The Performance of Wireless Mesh Networks with Apparent Link Failures

Abstract

A wireless multi-hop network is a network consisting of a group of nodes interconnected by the means of wireless links. The nodes in such a network, which are often self-configured and self-organized, communicate with each other over multiple hops through a routing protocol. Examples of such networks include Wireless Mesh Networks (WMNs) IEEE802.11s (2010), Mobile Ad Hoc Networks (MANETs) Chlamtac et al. (2003) and Wireless Sensor Networks (WSNs) Gharavi & Kumar (2003). The performance and the reliability of these networks depend heavily on the routing protocol’s capability to detect link failures between neighboring nodes as well as its link-maintenance mechanism to recover a path from source to destination when a link-failure happens. While MANETs generally appear more dynamic due to node mobility, the network topology for WMNs and WSNs remains comparatively stable. No matter which network form is concerned, however, these networks exhibit ad hoc features since wireless links are intrinsically unreliable. In the majority of cases, link failures are present in a multi-hop network regardless of the use of link-maintenance mechanisms. Sometimes link failures are unavoidable, such as when a mobile node deliberately leaves a network or is subject to the exhaustion of its battery power. In another case a link would cease to be operative when two nodes move outside each others’ radio transmission range. In addition to these, a set of link failures which we refer to as apparent link-failures exist. They are primarily caused by radio links being vulnerable to radio induced interference, but also appear when a link-maintenance mechanism erroneously assumes a link to be inoperable due to loss of beacons. A beacon is a short packet transmitted periodically to a node’s one-hop neighbors and its purpose is to detect neighbors and to keep links alive. Beacons are normally broadcast, and are thus not acknowledged, i.e. they are unreliable and vulnerable to overlapping transmissions from hidden nodes Tobagi & Kleinrock (1975). Moreover, common protection mechanisms against hidden nodes (such as RTS/CTS of the IEEE 802.11 MAC protocol IEEE802.11 (1997)) are not applicable, since unicast data transmission using RTS/CTS will only provide protection for packet reception at the node that issued the CTS.