JP6485811B2 - Node device and routing table management method - Google Patents

Description

  The present invention relates to a node device and a routing table management method in a structured overlay technique that handles range queries.

  In a structured overlay, a network in which a large number of computers such as computers (hereinafter referred to as “node devices” or simply “nodes”) are connected to each other by constructing an overlay network based on mathematical rules. It is a technology that enables discovery and notification. Structured overlays are attracting attention as a useful technique in large-scale systems such as distributed databases because they do not require centralized management of node information and behave autonomously.

  A structured overlay that handles range queries can be used to efficiently send messages to all nodes that have keys in the range by specifying the key range in a situation where each node has keys (values with a total order relationship). This refers to a structured overlay technology having a function capable of delivering

  Non-Patent Document 1 proposes an example of a structured overlay that handles range queries. In the example of Non-Patent Document 1, a range query is made possible by providing a logical network composed of nodes with a structure in which a skip list is multiplexed. That is, the whole has a hierarchical structure, and the lowest level is a bidirectional list in which all nodes are arranged in the order in which the keys are sorted. Each node has a k-ary random number sequence called a membership vector in addition to the key, and at level i, a bidirectional list is formed by nodes having the same prefix up to i digits of the membership vector. When performing a search, the operation starts from the highest level of the search start node, and repeats the operation of hopping within a range that does not pass the target key and lowering the level by one as in the Skip List. As a result, the upper level works as a shortcut link, and the target key can be reached with a small number of hops. In this method, the size of the route table held by each node and the route length at the time of retrieval are both O (log N), where N is the number of nodes.

  Non-Patent Document 2 proposes an example of a structured overlay that can flexibly manage a routing table. In the example of Non-Patent Document 2, an order relationship representing superiority or inferiority between routing tables is defined for a distributed hash table, and the improvement of the routing table is repeated accordingly. Construction and management are possible. As a result, when the number of nodes is small, the route length is set to O (1), and communication across ISPs (Internet Service Providers) in the lower network is reduced.

James Aspnes, Gauri Shah, “Skip Graphs”, ACM Transactions on Algorithms, pp.37: 1-37: 25, 2007. Hiroya Nagao and Kazuyuki Shudo, “Flexible Routing Table: An Overlay Network Routing Method Based on Ordering Relations in the Routing Table Space,” Advanced Computer Systems Symposium Proceedings, pp.117-125, 2011.

  In a conventional structured overlay that handles a range query as shown in Non-Patent Document 1, a node (entry) to be described in a routing table is selectively searched based only on specific elements. In the case of Non-Patent Document 1, a node whose membership vector matches a predetermined number of digits at each level and whose key is closest is searched for, and the information of the node is used as a route table entry. For this reason, a routing table cannot be constructed in consideration of elements other than the key and the membership vector, for example, communication delay with the partner node, affiliated ISP / AS (Autonomous System), etc., and query delivery delay increases. There are problems such as. The routing table size is O (log N) common to all nodes, and the routing table size cannot be changed according to the memory size of each node.

  On the other hand, there is a technique that realizes flexible routing table management for a distributed hash table as shown in Non-Patent Document 2. In the distributed hash table before Non-Patent Document 2, it is difficult to consider elements other than the node ID when constructing the routing table. However, with the method of Non-Patent Document 2, communication delay with the partner node and the affiliated ISP / AS The route table can be constructed in consideration of the above, and the size of the route table can be set for each node. However, queries that can be handled are limited to exact match queries and cannot handle range queries.

  As described above, in the structured overlay, it is difficult to handle both range queries and realize flexible routing table management. In particular, in the method in Non-Patent Document 2, although elements other than the node ID can be considered, the node ID is considered in order to realize the search efficiency of O (log N) in the search for the node ID. Is essential, and it is assumed that the node IDs are uniformly distributed in the numerical space. However, in Non-Patent Document 1, there is no assumption that keys to be searched (corresponding to the node IDs in Non-Patent Document 2) are uniformly distributed, only the assumption that there is a total order relationship. doing. For this reason, it is difficult to combine the method of Non-Patent Document 2 as it is with the method of Non-Patent Document 1.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a node device and a routing table management method capable of improving flexibility related to routing table construction in a structured overlay that handles range queries. Is to provide.

  According to an aspect of the present invention, an overlay network is configured by a plurality of node devices, each of the plurality of node devices has a value having a total order relationship, and is included in a range specified by a range query by the overlay network. In a communication system for delivering a message to a node device having a value, node information relating to another node device is collected, and the node information including the value possessed by the other node device is added as an entry to a route table, and the route It is determined whether or not the number of entries in the table exceeds a threshold, and when it is determined that the number of entries in the routing table exceeds the threshold, the threshold is exceeded from among the entries in the routing table. Several entries are selected, and the selected entries are deleted from the routing table.

  According to the present invention, flexible routing table management can be realized in a structured overlay that handles range queries.

The figure which shows the structural example of the communication system which concerns on embodiment. The block diagram which shows the structural example of each node shown in FIG. The figure which shows an example of the careful selection process by the routing table update part shown in FIG. The figure which shows the other example of the careful selection process by the routing table update part shown in FIG. 6 is a flowchart illustrating an example of a method for managing a routing table according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiment relates to a technique for managing a routing table in a logical network that handles range queries. In the embodiment, in order to increase the flexibility of routing table construction, a routing table is constructed by deleting unnecessary routing table entries instead of selectively adding necessary routing table entries. That is, when collecting routing table entries, it is added to the routing table without depending on specific elements, and when the number of entries preset for each node is exceeded, the excess number of entries is discarded. At this time, a different demand is reflected for each node in selecting an entry to be discarded. By repeating the above operations, the routing table can be adaptively improved and maintained for the environment of each node.

  FIG. 1 schematically shows an example of the overall configuration of a communication system according to an embodiment. A network 12 shown in FIG. 1 is a physical network such as the Internet, for example, and a plurality of nodes (six nodes A to F in FIG. 1) are connected to each other via the network 12 so as to communicate with each other. Specifically, node A and node E are connected to router 13, node C and node F are connected to router 14, node B and node D are connected to router 15, and router 13 and router 15 are connected to router 14. It is connected.

  The overlay network 11 is a virtual network constructed on the network 12. The overlay network 11 includes nodes A to F. The overlay network 11 is configured by all the nodes A to F included in the network 12 in the example illustrated in FIG. 1, but is not limited thereto, and is configured by a part of the nodes included in the network 12. Also good.

  In the overlay network 11, each of the nodes A to F holds a routing table and transmits or forwards a message according to its own routing table. Message transmission from a certain node to the target node is achieved by each node repeating the transfer of the message according to the routing table. In this embodiment, each of the nodes A to F has a value having a total order relationship (hereinafter referred to as “key”), and the target node has all keys having keys included in the key range specified by the range query. It is a node. In the present embodiment, each of the nodes A to F may have a random number sequence (hereinafter referred to as “membership vector”) in k notation independent of the key. Here, k is an integer of 2 or more.

  FIG. 2 schematically illustrates a configuration example of a node according to the embodiment. The nodes shown in FIG. 2 correspond to the nodes A to F shown in FIG. Here, description will be made assuming that the node shown in FIG. 2 is node A shown in FIG.

  The node A includes a communication processing unit 21, a node information collection unit 22, an update start determination unit 23, a route table update unit 24, a query processing unit 25, and a route table storage unit 26. The communication processing unit 21, the node information collection unit 22, the update start determination unit 23, the routing table update unit 24, and the query processing unit 25 are realized by causing a processor (not shown) to execute a computer program stored in a memory (not shown). be able to. The routing table storage unit 26 can be realized by a memory (not shown). The route table storage unit 26 stores a route table.

  The communication processing unit 21 performs processing for communicating with other nodes. Specifically, the communication processing unit 21 transmits a message to another node or receives a message from another node.

  The node information collection unit 22 collects node information regarding other nodes through the communication processing unit 21. Specifically, the node information collection unit 22 collects node information related to a node (for example, the node B) that is not yet registered in the route table in the route table storage unit 26. The node information collection unit 22 can collect node information without any restrictions. The node information includes, for example, an IP address, a port number, and a key. The IP address is an example of location information indicating the location on the lower network (network 12 shown in FIG. 1). The lower network is not limited to a TCP / IP-based network, and may be a network based on another protocol. The node information may further include a membership vector.

Node information is collected by sending a node information collection request via a known node (for example, node C) already registered in the routing table, and node information from node B or a node (for example, node D) that knows node B. May be actively performed, such as receiving In addition, node information is collected passively, such as reading information included in communication contents during communication performed for other purposes such as a range query transmitted from node E to node A. May be.
The node information collection unit 22 adds the collected node information as an entry to the route table.

  The update start determination unit 23 determines whether or not the number of entries in the routing table exceeds a predetermined routing table size (threshold). The routing table size may be different for each node. Further, the routing table size may be changed while the system is operating. When the update start determination unit 23 determines that the number of entries in the routing table exceeds the routing table size, the update start determination unit 23 gives an update processing start request to the routing table update unit 24.

  The routing table updating unit 24 receives the update processing start request from the update start determining unit 23 and updates the routing table. The routing table update unit 24 selects entries corresponding to the number exceeding the routing table size based on a predetermined rule, and deletes the selected entries from the routing table. This process is called careful selection of route table entries. The above rules can be based on any one or a combination of two or more update method examples shown in the following (1) to (4). By updating the routing table, the number of entries in the routing table becomes less than or equal to the routing table size.

  (1) In selecting an entry to be deleted, various demands different for each node can be reflected. For example, rules such as leaving a node in the same autonomous system (AS) as much as possible and leaving a node having a small round trip time (RTT) value can be provided. By providing such a rule, the message delivery delay can be reduced.

  (2) The routing table update unit 24 may include a routing table comparison unit 31 that compares a plurality of routing tables according to a predetermined criterion, as shown in FIG. The routing table updating unit 24 generates all routing tables that can be configured by careful selection, selects the most desirable routing table from these routing tables using the routing table comparison unit 31, and configures the selected routing table. Carefully select. The routing table comparison unit 31 can perform comparison based on the frequency distribution of keys in the routing table. For example, when the key space is a one-dimensional metric space, the routing table comparison unit 31 has a frequency distribution close to the exponential distribution based on the key of the node A when the key in the routing table of the node A is mapped. A criterion that the route table is more desirable may be used. For example, when the frequency distribution of the keys of the routing table 1 and the routing table 2 is as shown in FIG. 3B, the frequency distribution of the keys of the routing table 2 is closer to the exponential distribution, so that FIG. As shown, the output of the routing table comparison unit 31 is the routing table 2.

  (3) The routing table update unit 24 may perform careful selection for an entry group excluding sticky entries. The sticky entry is an entry that matches a predetermined condition among the entries in the routing table. For example, when all nodes registered in the routing table and themselves (own nodes) are arranged in the key order, nodes located before and after the own nodes are selected as sticky entries. In this case, the bidirectional list of level 0 in Non-Patent Document 1 is reproduced, and reachability is guaranteed.

  (4) The routing table update unit 24 may perform careful selection based on the membership vector of the entry in the routing table. In this case, each entry in the routing table further includes a membership vector, and the routing table update unit 24 compares the routing tables according to a predetermined criterion as shown in FIG. Part 41 is included. The routing table update unit 24 can select carefully based on the degree of coincidence between its membership vector and the membership vector of the entry in the routing table. As the matching degree, for example, there is a prefix matching length. The prefix match length indicates the number of digits whose prefix matches between its own membership vector and the membership vector of the entry in the routing table. For example, as shown in FIG. 4B, when the membership vector of itself (node A) is “001011...”, The prefix “0” is assigned to the membership vector “011101. Since they match, the prefix match length is 1, and the prefix “0010” of the membership vector “001000...” Matches, so the prefix match length is 4. The route table comparison unit 41 may use a criterion that the frequency distribution of the prefix match length of the membership vector is closer to a uniform distribution, which is a desirable route table. For example, when the frequency distribution of the prefix match lengths of the routing table 1 and the routing table 2 is as shown in FIG. 4B, the frequency distribution of the key of the routing table 2 is closer to the uniform distribution. As shown in 4 (a), the output of the route table comparison unit 41 is the route table 2. In this case, for each prefix match length of the membership vector, if two nodes having the closest key to the key of node A are included in the route table, the route length and route shown in Non-Patent Document 1 A topology with a table size of O (log N) is reproduced.

  The query processing unit 25 receives a range query specifying a key range, and determines a message transfer destination by referring to a routing table as necessary. The communication processing unit 21 transfers the message to the transfer destination determined by the query processing unit 25.

  Next, an example of a method for managing the routing table according to the embodiment will be described with reference to FIG.

In step S501 in FIG. 5, the node information collection unit 22 collects node information related to a node that is a routing table entry. In step S502, the node information collection unit 22 adds the collected node information to the route table. In step S503, the update start determination unit 23 determines whether the number of route table entries exceeds a predetermined route table size. If the number of routing table entries is less than or equal to the routing table size, the process returns to step S501. If the number of routing table entries exceeds the routing table size, the process proceeds to step S504. In step S504, the routing table update unit 24 updates the routing table. Specifically, the routing table update unit 24 selects a number of entries that exceed the routing table size from the routing table entries, and deletes the selected entries from the routing table.
By continuously repeating the operation shown in FIG. 5, the routing table can be improved and maintained adaptively to the environment of each node.

  Note that the determination process shown in step S503 is not limited to being executed after an entry is added to the routing table, and may be executed every time the routing table size is changed in each node, for example.

  As described above, according to the present embodiment, an overlay network is configured by a plurality of nodes, each of the plurality of node devices has a value having a total order relationship, and the range specified by the range query is set by the overlay network. In a communication system that distributes a message to a node having an included value, node information including the key of this node regarding other nodes is collected, this node information is added as an entry to the routing table, and an entry in the routing table When the number exceeds the routing table size, entries corresponding to the number exceeding the routing table size are selected from the entries in the routing table, and the selected entries are deleted from the routing table. This makes it possible to implement flexible routing table management, such as setting a routing table size for each node in a structured overlay that handles range queries.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

DESCRIPTION OF SYMBOLS 11 ... Overlay network, 12 ... Network, 13, 14, 15 ... Router, 21 ... Communication processing part, 22 ... Node information collection part, 23 ... Update start determination part, 24 ... Routing table update part, 25 ... Query processing part, 26: Route table storage unit, 31, 41: Route table comparison unit.

Claims (6)

An overlay network is configured by a plurality of node devices, and each of the plurality of node devices has a value having a total order relationship and a random number sequence different from the values, and is specified by a range query by the overlay network. A node device in a communication system for delivering a message to a node device having a value included in a range,
Collecting means for collecting node information relating to another node device and adding the node information including the value of the other node device as an entry to a routing table;
Determining means for determining whether the number of entries in the routing table exceeds a threshold;
Updating means for updating the routing table when it is determined that the number of entries in the routing table exceeds the threshold ;
Generating a plurality of routing table candidates configured by deleting a number of entries exceeding the threshold from the entries in the routing table;
Select a routing table candidate whose frequency distribution of prefix match length between the random number sequence of the own node device and the random number sequence of the node corresponding to the entry in the routing table candidate is the most uniform distribution,
Delete entries other than those constituting the selected routing table candidate from the routing table
An updating means configured to :
A node device comprising: An overlay network is configured by a plurality of node devices, each of the plurality of node devices has a key that is a value having a total order relationship, and a node having a key included in a range specified by a range query by the overlay network A node device in a communication system for delivering a message to a device,
Collecting means for collecting node information relating to another node device, and adding the node information including the key of the other node device as an entry to a routing table;
Determining means for determining whether the number of entries in the routing table exceeds a threshold;
Updating means for updating the routing table when it is determined that the number of entries in the routing table exceeds the threshold ;
Generating a plurality of routing table candidates configured by deleting a number of entries exceeding the threshold from the entries in the routing table;
If the key space is a one-dimensional metric space, select the route table candidate whose key frequency distribution in the route table candidate is closest to the exponential distribution,
Delete entries other than those constituting the selected routing table candidate from the routing table
An updating means configured to :
A node device comprising: The update unit generates the plurality of routing table candidates by selecting a number of entries exceeding the threshold from the entries in the routing table excluding entries that match a predetermined condition. The node device according to claim 1 or 2. The updating means selects a node device located before and after the own node device when the node device corresponding to the entry in the routing table and the own node device are arranged in the order of the values, and corresponds to the selected node device. 3. The node according to claim 1 , wherein the plurality of routing table candidates are generated by selecting as many entries as the number exceeding the threshold from the entries in the routing table excluding the entry to be processed. apparatus. An overlay network is configured by a plurality of node devices, and each of the plurality of node devices has a value having a total order relationship and a random number sequence different from the values, and is specified by a range query by the overlay network. A method for managing a routing table in a communication system that distributes a message to a node device having a value included in a range,
Collecting node information related to other node devices and adding the node information including the value of the other node devices as an entry to the routing table;
Determining whether the number of entries in the routing table exceeds a threshold;
Updating the routing table when it is determined that the number of entries in the routing table exceeds the threshold ;
With
Updating the routing table
Generating a plurality of routing table candidates configured by deleting a number of entries exceeding the threshold from the entries in the routing table;
Select the route table candidate whose frequency distribution of the prefix match length between the random number sequence of its own node device and the random number sequence of the node corresponding to the entry in the route table candidate is closest to the uniform distribution,
Delete entries other than those constituting the selected routing table candidate from the routing table
A routing table management method. An overlay network is configured by a plurality of node devices, each of the plurality of node devices has a key that is a value having a total order relationship, and a node having a key included in a range specified by a range query by the overlay network A method for managing a routing table in a communication system for delivering messages to a device, comprising:
Collecting node information relating to another node device, and adding the node information including the key of the other node device as an entry to the routing table;
Determining whether the number of entries in the routing table exceeds a threshold;
Updating the routing table when it is determined that the number of entries in the routing table exceeds the threshold ;
With
Updating the routing table
Generating a plurality of routing table candidates configured by deleting a number of entries exceeding the threshold from the entries in the routing table;
If the key space is a one-dimensional metric space, select the route table candidate whose key frequency distribution in the route table candidate is closest to the exponential distribution,
Delete entries other than those constituting the selected routing table candidate from the routing table
A routing table management method.