Results 1 - 10 of 128

Contention-aware admission control for ad hoc networks

by Yaling Yang, Robin Kravets
"... An admission control algorithm must coordinate between flows in order to provide guarantees about how the medium is shared. In wired networks, nodes can monitor the medium to see how much bandwidth is being used. However, in ad hoc networks, communication from one node may consume the bandwidth of n ..."
Abstract - Cited by 112 (3 self) - Add to MetaCart
An admission control algorithm must coordinate between flows in order to provide guarantees about how the medium is shared. In wired networks, nodes can monitor the medium to see how much bandwidth is being used. However, in ad hoc networks, communication from one node may consume the bandwidth of neighboring nodes. Therefore, the bandwidth consumption of flows and the available resources to a node are not local concepts, but related to the neighboring nodes in carriersensing range. Current solutions do not address how to perform admission control in such an environment so that the admitted flows in the network will not exceed network capacity. In this paper, we present a scalable and efficient admission control framework – Contention-aware Admission Control Protocol (CACP)- to support QoS in ad hoc networks. We demonstrate the effectiveness of CACP with both mathematical analysis and simulation results.
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Real-Time communication and coordination in embedded sensor networks

by John A. Stankovic, Tarek Abdelzaher, Chenyang Lu, Lui Sha, Jennifer Hou - PROCEEDINGS OF THE IEEE , 2003
"... Sensor networks can be considered distributed computing platforms with many severe constraints including limited CPU speed, memory size, power, and bandwidth. Individual nodes in sensor networks are typically unreliable and the network topology dynamically changes, possibly frequently. Sensor networ ..."
Abstract - Cited by 96 (11 self) - Add to MetaCart
Sensor networks can be considered distributed computing platforms with many severe constraints including limited CPU speed, memory size, power, and bandwidth. Individual nodes in sensor networks are typically unreliable and the network topology dynamically changes, possibly frequently. Sensor networks can also be considered a form of ad hoc network. However, here also many constraints in sensor networks are different or more severe. Sensor networks also differ because of their tight interaction with the physical environment via sensors and actuators. Due to all of these differences many solutions developed for general distributed computing platforms and for ad hoc networks cannot be applied to sensor networks. Many new and exciting research challenges exist. This paper discusses the state of the art and presents the key research challenges to be solved, some with initial solutions or approaches.

Understanding TCP fairness over Wireless LAN

by Saar Pilosof, Ramachandran Ramjee, Danny Raz, Ran Ramjee, Yuval Shavitt, Prasun Sinha - IEEE INFOCOM , 2003
"... As local area wireless networks based on the IEEE 802.11 standard see increasing public deployment, it is important to ensure that access to the network by different users remains fair. While fairness issues in 802.11 networks have been studied before, this paper is the first to focus on TCP fairnes ..."
Abstract - Cited by 78 (1 self) - Add to MetaCart
As local area wireless networks based on the IEEE 802.11 standard see increasing public deployment, it is important to ensure that access to the network by different users remains fair. While fairness issues in 802.11 networks have been studied before, this paper is the first to focus on TCP fairness in 802.11 networks in the presence of both mobile senders and receivers. In this paper, we evaluate extensively through analysis, simulation, and experimentation the interaction between the 802.11 MAC protocol and TCP. We identify four different regions of TCP unfairness that depend on the buffer availability at the base station, with some regions exhibiting significant unfairness of over 10 in terms of throughput ratio between upstream and downstream TCP flows. We also propose a simple solution that can be implemented at the base station above the MAC layer that ensures that different TCP flows share the 802.11 bandwidth equitably irrespective of the buffer availability at the base station. I.

Quality of Service Schemes for IEEE 802.11 Wireless LANs -- An Evaluation

by Anders Lindgren, Andreas Almquist, Olov Schelén , 2003
"... This paper evaluates four mechanisms for providing service differentiation in IEEE 802.11 wireless LANs. The evaluated schemes are the Point Coordinator Function (PCF) of IEEE 802.11, the Enhanced Distributed Coordinator Function (EDCF) of the proposed IEEE 802.11e extension to IEEE 802.11, Distribu ..."
Abstract - Cited by 69 (1 self) - Add to MetaCart
This paper evaluates four mechanisms for providing service differentiation in IEEE 802.11 wireless LANs. The evaluated schemes are the Point Coordinator Function (PCF) of IEEE 802.11, the Enhanced Distributed Coordinator Function (EDCF) of the proposed IEEE 802.11e extension to IEEE 802.11, Distributed Fair Scheduling (DFS), and Blackburst. The evaluation was done using the ns-2 simulator. Furthermore, the impact of some parameter settings on performance has also been investigated. The metrics used in the evaluation are throughput, medium utilization, collision rate, average access delay, and delay distribution for a variable load of real time and background traffic. The simulations show that the best performance is achieved by Blackburst. PCF and EDCF are also able to provide pretty good service differentiation. DFS can give a relative differentiation and consequently avoids starvation of low priority traffic.

Priority Scheduling in Wireless Ad Hoc Networks

by Xue Yang, Nitin H. Vaidya - In Proc. of ACM Mobihoc , 2002
"... Ad hoc networks formed without the aid of any established infrastructure are typically multi-hop networks. Location dependent contention and "hidden terminal" problem make priority scheduling in multi-hop networks significantly different from that in wireless LANs. Most of the prior work r ..."
Abstract - Cited by 63 (0 self) - Add to MetaCart
Ad hoc networks formed without the aid of any established infrastructure are typically multi-hop networks. Location dependent contention and "hidden terminal" problem make priority scheduling in multi-hop networks significantly different from that in wireless LANs. Most of the prior work related to priority scheduling addresses issues in wireless LANs. In this paper, priority scheduling in multi-hop networks is discussed. We propose a scheme using two narrowband busy tone signals to ensure medium access for high priority source stations. The simulation results demonstrate the e#ectiveness of the proposed scheme.
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Real-Time power-aware routing in sensor networks

by Octav Chipara, Zhimin He, Guoliang Xing, Qin Chen, Xiaorui Wang, Chenyang Lu, John Stankovic, Tarek Abdelzaher - In Proceeding of the IEEE International Workshop on Quality of Service (IWQoS , 2006
"... Abstract — Many wireless sensor network applications must resolve the inherent conflict between energy efficient communication and the need to achieve desired quality of service such as end-to-end communication delay. To address this challenge, we propose the Real-time Power-Aware Routing (RPAR) pro ..."
Abstract - Cited by 57 (8 self) - Add to MetaCart
Abstract — Many wireless sensor network applications must resolve the inherent conflict between energy efficient communication and the need to achieve desired quality of service such as end-to-end communication delay. To address this challenge, we propose the Real-time Power-Aware Routing (RPAR) protocol, which achieves application-specified communication delays at low energy cost by dynamically adapting transmission power and routing decisions. RPAR features a power-aware forwarding policy and an efficient neighborhood manager that are optimized for resource-constrained wireless sensors. Moreover, RPAR addresses important practical issues in wireless sensor networks, including lossy links, scalability, and severe memory and bandwidth constraints. Simulations based on a realistic radio model of MICA2 motes show that RPAR significantly reduces the number of deadlines missed and energy consumption compared to existing real-time and energy-efficient routing protocols. I.
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On real-time capacity limits of multihop wireless sensor networks

by Tarek F. Abdelzaher, Shashi Prabh, Raghu Kiran - In IEEE RTSS , 2004
"... Multihop wireless sensor networks have recently emerged as an important embedded computing platform. This paper defines a quantitative notion of real-time capacity of a wireless network. Real-time capacity describes how much real-time data the network can transfer by their deadlines. A capacity boun ..."
Abstract - Cited by 56 (5 self) - Add to MetaCart
Multihop wireless sensor networks have recently emerged as an important embedded computing platform. This paper defines a quantitative notion of real-time capacity of a wireless network. Real-time capacity describes how much real-time data the network can transfer by their deadlines. A capacity bound is derived that can be used as a sufficient schedulability condition for a class of fixedpriority packet scheduling algorithms. Using this bound, a designer can perform capacity planning prior to network deployment to ensure satisfaction of applications ’ real-time requirements. 1
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Techniques to Reduce IEEE 802.11b MAC Layer Handover Time

by Héctor Velayos, Gunnar Karlsson, Trita-imit-lcn R, Héctor Velayos, Gunnar Karlsson - ISSN 1651-7717, ISRN KTH/IMIT/LCN/R-03/02–SE, KTH , 2003
"... Abstract — In this paper we analyze link-layer handover times in wireless local area networks based on the IEEE 802.11b MAC protocol. Our measurements indicate that detection and search phases are the main contributors to the handover time. We show that detection time can be reduced by reacting quic ..."
Abstract - Cited by 54 (0 self) - Add to MetaCart
Abstract — In this paper we analyze link-layer handover times in wireless local area networks based on the IEEE 802.11b MAC protocol. Our measurements indicate that detection and search phases are the main contributors to the handover time. We show that detection time can be reduced by reacting quickly to packet losses and by using shorter beacon intervals. We also show that search time can be reduced by using active scanning. In this case, we calculate values for the two timers that control the duration of active scanning in order to reduce search time. Several simulations illustrate the achieved reduction in handover time. I.

Hot-Spot Congestion Relief in Public-area Wireless Networks

by Anand Balachandran, Paramvir Bahl, Geoffrey , 2002
"... Wireless LAN administrators are often called upon to deal with the problem of sporadic user congestion at certain popular spaces ("hot-spots") within the network. To address this problem, we describe and evaluate two new approaches, explicit channel switching and networkdirected roaming fo ..."
Abstract - Cited by 43 (3 self) - Add to MetaCart
Wireless LAN administrators are often called upon to deal with the problem of sporadic user congestion at certain popular spaces ("hot-spots") within the network. To address this problem, we describe and evaluate two new approaches, explicit channel switching and networkdirected roaming for providing hot-spot congestion relief while maintaining pre-negotiated user bandwidth agreements with the network. The goals of these algorithms are: (i) to accommodate more users by dynamically providing capacity where it is needed, when it is needed; (ii) to improve overall network utilization by making more efficient use of deployed resources; and (iii) to guarantee at least a minimum amount of bandwidth to users. We propose that both the network and its users should explicitly and cooperatively adapt themselves to changing load conditions depending on their geographic location within the network. We describe how these algorithms enable the network to transparently adapt to user demands and balance load across its access points (APs). We evaluate the effectiveness of these algorithms on improving user service rates and network utilization using simulations. Our algorithms improve the degree of load balance in the system by over 30%, and user bandwidth allocation by up to 52% in comparison to existing schemes that offer little or no load balancing. 1.
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Techniques to reduce IEEE 802.11b handoff time

by Héctor Velayos, Gunnar Karlsson - in Proc. International Conference on Computer Communications (ICC , 2004
"... Abstract—We propose and evaluate via simulations techniques to minimize the IEEE 802.11b handoff time. We describe the handoff procedure and divide it into three phases. Our main contribution is a set of techniques to reduce the two longer phases, detection and search I. ..."
Abstract - Cited by 42 (1 self) - Add to MetaCart
Abstract—We propose and evaluate via simulations techniques to minimize the IEEE 802.11b handoff time. We describe the handoff procedure and divide it into three phases. Our main contribution is a set of techniques to reduce the two longer phases, detection and search I.
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