# Route Availability as a Communication Quality Metric of a Mobile Ad Hoc Network
## 1 Introduction  
In recent years, there has been a sharp increase in demand for video communication [1] and a widespread use of drones. Consequently, the need to study video communication in MANETs (mobile ad hoc networks) is growing. Since MANETs use ad hoc communication between mobile terminals, they do not depend on any communication infrastructure. They can be employed for urgent delivery of medical or emergency videos in the event of a disaster, or for multi-hop transfer of videos between drones. Thus, expectations are rising that they can be used for M2M (machine-to-machine) communication. However, unlike conventional networks, such as the Internet, MANETs can experience a degradation in communication quality due to a number of factors that increase instability, such as the radio environment, multi-hop communication, node mobility, and variations among communication terminals in remaining battery levels and performance.  
Metrics used to represent the data communication quality of MANETs are packet loss rate [2, 3] and throughput [2, 4, 5, 6], end-to-end delay [2, 5, 7, 8], and packet delivery ratio (PDR) [2, 4, 6, 7, 9]; these have been used in IP (Internet Protocol) networks. These are designed for application to data communication after communication routes have been established, and thus are not necessarily a suitable metric to assess the communication quality for networks like MANETs in which routes are not uniform because they are constantly disconnected and re-established as a result of node mobility. Regarding communication route establishment, routing overhead [2, 5, 7], path length [2], and path lifetime [8, 10, 11] are used as metrics to assess the performance of routing protocols and routes. For applications such as video streaming, in which the user's quality of experience is important, jitter [6] and MoS (Mean Opinion Score) [9, 12, 13] are also used in addition to the above metrics.  
The authors previously proposed a concept of route availability (RA) as a metric of route nonuniformity in a MANET and a calculation method of RA [14]. However, the network environment used to verify this calculation method was a simple one that simulated network disconnections and connections using the Netem [15] shell script. Thus, it did not incorporate node mobility and the procedure for route establishment using a routing protocol, which are main features of MANETs. The paper presented no method of measuring route feature values, which are needed to calculate RA based on the routing protocol. To further refine the concept of RA, in the current paper we build an environment that emulates a MANET capable of video streaming. We develop a method of calculating RA for two representative MANET routing protocols: AODV (Ad hoc On-Demand Distance Vector) [16] and OLSR (Optimized Link State Routing) [17]. We study the relationship between RA and conventional network quality of service (QoS) metrics (packet loss rate and throughput). Using a subjective quality assessment test of videos delivered in video streaming, we obtain the degradation mean opinion score (DMOS) and examine how it relates to the quality of experience (QoE) metrics. Section 2 summarizes related studies and indicates where the present research fits in relation to these studies. Section 3 presents an RA model and methods of measuring RA for AODV and OLSR. Section 4 describes the evaluation environment we have built. Section 5 presents the evaluation experiments we have carried out and discusses the experiment results. Finally, Section 6 gives conclusions.