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BANDWIDTH ESTIMATION IN WIRELESS LANS FOR MULTIMEDIA STREAMING SERVICES 1 Heung Ki Lee 1Varrian Hall 2Ki Hwan Yum 3Kyoung Ill Kim and 1Eun Jung Kim 1 Texas A M University 2University of Texas at San Antonio 3 ETRI Electronics and Telecommunication Research Institute hklee cystar ejkim cs tamu edu yum cs utsa edu kki etri re kr estimating the point in time to change the bit rate of the transmitted bit stream Estimating the available network bandwidth in a WLAN is very challenging and crucial for multimedia streaming services Although there can be various wireless environments where multimedia services are provided we mainly focus on the LAN WAN shown in Figure 1 In this figure an Internet based Set Top Box STB is the interface between a wired network and a wireless network Even though wired networks can provide high and stable bandwidths fragile wireless networks may not support it Therefore for layered streaming services it is very critical for the STB to know the available wireless network bandwidth In a wireless network the IEEE 802 11 protocol in Distributed Co ordination Function DCF mode based on CSMA CA algorithm is becoming very popular Previous works 4 7 8 based on the bandwidth estimation of wired environments are not applicable to wireless networks that use the DCF protocol Multimedia streaming is a soft realtime service where each frame is delay sensitive Swiftness and availability is critical for real time system During bandwidth deviations the rate of the transmitted multimedia streams should change expeditiously The accuracy of previous works Spruce 4 and ProbeGap 8 is dependent on probing time and the volume of the packets for probing ProbeGap produces good estimates at low cross traffic rates 2 Mbps cross traffic regardless of the cross traffic packet size however it significantly overestimates available bandwidth when the cross traffic is high 4 Mbps cross traffic generated with 300 byte packets 8 Influence by cross traffic on probe packet sequences



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