculation server, 100, 201 ... Topology acquisition part, 101, 201 ... Topology deformation | transformation part, 102 ... 1st solution part, 103 ... Multiplex number calculation part, 104 ... 2nd solution part, 105 ... Path | route notification part, 203 ... Link independent route number output unit, 204 ... Route setting unit, 204a ... Link cost update unit, 205 ... Route notification unit

Claims (10)

Content to be distributed is divided into N groups and divided into multiple groups, and each partial content is distributed from a distribution source node on the network to a plurality of distribution destination nodes through a plurality of routes via a relay node to which network coding is applied. Content distribution network
Each of the relay nodes restricts the scope of application of network encoding to partial contents belonging to the same group and having different distribution destination nodes. In a relay node that divides the content into N and applies network coding to each partial content classified into a plurality of groups,
A relay node, characterized in that the application range of network encoding is limited to partial contents belonging to the same group and having different delivery destination nodes. Content to be distributed is divided into N groups by dividing it into N groups using the (K, N) threshold secret sharing method, and each partial content is distributed from the distribution source node on the network to the multiple distribution destination nodes. A route calculation apparatus for a content distribution system in which a plurality of routes are distributed via a relay node that applies network coding only to partial content with different destination nodes,
Based on the topology of the encoded network, the maximum number m of link-independent paths from a plurality of distribution source nodes to each distribution destination node is solved by the first integer programming method, and the link-independent paths for each distribution destination node A first solution means for obtaining a minimum number M of the maximum number m of
Multiplex number calculating means for calculating the minimum number of links F that can include N-K + 1 paths when N paths are evenly distributed to M links;
Minimizing the expected value of the number of destination nodes that cannot restore the original content due to the occurrence of a multi-link failure that causes a link failure in F or less link pairs including N-K + 1 or more routes Second solving means for solving N routes to each delivery destination node by a second integer programming method,
In the second solving means, the use bandwidth of the outgoing link of each relay node is estimated to a value obtained by adding the maximum value of the number of routes passing through the outgoing link to the same destination in each group for all groups, A route calculation apparatus of a content distribution system, wherein a restriction condition is imposed such that all the partial contents of the same group are lost when the encoded partial contents are lost. Virtual topology conversion means for converting the topology of the network into a virtual topology in which a pseudo source node is virtually provided upstream of each distribution source node and connected to each distribution source node by a virtual link;
The first solving unit and the second solving unit set the capacity of each virtual link connected to each distribution source node to a value corresponding to the number of partial contents held by the distribution source node, and 3. The route calculation apparatus for a content distribution system according to claim 2, wherein a route from the node to each of the distribution destination nodes via each virtual link and each distribution source node is obtained. Content to be distributed is divided into N groups by dividing it into N groups using the (K, N) threshold secret sharing method, and each partial content is distributed from the distribution source node on the network to a plurality of distribution destination nodes. A route calculation apparatus for a content distribution system in which a plurality of routes are distributed via a relay node that applies network coding only to partial content with different destination nodes,
While updating the cost of each link to the content delivery route that reduces the expected value of the number of delivery destination nodes that can no longer restore the original content due to multi-link failure, until the number of routes to each delivery destination node reaches N, Comprising a route setting means for repeating the minimum cost route calculation and setting for each delivery destination node;
The route setting means uses a method of updating the cost of each link, wherein the total number of routes included in the group group to which the already calculated distribution route and the newly calculated distribution route belong is N−K + 1 or less. Depending on whether or not
If the total number of routes is N−K + 1 or less, the link cost is defined as the link cost update value with the probability that all the partial contents transferred to the delivery destination node will be lost when the new delivery route passes through the link. Is added to
If the total number of routes exceeds N-K + 1, there is a probability that N-K + 1 or more partial contents transferred to the delivery destination node through the new delivery route through the link will be lost. A route calculation device for a content distribution system, wherein a link cost update value is added to a link cost.   6. The content distribution according to claim 3, wherein the partial contents are classified so that a plurality of partial contents distributed in the same distribution source node do not belong to the same group. System route calculator. Content to be distributed is divided into N groups by dividing it into N groups using the (K, N) threshold secret sharing method, and each partial content is distributed from the distribution source node on the network to a plurality of distribution destination nodes. A route calculation method for a content distribution system in which a plurality of routes are distributed via a relay node that applies network coding only to partial content with different destination nodes,
Based on the topology of the encoding network, the computer solves the maximum number m of link-independent paths from each distribution source node to the distribution destination node by the first integer programming method, The procedure for obtaining the minimum number M of the maximum number m of routes,
A procedure for calculating the minimum number of links F that can include N−K + 1 paths when the computer equally distributes N paths to M links;
Minimize the expected value of the number of destination nodes where the computer cannot restore the original content due to the occurrence of a multi-link failure that causes a link failure in F or less link pairs that include N-K + 1 or more routes And solving the N routes to each delivery destination node by the second integer programming method,
In the second integer programming method, the use bandwidth of the outgoing link of each relay node is estimated to a value obtained by adding the maximum value of the number of routes passing through the outgoing link to the same destination in each group for all groups. A route calculation method for a content distribution system, in which a restriction condition is imposed so that all partial contents of the same group are lost when network-encoded partial contents are lost. A procedure in which a computer virtually establishes a pseudo-origin node upstream of each distribution source node and connects to each distribution source node with a virtual link;
A procedure in which the computer further sets a capacity of a virtual link connected to each distribution source node to a value corresponding to the number of partial contents held by the distribution source node;
The first integer programming method and the second integer programming method are characterized in that a route from the pseudo source node to each distribution destination node via each virtual link and each distribution source node is obtained. 8. The route calculation method for the content distribution system according to 7. Content to be distributed is divided into N groups by dividing it into N groups using the (K, N) threshold secret sharing method, and each partial content is distributed from the distribution source node on the network to a plurality of distribution destination nodes. A route calculation method for a content distribution system in which a plurality of routes are distributed via a relay node that applies network coding only to partial content with different destination nodes,
While updating the cost of each link to the content delivery route that reduces the expected value of the number of delivery destination nodes that can no longer restore the original content due to multi-link failure, until the number of routes to each delivery destination node reaches N, Repeat the minimum cost route calculation and set for each destination node.
Depending on whether or not the total number of routes included in the group to which the distribution route that has already been calculated and the distribution route that is newly calculated belongs is less than or equal to N-K + 1, Different,
If the total number of routes is N−K + 1 or less, the link cost is defined as the link cost update value with the probability that all the partial contents transferred to the delivery destination node will be lost when the new delivery route passes through the link. Is added to
If the total number of routes exceeds N-K + 1, there is a probability that N-K + 1 or more partial contents transferred to the delivery destination node through the new delivery route through the link will be lost. A route calculation method for a content distribution system, wherein a link cost update value is added to a link cost.   The content distribution according to any one of claims 7 to 9, wherein the partial contents are classified so that a plurality of partial contents distributed in the same distribution source node do not belong to the same group. System route calculation method.