Providing forwarding assurance in multi-hop wireless networks

The Assured Forwarding (AF) service in a differentiated services network offers different levels of forwarding assurance for IP packets. In the wired Internet, the AF service is implemented as a queue management scheme associated with a drop policy in each router. In multi-hop wireless networks, however, queue management in each node is not enough to provide service differentiation globally since resource is shared among neighboring nodes. Hence, several studies for the AF service in wireless networks have proposed to manipulate the contention window size to provide service differentiation. The contention window size based differentiation scheme provides the AF service by transmitting packets in a higher class with a smaller contention window. However, since network congestion in multi-hop wireless networks causes packet losses at the link layer, the contention window size based differentiation scheme is not sufficient to provide the AF service. In this paper, we propose a rate control scheme to control load on the shared channel by adjusting sending rate according to the estimated channel state and the amount of AF traffic. We further propose a RTS retry limit adaptation scheme to compensate the rate control scheme when the accurate estimation of the channel state is not easy. Throughout extensive simulations, we show that proposed schemes are effective to differentiate forwarding assurance in multi-hop wireless networks. ∗A preliminary version of this paper has been presented in IEEE MASS 2008.