# Route Availability as a Communication Quality Metric of a Mobile Ad Hoc Network
## 3 Route Nonuniformity Path Modelling
### How to Measure Route Feature Values for RA Calculation
#### 3.2.2 How to Measure Route Feature Values for OLSR  
OLSR 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. As shown in Figure 5, connected time and disconnected time can be measured based on the time when additions to or deletions from the route entry occurred at the source node, as is the case with AODV. Additions or deletions occur when TC messages are sent. If TC messages are sent at long intervals,  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Previous Event** & **Latest Event** & **Processing** \\ \hline Addition to the entry & Addition to the entry & Treated as an exception \\ Addition to the entry & Deletion from the entry & Connection \\ Deletion from the entry & Addition to the entry & Disconnection \\ Deletion from the entry & Deletion from the entry & Treated as an exception \\ \hline \hline \end{tabular}
\end{table}
Table 2: Determination of connection/disconnection for AODV (Ad hoc On-Demand Distance Vector).  
Figure 4: Sequence of measuring route feature values for Ad hoc On-Demand Distance Vector (AODV). (a) Measurement triggers with Route REPIies (RREPs) and Route ERRors (RERs); (b) Measurement triggers with HELLOs.  
failures to detect disconnections or to find a route that can be established may occur. In such cases, disconnections and connections as determined based on additions and deletions can be different from actual disconnections and connections. Impacts of failures to detect disconnections are considered in Section 5. Determination of disconnections and connections based on entry updates with HELLOs is similar to that for AODV shown in Figure 4b. However, with OLSR, entry updates with HELLOs can occur even if one relay node is involved. The sequence for a case involving one relay node is shown in Figure 5b.  
As with AODV, route connections and disconnections are determined based on the combination of the previous event and the latest event as shown in Table 3. Consecutive additions or consecutive deletions are treated as exceptions. An event once used is not used in the next attempt to determine connection or disconnection. With OLSR, an addition occurs when the relay node moves and the route used changes as a result. Therefore, an addition that follows an addition is not treated as an exception. Rather, it is determined that the route used has been changed. The period between an addition and the next deletion is judged to be connected time. Conversely, the period between a deletion and the next deletion is judged to be connected time. The period between a deletion and the next deletion is judged to be connected time.  
Figure 5: Sequence of measuring route feature values for Optimized Link State Routing (OLSR). (a) Measurement triggers with topology control (TC) messages; (b) Measurement triggers with HELLOs for a case involving one relay node.  
addition is treated as disconnected time. An exception is a case where an unexpected combination of events occurs. When this happens, an alarm is issued and the processing is stopped. The end of communication is defined as the time when the application of the sending side is closed.