This paper considers measurement-based admissions control procedures for Controlled-Load services [Wro96]. First, we discuss some of the factors that reduce the requirements on a measurement-based admissions control procedure in an Internet environment with a strong mix of realtime and data traffic. Next, we discuss measurement-based admissions control procedures for Controlled-Load services that are based on the approach of equivalent capacity. Finally, we show some measurements of audio traffic for small audioconferences, and discuss why such traffic could be among the most problematic for measurement-based admissions control procedures. 1 Introduction This paper makes several observations about measurement-based admissions control procedures for Controlled-Load services [Wro96]. We begin with a general discussion of the factors that would allow a measurement-based admissions control procedure to succeed even in the presence of traffic that is difficult to predict. Next, we discuss ...

One purpose of the MBone is to study the performance of multicast and real-time protocols in global conferencing applications. Part of this evaluation is dependent on understanding how the MBone is used and developing realistic workloads and usage models to assist in protocol evaluation. We have developed a tool, called Mlisten, to accurately collect the join/leave times for multicast group members in MBone audio sessions. Using data collected with Mlisten and a set of analysis tools, we report statistics about several MBone audio sessions including member inter-arrival times and durations, multicast tree routinginformation,and group spatial characteristics. Data was also collected and analyzed for all active sessions to produce information about movement among multicast groups. 1 Introduction The Multicast Backbone (MBone) is a virtual network overlaying the Internet[3]. It provides one-to-many, best effort delivery of real-time multimedia data between MBoneconnected hosts. The MBone...

The Multicast Backbone (MBone), the Internet's multicast research infrastructure, has existed since the early 1990s. Since its inception, there have been few formal studies investigating the "state of multicast", i.e. the success of multicast deployment. Our work attempts to understand (1) how the MBone is used, (2) how multicast deployment has progressed, and (3) what barriers exist for the continued deployment of multicast. Future research and deployment efforts would benefit significantly with answers to these macro-scale questions. Our work is based on data sets collected over a 4.5 year period. These data sets include join/leave statistics for many of the MBone sessions advertised through the MBone's session directory tool. Using this data, we examine characteristics about the number and frequency of multicast groups and about the users participating in these groups. In addition, we attempt to qualify the accuracy of our results by examining other sources of multicast traffic stat...

As the Internet is expected to better support multimedia applications, new services will need to be deployed. An example of one of these next-generation services is multicast communication, the one-to-many delivery of data. Over the last ten years, multicast research as well as deployment efforts have both been major areas of interest. In order to bridge the gap between the initial deployment experiments and the availability of multicast as a robust network service, there needs to be a full complement of multicast monitoring tools. In this paper we first survey the debugging, modeling, and management tools that have evolved along side the Internet's multicast infrastructure. Through this survey, we have observed important generalizations in three areas: (1) the challenges unique to monitoring multicast, (2) a methodology common to many multicast monitoring tools/systems, and (3) a set of considerations important to the development of new tools/systems. Using these generalizations we present two of our efforts to evaluate multicast reachability in the Internet. We also use these generalizations to evaluate some of the more recent efforts to develop large-scale management platforms.

The phenomenal growths of group communications and QoS-aware applications over the Internet have respectively accelerated the development of two key technologies, namely, multicasting and Differentiated Services (DiffServ). Although both are complementary technologies, the integration of the two technologies is a nontrivial task due to architectural conflicts between multicasting and DiffServ. In this paper, we propose an approach for providing multicast support across a DiffServ domain that is scalable in terms of group size, network size, and number of groups. We analyze our approach in a detailed manner for feasibility, adaptiveness, and deployment considerations.

With rapid progress in both computers and networks, real-time multimedia applications are now possible on the Internet. Since the Internet was designed to support traditional applications, multimedia applications on the Internet often suffer from unacceptable delay, jitter and data loss. Among these, data loss often has the largest impact on quality. In this paper, we propose a new forward error correction technique for video that compensates for lost packets, while maintaining minimal delay. Our approach transmits a small, low-quality redundant frame after each full-quality primary frame. In the event the primary frame is lost, we display the low-quality frame, rather than display the previous frame or retransmit the primary frame. To evaluate our approach, we simulated the effect of network data loss on MPEG video clips and repaired the data loss by using redundancy frames. We conducted user studies that experimentally measured users' opinions on the quality of the video streams in the presence of data loss, both with and without our redundancy approach. In addition, we analyzed the system overhead incurred by the redundancy. We find that video redundancy can greatly improve the perceptual quality of video in the presence of network data loss. The system overhead that redundancy introduces is dependent on the quality of the redundant frames, but a typical redundancy overhead will be approximately 10% that of the original frames.

Much of our current understanding of the operational aspects and the network requirements of multicast communication derives from the MBone. As an experimental network that overlays the Internet, the MBone has served as the testbed for multicast protocols. This work has led to the development of audio and video conferencing tools that have been used extensively recently. This paper describes our efforts in developing and using a measurement tool, called Mlisten, for characterizing the dynamic behavior in MBone sessions. Such a characterization will be of great benefit in understanding how any future networking infrastructure with multicast and real-time capabilities will be used. We discuss the challenges in monitoring MBone session participation and report on a methodology for pre-processing observed data to make it better reflect the true behavior of members in an MBone session. We also report on the results of using Mlisten to determine temporal, geographical and resource usage char...

The future Internet will very likely include some components based on Asynchronous Transfer Mode (ATM), as well as existing network technologies. This environment produces the possibility of using one of the strengths of ATM (namely, quality-of-service guarantees) to improve the performance of Internet traffic. In this report, we document some of our work in progress on the use of performance-guaranteed ATM virtual circuits to carry IP datagrams. We are currently addressing the implications of various IP-over-ATM strategies on network performance, particularly those aspects relating to quality of service, multiplexing, and virtual circuit management. We are evaluating these performance effects using INSANE, a new object-oriented, discrete-event network simulator. 1 Introduction The construction and deployment of Asynchronous Transfer Mode (ATM) networks are a recent development in the field of computer communications. Integrating this new technology into the existing Internet require...

IP multicast is gaining acceptance among service providers as the protocols and infrastructure mature. Yet characteristics of multicast traffic remain poorly understood. Using passive OC-12 monitors we observe multicast traffic on links connecting aggregated customers and peer networks to our native multicast backbone network. We first refine existing traffic flow profiling methodologies via an exploration of temporal differences in multicast packet trains. Based on this framework we collect multicast flow traces from four geographically dispersed nodes in the vBNS network over a one-month period. We present multicastspecific traffic characteristics including packet and flow size distributions, packet duplication and fragmentation, address accumulation and address space distributions. We analyze the distribution of sources per group and the implications on the applicability of emerging single-source protocols. Analysis reveals results contrary to prevailing wisdom, including: (i) a preponderance of single-packet flows; (ii) a highly variable packet size distribution, with many large packets and strong modes; (iii) the existence of fragmented multicast traffic; and (iv) an insignificant number of simultaneous multiple-source groups. Based on our analysis, we recommend policies for deployment and improvements to protocol implementations.

With rapid progress in both computers and networks, real-time multimedia applications are now possible on the Internet. Since the Internet was designed to support traditional applications, multimedia applications on the Internet often suffer from unacceptable delay, jitter and data loss. Among these, data loss has the largest impact on quality. Current techniques that correct packet loss often result in unacceptable delays. In this thesis, we propose a new forward error correction technique for video that compensates for lost packets, while maintaining minimal delay. Our approach transmits a small, lowquality redundant frame after each full-quality primary frame. In the event the primary frame is lost, we display the low-quality frame, rather than display the previous frame or retransmit the primary frame. To evaluate our approach, we simulated the effect of data loss over network and repair the data loss by using the redundancy frame. We conducted user studies to experimentally measure users' opinions on the quality of video streams in the presence of data loss, both with and without our redundancy approach. In addition we analyzed the system overhead incurred by the redundancy. Result of the user study shows that video redundancy can greatly improve the perceptual quality of transmitted video stream in the presence of data loss. The system overhead that redundancy introduces is dependent on the quality of the redundant frames, but a typical redundancy overhead will be approximately 10% that of primary frames alone. 2 Acknowledgements I would like to express my gratitude to my advisor Prof. Mark Claypool for his continuous support and help on all aspects from technical to material. His guidance and advice helped me overcome many technical obstacles that would take ...