A link-state based on-demand routing protocol supporting real-time traffic for wireless mobile ad hoc networks

Abstract

Wireless ad hoc networks have gained a lot of popularity since their introduction and as many wireless network interface cards provide support for ad hoc networking, such networks have also seen real-life deployment for non-specialized purposes. Wireless mobile ad hoc networks (MANETs) are currently the most common type of ad hoc networks, and such networks are especially esteemed for their mobility support and ease of deployment due to their ad hoc nature. As most common network applications, such as the Web, FTP, email, and instant messaging, are data-centric and do not operate under strict time constraints, MANETs have been deployed to enable such non-real-time applications in the past. However, with the increasing use of real-time applications over ad hoc networks, such as teleconferencing, VoIP, and security and tracking applications where timeliness is of importance, real-time traffic support in multi-hop wireless mobile ad hoc networks has become an issue. We propose an event-driven, link-state based, on-demand routing protocol to enable real-time traffic support in such multi-hop wireless mobile ad hoc networks. Our protocol, which is named Elessar, is based on link-state topology dissemination, but instead of the more common periodic link-state messaging scheme, we employ event-driven link-state messages in Elessar, where topology changes are the events of interest. Through such an approach, we aim to lower the overhead of our protocol, especially for low-mobility cases, which is currently the most commonly encountered case with ad hoc networks deployed with machines directly interacting with humans, such as PDAs and laptops. Due to its link-state nature, our protocol is able to support non-real-time traffic without any further action. In order to support real-time traffic, however, we employ a direct cost dissemination mechanism, which only operates on-demand when there are one or more real-time flows in the network. We aim to provide soft quality-of-service (QoS) guarantees to real-time flows through intelligent path selection, without any resource reservation. We also aim to provide such QoS guarantees throughout the lifetime of a real-time flow, even in the face of node failures and mobility, by dynamic path adaptation during the lifetime of the flow. Elessar is able to support real-time and non-real-time traffic concurrently, as well as various different types of concurrent real-time traffic, such as delay- and loss-sensitive traffic. Our protocol, therefore, does not aim to support a single type of real-time traffic, but rather a plethora of different types of real-time traffic. Elessar is completely distributed, dynamic and adaptive, and does not require the underlying MAC protocol to be QoS-aware. We analyse our design choices and the performance of our protocol through realistic simulation experiments conducted on the OMNeT++ discrete event simulation platform, using the INET framework. We have used the IEEE 802.11b MAC protocol during our simulations and have employed the random waypoint mobility model to simulate mobility. Our experimental results show that Elessar is able to efficiently provide real-time traffic support for different types of traf- fic flows, even in the face of mobility. Our protocol operates best for smallto-medium-sized networks where mobility rates are low-to-medium. Once the mobility rate exceeds a certain threshold, intelligent path selection cannot cope satisfactorily with the high dynamism of the environment and the overhead of Elessar exceeds acceptable levels due to its event-driven link-state nature.