Update Message Delay: An Approach for Improving Distance Vector Routing in Wireless Ad Hoc Networks Ralph Jansen, Sven Hanemann and Bernd Freisleben Department of Mathematics and Computer Science, University of Marburg Hans-Meerwein-Str., D-35032 Marburg, Germany E-Mail: {jansen,hanemann,freisleb}@informatik.uni-marburg.de Abstract An ad hoc network is a collection of mobile nodes with wireless communication facilities forming a temporary net- work without relying on any existing infrastructure. Limited available bandwidth and highly dynamic network topology due to continuously moving nodes require dedicated rout- ing algorithms to achieve reliable communication. In this paper, we present an approach to improve the bandwidth consumption of proactive ad hoc routing algorithms by ap- propriately delaying particular routing messages. The pro- posal is analyzed via simulations, and it will be shown that message reductions are possible if the update message de- lay method is used by a distance vector algorithm within an ad hoc network. Keywords: wireless networks, ad hoc networks, routing pro- tocols, distance vector routing Corresponding author: Bernd Freisleben 1 Introduction Wireless ad hoc networks consist of an ensemble of mo- bile nodes operating in a particular area without using any existing infrastructure. Each mobile node acts as an in- termediate router forwarding messages received by other nodes. Thus, a wireless ad hoc network is only operational if nodes offer their forwarding capabilities to other nodes. The special conditions of wireless communication like lim- ited transmission range, limited bandwidth and possible in- terference require dedicated routing algorithms. Many rout- ing protocols show their least desirable behavior when pre- sented with these conditions. Routing protocols for wireless ad hoc networks can be broadly classified into reactive and proactive algorithms. Reactive routing algorithms rely on flooding to establish new routes that replace invalid routes due to node move- ment. Proactive routing algorithms usually constantly up- date routing tables among nodes. Both methods consume a certain percentage of the available bandwidth for routing purposes, which increases with node movements. Existing reactive routing algorithms like DSR [9] and AODV [12] invoke their route determination procedure only on demand through a query/reply approach. They have been optimized by computing multiple and link disjoint paths during the initial path finding process [10, 14] to counter the increasing bandwidth demands caused by route finding and establishment for rising node movement speeds. Another approach [4] is to add proactive route maintenance and se- lection methods to a reactive routing protocol like DSR to reduce the number of broken paths. However, bandwidth consumption is increased with this approach. Proactive routing algorithms like DSDV [11] or WRP [8] maintain routes between nodes all the time. In fact, most protocols try to maintain shortest paths all the time. A consequence of maintaining shortest paths is that if the net- work topology changes, the control overhead increases sig- nificantly. Several protocols have been proposed that avoid this problem by reduced path optimization or by adapting existing protocols (e.g. WRP-Lite [13]) to use paths as long as they are valid and update them only when a path becomes invalid (so called event driven updates). In this paper, we present a new approach to further re- duce bandwidth consumption of distance vector routing algorithms based on the tree exchange routing algorithm (TERA) which we have previously developed to achieve fast convergence, avoid the count to infinity problem and eliminate routing loops quickly [7,15]. TERA limits path optimization to a user defined level, which prevents the re- peated recalculation of already known routes at minor topol- ogy changes. Since TERA is a proactive algorithm, it ini- tiates routing message “waves” starting at one point and propagating through the network whenever a route is lost,