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Abstract

Call Admission Control is one of the main mechanisms allowing an efficient protection of active flows, especially on a wireless network using a distributed access scheme as is the case for IEEE 802.11e EDCA. We proposed in a previous paper [7] a hybrid admission control algorithm (based on analytical model and on measurements) for EDCA which have proven to perform well when compared to another reference algorithm. We present here general modifications to hybrid admission control algorithms. These modifications are applied to our proposed algorithm and analyzed via simulation. Analysis clearly shows the advantages of these modifications.

Abstract

In this paper, we address the problem of route fragility in backhaul wireless mesh networks. Mesh routing protocols rely on intermediate nodes in the multihop path to forward data and detect route breakage. An intermediate node reports the link to next hop as broken after a fixed number of unsuccessful packet transmission attempts at the MAC layer. Transmission failure of a single packet on any link in the multihop path thus renders the route unusable. In practice, many transmission failures are isolated and temporary, caused by transient congestion on the wireless link. False route failures triggered by temporary transmission failures render otherwise good routes as unusable and degrade performance. We propose a novel route maintenance mechanism Congestion Aware Routing (CAR) which addresses this problem and makes a more "informed" decision about the link status. CAR uses estimation of medium congestion and the frequency and distribution of link failures to distinguish between broken (or poor quality) links from those experiencing temporary losses. Simulation results for TCP traffic show that CAR can provide up to 15% higher throughput, 50% delay reduction with 8 times smaller routing overhead.

Mots-Clés / Keywords

Abstract

One of the main Quality of Service mechanisms, allowing mainly the protection of already active flows, is admission control. This is even truer on the MAC level of 802.11 based networks due to scarce resources. We present in this paper a hybrid admission control algorithm for IEEE 802.11e EDCA. The algorithm uses the synthetic Markov chain model of EDCA that we developed in previous work injecting into it network state measurements. Simulations and results presented in this paper show a good protection of admitted flows and a good utilization of the network resources.

Abstract

This paper proposes a very simple reduced abstract model of the behavior of the EDCA (Enhanced Distributed Channel Access) access mode with respect to an access category under saturation. This model is derived from a Markov chain model of EDCA using reduction techniques. Closed-form expressions of common performance metrics (i.e. mean throughput, mean access delay and packet drop probability of an access category) are given and insight into the potential applications of this model are briefly presented.

Abstract

Wireless Mesh Networks offer promising solutions for extending the coverage of wireless local area networks along with increased communication reliability. The wireless mesh backbone serves as an access network for a large number of heterogeneous networks, providing them internet connectivity. Comprising of dedicated routers, the backbone differs significantly from conventional ad hoc networks due to lack of mobility and energy constraints. Classical ad hoc routing protocols developed for typical ad hoc networks, concentrate on mobility and energy conservation and their suitability and possible adoption for the backbone warrants careful evaluation. In this paper, we analyze the performance of four popular ad hoc routing protocols including two reactive (DSR, AODV) and two proactive (OLSR, DSDV) protocols for the mesh backbone using simulation. We provide results for routing overhead, packet delivery fraction and end-to-end delay metrics. Optimizations for these protocols are proposed and design directions for future backbone routing protocols are outlined.

Mots-Clés / Keywords

Abstract

IEEE 802.11e specifies the Enhanced Distributed Channel Access (EDCA) for distributed access with traffic differentiation to a Wireless Local Area Network (WLAN). Traffic differentiation led to introducing several traffic queues within each station, thus introducing virtual collision. In this paper, we present a pattern based Markov chain model of EDCA including the virtual collision phenomenon not found in previous work. We also correct the misconceptions found in existing Markov chain models of EDCA (Kong et al., 2004). We thus obtain a more realistic model of IEEE 802.11e EDCA which will allow a more precise performance analysis that may be used for admission control.

Mots-Clés / Keywords