Abstract not found

Providing quality of service in random access multi-hop wireless networks requires support from both medium access and packet scheduling algorithms. However, due to the distributed nature of ad hoc networks, nodes may not be able to determine the next packet that would be transmitted in a (hypothetical) centralized and ideal dynamic priority scheduler. In this paper, we develop two mechanisms for QoS communication in multi-hop wireless networks. First, we devise distributed priority scheduling, a technique that piggybacks the priority tag of a node’s head-of-line packet onto handshake and data packets; e.g., RTS/DATA packets in IEEE 802.11. By monitoring transmitted packets, each node maintains a scheduling table which is used to assess the node’s priority level relative to other nodes. We then incorporate this scheduling table into existing IEEE 802.11 priority back-off schemes to approximate the idealized schedule. Second, we observe that congestion, link errors, and the random nature of medium access prohibit an exact realization of the ideal schedule. Consequently, we devise a scheduling scheme termed multi-hop coordination so that downstream nodes can increase a packet’s relative priority to make up for excessive delays incurred upstream. We next develop a simple analytical model to quantitatively explore these two mechanisms. In the former case, we study the impact of the probability of overhearing another packet’s priority index on the scheme’s ability to achieve the ideal schedule. In the latter case, we explore the role of multi-hop coordination in increasing the probability that a packet satisfies its end-to-end QoS target. Finally, we perform a set of ns-2 simulations to study the scheme’s performance under more realistic conditions. 1.

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Providing quality of service in random access multi-hop wireless networks requires support from both medium access and packet scheduling algorithms. However, due to the distributed nature of ad hoc networks, nodes may not be able to determine the next packet that would be transmitted in a (hypothet-ical) centralized and ideal dynamic priority scheduler. In this paper, we develop two mechanisms for

Most previous work on medium access control (MAC) protocols for wireless ad hoc networks has focused on the twin goals of maximising throughput and minimising average packet delay as required for general-purpose applications.

Recent advances in technology have made it possible to cram computing and networking technology into ever smaller portable devices. As those devices incorporate more data and services, enabling them to participate in ad-hoc networks can

this paper, the challenges imposed on the standard TCP in the wireless ad hoc network environment are first identified. Then some existing solutions are discussed according to their design philosophy. Finally, some suggestions regarding future research issues are presented

Providing service differentiation in IEEE802.11 Wireless LANs [3] has been investigated by many researchers ([2], [5], [6], [7], [9], [13]). It has been shown [1] that some distributed schedulers such as DFS [9] and EDCF [5] can achieve high throughput and certain service differentiation comparing to DCF and PCF provided that the traffic load in the system is low or medium. However, those strategies do not support flow reservation and thus cannot guarantee QoS requirements of high priority real-time flows under overloading network traffics. In this paper, we present a MAC layer flow reservation and admission control scheme for distributed scheduling strategies in the aim of achieving QoS guarantee in IEEE802.11 wireless LANs. Our approach has several desirable features: (1) It can work with most of the distributed scheduling strategies like DCF, DFS, EDCF without modification of the underlying scheduling mechanism. (2) A dynamic priority re-allocation method is integrated with the admission control to further improve system throughput. (3) Misuse of priority can be easily handled. Simulation of our proposed reservation scheme upon various distributed scheduling strategies has been conducted, and results show that this scheme can achieve low collision rate, high throughput, and less delay.

Communication optimization plays an important role in building networked distributed applications. In this paper, we systematically evaluate four bandwidth reduction algorithms, namely direct sending, delta-encoding, fix-sized blocking, and vary-sized blocking, using five types of documents including source code, images, Web contents, Microsoft Word documents, and Latex files. The experiments were performed under four representative network connection technologies. Performance evaluation results show that different approaches have different performance in terms of different metrics. Completely different results can be achieved by the same algorithm with respect to different types of documents. Network condition can affect some algorithms substantially. Furthermore, the effect of block size to the system performance was also studied. 1

In recent years, fair scheduling and quality of service (QoS) in wireless LANs have received significant attention from the networking research community. This paper presents a distributed algorithm for priority and fair scheduling in a wireless LAN. The proposed protocol is derived from HIPERLAN which is a wireless LAN standard defined by ETSI. The proposed protocol supports multiple priorities, as well as a mechanism (using weights) for controlling the way bandwidth is shared by ows within a given priority level.