The Analysis of System Capacity of VoIP System Supporting CBRand VBR Traffic in IEEE802.11b WLAN Under DCF Mode

1IntroductionVoIP over IEEE802 .11[1]WLANis supposedto be-come an i mportant application. The IEEE 802 .11 hastwo different channel accessing mechanisms , namely,the DCFand Point Coordination Function (PCF) .DCFis based onthe Carrier Sense Multiple Access with Colli-sion Avoidance (CSMA/CA) channel accessing mecha-nism, while PCF is based on the polling technique .Here we only consider that the wireless networks oper-ate using the DCF MAC protocol ( without theRTS/CTS mech…

The Analysis of System Capacity of VoIP System Supporting CBR and VBR Traffic in IEEE 802.11b WLAN Under DCF Mode

In this paper, the capability of IEEE 802.11b Distributed Coordination Function (DCF) mode supporting of Constant Bit Rate (CBR) and Variable Bit Rate (VBR) Voice over IP (VoIP) traffic is investigated. Then, the capacity of 802.11b Wireless Local Area Network (WLAN) system carrying voice calls in a wide range of scenarios, including varying delay and packet loss rate constraints is analyzed and evaluated. Both G.711 and G.729 voice encoding schemes and a range of voice inter-arrival time are considered. The analyses and simulation results show that capacity is highly sensitive to the delay budget allocated to the sum of packetization and wireless network delays. For a given packet loss rate constrained, G.729 is shown to have a capacity greater than that when G.711 is used. The simulation results show that by supporting VBR under DCF mode the network has the approximately twice much capacity as supporting CBR has, regardless of the encoding schemes and the inter-arrival time.