The Impact of Routing Protocols on the Performance of TCP in VANETs

Due to its implementation maturity, TCP is regarded as the de facto reliable transport protocol for Vehicular Ad Hoc Networks (VANETs). However, assumptions made at TCP's inception reflected characteristics of the prevalent and reliable infrastructure of wired networks where congestion is the main cause of packet loss. In Contrast, VANETs are characterized by high vehicles' velocities, this can give rise to frequent network disconnections, resulting in packet loss which is not caused by congestion. Nonetheless, TCP still interprets such packet loss as a sign of congestion, and consequently reduces its sending rate unnecessarily, leading to network performance degradation. This paper investigates using simulations the intricate interaction between a typical representative TCP variant namely TCP NewReno and three popular routing protocols namely AODV, DSR and OLSR over a platoon of vehicles on a highway in scenarios involving consistent and frequent route failures. Our study aims to shed some insight into the behaviour of TCP and routing protocols, and provides a clear assessment of system performance in such constantly occurring route breakages. Our simulation results reveal that the detrimental performance effects of the consecutive RTOs of TCP are more pronounced for OLSR, and to a lesser extent for AODV. Our results also indicate that DSR is the most immune to such effects in most considered scenarios.