In this paper, variable bit rate (VBR) streams with long range dependency over IEEE 802.16 broadband networks are investigated. Real-time VBR buffering of streams to smooth bursts is not sufficient, and efficient resource multiplexing must instead be used for adequate delay performance. A data rate control mechanism is derived for the case in which the uplink channel provides real-time polling bandwidth allocation service and the traffic rate parameter remains constant. That is, the Worldwide Interoperability for Microwave Access (WiMAX) system uses a VBR real-time polling service (rtPS) that results in additional access latency jitter and bandwidth allocation problems for transmitted multimedia stream variable data rates when the base station regular time interval polling to 802.16 entity (SSs) for contention bandwidth request period. However, this scheduling algorithm solves the SS bandwidth resource allocation problem, and depends on initial values provided by an extended real-time polling service (ertPS) during a specified period. This paper adopted a fairness bandwidth allocation max-min algorithm as the scheduling mechanism, and its only restriction is a time constraint condition to transmit real-time VBR stream in an 802.16 wireless broadband environment. In addition, to analyze the VBR stream capacity, we utilize an NS2 simulation, and show that the ertPS, according the fairness algorithm mechanism, can support service to more VBR stream users than other rtPS scheduler algorithms. It is hoped that the fairness bandwidth allocation max-min algorithm presented simulation result will draw analyzing to the stable VBR frame transmission for real-time multimedia streaming by WiMAX.

Geocasting, a variant of conventional multicasting, uses the location technology to deliver messages. However, recent geocast protocols extensively use flooding and broadcasting approaches. When network load is heavy, the chance of collision will be increased and then packets will probably be damaged or lost. The purpose of this paper is to propose an Adaptive Handshaking-Based Geocasting protocol (AHBG). In this protocol, we employ handshaking-based forwarding for data transmission instead of flooding. Simulation results show that AHBG achieves high delivery ratio (nearly 100%) with low overhead (at least 21% reduction compared with other protocols).

In a networked virtual environment (NVE), participants exchange their information on the network by sending messages. When a message is generated, usually only part of the entities are interested in it, so it would be superfluous to other entities. In order to reduce the wastefulness of bandwidth, the system always employs a grouping scheme to divide the entities into groups and only sends messages to the groups that would be interested in them. In this paper, we describe two well-known grouping strategies: entity-based grouping and cell-based grouping, and propose the tracking-needless grouping strategy for reducing the overhead of message sending. The simulation results show that it facilitates designing an efficient and scalable NVE system. Finally, we evaluate the influence of cell size on two aspects: grouping overhead and bandwidth requirement.

This paper presents a resource reservation scheme with dynamic grouping to support quality of service (QoS) guarantees in the next generation wireless networks. The proposed scheme is based on probabilistic resource estimation to provide QoS guarantees for multimedia traffic in cellular networks. We establish several reservation time-sections, called groups, according to the mobility information of mobile hosts of each base station. The amount of reserved bandwidth for each base station is dynamically adjusted for each reservation group. The performance of the proposed schemes is compared to the semi-reservation scheme. The simulation results show that the resource reservation scheme with dynamic grouping provides less connection-blocking rate and less connection-dropping rate, and achieves high bandwidth utilization.

In wireless networks carrying multimedia traffic (voice, video, data, and image), it becomes necessary to provide a quality-of-service(QoS) guarantee for multimedia traffic connections supported by the network. In order to provide mobile hosts with high QoS in the next-generation wireless networks, efficient and better bandwidth reservation schemes must be designed. This paper presents a novel dynamic-grouping bandwidth reservation scheme as a solution to support QoS guarantees in the next-generation wireless networks. The proposed scheme is based on the probabilistic resource estimation to provide QoS guarantees for multimedia traffic in wireless cellular networks. We establish several reservation time sections, called groups, according to the mobility information of mobile hosts of each base station. The amount of reserved bandwidth for each base station is dynamically adjusted for each reservation group. We use the dynamic-grouping bandwidth reservation scheme to reduce the connection blocking rate and connection dropping rate, while increasing the bandwidth utilization. The simulation results show that the dynamic-grouping bandwidth reservation scheme provides less connection-blocking rate and less connection-dropping rate and achieves high bandwidth utilization.

Torus/mesh-based machines have received increasing attention. It is natural to identify the maximum healthy submeshes in a faulty torus/mesh so as to lower potential performance degradation, because the time for executing a parallel algorithm tends to depend on the size of the assigned submesh. This paper proposes an efficient approach for identifying all the maximum healthy submeshes present in a faulty torus/mesh. The proposed approach is based on manipulating set expressions, with the search space reduced considerably by taking advantage of the interesting properties of a faulty torus/mesh. This procedure is a distributed one, because every healthy node performs the same procedure independently and concurrently. We show that the proposed scheme may outperform previous methods.

Compaction relocates active subcubes in a fragmented hypercube so as to produce a contiguous free region and eliminate the adverse impact of fragmentation on performance. The overhead of compaction is often contributed primarily by task migration, which makes use of disjoint paths for transmitting migrated data. Since task migration usually involves transmitting a large amount of data, the time required for migration with single paths is long, making compaction an undesirably lengthy process. This paper considers fast compaction through the use of all disjoint paths in existence for migration simultaneously from a source subcube to its target subcube, effectively reducing the size of data transmitted over a path and shortening the migration time. This approach leads to considerable savings in the compaction time for hypercubes which support circuit switching or wormhole routing, when compared with that using single migration paths.

Repeated subcube allocation and deallocation in hypercubes tend to cause fragmentation, which can be taken care of by task migration. Earlier task migration dealt with the establishment of a single path from each participating node for transmitting migrated information. The time required for migration with single paths is long, if a large amount of information is moved in hypercubes. This paper considers speedy task migration in that two disjoint paths are created between every pair of corresponding nodes for delivering migrated information simultaneously, reducing the size of data transmitted over a path. All migration paths selected are pairwise disjoint and contain no link of active subcubes, so that task migration can be performed quickly and on-line without interrupting the execution of other jobs. Our approach could lead to a considerable savings in the migration time for contemporary hypercube systems, where circuit switching or wormhole routing is implemented.

A hypercube may operate in a gracefully degraded manner, after faults arise, by supporting the execution of parallel algorithms in smaller fault-free subcubes. In order to reduce execution slowdown in a hypercube with given faults, it is essential to identify the maximum healthy subcubes in the faulty hypercube because the time for executing a parallel algorithm tends to depend on the dimension of the assigned subcube. The paper describes an efficient procedure capable of determining all maximum fault-free subcubes in a faulty hypercube. The procedure is a distributed one, since every healthy node next to a failed component performs the same procedure independently and concurrently. Based on interesting properties of faulty hypercubes, this procedure exhibits empirically polynomial time complexity with respect to the system dimension and the number of faults, for a practical range of dimensions. It compares favorably with prior methods when the number of faults is in the order of the system dimension. This procedure can deal with node failures and link failures uniformly and equally efficiently.

An incomplete hypercube possesses virtually every advantage of complete hypercubes, including simple deadlock-free routing, a small diameter, bounded link traffic density, a good support of parallel algorithms, and so on. It is natural to reconfigure a faulty hypercube into a maximum incomplete cube so as to lower potential performance degradation, because a hypercube so reconfigured often results in a much larger system than what is attainable according to any conventional reconfiguration scheme which identifies only complete subcubes. A maximum incomplete subcube involves one maximum complete subcube, plus certain smaller complete subcubes, and, thus, may accommodate multiple jobs of different sizes simultaneously, delivering a higher performance level. This paper proposes an efficient approach for identifying all the maximum incomplete subcubes present in a faulty hypercube. The proposed approach is on the basis of manipulating Boolean expressions, with the search space reduced considerably by taking advantage of the basic properties of faulty hypercubes during expression manipulation. It is distributed, in that every healthy node executes the same identification algorithm independently, at the same time, it is confirmed by fault simulation that our approach indeed gives rise to significantly larger reconfigured systems and requires short execution times.

While a certain resource in the hypercube may be shared by cube nodes to lower the cost, multiple copies of a shared resource often exist in the hypercube to reduce contention, and thus the potential delay, in fetching any shared copy. It is desirable that one employs as few resource copies as possible to ensure that every node is able to reach the resource in a given number of hops, achieving efficient resource placement. This placement method also keeps system performance degradation minimal after one resource copy becomes unavailable due to a fault. First, we consider placing multiple copies of a certain resource in a way that every cube node without the resource is adjacent to a specified number of resource copies. The use of our developed perfect and quasiperfect multiple-adjacency codes makes it possible to arrive at efficient solutions to this placement problem in a simple and systematic manner for an arbitrary hypercube. We then deal with the generalized resource placement in the hypercube such that every node without the resource can reach no less than a specified number of resource copies in no more than a certain number of hops, using as few resource copies as possible. Our placement results yield lowest potential access contention for a given number of resource copies (i.e., cost), particularly useful for large-scale hypercubes.>

Since the hypercube is not incrementally scalable, a variant hypercube topology with more flexibility in the system size, called an incomplete hypercube, is examined. An incomplete hypercube may also result from a complete hypercube which operates in a degraded manner after some nodes fail. Elementary properties, including diameter, mean internode distance, and traffic density, of incomplete hypercubes with size 2/sup n/+2/sup k/, 0/spl les/k/spl les/n, are derived. Interestingly, traffic density over links in such an incomplete hypercube is found to be bounded by 2 (messages per link per unit time), despite its structural nonhomogeneity. Thus, cube links can easily be constructed so as to avoid any single point of congestion, guaranteeing good performance. The minimum incomplete hypercubes able to embed binary trees with node adjacencies preserved are determined.>