BANDWIDTH ESTIMATION IN WIRELESS LANS FOR MULTIMEDIA STREAMIABSTRACTBANDWIDTH ESTIMATION IN WIRELESS LANS FOR MULTIMEDIA STREAMING SERVICES 1Heung 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, 3ETRI (Electronics and Telecommunication Research Institute) {hklee, cystar, ejkim}@cs.tamu.edu, [email protected], [email protected] ABSTRACT The popularity of multimedia streaming services via wireless networks presents major challenges in the management of network bandwidth. One challenge is to quickly and precisely estimate the available bandwidth for the decision of streaming rates of layered and scalable multimedia services. Previous works based on wired networks are too burdensome to be applied to multimedia applications in wireless networks. In this paper, a new method, IdleGap, is suggested to estimate the available bandwidth of a wireless LAN based on the information from a low layer in the protocol stack. We use a network simulation tool, NS-2, to evaluate our new method with various range of cross traffic and observation times. Our simulation results show that IdleGap accurately estimates the available bandwidth for all ranges of cross traffic (100Kbps ~ 1Mbps) with a very short observation time of 10 seconds. 1. INTRODUCTION Since introduced commercially in 1995, multimedia streaming services have become one of the most promising Internet services currently available. In addition, Wireless Local Area Networks (WLANs) make multimedia streams commonplace, and terminals are diversifying into hand-held devices such as PDAs, laptops and audio/video players. These heterogeneous devices have different access patterns and mobility [1]. Most multimedia streams are hungry for stable network bandwidth, but a shared-medium WLAN may not support it. To meet their bandwidth requirements, rate scalability can be achieved by layered video representation [2,3]. However, there are still problems in 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 real-time 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 causes probe packets in sequences to be split up or even lost. Our contribution in this paper is two-fold. First, we suggest IdleGap, which is a bandwidth estimation tool for a real-time system in a wireless network. Second, our system is independent of cross traffic. We estimate the available bandwidth via the ratio of free time in the wireless links. To get the ratio of idle time in a wireless network, information from network management at the low layer is used. It provides us with an efficient and fast method for estimating the available bandwidth. The rest of the paper is organized as follows. Section 2 shows the related work in estimating bandwidth and discusses the Cross layer. In Section 3, our new method, Figure 1. Stream Service Based on Set Top Box and 802.11 1IdleGap, is proposed and known challenges in bandwidth estimation are addressed. After presenting the results of our method and other tools in Section 4, we conclude this paper in Section 5. 2. RELATED WORK 2.1 Estimation of Bandwidth in Broadband Networks Since the introduction of Cprobe [12], a method for estimating bandwidth using Internet Control Message Protocol (ICMP) packet trains, many tools have been suggested. Spruce [4] and IGI [5] use the interval of consecutive probe packets, since the interval or gap between probe packets is increased in heavy cross traffic. Topp [6] and Pathload [7] are based on the rate of incoming packets. The comparison of the incoming rate from the sender side to the outgoing rate at the receiver side reveals the incoming rate to be less than or equal to the available bandwidth of the probing link. In Probegap[8], the link’s idle time is the milestone for bandwidth estimation of a wireless network. 2.2 Cross Layer Feedback For efficient mobile device communication and interaction, cross layer feedback is performed by a mobile device accessing its own protocol stack layers that contain information from transmitted packets. Cross layer feedback allows interaction between a layer and any other layer in the protocol stack. Packet information retrieval across the protocol stack layers (cross layer) provides very useful information about mobile devices in the wireless network. Several studies [9,10,11,12] revealed interaction among other layers for improving the system. In [9], the central bandwidth manager controls client traffic by updating the Defer time within the MAC layer. [10] suggested a 802.11 management method that processes the captured frame to get the available bandwidth. For a QoS-sensitve application, a different priority at the MAC layer may be assigned based on the applications [11]. 3. IDLEGAP USING NETWORK ALLOCATION VECTOR 3.1 Background Bandwidth estimation is a prerequisite problem for