JP6592809B2 - Network system, node device, cache method, and program - Google Patents

Description

  The present invention relates to a network system, a cache method, and a cache program.

  Conventionally, various techniques for intermediately caching files transmitted between computers connected to a network have been proposed. By downloading the cache file instead of the original file, concentration of access to the original file can be avoided and the time until the download is completed on the receiving side can be shortened.

  For example, a technique has been proposed in which the upper cache server receives a notification of the reference count of an object to be deleted in the lower cache server, and determines whether to cache the object based on the cumulative reference count of the deleted object. (For example, Patent Document 1).

  Further, the cache control device estimates the propagation amount of a request transferred in the distributed cache system due to a cache miss for a request received from the outside of the distributed cache system, and based on the estimated propagation amount of the request. Also proposed is a technique for estimating the total cost for storing and distributing data corresponding to a request and updating the initial value of the time (TTL) for storing data in the cache memory so as to reduce the estimated cost (For example, Patent Document 2).

  Also, a content storage node (CSN) is allocated between a local space for storing locally popular content objects and a federated space for storing some of the less popular content objects. A local space is adapted to store available content objects with a relatively high level of usefulness, and a federated space is useful in cooperation with the federated space of other CSNs Adapted to store at least a portion of available content objects with relatively low sex levels, and content objects are moved between local space and federated space in response to a difference in usefulness level There is also a proposed technique (for example, Patent Document 3).

JP 2004-264958 A JP 2016-48498 A Special table 2012-518841 gazette

  Conventionally, when a file is cached in a distributed manner in a plurality of nodes constituting a network system, it generally takes time to determine a file arrangement that can avoid concentration of access and reduce the entire communication amount. There was a problem.

  An object of the present invention is to provide a network system capable of avoiding concentration of access to files and reducing the entire communication amount with a simple configuration.

  The network system according to the present invention includes a plurality of node devices that temporarily hold files to be transmitted / received and serve as file request sources, and the node devices belong to any one of hierarchically connected networks. The node device is a group for specifying a file to be held by the node device, and belongs to one of a plurality of groups assigned to the hierarchy, and the file is information indicating zero or more groups. When the node device receives the file associated with the information indicating the group to which the node device belongs, the information indicating the group and the group in which the file is held is included. A cache holding unit that temporarily holds the file as a cache file, and a cache file corresponding to the file requested by the requesting node device when the cache file is held by the requesting node device. Correspond to the file requested by the requesting node device. If you do not maintain a cache file based on the information indicating the group, and a relay unit that requests the file to other nodes belonging to the same layer or other layers.

  In this way, a distributed cooperative system can be realized by distributing node devices belonging to any group on the network. That is, the information indicating the group associated with the file includes information for specifying the hierarchy and group in which the file is held, so that the cache holding unit can easily specify the file to be held by itself. Further, the relay unit can easily determine whether the file request destination should be the same hierarchy or the upper or lower hierarchy based on the information indicating the group. That is, with a simple configuration, it is possible to avoid concentration of access to the original file and to reduce the entire communication amount.

  The access management device further includes an access management device that calculates the frequency of access to the file, and the access management device includes a group that is associated with the file so that the calculated high frequency file is held in a lower hierarchy than the low frequency file. The information shown may be changed. In this way, a file that is highly likely to be transmitted and received can be cached on the network at a location close to the file request source. Therefore, concentration of access to the original file can be avoided and the entire communication amount can be reduced.

  In addition, the access management device changes information indicating a group associated with a file so that a file with a high frequency is held by a node device belonging to more groups in the same hierarchy than a file with a low frequency. Also good. Even with such a configuration, a file that is highly likely to be transmitted and received can be cached on the network at a location close to the file request source.

  In addition, a group may be assigned to a plurality of node devices so as to reduce the bias in the network topology. Even with such a configuration, a file that is highly likely to be transmitted and received can be cached on the network at a location close to the file request source.

  In addition, when at least some of the node devices are connected to a plurality of networks belonging to the same hierarchy, and the relay unit requests a file from another node device belonging to the same hierarchy, the plurality of nodes belonging to the same hierarchy are You may make it request | require to either of the networks. For example, it may be connected to a network using terminal-to-terminal communication or PLC separately from a network provided by an ISP. In this way, the network to be used can be changed according to the status of the communication band, etc., and the load on the network can be reduced and the effective speed of file transmission / reception can be improved.

The node device according to the present invention belongs to any one of hierarchically connected networks, and temporarily holds files to be transmitted and received. A group for identifying a file to be held by itself belongs to one of a plurality of groups assigned to the hierarchy, and the file is associated with information indicating zero or more groups. The information shown includes information for specifying the hierarchy and group in which the file is held. When a file associated with information indicating the group to which the file belongs is received, the file is temporarily held as a cache file. A cache holding unit, a cache transmitting unit that transmits the cache file to the requesting node device when the cache file corresponding to the file requested by the requesting node device is held, and the requesting node If the device does not have a cache file corresponding to the requested file, Based on the information indicating the-loop, and a relay unit that requests the file to other nodes belonging to the same layer or other layers.

  A distributed cooperative system can be realized by distributing the above-mentioned node devices belonging to any group on the network. That is, the information indicating the group associated with the file includes information for specifying the hierarchy and group in which the file is held, so that the cache holding unit can easily specify the file to be held by itself. Further, the relay unit can easily determine whether the file request destination should be the same hierarchy or the upper or lower hierarchy based on the information indicating the group. That is, with a simple configuration, it is possible to avoid concentration of access to the original file and to reduce the entire communication amount.

  The contents described in the means for solving the problems can be combined as much as possible without departing from the problems and technical ideas of the present invention. The contents of the means for solving the problems can be provided as a device such as a computer or a system including a plurality of devices, a method executed by the computer, or a program executed by the computer. A recording medium that holds the program may be provided.

  With a simple configuration, it is possible to provide a network system that can avoid concentration of access to files and reduce the entire communication amount.

It is a figure which shows an example of a structure of a network system. It is a figure which shows an example of the computer connected to one network equivalent to the tier 3. It is a figure for demonstrating an example of allocation of the node connected to the network which forms a some hierarchy, and a group. It is a figure for demonstrating the information which shows a group attached | subjected to a file. It is a block diagram which shows an example of a structure of a node. It is a block diagram which shows an example of a structure of a delivery server. It is a processing flowchart which shows an example of the file delivery process which a network system performs. It is a processing flowchart which shows an example of the cache object update process which changes the file of cache object. It is a figure which shows an example of the tag which shows the order | rank based on the access count to the file in a predetermined period, and the group allocated in relation to the said file. It is a graph which shows the file cached on one mesh type | mold network, and its number. It is a block diagram which shows an example of a device configuration in a house when a network system is applied to a CATV network. It is a figure which shows the example which forms the network of the area | region which connects a neighboring node with the network which ISP provides.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, the structure of embodiment is an illustration and this invention is not limited to the structure shown in embodiment.

<Network configuration>
FIG. 1 is a diagram illustrating an example of a configuration of a network system 1 according to the embodiment. The network system 1 according to the embodiment includes a plurality of networks 2 connected in a hierarchical manner. The network 2 is, for example, an autonomous system (AS) managed by an Internet Service Provider (ISP), and is referred to as Tier 1, Tier 2, and Tier 3 from the upper layer. The network 2 is connected to a plurality of computers (not shown) that are communicably connected via an electric communication line. The computer stores various types of electronic data (also referred to as “files”) stored in itself with other computers via the network 2 to which the computer is connected or the network 2 corresponding to the upper hierarchy. You can send and receive.

  When communication is performed between two computers connected to one network 2, for example, an ISP that controls the network 2 can complete the communication by the infrastructure managed by the ISP. Further, peering for transferring traffic between computers connected to the network 2 between the networks 2 belonging to the same level may be performed. Moreover, between the networks 2 belonging to the upper and lower layers, a transit may be performed in which the traffic of a computer connected to the lower network 2 is further transferred to another network 2 via the upper network 2. At this time, the ISP that manages the lower network 2 incurs a chargeable cost for using the upper network 2. Therefore, in each network 2, it is desirable that communication to the upper network 2 is reduced. In the present embodiment, when a file is received from a content provider server (also referred to as a “distribution server”) 3 connected to any network 2, the probability that the file is cached at a location near the requesting computer And particularly reduce traffic between the networks 2. In addition, under a network provided by an ISP, a user may construct a LAN (Local Area Network) in a building, for example. Generally, the communication speed differs between a network provided by an ISP and a LAN. When transmitting or receiving any data, it is preferable that the communication cost defined by the number of hops and the communication speed be kept low. In the present embodiment, a different unit managed by an ISP or user is referred to as another network, and the connected network is referred to as a hierarchy in order from the tier 1. Note that peering between networks belonging to upper and lower layers may be included.

FIG. 2 is a diagram illustrating an example of a computer 4 connected to one network 2 corresponding to the tier 3. In this embodiment, by adding a function of holding a cache to a PC (Personal Computer) installed in a home such as a detached house or an apartment house, or by installing a cache server in combination with a CATV (Cable Television) viewing device. Realize a system that maintains a cache on the network. In the present embodiment, the computer 4 connected to the network 2 is also referred to as a “node” or a “node device”. Each node temporarily stores (caches) a file to be transmitted and received as a cache file, and transmits the cache file in response to a request for the same file.

In this embodiment, a plurality of nodes distribute and cache the same file. Then, the node requesting the file download receives the file from the node having the smallest hop count from the own node among the nodes that cache the file, for example. Specifically, a group for specifying a file to be held by each node is defined in advance. In other words, each node belongs to one of a plurality of predetermined groups. In the example of FIG. 2, hatching in a circle attached to each node represents a group to which the node belongs. Further, in the present embodiment, a plurality of different groups are assigned for each layer to the network 2 having a plurality of layers. Then, it is made to know which hierarchy a group is assigned to. Note that the number of types of groups is not limited to four, and the number of nodes belonging to one group is not particularly limited.

  FIG. 3 is a diagram for explaining an example of assignment of nodes and groups connected to the network 2 forming a plurality of hierarchies. Each network 2 includes a plurality of nodes connected by a network topology such as a mesh type, a full mesh type, a ring type, and a bus type. Each node is associated with one of the groups assigned to the hierarchy to which the node belongs. In the example of FIG. 3, four groups are assigned to each layer.

  In addition, the assignment of groups to nodes is performed so that the same group is not biased in the network 2. That is, when connecting a new node to the network 2, for example, for a plurality of groups, among other nodes already existing on the network 2, a group attached to a node with a small number of hops or a short circuit path length. Are removed in order, and the remaining group is assigned to a new node. In a mesh-type or ring-type network, so-called four-color theorem may be applied to assign groups so that adjacent nodes do not belong to the same group.

  On the other hand, each file has information indicating zero or more groups in which the file should be cached. Each node caches the file when transmitting / receiving (including relaying) the file having information indicating the group to which the node belongs.

FIG. 4 is a diagram for explaining information indicating a group attached to a file. A file 5 in FIG. 4 is various electronic data generated, read, written, and stored by a computer, and is a moving image, a document, an application execution file, or the like. In particular, high-resolution video content, VR (Virtual Reality) content including 360 ° information,
The capacity per file is large and content is rarely updated. Therefore, in a so-called CDN (Contents Delivery Network), if content with high access frequency is targeted for caching, it can be expected that the effect of reducing traffic by the cache will increase. Further, the file 5 is associated with information indicating zero or more of the above-described groups. In the example of FIG. 3, a group combination represented by a hatching pattern is associated with one file 5 as shown in the balloon. The group combination shown in FIG. 4 has 0 to 4 groups assigned to any of the three layers.

  The association of a group with a file is set in each node by, for example, holding a tag represented by a bit string having the number of digits corresponding to the number of groups in association with the identification information of the file. Further, such a file list may be stored in a database table in each node. Further, such association is centrally managed by a management device such as the distribution server 3 on the network 2, for example, and a list of files to be cached is broadcast to the nodes on the network and held in the storage device of each node. Alternatively, each node may be read from a management apparatus on the network at an arbitrary timing.

If there are four groups in three layers, (2 ⁴ ) ^three types of tags can be generated by a 4-digit bit string. In this embodiment, a certain file is cached in any hierarchy, and (2 ⁴ ) × 3 types of tags are used. In the present embodiment, the more frequently accessed files are cached in the lower network 2. Further, a file that is frequently accessed may be cached in many groups. Further, it is not necessary to associate a group with every file, and a file with a tag of “0000 0000 0000” indicates a file that is not cached in any hierarchy.

  When each node receives a file having information indicating a group to which the node belongs, each node caches the file and outputs information cached by itself in response to a request from another node.

<Node configuration>
FIG. 5 is a block diagram illustrating an example of the configuration of a node. The node 4 is a general computer and includes a communication I / F 41, a storage device 42, an input / output device 43, a processor 44, and a bus 45.

  The communication I / F 41 is, for example, a network card, and communicates with other computers via the links shown in FIGS. 1 to 3 based on a predetermined protocol. For example, the file 5 is transmitted / received between the nodes.

  The storage device 42 includes a main storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and an auxiliary storage device (secondary storage) such as an HDD (Hard-disk Drive), an SSD (Solid State Drive), and a flash memory. Device). The main storage device temporarily stores programs and data read by the processor and secures a work area for the processor. The auxiliary storage device stores a program executed by the processor, a cache of files to be transmitted and received, information indicating a group to which the node 4 belongs, and the like.

  The input / output device 43 is, for example, an input device such as a keyboard and a mouse, an output device such as a monitor, and a user interface such as a touch panel. For example, the user requests the distribution server to send a file via the input / output device 43 or reads the received file to display it.

The processor 44 is an arithmetic processing unit such as a CPU (Central Processing Unit), and performs each process according to the present embodiment by executing an application (also referred to as a program or software). In the example of FIG. 3, functional blocks are shown in the processor 44. The processor 44 functions as, for example, the processing units of the file request unit 441, the relay unit 442, the cache holding unit 443, the cache transmission unit 444, and the cache deletion unit 445. The file request unit 441 requests the file delivery server connected via the network to transmit a file based on, for example, a user operation. When the node 4 is located on the path between another node and the distribution server, the relay unit 442 relays a file transmission request from another node to the distribution server and a file to be transmitted to another node. The cache holding unit 443 determines whether or not to hold the received file based on information indicating the group associated with the file, and temporarily holds it in the storage device 42. In response to a request for a file from another node to the distribution server, the cache transmission unit 444 transmits the cached file to the other node device when cached in the storage device 42 of the node 4. The cache deletion unit 445 deletes the cache stored in the storage device 42 based on a predetermined rule.

  The components as described above are connected via the bus 45.

<Configuration of distribution server>
FIG. 6 is a block diagram illustrating an example of the configuration of the distribution server. The distribution server 3 such as a content provider is also a general computer, and includes a communication I / F 31, a storage device 32, an input / output device 33, a processor 34, and a bus 35.

  The communication I / F 31 is, for example, a network card, and communicates with other computers via the links shown in FIGS. 1 to 3 based on a predetermined protocol. For example, the file 5 is transmitted / received to / from other nodes to be linked.

  The storage device 32 is a main storage device such as a RAM or a ROM, and an auxiliary storage device such as an HDD, an SSD, or a flash memory. The main storage device temporarily stores programs and data read by the processor and secures a work area for the processor. It is assumed that the auxiliary storage device stores a program executed by the processor, an original file to be distributed, and the like. In addition, information indicating a group that caches the file may be stored in association with each file. Further, the transmission requests for the files may be counted, and the group setting for caching each file may be changed based on the frequency in a predetermined period.

  The input / output device 33 is, for example, an input device such as a keyboard and a mouse, an output device such as a monitor, and a user interface such as a touch panel.

  The processor 34 is an arithmetic processing unit such as a CPU, and performs each process according to the present embodiment by executing an application. In the example of FIG. 6, functional blocks are shown in the processor 34. The processor 34 functions as, for example, the processing units of the file distribution unit 341, the frequency calculation unit 342, and the setting change unit 343. The file delivery unit 341 reads the file that has received the transmission request from the storage device 32 and transmits the file to the requesting node. The frequency calculation unit 342 counts the number of accesses for each file, and calculates the access frequency within a predetermined period. The setting change unit 343 changes information indicating a group for caching each file according to the access frequency. As the setting is changed, the setting changing unit 343 may transmit information instructing deletion of a specific cache file to a node on the network.

  The components as described above are connected via the bus 35.

<File delivery processing>
FIG. 7 is a process flow diagram illustrating an example of a file distribution process performed by the network system. The request source node in FIG. 7 corresponds to one of the nodes illustrated in FIG. 4 and the like, and includes the functional unit illustrated in FIG. The distribution server in FIG. 7 corresponds to the distribution server 3 illustrated in FIG. 1 and includes the functional unit illustrated in FIG. Also, the relay node in FIG. 7 corresponds to a node that exists on the path between the request source node and the distribution server 3 in FIGS. That is, there may be cases where two or more relay nodes are routed. In FIG. 7, one relay node is shown for convenience.

First, the file request unit 441 of the request source node requests transmission of a file held by the distribution server (FIG. 7: S1). On the other hand, the relay unit 442 of the relay node receives the request (S2), and determines whether the cache file corresponding to the storage device 42 of the own node is held (S3). When the cache is held (S3: Yes), the cache transmission unit 444 of the relay node transmits the cache file to the request source node (S4). If the relay node does not hold the cache (S3: No), the relay unit 442 of the relay node relays the request to an adjacent relay node (not shown) or the distribution server (S5). If there are a plurality of relay nodes, the same processing is repeated. In the present embodiment, each node can know in which hierarchy it is cached from the bit position of the tag indicating the group. Therefore, each node can transfer the request to the upper layer network or the same layer network based on the bit position of the tag of the requested file. Then, the file distribution unit 341 of the distribution server 3 receives the transmission request for the file (S6), reads the corresponding file from the storage device 32, and transmits it (S7). On the other hand, the relay unit 442 of the relay node relays the file to the requesting node (S8). Then, after S8 or after the relay node transmits the cache in S4, the file request unit 441 of the requesting node receives the file requested in S1 (S9). When transmitting a file to the requesting node in S8, the cache holding unit 443 of the relay node determines whether the file is a target to be cached in the own node (S10). In this step, it is determined whether information indicating the group to which the own node belongs is associated with the file. The association between the file and the information indicating the group can be stored in a database table or file held by the storage device 42 of the own node or a predetermined device on the network. If it is determined that the relayed file is to be cached (S10: Yes), the relay node cache holding unit 443 temporarily holds the file in the storage device. On the other hand, if it is determined that the relayed file is not to be cached, the relay node does not hold the file. The network system 1 repeats the file distribution process as shown in FIG. 5 in response to a file transmission request from the request source node.

<Effect>
According to the present embodiment, nodes that cache the same file are distributed on the network by a simple method of grouping nodes so that the same group is not biased in the network 2, and some nodes are close to each other to some extent. A sub-optimal cache arrangement in which a cache server belonging to each group exists at the specified position can be realized. At this time, if the file with higher access frequency is cached in the lower network 2, the file can be transmitted from a position closer to the request source. In addition, as shown in FIG. 4, information indicating a plurality of groups may be associated with one file. If a file having a higher access frequency is cached by nodes belonging to more groups, the cache hit rate on the network can be improved.

<Cache target update processing>
In the network system described above, the priority of the cache for the file may be determined, and information indicating a group associated with the file (a list of files to be cached) may be dynamically changed. The priority of the cache is determined based on the access frequency to each file calculated by the frequency calculation unit 342 of the distribution server 3. The distribution server 3 is an example of an “access management apparatus” according to the present invention that calculates the frequency of access to a file and determines a file to be cached. Note that an access management device may be provided in any one of the networks 2 separately from the distribution server 3.

  FIG. 8 is a process flow diagram illustrating an example of a cache target update process for changing a cache target file. For example, the network system may perform processing as shown in FIG. 8 in addition to the file distribution processing shown in FIG.

First, the relay node counts the number of times the cache file has been transmitted in response to the request, and transmits the number of times to the distribution server 3 at a predetermined timing (FIG. 8: S21). On the other hand, the distribution server 3 receives the number of file transmissions from each relay node and stores the number of accesses for each file (S22). In this step, an access log for counting the number of accesses may be received. For example, when the distribution server 3 transmits a file in S7 of FIG. 7, the distribution server 3 further writes an access log to the file in the storage device 32 (S23).

  The distribution server 3 calculates the number of accesses to each file (that is, the access frequency) in a predetermined period at a predetermined timing (not shown), and the higher the frequency, the higher the cache priority. Have many groups cache. That is, information indicating more groups is associated with the file. Specifically, first, the frequency calculation unit 342 determines whether it is time to update the cache target (S24). For example, when a predetermined operation time has arrived or when a condition such as a predetermined period has elapsed since the previous process is satisfied, it is determined that the timing is to update the cache target. If it is determined that it is not time to update the cache target, the distribution server 3 does not perform any particular processing. On the other hand, when it is determined that it is time to update the cache target (S24: Yes), the frequency calculation unit 342 calculates the access frequency for each file and determines the cache target (S25).

  FIG. 9 is a diagram illustrating an example of a tag indicating a rank based on the number of accesses to a file in a predetermined period and a group assigned in association with the file. The distribution server 3 aggregates an access log for the file transmitted by the distribution server 3 in response to the request and an access log indicating that the relay node has transmitted the cache for a predetermined period, for each file as shown in FIG. Generate statistical data. The table shown in FIG. 9 includes items of “rank”, “hierarchy”, “number of groups”, and “tag”. In the “rank” field, a rank range determined based on the frequency of access to a file in a predetermined period is recorded. In S25 of FIG. 8, the order in a predetermined period is determined. In the “hierarchy” field, a hierarchy for caching files of each rank is shown. The “number of groups” field indicates the number of groups that cache the files of each rank. In the “tag” field, information indicating a group that caches files of respective ranks is recorded in the tag format described above.

  The setting change unit 343 determines a group for caching each file according to the access frequency (FIG. 8: S25). In this step, a cache group is assigned to each file. First, the degree of popularity shown in FIG. 9 is determined based on the number of accesses during a predetermined period. For example, when nodes are divided into 12 groups in 3 layers, the degree of popularity is classified into 13 levels. Also, in each hierarchy, files belonging to the most popular level are cached in all four groups assigned to the hierarchy, and files belonging to the second most popular level are cached in three groups. Files belonging to the most popular level are cached in two groups, and files belonging to the fourth most popular level are cached in one group. It is assumed that files belonging to the least popular level are not cached in any group.

  In this manner, the number of groups of nodes that cache the file is determined according to the degree of popularity, and thereafter, combinations of groups are cyclically assigned to files to which the same number of groups are assigned. For example, tags determined by cyclically assigning combinations of three groups are recorded in the “tag” field of the records of ranks 21 to 100 in FIG. In S25, the tag associated with the file is updated based on the access frequency to each file in the most recent predetermined period.

Then, the setting change unit 343 distributes a list indicating the group whose files are to be cached to each node (FIG. 8: S26). In this step, for example, the information shown in the “file name” and “tag” columns in FIG. 9 is broadcast to each node. When the relay node receives the list, the relay node holds the list in the storage device 42 and thereafter determines a target file to be cached by the own node based on the list (S27). Based on such information indicating the group of the list, each node can easily determine whether the request destination of the file should be the same hierarchy or the upper or lower hierarchy. Further, according to the contents of the updated list, for example, the cache deletion unit 445 may delete unnecessary caches.

<Effect>
According to the cache target update process, a file that is newly distributed from the distribution server can be cached according to the number of subsequent accesses, and even when the tendency of access frequency to existing files changes The settings can be changed to keep up and improve the cache hit rate in the network following changes. The access frequency may be calculated and the list of files to be cached may be updated by a management device on a network different from the distribution server 3. In addition, an access log to a file stored in each relay node may be held in a predetermined device on the network so that the distribution server 3 or the management device can read the access log in each relay node.

<Files to be cached and the number of nodes that cache the files>
In this embodiment, a file having a high access frequency is targeted for caching, and the higher the access frequency is, the more nodes are cached in the network. The number of nodes that cache files can be arbitrarily set by the user. Note that the number of nodes that cache files depends on the number of nodes that belong to each group connected to the network and the number of groups that hold the files set in association with the files. The number of nodes that cache files may be determined according to a sub-optimal cache arrangement obtained using, for example, a genetic algorithm.

FIG. 10 is a graph showing files and the number of files cached on one mesh network. The horizontal axis in FIG. 10 represents the serial numbers of files sorted in descending order of access frequency, and the vertical axis represents the number of nodes that cache each file. The setting of a tag attached to a file may be determined according to the type of file cached on a node and the number of nodes that cache the same file in a cache arrangement obtained using a genetic algorithm. The broken line in FIG. 10 represents the relationship between a file in a sub-optimal cache arrangement obtained by a genetic algorithm (GA) and the number of files to be cached on the network in a mesh network. . A solid line is an example in which the network system according to the present embodiment approximates the number of cache files in the network obtained by the genetic algorithm. In the present embodiment, the number of nodes on the network that caches the file can be adjusted by changing the group assigned to each file, which is represented by the tag described above. Further, by making the number of types of groups larger than 4, it is possible to improve the accuracy of approximation for the sub-optimal arrangement. Even in a hierarchically connected network according to the present embodiment, a plurality of files that are accessed at a predetermined frequency are defined, and the above files are set to approximate values of a sub-optimal cache arrangement obtained by some algorithm. It is also possible to determine at least one of a group to be assigned to and a group to be assigned to a node on the network.

For example, as shown in FIG. 9, the number and hierarchy of groups that cache files are determined for each degree of popularity, such as within 20th, 21st to 100th, 101st to 250th,. Then, tags associated with the degree of popularity are cyclically assigned in order from the top. The tag is described by a 12-bit bit vector indicating a hierarchy and a group to hold the file. The bit vector is formed by connecting digits representing groups in each layer in a predetermined order. In FIG. 9, the left 4 bits indicate whether files are cached in the four groups assigned to the first hierarchy. Similarly, the central 4 bits represent whether the file is cached in the four groups assigned to the second hierarchy. The four bits on the right represent whether or not files are cached in the four groups assigned to the third hierarchy. In this way, a file is associated with zero or more groups that should cache the file and information indicating the hierarchy to which the group belongs.

<CATV system>
FIG. 11 is a block diagram illustrating an example of a home device configuration when the network system according to the embodiment is applied to a CATV network. The CATV viewing system 6 in FIG. 11 includes a protector 61, a booster 62, a distributor 63, an STB (Set-Top Box) 64, a recording device 65, a receiver 66, a modem 67, and a cache server 68. A router 69, an IP-VoD STB 70, and a PC 71. The protector 61 is provided between the service line and the home system, and is a device for protecting the home device from an abnormal current caused by a lightning strike or the like. The booster 62 is connected to the protector 61 with a coaxial cable, and amplifies the packaging signal to be transmitted. The distributor 63 is connected to the booster 62 through a coaxial cable, and distributes signal lines to a plurality of STBs 64, for example. The STB 64 is connected to the distributor 63 via a coaxial cable, receives a broadcast signal, and outputs a video. The recording device 65 is connected to the STB 64 via a LAN cable or the like and records a broadcast. The receiver 66 is connected to the recording device 65 via an HDMI (registered trademark, High-Definition Multimedia Interface) cable or the like, and displays a broadcast. The modem 67 is connected to the protector 61 through a coaxial cable or the like and performs data communication. The cache server 68 is a computer such as the node shown in FIG. 5, for example, and is connected to the modem 67 by a LAN cable or the like. Further, the cache server 68 installed in a plurality of homes distributes and caches VoD (Video On Demand) content, VR content, and the like based on the assigned group. The router 69 is connected to the cache server 68 via a LAN cable or the like, and relays data communication to a home network. The IP-VoD STB 70 is connected to the router 69 by, for example, a LAN cable, and reproduces a moving image distributed by data communication via the Internet. Note that the IP-VoD STB 70 may connect the STB 64 and the receiver 66 via, for example, an HDMI cable so that the output from the existing STB 64 is passed through to the receiver 66. The PC 71 is connected to a router and performs data communication. The file to be transmitted / received is encrypted by DRM (Digital Rights Management), for example, STB64, IP-VoD STB7.
0 etc. are decoded and reproduced as appropriate.

  In this way, by adding the cache server 68 to the CATV viewing system and causing it to function as a node according to the present embodiment, a network system that transmits and receives a cache between user's home facilities can be realized. In the system as shown in FIG. 11, not only files with high access frequency are targeted for caching, but also contents within a predetermined period from the public where demand for so-called miss delivery is generally high may be targeted for caching in advance. Good. Further, the cache server 68 may be an apparatus integrated with the router 69, the STB 64, the IP-VoD STB 70, or the like.

<Modification 2>
FIG. 12 is a diagram showing an example of forming a regional network that connects neighboring nodes together with a network provided by an ISP. For example, using a wireless communication between terminals, a LAN connecting between buildings or between buildings, power line communication (PLC), or the like, a mesh network is formed by nodes that are relatively close to each other. In the example of FIG. 12, the node 4 connected to the network 2 provided by the ISP 1 or ISP 2 forms a local CDN 7 (dashed link) by directly linking at a relatively short distance apart from the network 2. Yes. The local CDN 7 is another network in the same layer as the ISP network 2, and the node 4 in FIG. 12 can be said to be connected to a plurality of networks in the same layer. The node 4 can use either the ISP network 2 or the regional CDN 7 when requesting a cached file in the same hierarchy. For example, the file request unit 441 and the relay unit 442 of each node 4 use the ISP network 2 or the local CDN 7 according to this modification according to the use state (congestion state) of the network bandwidth. It may be determined.

  According to this modification, users using different ISPs can use the cache. In particular, the effective speed can be improved by directly linking neighboring nodes having a short path length.

  The matters described in the above embodiments and modifications can be implemented in appropriate combination.

<Others>
The present invention includes a computer program that executes the above-described processing. Furthermore, a computer-readable recording medium on which the program is recorded also belongs to the category of the present invention. With respect to the recording medium on which the program is recorded, the above-described processing can be performed by causing the computer to read and execute the program on the recording medium.

  Here, the computer-readable recording medium refers to a recording medium in which information such as data and programs is accumulated by electrical, magnetic, optical, mechanical, or chemical action and can be read from a computer. Examples of such a recording medium that can be removed from the computer include a flexible disk, a magneto-optical disk, an optical disk, a magnetic tape, and a memory card. In addition, examples of the recording medium fixed to the computer include a hard disk drive and a ROM.

1: Network system 2: Network 3: Distribution server 31: Communication I / F
32: Storage device 33: Input / output device 34: Processor 341: File distribution unit 342: Frequency calculation unit 343: Setting change unit 35: Bus 4: Node (computer)
41: Communication I / F
42: storage device 43: input / output device 44: processor 441: file request unit 442: relay unit 443: cache holding unit 444: cache transmission unit 445: cache deletion unit 45: bus 5: file 6: CATV viewing system 61: security Device 62: Booster 63: Distributor 65: Recording device 66: Receiver 67: Modem 68: Cache server 69: Router 70: IP-VoD STB
71: PC

Claims (8)

A plurality of node devices that temporarily hold files to be transmitted and received, the node devices are network systems belonging to one of the hierarchically connected networks,
The node device is a group for specifying a file to be held by the node device, and belongs to one of a plurality of groups assigned to the hierarchy,
The file is associated with information indicating the group of zero or more;
The information indicating the group includes information for specifying the hierarchy in which the file is held and the group,
The node device is
When the file associated with the information indicating the group to which the node device belongs is received, a cache holding unit that temporarily holds the file as a cache file;
A cache transmission unit that transmits the cache file to the requesting node device when the requesting node device holds the cache file corresponding to the file requested;
When the requesting node device does not hold the cache file corresponding to the requested file, the file is transferred to another node device belonging to the same layer or another layer based on the information indicating the group. A requesting relay section;
Including network systems. An access management device for calculating the frequency of access to the file;
The network according to claim 1, wherein the access management device changes information indicating the group associated with the file so that the calculated high-frequency file is held in a lower hierarchy than the low-frequency file. system. The access management device stores information indicating the group to be associated with the file so that the high-frequency file is held by the node device belonging to the group more in the same hierarchy than the low-frequency file. The network system according to claim 2 to be changed. The network system according to any one of claims 1 to 3, wherein the group is allocated to a plurality of the node devices so as to reduce a bias in a network topology. At least some of the node devices are connected to a plurality of networks belonging to the same hierarchy, and the relay unit belongs to the same hierarchy when requesting the file to another node device belonging to the same hierarchy The network system according to any one of claims 1 to 4, wherein the request is made to any one of a plurality of networks. A node device that belongs to one of the hierarchically connected networks and temporarily holds files to be transmitted and received,
It is a group for identifying the file that it should keep and belongs to one of multiple groups assigned to the hierarchy,
The file is associated with information indicating the group of zero or more;
The information indicating the group includes information for specifying the hierarchy in which the file is held and the group,
When the file associated with the information indicating the group to which it belongs is received, a cache holding unit that temporarily holds the file as a cache file;
A cache transmission unit that transmits the cache file to the requesting node device when the requesting node device holds the cache file corresponding to the file requested;
When the requesting node device does not hold the cache file corresponding to the requested file, the file is transferred to another node device belonging to the same layer or another layer based on the information indicating the group. A requesting relay section;
Node equipment including A cache method executed by a node device that belongs to one of hierarchically connected networks and temporarily holds a file to be transmitted and received,
The node device is a group for specifying a file to be held by itself and belongs to one of a plurality of groups assigned to a hierarchy,
The file is associated with information indicating the group of zero or more;
The information indicating the group includes information for specifying the hierarchy in which the file is held and the group,
If the file associated with the information indicating the group to which it belongs is received, temporarily holding the file as a cache file;
When the requesting node device holds the cache file corresponding to the requested file, transmitting the cache file to the requesting node device;
When the requesting node device does not hold the cache file corresponding to the requested file, the file is transferred to another node device belonging to the same layer or another layer based on the information indicating the group. Requesting steps,
Caching method including. A program that belongs to one of the hierarchically connected networks and is executed by a node device that temporarily holds files to be transmitted and received,
The node device is a group for specifying a file to be held by itself and belongs to one of a plurality of groups assigned to a hierarchy,
The file is associated with information indicating the group of zero or more;
The information indicating the group includes information for specifying the hierarchy in which the file is held and the group,
If the file associated with the information indicating the group to which it belongs is received, temporarily holding the file as a cache file;
When the requesting node device holds the cache file corresponding to the requested file, transmitting the cache file to the requesting node device;
When the requesting node device does not hold the cache file corresponding to the requested file, the file is transferred to another node device belonging to the same layer or another layer based on the information indicating the group. Requesting steps,
A program that executes

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