# DMRVR: Dynamic Milk-Run Vehicle Routing Solution Using Fog-Based Vehicular Ad Hoc Networks
## 3 DMRVR Solution
### Vehicular Network Model  
The two main features in GeoNetworking are addressing and routing/forwarding. Due to special requirements for information dissemination, GeoNetworking uses a slightly modified approach for addressing compared to most modern networks. The target receivers of a data packet may be specified by the following addressing schemes:  
* **GeoUnicast**: is a scheme similar to the common unicast. The unique node identifier and the node geographic position are used to route the packet towards the destination. If the location of the destination is not known by the original node, this information is acquired by the location service [21; 22];
* **Topological Broadcast**: this scheme addresses all nodes that can be reached with most \(n\) hops. The process is similar to common broadcast, with the addition of a distance control feature for the dissemination [21; 22]. * **GeoAnycast and GeoBroadcast**: these schemes address at least one or all nodes inside a specified destination area, respectively. The destination area is defined and provided by the upper network layer of the sender that makes the request [21; 22; 48]. Figure 2: Dynamic Milk-run strategy. The routing and forwarding operations may have different characteristics, depending on the type of addressing scheme, which demand specific algorithms. Routing protocols are one of the principal elements of vehicular networks, and they allow message routing in different conditions [49]. The line forwarding process is used at different moments by GeoUnicast, GeoBroadcast, and GeoAnycast addressing schemes. In GeoUnicast, the packet must be forwarded to the destination node location. In GeoBroadcast and GeoAnycast, if the sender node is not in the destination area, the line forwarding is used to route the packet until it reaches the destination area. Once the packet reaches the destination area, GeoBroadcast can use different flooding algorithms [21; 22; 48; 50]. Line forwarding can use two basic approaches [21]: Greedy Forwarding (GF) and Contention-Based Forwarding (CBF). In greedy forwarding, the next hop is selected explicitly by the current forwarder (sender-based approach). In contention-based forwarding, the selection is made implicitly among all candidate nodes through a decentralized coordination function (receiver-based approach). To improve the GeoBroadcast flooding efficiency, CBF can also be used. The proposed solution relies on a hybrid vehicular network architecture, where V2V and V2I communications take place. RSUs are placed at the logistics operator, at the suppliers, and at some strategic locations. They offer higher communication coverage and intermediary nodes for the message dissemination protocol. Figure 3 illustrates the DMRVR solution. For communication technology, DMRVR adopts ETSI ITS-G5 and the IEEE 802.11p standards. The logistics operator and pickup vehicles perform the solution by acting as fog nodes. The other vehicles on the road and RSUs are considered fog relays. Without using the Internet, the _LogisticsService_ application sends messages to the _VehicleService_ through the IEEE 802.11p network. Unicast protocols are unsuitable for reliable communication because of the head of line blocking problem in vehicular networks. This problem occurs when a node sends messages to an unavailable node in the network [51]. The use of a topologically-scoped broadcast protocol also does not meet the proposed solution requirements because the amount of hops is set when the message is sent. The message may not reach the destination node. Thus, this protocol is more used in applications where the number of hops is small. Figure 3: DMRVR solution. Due to the issues mentioned above, the DMRVR solution applies the message dissemination GeoBroadcast protocol defined by ETSI ITS-G5 [22,48,50]. This protocol broadcasts messages to a targeted area. Only the destination nodes (pickup vehicles) can understand the message.