VoIP Call Simulation over Wireless Local Area Network

Information Engineering
Huda Mohammad Khalid Abdul Wahid

Two of the major developments reshaping the telecommunication landscape are mobile wireless connectivity and the migration of voice telephone services to IP technology. These two ideas come together in networks that carry voice services over a wireless LAN (VoWLAN). However, the intrinsic characteristics of each of them cause specific issues to appear that must be addressed in order to ensure a successful deployment.
In this thesis, a Cross layer Call Admission Control (CCAC) scheme is modified and used to enhance VoWLAN performance. This scheme consists of three parts. The first part monitors the MAC layer for any change in the transmission rate. The second one is a call admission control part and the third is responsible for monitoring the Real Time Control Protocol Receiver Reports (RTCPRRs) at the application layer for any degradation in VoIP quality in case of handoff or congestion.
The enhancement of performance in this scheme is done by either changing the VoIP packet size or codec type. This has been proved through five groups of extensive simulation scenarios using OPNET 14.5 Modeler for the popular IEEE 802.11 WLAN standards (a, b, g, and e), using different packet size, data rate and codec types.
The first group of scenarios examines the VoIP capacity in a single cell WLAN for three standards which are (a, b, and g). Results show that a and g-standards enhanced VoIP capacity by 100% compared with b-standard since they provide high transmission rate up to 54Mbps with a packet size up to 5 frames.
The QoS enhancement provided by WLAN e-standard has been examined in the second group of scenarios. Results show that MOS is enhanced by (11.12%), jitter is reduced by (-98.9%), End-to-End delay is reduced by (-29.4%), Packet loss is reduced by (-71.43%), and throughput is enhanced by (27.8%) when the cell is loaded with other application in addition to VoIP. The effect of using different CODECs has been examined in third group by comparing them with G.711 CODEC, G.726 can enhance VoIP capacity by (15.38%), while G.729A can enhance it by (36.36%), and G.723 can enhance it by (63.63%) with acceptable QoS.
Results of the fourth group show that increasing packet size can decrease handoff delay. While the results of the fifth group prove that adapting the packet size or CODEC type enhanced the VoIP capacity and QoS in wireless campus network in case of congestion and rate adaptation.