Browsing by Subject "throughput"

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    An analytical model of IEEE 80211 DCF for multi-hop wireless networks and its application to goodput and energy analysis
    (2010) Aydoğdu, Canan
    In this thesis, we present an analytical model for the IEEE 802.11 DCF in multihop networks that considers hidden terminals and works for a large range of traffic loads. A goodput model which considers rate reduction due to collisions, retransmissions and hidden terminals, and an energy model, which considers energy consumption due to collisions, retransmissions, exponential backoff and freezing mechanisms, and overhearing of nodes, are proposed and used to analyze the goodput and energy performance of various routing strategies in IEEE 802.11 DCF based multi-hop wireless networks. Moreover, an adaptive routing algorithm which determines the optimum routing strategy adaptively according to the network and traffic conditions is suggested. Viewed from goodput aspect the results are as follows: Under light traf- fic, arrival rate of packets is dominant, making any routing strategy equivalently optimum. Under moderate traffic, concurrent transmissions dominate and multihop transmissions become more advantageous. At heavy traffic, multi-hoppingbecomes unstable due to increased packet collisions and excessive traffic congestion, and direct transmission increases goodput. From a throughput aspect, it is shown that throughput is topology dependent rather than traffic load dependent, and multi-hopping is optimum for large networks whereas direct transmissions may increase the throughput for small networks. Viewed from energy aspect similar results are obtained: Under light traf- fic, energy spent during idle mode dominates in the energy model, making any routing strategy nearly optimum. Under moderate traffic, energy spent during idle and receive modes dominates and multi-hop transmissions become more advantageous as the optimum hop number varies with processing power consumed at intermediate nodes. At the very heavy traffic conditions, multi-hopping becomes unstable due to increased collisions and direct transmission becomes more energy-efficient.The choice of hop-count in routing strategy is observed to affect energyefficiency and goodput more for large and homogeneous networks where it is possible to use shorter hops each covering similar distances. The results indicate that a cross-layer routing approach, which takes energy expenditure due to MAC contentions into account and dynamically changes the routing strategy according to the network traffic load, can increase goodput by at least 18% and save energy by at least 21% in a realistic wireless network where the network traffic load changes in time. The goodput gain increases up to 222% and energy saving up to 68% for denser networks where multi-hopping with much shorter hops becomes possible.
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    ItemOpen Access
    Delay-bounded rate adaptive shaper for TCP traffic in DiffServ Internet
    (2002) Balkaş, Yakup
    Applications with different quality requirements set out the need for different Qualities of Service (QoS) to be provided in Internet. Differentiated Services (DiffServ) model is an architecture proposed to provide QoS in the Internet in a scalable way. Assured Forwarding Per Hop Behavior (AF PHB) is a QoS service class which provides a loss sensitive service. The DiffServ Service Provider (SP) delivers services to customers where traffic parameters are quantified in a Service Level Agreement (SLA). The incoming traffic from customers are policed in order to make sure that they meet the specifications in the SLA. The portion of traffic that is nonconformant with the SLA is not guaranteed to receive the service quality specified in the SLA. Shapers delay nonconformant packets in order to increase the ratio of traffic that is within the bounds specified in the SLA. If nonconformant traffic is tolerated in the SP network up to some extent, increasing the ratio of traffic that is complying with specifications in the SLA may lead to unnecessary delaying of packets and may decrease throughput. In this thesis, a shaper, called Delay-Bounded Rate-Adaptive Shaper (DBRAS), is introduced which tries to increase the ratio of traffic that conforms to the SLA while satisfying an upper-bound (Dmax) in the amount of delay it can apply to incoming packets (shaping delay). By avoiding unnecessarily large shaping delays, it is shown that throughput is increased. In order to have the shaper to adapt to changes in network topology, traffic, and different propagation delays, an adjustment algorithm is proposed where the shaper dynamically adjusts its Dmax value in order to increase throughput. The resulting shaper is called Dynamic DBRAS (D-DBRAS). The heuristic adjustment algorithm is greedy in that it adapts the maximum shaping delay in the direction where throughput increases. Results obtained from simulations show that throughput of TCP in AF PHB shaped by D-DBRAS can be increased by up to 65% compared with unshaped traffic. Simulations are performed in order to analyze effects of parameters such as propagation delay, buffer threshold levels, and offered traffic on the performance of D-DBRAS. It is also shown through simulations that by using the adjustment algorithm, the maximum shaping delay, Dmax, converges to regimes where throughput increases in response to changes in offered traffic.