An IP passing protocol for vehicular ad hoc networks with network fragmentation

When a vehicle is moving fast in a highway, how to effectively reduce the handoff delay and maintain the connectivity of the vehicle to the Internet is an important issue. The existing IP passing protocol may be able to reduce the handoff delay and maintain the connectivity of the vehicle to the Internet when all the vehicles are connected. However, when the vehicle density is low or the speeds of vehicles are varied, the vehicle may not be able to communicate with the intended vehicle either directly or through multi-hop relays because of network fragmentation. Hence, when network fragmentation occurs, a vehicle cannot pass its IP address to the intended vehicle through existing IP passing protocols and thus incurs longer handoff latency and higher packet loss rate, and these would lower down the throughput of the network. To improve existing IP passing protocols, we propose an IP passing protocol for VANETs with network fragmentation. The proposed protocol can postpone the time to release IP addresses to the DHCP server (extend IP lifetime) and select a faster way to get the vehicle’s new IP address. During the extended IP lifetime, the vehicle can acquire an IP address through multi-hop relays from the vehicles on the lanes of the same or opposite direction, and thus reduces handoff delay and maintain the connectivity to the Internet. Simulation results have shown that the proposed scheme is able to reduce IP acquisition time, handoff latency, packet loss rate, and extend IP lifetime.