We present a novel approach for minimizing the energy consumption of medium access control (MAC) protocols developed for duty-cycled wireless sensor networks (WSN) for the unslotted IEEE 802.15.4 standard while guaranteeing delay and reliability constraints. The main challenge in this optimization is the random access associated with the existing IEEE 802.15.4 hardware and MAC specification that prevents controlling the exact transmission time of the packets. Data traffic, network topology, MAC, and the key parameters of duty cycles (sleep and wake time) determine the amount of random access, which in turn determines delay, reliability and energy consumption. We formulate and solve an optimization problem where the objective function is the total energy consumption in transmit, receive, listen and sleep states, subject to constraints of delay and reliability of the packet delivery and the decision variables are the sleep and wake time of the receivers. The optimal solution can be easily implemented on existing IEEE 802.15.4 hardware platforms, by storing light look-up tables in the receiver nodes. Numerical results show that the protocol outperforms significantly existing solutions.
Dynamic Source Routing (DSR) is an efficient on-demand routing protocol for ad hoc networks, in which only needed routes are found and maintained. Route caching is necessary to avoid the need for discovering a route before each data packet is sent. The best cache structure is the link cache, which, in contrast to path cache, effectively utilizes all of the information that nodes have the potential to learn. Because of mobility, cached links might become stale. A mechanism to delete invalid links from the cache is necessary. The goal of this work is to develop a caching strategy that permits nodes to update their cache, when the topology of the network changes. To achieve it, all reachable nodes that have cached a broken link are notified when it fails. The designed caching strategy and the normal operation of DSR are compared showing that our approach outperforms the DSR protocol.
SUMMARYThis paper presents a new numerical method to analyse steady-state TCP throughputs in DiffServ networks. Different TCP models are briefly reviewed, and a Markov chain is used to capture the behaviour of a multirandom early detection (RED) queue. The established closed network model couples models for TCP, marking device and multi-RED queue. We assess accuracy and limits of the technique, and apply it for a discusion of parameter settings for marking devices.
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