# Evaluation of VoIP QoS Performance in Wireless Mesh Networks
## 2 VoIP Application and Scenarios
### VoIP Implementation Scenarios
#### 2.2.1 Emergency Relief Deployment  
In case of emergency situations, the most vital means of communication is voice communication [40]. In such cases, affected people and those who approach them to provide help, directly turn to voice calls [41]. In some countries and regions, VoIP services must be connected with the emergency services like in the USA (911), Europe (112 [42]), or the United Kingdom (999 [43]). Hence, all public and private computer network installations with the need for voice communication should provide VoIP services with integration to the emergency services.  
VoIP could be the main means of communication or the backup system to an existing wired connection; in case of large-scale disasters, regular communication systems are also damaged and not responsive, as happened during Hurricane Katrina in the United States [44]. Security of the WMN in case of disaster is also a concern and various security solutions are reviewed in [40]; however, this aspect is not in the scope of this paper. In most emergency cases, the terrain, distance among nodes and number of nodes make each scenario different. Some main emergency scenarios are explained in detail in next paragraphs. The only challenging issue with VoIP over IP networks is the nodes location  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Solution Name** & **Advantages** & **Limitations** \\ \hline \multirow{4}{*}{Packet aggregation [30]} & Avoids redundant packet headers, improves VoIP quality to some extent in special cases & Packetization and de-packetization delay is added. Takes more time to route large packets. Packetizing the packets travelling to different destinations is difficult in the relay nodes \\ \hline \multirow{2}{*}{Priority schedulers [33]} & Improves VoIP performance to some extent & In case of a continuous flow, creates problem for low priority packets; does not work well for high loads \\ \hline \multirow{2}{*}{Load-aware mobility [10]} & Load balancing of mesh nodes & Association phase gets delayed; does not perform well for high loads \\ \hline \multirow{2}{*}{Gateway placement [34]} & Improves performance for a limited number of hops and if the nodes are communicating to external nodes & Does not solve the problem of mesh nodes communicating internally. \\ \hline Traffic allocation for delay variation optimization & Improves the delay factor using multiple paths and preferring paths with least amount of delay & This type of routing adds extra load. Puts route under continuous computation process \\ \hline \multirow{4}{*}{QoS Aware routing [36]} & \multirow{4}{*}{Prefers routes with least amount of load} & Segmentation and use of several routing protocols adds to network complexity. May not work with high number of nodes due to multicasting function \\ \hline Secure routing with QoS amplification SRQA [37] & Solves interference issues & Only addresses signal to noise ratio \\ \hline \multirow{2}{*}{Local packet recovery [38]} & Recovering sporadic and link failure packet loss & Only addresses packet loss factor \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._reporting, which is not directly provided to the emergency services and requires the caller to report its location to the emergency team verbally. Alternatively, the service could be integrated with GPS and the exact location could be reported via purpose-built applications for disaster relief situations [45].