I mean which addresses are used for sending messages, logical or physical? how vehicles are identified uniquely? I am having confusion ,please clear my doubts?
Just think how your wifi or wireless network (or bluetooth device) works.. or just think how you connect two laptops when you dont have an internet connectivity. You will be using the physical address right? this itself is the basic principle behind VANETs also. Since it is an ad-hoc network it is always basically deepening on your physical address (unique) of the machine. But today vehicles use TCP/IP to communicate with centralized servers through cellular networks. However many vehicular applications, such as information sharing for safety and real time traffic purposes, desire direct V2V communications which is difficult to achieve using the existing solutions. Hence we can go for the concept of Information Centric Networking (ICN) or Named Data Networking (NDN) [Ref.: Data naming in Vehicle-to-Vehicle communications].
Just see the following papers
Content Routing In the Vehicle Cloud
Vehicular Cloud Networking: Architecture and Design Principles
Networking Named Content
Exploiting the Wisdom of the Crowd: Localized, Distributed Information-Centric VANETs