## 2 Related Works
### Gateway
The gateway placement strategy is to minimize the total cost of gateway deployment, while ensuring that a vehicle can connect to an internet gateway (using multi-hop communications) with a probability greater than a specified threshold. This cost-minimization problem is formulated using binary integer programming, and applied to a realistic city scenario, consisting of the roads around the University of Waterloo, Waterloo, ON, Canada. On the other hand, the developed packet routing scheme is based on a multichannel medium access control protocol, known as VeMAC, using time division multiple access. The performance of this cross-layer design is evaluated for a multichannel VANET in a highway scenario, mainly in terms of the end-to-end packet delivery delay. The end-to-end delay is calculated by modeling each relay vehicle as a queuing system, in which the packets are served in batches of no more than a specified maximum batch size [7]. [PERSON] et al. proposed the connectivity-aware minimum-delay geographic routing (CMGR) protocol for vehicular ad hoc networks (VANETs), which adapts well to continuously changing network status in such networks. When the network is sparse, CMGR takes the connectivity of routes into consideration in its route selection logic to maximize the chance of packet reception. On the other hand, in situations with dense network nodes, CMGR determines the routes with adequate connectivity and selects among them the route with the minimum delay. The performance limitations of CMGR in special vehicular networking situations are studied and addressed. These situations, which include the case where the target vehicle has moved away from its expected location and the case where traffic in a road junction is so sparse that no next-hop vehicle can be found on the intended out-going road, are also problematic in most routing protocols for VANETs. Finally, the proposed protocol is compared with two plausible geographic connectivity-aware routing protocols for VANETs, A-STAR, and vehicle-assisted data delivery (VADD) [8]. [PERSON] et al. proposed a new combinatorial optimization problem that arises from the framework of rule-based risk mitigation policies for the routing of gateway location problem (GLP) hazardous materials vehicles. GLP consists of locating a fixed number of check points (so called gateways) selected out of a set of candidate sites and routing each vehicle through one assigned gateway in such a way that the sum of the risks of vehicle itineraries is minimized. This paper addresses a GLP preparatory step, that is, how to select candidate sites, and it investigates the impact of different information guided policies for determining such a set. All policies consist of selecting a ground set and sampling it according to a probability distribution law. A few criteria are proposed for generating ground sets as well as a few probability distribution laws. A deterministic variant based on a cardinality constrained covering model is also proposed for generating candidate site sets [9]. [PERSON] et al. proposes a synchronization mechanism for FlexRay and Ethernet audio video bridging (AVB) network that guarantees a high quality-of-service. Moreover, this study uses an in-vehicle network environment that consists of FlexRay and Ethernet AVB networks using an embedded system, which is integrated and synchronized by the gateway. The synchronization mechanism provides the timing guarantees for the FlexRay network that are similar to those of the Ethernet AVB network. Figure 1 shows the use of the Ethernet AVB switch to communicate between the event-based CAN protocol and the timing-based FlexRay protocol [10]. [PERSON] et al. proposed a reliable quality of service (QoS) aware and location aided gateway discovery protocol for vehicular networks by the name of fault tolerant location-based gateway advertisement and discovery. One of the features of this protocol is its ability to tolerate gateway routers and/or road vehicle failure.