# Route Availability as a Communication Quality Metric of a Mobile Ad Hoc Network
## 3 Route Nonuniformity Path Modelling
### Route Availability (RA) of a MANET  
Routing protocols for MANETs can be classified into a reactive type and a proactive type. A representative reactive routing protocol is AODV, which establishes a route only when a node that wants to establish a route has sent a route request message, called an RREQ (Route REQuest), and has received a route reply message, called an RREP (Route REPIy), from the destination node. An advantage of this protocol is that it requires fewer control messages than proactive protocols. A representative proactive routing protocol is OLSR, which constantly ensures that communication is possible by making nodes adjacent to each other exchange topology control (TC) messages periodically to keep their route information up to date. In a MANET, there is a procedure for nodes to discover  
Figure 1: Position of the present research. MANET: mobile ad hoc network; QoE: quality of experience; QoS: quality of service.  
adjacent nodes by exchanging HELLO messages periodically. However, this is only a supplementary procedure in AODV.  
The route between a sending node and its destination node is not always the same because relay nodes move, changing the network topology, and because nodes have different performance and different remaining battery levels. During application communication time, the route is disconnected and re-established in accordance with the routing protocol used--AODV or OLSR. Figure 2 shows an example of route state transitions in a MANET in which the sending node sends a video captured by a drone or a network camera to a smartphone, which is the destination node. State {path (t1)} is a state in which a route has been established. When a relay node involved departs from the established route, the route is disconnected. This is state {path (t2)}. Next, a new adjacent node that can serve as a relay node is discovered, and the route is re-established. This is state {path (t3)}. Note that the relay nodes involved in state {path (t1)} are not necessarily the same as those involved in state {path (t3)}.  
Since route nonuniformity frequently causes route disconnections, we focus on route connections and disconnections as state elements that characterize route nonuniformity. Changes in the route between the sending and destination nodes over time are shown in Figure 3. Figure 3 shows alterations of connected time and disconnected time of a route over communication time. A long connected time indicates that the route is stable, and a long disconnected time means that the route is unstable. The greater the ratio of connected time to the entire communication time, the more stable routes the network topology of the MANET provides. A large ratio of disconnected time is an indication that routes in that network topology are unstable. Thus, route availability can be calculated by measuring the percentages of total connected time and total disconnected time over communication time.  
From Figure 3, the total connected time and the total disconnected time are calculated using Equations (1) and (2), respectively, where \(m\) is the number of disconnections and \(n\) is the number of  
Figure 3: Changes in connected and disconnected states over time.  
Figure 2: Example of route state transitions in a MANET for video streaming.  
connections. The time from completion of route establishment to termination of data communication is defined as Equation (3). Using these, RA is defined as Equation (4).  
\[\text{Total connected time}\;(\text{C}_{\text{T}})=\sum_{i=1}^{n}c_{i} \tag{1}\]  
\[\text{Total disconnected time}(\text{D}_{\text{T}})=\sum_{i=1}^{m}d_{i} \tag{2}\]  
\[\text{Communication time}\;(\text{S}_{\text{T}})=\text{C}_{\text{T}}+\text{D}_{ \text{T}} \tag{3}\]  
\[\text{RA}=\;\text{C}_{\text{T}}/\text{S}_{\text{T}} \tag{4}\]