Effect of content popularity, number of contents and a cellular backup network on the performance of content distribution protocols in urban VANET scenarios

Different types of infotainment and traffic efficiency applications make use of content distribution protocols in vehicular networks. Current research on content distribution has been focused on designing efficient protocols, but it has put little effort in modeling the nature of the applications that consume and generate those contents, or in studying the internetworking with cellular networks. This paper studies the effects of application characteristics on the performance of push- and pull-based content distribution protocols in VANETs. In particular, it considers the total number of contents being distributed, the popularity of those contents, and the utilization of a cellular backup network to guarantee a level of service for delay-bounded applications. We also propose the Multi-Hop To Infostation (MHTI) protocol: a pull-based, multi-hop protocol that sends content requests towards the closest infostation. Requests can be satisfied before reaching the infostation by any vehicle in the path that has cached the requested content. Our analysis indicates that the performance of push- and pull-based protocols is only satisfactory in scenarios with a low number of contents or highly popular ones, while MHTI also exhibits a good performance with a large number of contents, and it takes advantage from different content popularities to obtain a high number of contents through the VANET.