Abstract-While several cluster based routing algorithms have been proposed for ad hoc networks, there is a lack of formal mathematical analysis of these algorithms. Specifically, there is no published investigation of the relation between routing overhead on one hand and route request pattern (traffic) on the other. This paper provides a mathematical framework for quantifying the overhead of a cluster-based routing protocol. We explicitly model the application-level traffic in terms of the statistical description of the number of hops between a source and a destination. I. INTRODUCTION Ad hoc networks are comprised of nodes that perform multi hop packet forwarding over wireless links. The routing protocols for ad hoc networks can be divided into two categories based on when and how the routes are discovered: proactive and reactive. In proactive routing protocols, consistent and up-to-date routing information to all nodes is maintained at each node, whereas in reactive routing the routes are created only when needed. In this paper, we focus on reactive routing protocols.To support large scale ad hoc networks, numerous clusterbased routing algorithms have been proposed [1], [2]. In cluster-based routing, the network is dynamically organized into partitions called clusters with the objective of maintaining a relatively stable effective topology. The membership in each cluster changes over time in response to node mobility, node failure or new node arrival. Clustering techniques are expected to achieve better scalability since most of the topology changes within a cluster are hidden from the rest of the network. However, clustering incurs a cluster maintenance overhead, which is the amount of control packets needed to maintain the cluster membership information.In hierarchical routing protocols, intra-cluster (inter-cluster) routing refers to the routing algorithm used to find a route between a source and destination within the same (belonging to different) clusters. Typically, inter-cluster routing is reactive while intra-cluster routing is proactive.In this paper, we develop an analytical model that captures the essential characteristics of cluster-based routing