Toward end-to-end control in VANETs

In emerging non-safety unicast applications of vehicular ad hoc networks (VANETs) such as Internet Access, Content, Map, or Database Download (CMDD), end-to-end (e.g., connection-oriented) transmission control must be employed to guarantee a desired level of performance. Designing a Transport Control Protocol (TCP) in VANETs is a very challenging task as the end-to-end data transmission involves multi-hop wireless transmission. The mobility and wireless channel conditions (such as fading, shadowing, multipath, etc.) exacerbate the well-known problems of using TCP over wireless links. In this paper, it is shown that casting the end-to-end flow control as a routing problem whereby the stability of each link is ensured in a dynamic fashion is a powerful approach to guaranteeing the stability of a multi-hop end-to-end route. Unlike the existing bottom-up approaches, a cross-layer design paradigm whereby the network layer utilizes the transport layer information in making routing decisions is shown to be beneficial. Finally, a new VANET Transport Control Protocol is proposed which can detect packet losses, identify the different causes of such losses (such as congestion, disconnection due to mobility, wireless channel conditions), and resolve such problems using different and suitable mechanisms for each case. The proposed new approach seems very promising for delay-tolerant applications such as Instant Messaging and Internet Access as it can support end-to-end control in these applications for up to 5 hops.