In software defined network (SDN), packet processing is commonly implemented using match-action model, where packets are processed based on matched actions in match action table. Due to the limited FPGA on-board resources, it is an important challenge to achieve large-scale high throughput based on exact matching (EM), while solving hash conflicts and out-of-order problems. To address these issues, this study proposed an FPGA-based EM table that leverages shared rule tables across multiple pipelines to eliminate memory replication and enhance overall throughput. An out-of-order reordering function is used to ensure packet sequencing within the pipelines. Moreover, to handle collisions and increase load factor of hash table, multiple hash table blocks are combined and an auxiliary CAM-based EM table is integrated in each pipeline. To the best of our knowledge, this is the first time that the proposed design considers the recovery of out-of-order operations in multi-channel EM table for high-speed network packets processing application. Furthermore, it is implemented on Xilinx Alveo U250 field programmable gate arrays, which has a million rules and achieves a processing speed of 200 million operations per second, theoretically enabling throughput exceeding 100 Gbps for 64-Byte size packets.

DHT routing algorithms can provide efficient mechanisms for resource placement and lookup for distributed file sharing systems. However, we must still deal with irregular and frequent join/leave of nodes and the problem of load unbalancing between nodes in DHT-based file sharing systems. This paper presents an efficient file backup scheme based on dynamic DHT key space clustering in order to guarantee data availability and support load balancing. The main idea of our method is to dynamically divide the DHT network into a number of clusters, each of which locally stores and maintains data chunks of data files to guarantee the data availability of user data files even when node churn occurs. Further, high-capacity nodes in clusters are selected as backup nodes to achieve adequate load balancing. Simulation results demonstrate the superior effectiveness of the proposed scheme over other file replication schemes.

We design a new hash table for high-speed networking that reduces main memory accesses even when the ratio of inserted items to the table size is high, at which point previous schemes no longer work. This improvement comes from a new design of a summary, called expanded keys, exploiting recent multiple hash functions and Bloom filter theories.

This paper proposes a consistency maintenance scheme for P2P file sharing systems. The basic idea of the proposed scheme is to construct a static tree for each shared file to efficiently propagate the update information to all replica peers. The link to the root of the trees is acquired by referring to a Chord ring which stores the mapping from the set of shared files to the set of tree roots. The performance of the scheme is evaluated by simulation. The simulation result indicates that: 1) it reduces the number of messages in the Li's scheme by 54%, 2) it reduces the propagation delay of the scheme by more than 10%, and 3) the increase of the delay due to peer churns is effectively bounded provided that the percentage of leaving peers is less than 40%.

At present, vast numbers of information resources are available on the Internet. However, one emerging issue is how to search and exploit these information resources in an efficient and flexible manner with high scalability. In this study, we focused our attention on the design of a distributed hash table (DHT)-based search system that supports efficient scalable multi-attribute queries of information resources in a distributed manner. Our proposed system, named D-AVTree, is built on top of a ring-based DHT, which partitions a one-dimensional key space across nodes in the system. It utilizes a descriptive naming scheme, which names each resource using an attribute-value (AV) tree, and the resource names are mapped to d-bit keys in order to distribute the resource information to responsible nodes based on a DHT routing algorithm. Our mapping scheme maps each AV branch of a resource name to a d-bit key where AV branches that share a subsequence of AV pairs are mapped to a continuous portion of the key space. Therefore, our mapping scheme ensures that the number of resources distributed to a node is small and it facilitates efficient multi-attribute queries by querying only a small number of nodes. Further, the scheme has good compatibility with key-based load balancing algorithms for DHT-based networks. Our system can achieve both efficiency and a good degree of load balancing even when the distribution of AV pairs in the resource names is skewed. Our simulation results demonstrated the efficiency of our solution in terms of the distribution cost, query hit ratio, and the degree of load balancing compared with conventional approaches.

Reducing the time complexity of character matching is critical to the development of efficient Japanese Optical Character Recognition (OCR) systems. To shorten the processing time, recognition is usually split into separate pre-classification and precise recognition stages. For high overall recognition performance, the pre-classification stage must both have very high classification accuracy and return only a small number of putative character categories for further processing. Furthermore, for any practical system, the speed of the pre-classification stage is also critical. The associative matching (AM) method has often been used for fast pre-classification because of its use of a hash table and reliance on just logical bit operations to select categories, both of which make it highly efficient. However, a certain level of redundancy exists in the hash table because it is constructed using only the minimum and maximum values of the data on each axis and therefore does not take account of the distribution of the data. We propose a novel method based on the AM method that satisfies the performance criteria described above but in a fraction of the time by modifying the hash table to reduce the range of each category of training characters. Furthermore, we show that our approach outperforms pre-classification by VQ clustering, ANN, LSH and AM in terms of classification accuracy, reducing the number of candidate categories and total processing time across an evaluation test set comprising 116,528 Japanese character images.

In this paper, we study the problem of efficient processing of conjunctive queries in Peer-to-Peer systems based on Distributed Hash Tables (P2P DHT, for short). The basic idea of our approach is to cache the search result for the queries submitted in the past, and to use them to improve the performance of succeeding query processing. More concretely, we propose to adopt Bloom filters as a concrete implementation of such a result cache rather than a list of items used in many conventional schemes. By taking such an approach, the cache size for each conjunctive query becomes as small as the size of each file index. The performance of the proposed scheme is evaluated by simulation. The result of simulation indicates that the proposed scheme is particularly effective when the size of available memory in each peer is bounded by a small value, and when the number of peers is 100, it reduces the amount of data transmissions of previous schemes by 75%.

Many services rely on the Internet to provide their customers with immediate access to information. To provide a stable service to a large number of customers, a service provider needs to monitor demand fluctuations and adjust the number and the location of replica servers around the world. Unfortunately, Flash crowds make it quite difficult to determine good number and locations of replica servers because they must be repositioned very quickly to respond to rapidly changing demands. We are developing ExaPeer, an infrastructure for dynamically repositioning replica servers on the Internet on the basis of demand fluctuations. In this paper we introduce ExaPeer Server Reposition (EPSR), a mechanism that quickly finds appropriate number and locations of replica servers. EPSR is designed to be lightweight and responsive to Flash crowds. EPSR enables us to position replica servers so that no server becomes overloaded. Even though no dedicated server collects global information such as the distribution of clients or the load of all servers over the Internet, the peer-to-peer approach enables EPSR to find number and locations of replica servers quickly enough to respond to flash crowds. Simulation results demonstrate that EPSR locates high-demand areas, estimates their scale correctly and determines appropriate number and locations of replica servers even if the demand for a service increases/decreases rapidly.

To realize huge-scale information services, many Distributed Hash Table (DHT) based systems have been proposed. For example, there are some proposals to manage item-level product traceability information with DHTs. In such an application, each entry of a huge number of item-level IDs need to be available on a DHT. To ensure data availability, the soft-state approach has been employed in previous works. However, this does not scale well against the number of entries on a DHT. As we expect 1010 products in the traceability case, the soft-state approach is unacceptable. In this paper, we propose Distributed-to-Distributed Data Copy (D3C). With D3C, users can reconstruct the data as they detect data loss, or even migrate to another DHT system. We show why it scales well against the number of entries on a DHT. We have confirmed our approach with a prototype. Evaluation shows our approach fits well on a DHT with a low rate of failure and a huge number of data entries.

A multiple stream join is one of the most important but high cost operations in ubiquitous streaming services. In this paper, we propose a newly improved and practical algorithm for joining multiple streams called AMJoin, which improves the multiple join performance by guaranteeing the detection of join failures in constant time. To achieve this goal, we first design a new data structure called BiHT (Bit-vector Hash Table) and present the overall behavior of AMJoin in detail. In addition, we show various experimental results and their analyses for clarifying its efficiency and practicability.

Mobile Ad Hoc Networks (MANETs) are temporal and infrastructure-independent wireless networks that consist of mobile nodes. For instance, a MANET can be used as an emergent network for communication among people when a disaster occurred. Since there is no central server in the network, each node has to find out its desired information (objects) by itself. Constructing a mobile Peer-to-Peer (P2P) network over the MANET can support the object search. Some researchers proposed construction schemes of mobile P2P networks, such as Ekta and MADPastry. They integrated DHT-based application-layer routing and network-layer routing to increase search efficiency. Furthermore, MADPastry proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments where nodes quickly move around. In this paper, we focus on route disappearances in the network layer which cause the deterioration of search efficiency. We describe the detail of this problem and evaluate quantitatively it through simulation experiments. We extend MADPastry by introducing a method sharing objects among nodes in a cluster. Through simulation experiments, we show that the proposed method can achieve up to 2.5 times larger success rate of object search than MADPastry.

In this paper, we propose a new method to enhance the fault-tolerance of the Content Addressable Network (CAN), which is known as a typical pure P2P system based on the notion of Distributed Hash Table (DHT). The basic idea of the proposed method is to introduce redundancy to the management of index information distributed over the nodes in the given P2P network, by allowing each index to be assigned to several nodes, which was restricted to be one in the original CAN system. To keep the consistency among several copies of indices, we propose an efficient synchronization scheme based on the notion of labels assigned to each copy in a distinct manner. The performance of the proposed scheme is evaluated by simulation. The result of simulations indicates that the proposed scheme significantly enhances the fault-tolerance of the CAN system.

Content-Addressable Network (CAN) provides a mechanism that could retrieve objects in a P2P network by maintaining indices to those objects in a fully decentralized manner. In the CAN system, index caching is a useful technique for reducing the response time of retrieving objects. The key points of effective caching techniques are to improve cache hit ratio by actively sharing caches distributed over the P2P network with every node and to reduce a maintenance and/or routing overhead for locating the cache of a requested index. In this paper, we propose a new caching technique based on the notion of proxy-type caching techniques which have been widely used in WWW systems. It can achieve active cache sharing by incorporating the concept of proxy caching into the index access mechanism and locate a closer proxy cache of a requested index with a little routing overhead. By the result of simulations, we conclude that it can improve the response time of retrieving indices by 30% compared with conventional caching techniques.

Building next generation routers with the capability of forwarding multiple millions of packets per second is required for the increasing demand for high bandwidth on the Internet. Reducing the required memory size of the forwarding table is a possible solution since small forwarding table can be integrated into the application specific integrated circuit (ASIC). In this paper a hash technique is developed to reduce the size of the IP forwarding table. The proposed data structure is a compressed 8-8-8-8 multibit trie that is based on hash tables of 4-bit addresses. Two optimization techniques are also proposed to further improve the performance of the proposed schemes. Our experimental results show that the proposed hashing-based schemes are better than the Small Forwarding Table scheme both in memory size and lookup latency.

Many P2P lookup services based on distributed hash tables (DHT) have appeared recently. These schemes are built upon overlay networks and ignore distance to the target resources. As a result, P2P lookups often suffer from unnecessarily long routes in the underlay network, which we call overlay dilation. This paper proposes a new scheme for resource routing, called hybrid hierarchical overlay routing, dubbed Hyho. We introduce distance-weighted Bloom filters (dwBFs) as a concise representation of routing information for scattered resources in overlay networks. To further reduce the size of Bloom filters, so that they are linear in the number of distinct resources, Hyho splits overlay networks in accordance with DHT, where each subnetwork has a smaller set of resources and spans the entire network thinly. As a result, Hyho constructs a hierarchical overlay network and routes requests accordingly. Simulation results show that Hyho can reduce overlay dilation to one half that yielded by the Chord lookup service.