Thesis title: Disruption Tolerant Networking over IEEE 802.11 WLANs
802.11 Wireless LANs were first introduced in late 1990s to provide wireless network services. 802.11 networks use a small base station, an Access Point (AP),which provideswireless connectivity to the mobile nodes. Over the years WLANs have seen massive deployment across most of the developed cities in both domestic and commercial sectors, for example, in houses, shopping malls, airports, etc. The coverage region of a WLAN AP is small, and is typically restricted to a certain indoor area. Because of the limited coverage area, WLANs do not offer network services in the outdoor environments. However, the idea of using these already available 802.11 APs from outdoor environments has recently come under scrutiny. The research community is interested in examining the use of these indoor APs from fast moving vehicles. The use of Information and Communication Technologies (ICT) from vehicles is envisaged to support on-road safety applications and broadband services on the move. Using 802.11 APs from vehicles is challenging because they are not inherently designed to support outdoor services. Among the various challenges associated with 802.11-based vehicular communications, this thesis focuses on two key issues, namely disruption and handover latency.
Although WLAN APs exist in large numbers across the roads in most developed cities, the placement of these APs is highly unplanned. Due to this unplanned deployment, WLAN APs cannot support continuous connectivity over a large mobility domain. A vehicle trying to use such opportunistically encountered APs faces periods of connectivity and disconnectivity on the move. In the vehicular context, this irregularity is called disruption. While some previous works have focused on reducing disruption, this thesis explores a completely new research direction - mathematically modelling disruption. A mathematical model has been developed that can measure disruption and comparatively analyze different areas of the city in terms of irregularity in the network services. Secondly, a vehicle spends very little time within the footprint of an AP, most of which is wasted in executing lengthy handover procedures. Therefore, the second major challenge is to reduce the handover latency so that the vehicles can make quick connections with the APs encountered during a drive. This work performs experimental delay analysis and proposes modifications in the conventional procedures to enable fast handovers.