Lookup Process Research Articles

ID Repetition in Structured P2P Networks

Identity (ID) uniqueness is essential in distributed hash table (DHT)-based systems, as peer lookup and resource searching rely on ID matching. However, many DHT implementations in the wild, such as Kad and Mainline, do not enforce such uniqueness. Most previous works and measurements on DHTs do not take into account that IDs among peers may not be unique. Unfortunately, we observe that a significant portion of peers, i.e. 19.5% of the peers in Kad and 4.0% of the peers in Mainline, do not have unique IDs. These repetitions would mislead the measurements and modeling on those networks. We further focus on investigating the repetition in Kad considering its wider usage and more serious situation of repetition. We observe that there are a large number of peers that frequently change their UDP ports, and there are a few IDs that repeat for a large number of times and all peers with these IDs do not respond to Kad protocol. We also analyze the effects of ID repetitions under simplified settings and find that the current repetition degrades Kad's performance on publishing and searching, but has insignificant effect on lookup process. These measurement and analysis are useful to further determine the sources of repetitions and are also useful for finding suitable parameters in publishing and searching processes in DHT networks without compulsive ID uniqueness.

Unicube for Dynamic Environment Mapping

Cube mapping is widely used in many graphics applications due to the availability of hardware support. However, it does not sample the spherical surface evenly. Recently, a uniform spherical mapping, isocube mapping, was proposed. It exploits the six-face structure used in cube mapping and samples the spherical surface evenly. Unfortunately, some texels in isocube mapping are not rectilinear. This nonrectilinear property may degrade the filtering quality. This paper proposes a novel spherical mapping, namely unicube mapping. It has the advantages of cube mapping (exploitation of hardware and rectilinear structure) and isocube mapping (evenly sampling pattern). In the implementation, unicube mapping uses a simple function to modify the lookup vector before the conventional cube map lookup process. Hence, unicube mapping fully exploits the cube map hardware for real-time filtering and lookup. More importantly, its rectilinear partition structure allows a direct and real-time acquisition of the texture environment. This property facilitates dynamic environment mapping in a real time manner.

Localized Distance-Sensitive Service Discovery in Wireless Sensor and Actor Networks

We formalize the distance-sensitive service discovery problem in wireless sensor and actor networks, and propose a novel localized algorithm, iMesh. Unlike existing solutions, iMesh uses no global computation and generates constant per-node storage load. In iMesh, new service providers (i.e., actors) publish their location information in four directions, updating an information mesh. Information propagation for relatively remote services is restricted by a blocking rule, which also updates the mesh structure. Based on an extension rule, nodes along mesh edges may further advertise newly arrived relatively near service by backward distance-limited transmissions, replacing previously closer service location. The final information mesh is a planar structure constituted by the information propagation paths. It stores locations of all the service providers and serves as service directory. Service consumers (i.e., sensors) conduct a lookup process restricted within their home mesh cells to discover nearby services. We analytically study the properties of iMesh including construction cost and distance sensitivity over a static network model. We evaluate its performance in static/dynamic network scenarios through extensive simulation. Simulation results verify our theoretical findings and show that iMesh guarantees nearby (closest) service selection with very high probability, Gt99 percent (respectively, Gt95 percent).

DRES: Dynamic Range Encoding Scheme for TCAM Coprocessors

One of the most critical resource management issues in the use of ternary content-addressable memory (TCAM) for packet classification/filtering is how to effectively support filtering rules with ranges, known as range matching. In this paper, the dynamic range encoding scheme (DRES) is proposed to significantly improve the TCAM storage efficiency for range matching. Unlike the existing range encoding schemes requiring additional hardware support, DRES uses the TCAM coprocessor itself to assist range encoding. Hence, DRES can be readily programmed in a network processor using a TCAM coprocessor for packet classification. A salient feature of DRES is its ability to allow a subset of ranges to be encoded and, hence, to have full control over the range code size. This advantage allows DRES to exploit the TCAM structure to maximize the TCAM storage efficiency. DRES is a comprehensive solution, including a dynamic range selection algorithm, a search key encoding scheme, a range encoding scheme, and a dynamic encoded range update algorithm. Although the dynamic range selection algorithm running in the software allows optimal selection of ranges to be encoded to fully utilize the TCAM storage, the dynamic encoded range update algorithm allows the TCAM database to be updated lock free without interrupting the TCAM database lookup process. DRES is evaluated based on real-world databases and the results show that DRES can reduce the TCAM storage expansion ratio from 6.20 to 1.23. The performance analysis of DRES based on a probabilistic model demonstrates that DRES significantly improves the TCAM storage efficiency for a wide spectrum of range distributions.

First-Class Object Sets

Abstract. Typically, objects are monolithic entities with a fixed interface. To increase the flexibility in this area, this paper presents first-class object sets as a language construct. An object set offers an interface which is a disjoint union of the interfaces of its member objects. It may also be used for a special kind of method invocation involving multiple<br />objects in a dynamic lookup process. With support for feature access and late-bound method calls object sets are similar to ordinary objects, only more flexible. The approach is made precise by means of a small calculus, and the soundness of its type system is shown by a mechanically checked proof in Coq.

A Hybrid Peer-to-Peer Lookup Service Algorithm on Distributed Hash Table

An application using a distributed hash table (DHT) with N nodes must choose a DHT protocol from the spectrum between O(1) lookup protocols and O(logN). However, various applications under different network churns require that an idea DHT would be adaptive in according with the churn rates. ROAD (routing on active and demand), a new lookup algorithm, adjusts itself to provide the best performance across a range of lookup delay and churn rates. The key challenges in the design of ROAD are the algorithms that construct the routing table’s size and decrease the delay. It will speed up the lookup process and reduce the service delay with the expressed routing table and power sorting multicast algorithm. Simulations show that ROAD maintains an efficient lookup delay versus churn rate tradeoff than the existing DHTs. ROAD should be expanded into a mechanism that provides some kinds of lookup services with a range of qualities of service through super-peers choosing methods.

Optimal XOR hashing for non-uniformly distributed address lookup in computer networks

Hashing algorithms have been widely adopted to provide a fast address lookup process which involves a search through a large database to find a record associated with a given key. Modern examples include address lookup in network routers for a forwarding outgoing link, rule-matching in intrusion detection systems comparing incoming packets with a large database, etc. Hashing algorithms involve transforming a key inside each target data to a hash value hoping that the hashing would render the database a uniform distribution with respect to this new hash value. When the database are already key-wise uniformly distributed, any regular hashing algorithm would easily lead to perfectly uniform distribution after the hashing. On the other hand, if records in the database are instead not uniformly distributed, then different hashing functions would lead to different performance. This paper addresses the cases when such distribution follows a natural negative linear distribution, a partial negative linear distribution, or an exponential distribution which are found to closely approximate many real-life database distributions. For each of these distributions, we derive a general formula for calculating the distribution variance produced by any given non-overlapping bit-grouping XOR hashing function. Such a distribution variance from the hashing directly translates to performance variations in searching. Through this, the best XOR hashing function can be easily determined for any given key size and any given hashing target size.

One-Dimensional Turbulence-based closure for turbulent non-premixed flames

A new One-Dimensional Turbulence (ODT) based closure model for turbulent non-premixed flames is proposed. The model is based on the tabulation of scalar statistics based on two parameters, which measure the extent of mixing and entrainment. The table is generated using different realisations of stand-alone ODT simulations of turbulent jet diffusion flames. The table look-up process is coupled with a Reynolds-Averaged Navier-Stokes (RANS) computation. The scope of the ODT formulation is to predict thermo-chemical scalars statistics in sample space; while its coupling with RANS reproduces these statistics in 3D space. The resulting formulation yields reasonably good agreement with experimental data.

An Ip Packet Forwarding Technique Based on A New Structure of Lookup Table

In computer networks nowadays, high-speed routers are compulsory to deliver the incoming packet to its destination. There are two parameters that exist in all lookup techniques that directly affect performance results: data structure size and number of lookup table accesses. With these remarks in mind, the specific goals of this paper are: (i) Design a data structure for storing an IP lookup table that enhances the lookup process, (ii) Produce an IP lookup algorithm that has a bounded worst-case number of accesses lower than contemporary techniques, and (iii) Improve updating and deletion operations that do not create a bottleneck to efficient forwarding.This paper investigates a suitable data structure of the routing table in order to minimize the total routing time. The investigated structure of the routing table is based on RapidBase technique. It contains all the information necessary to forward an IP data packet toward its destination. The properties of the created routing table facilitate searching for the best matching prefix quicker than when using the current routing table where packets do not have to be queued before lookup. Additionally, the proposed algorithm’s effectiveness is deliberated via simulation. A comparative study with recently published algorithms shows that our proposed scheme has a great impact on shortening the route lookup and update operations. For more enhancements, combinations of the proposed algorithm with the most popular algorithms are also studied.

A 2x load/store pipe for a low-power 1-GHz embedded processor

The load/store pipe for a low-power 1-GHz embedded processor is described. For area savings and logic complexity reduction, the load/store pipe is clocked at twice the frequency of the processor core. It can sustain two load or store operations per core clock cycle with zero load to use issue latency. The address generation unit for one of the two load/store pipes takes advantage of the common addressing mode in MIPS 64 ISA to generate the address within a core clock phase. Phase borrowing is employed in the translation lookaside buffer (TLB) design to enable a lookup process within a core clock phase. The data cache design enables the activation of a minimum number of data bank arrays for power savings. Small-swing differential buses are used for multiple address and data buses for improved signal transmission latency. The quadrature clocks used to derive the 2/spl times/ clock are generated with a novel 4-to-1 divider and distributed with matched paths, all to reduce the duty cycle variation of the 2/spl times/ clock phase. The design has been implemented in a 0.13-/spl mu/m CMOS process.

Using Perceptual Texture Masking for Efficient Image Synthesis

Texture mapping has become indispensable in image synthesis as an inexpensive source of rich visual detail. Less obvious, but just as useful, is its ability to mask image errors due to inaccuracies in geometry or lighting. This ability can be used to substantially accelerate rendering by eliminating computations when the resulting errors will be perceptually insignificant. Our new method precomputes the masking ability of textures using aspects of the JPEG image compression standard. This extra information is stored as threshold elevation factors in the texture's mip-map and interpolated at image generation time as part of the normal texture lookup process. Any algorithm which uses error tolerances or visibility thresholds can then take advantage of texture masking. Applications to adaptive shadow testing, irradiance caching, and path tracing are demonstrated. Unlike prior methods, our approach does not require that initial images be computed before masking can be exploited and incurs only negligible runtime computational overhead. Thus, it is much easier to integrate with existing rendering systems for both static and dynamic scenes and yields computational savings even when only small amounts of texture masking are present. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture

Routing with a clue

We suggest a new simple forwarding technique to speed up IP destination address lookup. The technique is a natural extension of IP, requires 5 bits in the IP header (IPv4, 7 in IPv6), and performs IP lookup nearly as fast as IP/Tag switching but with a smaller memory requirement and a much simpler protocol. The basic idea is that each router adds a to each packet, telling its downstream router where it ended the IP lookup. Since the forwarding tables of neighboring routers are similar, the clue either directly determines the best prefix match for the downstream router, or provides the downstream router with a good point to start its IP lookup. The new scheme thus prevents repeated computations and distributes the lookup process across the routers along the packet path. Each router starts the lookup computation at the point its upstream neighbor has finished. Furthermore, the new scheme is easily assimilated into heterogeneous IP networks, does not require routers coordination, and requires no setup time. Even a flow of one packet enjoys the benefits of the scheme without any additional overhead. The speedup we achieve is about 10 times faster than current standard techniques. In a sense, this paper shows that the current routers employed in the Internet are clue-less; namely, it is possible to speed up the IP lookup by an order of magnitude without any major changes to the existing protocols.

The role of phonological codes in integrating information across saccadic eye movements in Chinese character identification.

Prior research has generally assumed either that phonological codes do not contribute to Chinese character identification or that they do so only through a look-up process at the character level. In 3 experiments, a homophone seen parafoveally aided the identification of a target character that was fixated following an eye movement to the preview location. Moreover, high-frequency phonetically regular characters were named faster than high-frequency, phonetically irregular characters. Thus, both lexical and sublexical phonological codes of Chinese characters are involved early in the process of character identification. Orthographic information from the preview was also used in character identification, as orthographically similar previews facilitated target identification as well. The evidence for the extraction of semantic information from parafoveal previews was mixed, as synonym previews facilitated in Experiment 2 but not in Experiment 1.

The role of phonological codes in integrating information across saccadic eye movements in Chinese character identification.

Prior research has generally assumed either that phonological codes do not contribute to Chinese character identification or that they do so only through a look-up process at the character level. In 3 experiments, a homophone seen parafoveally aided the identification of a target character that was fixated following an eye movement to the preview location. Moreover, high-frequency phonetically regular characters were named faster than high-frequency, phonetically irregular characters. Thus, both lexical and sublexical phonological codes of Chinese characters are involved early in the process of character identification. Orthographic information from the preview was also used in character identification, as orthographically similar previews facilitated target identification as well. The evidence for the extraction of semantic information from parafoveal previews was mixed, as synonym previews facilitated in Experiment 2 but not in Experiment 1.

Routing with a clue

We suggest a new simple forwarding technique to speed-up IP destination address lookup. The technique is a natural extension of IP, requires 5 bits in the IP header (IPv4, 7 in IPv6) and performs IP lookup nearly as fast as IP/Tag-switching but with a smaller memory requirement and a much simpler protocol. The basic idea is that each router adds a "clue" to each packet, telling its downstream router where it ended the IP lookup. Since the forwarding tables of neighboring routers are similar, the clue either directly determines the best prefix match for the downstream router, or provides the downstream router with a good point to start its IP lookup. The new scheme thus prevents repeated computations and distributes the lookup process across the routers along the packet path. Each router starts the lookup computation at the point its up-stream neighbor has finished. Furthermore, the new scheme is easily assimilated into heterogeneous IP networks, does not require routers coordination, and requires no setup time. Even a flow of one packet enjoys the benefits of the scheme without any additional overhead. The speedup we achieve is about 10 times faster than current standard techniques. In a sense this paper shows that the current routers employed in the Internet are clue-less; Namely, it is possible to speedup the IP-lookup by an order of magnitude without any major changes to the existing protocols.

Integrating gestures into the user-interface management system

We describe a gesture as an alternative for users to convey commands to the user interface. Issuing a command and manipulating an object can be done in one stroke. The number of our representations required to represent a gesture is small (2 to 4 for the 26 small letters and the 10 digits), so we can save storage space and time for the look-up process. Our detecting algorithm is good at handling circular gestures, which increases the success rate of gestural recognition. The system can be trained by each end user to accept variations for any gesture.

Efficient implementation of binary morphological image processing

Morphological image processing is an important tool for a broad range of problems in image processing. A 512-entry table lookup method is used for real-time implementation. But it is not efficient to transfer this method directly into software. The author proposes a fast software implementation technique, in which a 256-entry lookup table containing neighborhood information is built and a dynamic table lookup process is applied to reduce the number of logical matching operations and the number of accesses of the neighboring pixels. In this proposed method only the foreground pixels, which are pixels on the object, are processed. Among the foreground pixels, only at the starting pixel of each "run" of l's is it necessary to read the eight neighboring pixels. For the other pixels, it is necessary to read only three neighbors. This method shows a significant improvement in timesaving. In addition, for systems supporting fast access to consecutive address memory, the author proposes another implementation, which treats the image as a contiguous block of memory. Thus advantage is taken of RAM technology.

Using the English Dictionary for Comprehension

A linguist's view of dictionary use for comprehension is offered which highlights the positive contribution the learner-user has to make even when using a good dictionary. The look-up process is analysed into seven main steps. In most of these, the proficient user, far from performing a purely mechanical operation, is often required to formulate and pursue several hypotheses and make use of prior knowledge of various sorts, especially information derived from context. Analysis in some detail is provided for those steps that are usually glossed over-namely, the search for an item in more than one location, the choice of the relevant sense, and the fitting of definitional information to the source context of the unknown word.

Generic Fault Characterizations for Table Look-Up Coverage Bounding

Given any combinational, internal fan-out-free network and any complete single fault detection test set (SFDTS) for the network, we consider in this paper the problem of determining the minimal extent to which that SFDTS will cover multiple faults in the network. The basis of our approach is the development of a generic perspective to multiple faults which uses a representation of such faults called an L-expression. This perspective leads to a technique for obtaining the greatest lower bound on the multiple fault coverage capability of an SFDTS by means of a simple table look-up process. In addition to generalizing previously known results regarding multiple fault coverage, two particularly interesting results obtained from this approach are as follows: 1) On the average, every SFDTS for an internal fan-out-free network covers 92 percent of all multiple faults of sizes 8 and less. 2) On the average, every SFDTS for an internal fan-out-free network covers at least 46.1 percent of all multiple faults.

A Scatter Storage Scheme for Dictionary Lookups

Scatter storage schemes are examined with respect to their applicability to dictionary lookup procedures. Of particular interest are virtual scatter methods which combine the advantages of rapid search speed and reasonable storage requirements. The theoretical aspects of computing hash addresses are developed, and several algorithms are evaluated. Finally, experiments with an actual text lookup process are described, and a possible library application is discussed.