6. Inter ISP Roaming for Vehicular Communications

HMM λ ^r = { π, A _ij ^r , B _j (k) ^r } (where r denotes geographical regions such that r = 1 to R) has been developed in the previous chapter. The developed model λ gives mathematical representation of 802.11-based vehicular communications. It has been demonstrated that the model λ can give a comparative evaluation of disruption in different areas in terms of state probability (SP) and encounter probability (EP). It has also been shown mathematically in the previous chapter that a high number of AP encounters correspond to a larger EP and hence reduced disruption. The encountered APs are either open or closed. Recall from Sect. 3.​3.​1 that the open APs can be accessed by the walkup users but the closed APs require user credentials before allowing the network access. In order to increase the number of APs encountered during a drive (and hence increase EP), the closed APs should also be made available to the vehicles. This would simply increase the number of usable APs encountered during a drive. One way to make use of the closed APs is through the inter ISP roaming. In a nutshell, inter ISP roaming allows the mobile nodes to use the resources of the ISP they are not originally subscribed to. Therefore, inter ISP roaming mechanism can open the previously closed APs to the vehicles, thus increasing the total number of usable AP encounters.