This paper provides an analytical framework for estimating the routing overhead due to mobility and link breakage. Detailed analysis is presented for estimating the number of control packets (RREQ, RREP and RERR) as a function of time, number of nodes, node degree, transmission range, mobility of nodes, average hop count and link density. In order to validate the proposed model, two on-demand routing protocols namely ad hoc on demand distance vector (AODV) routing and dynamic source routing (DSR) are analyzed and compared in terms of normalized load. The quantitative and simulation results presented in this paper are useful for selecting a suitable on-demand routing protocol and for designing novel and efficient routing protocols for ad-hoc wireless networks.