Streaming audio and video applications are becoming increasingly popular on the Internet, and the lack of effective congestion control in such applications is now a cause for significant concern. The problem is one of adapting the compression without requiring video-servers to re-encode the data, and fitting the resulting stream into the rapidly varying available bandwidth. At the same time, rapid fluctuations in quality will be disturbing to the users and should be avoided.In this paper we present a mechanism for using layered video in the context of unicast congestion control. This quality adaptation mechanism adds and drops layers of the video stream to perform long-term coarse-grain adaptation, while using a TCP-friendly congestion control mechanism to react to congestion on very short timescales. The mismatches between the two timescales are absorbed using buffering at the receiver. We present an efficient-scheme for the distribution of buffering among the active layers. Our scheme allows the server to trade short-term improvement for long-term smoothing of quality. We discuss the issues involved in implementing and tuning such a mechanism, and present our simulation results.

https://cseweb.ucsd.edu/classes/fa01/cse222/papers/handley-rap-sigcomm99.pdf

Quality adaptation for congestion controlled video playback over the Internet

The use of scalable video with layered multicast has been shown to be an effective method to achieve rate control in heterogeneous networks. We propose the use of layered forward error correction (FEC) as an error-control mechanism in a layered multicast framework. By organizing FEC into multiple layers, receivers can obtain different levels of protection commensurate with their respective channel conditions. Efficient network utilization is achieved as FEC streams are multicast, and only to receivers that need them. Furthermore, FEC is used without overall rate expansion by selectively dropping data layers to make room for FEC layers. Effects of bursty losses are amortized by staggering the FEC streams in time, giving rise to a tradeoff between delay and quality. For rate control at the receivers, we propose an equation-based approach that computes network usage as a function of measured network characteristics. We show that equation-based rate control achieves more fair bandwidth sharing amongst competing sessions as compared to existing multicast rate control schemes such as RLM and RLC. Fairness is achieved since competing sessions sharing a path will measure similar network characteristics. Simulations and actual MBONE experiments are performed using error-resilient, scalable video compression. We find that video quality is significantly improved at the same communication rate when layered FEC is used.

/pdf/video-multicast-using-layered-fec-and-scalable-compression-bmbj3uqho3.pdf

Video multicast using layered FEC and scalable compression

Streaming audio and video applications are becoming increasingly popular on the Internet, and the lack of effective congestion control in such applications is now a cause for significant concern. The problem is one of adapting the compression without requiring video servers to reencode the data, and fitting the resulting stream into the rapidly varying available bandwidth. At the same time, rapid fluctuations in quality will be disturbing to the users and should be avoided. We present a mechanism for using layered video in the context of unicast congestion control. This quality adaptation mechanism adds and drops layers of the video stream to perform long-term coarse-grain adaptation, while using a TCP-friendly congestion control mechanism to react to congestion on very short timescales. The mismatches between the two timescales are absorbed using buffering at the receiver. We present an efficient scheme for the distribution of available bandwidth among the active layers. Our scheme allows the server to trade short-term improvement for long-term smoothing of quality. We discuss the issues involved in implementing and tuning such a mechanism, and present our simulation results.

Layered quality adaptation for Internet video streaming

Congestion and flow control is an integral part of any Internet data transport protocol. It is widely accepted that the congestion avoidance mechanisms of TCP have been one of the key contributors to the success of the Internet. However, TCP is ill-suited to real-time multimedia streaming applications. Its bursty transmission, and abrupt and frequent wide rate fluctuations cause high delay jitters and sudden quality degradation of multimedia applications. For asymmetric networks such as wireless networks, cable modems, ADSL, and satellite networks, transmitting feedback for (almost) every packet received as it is done in TCP causes congestion in the reverse path. In this environment, TCP may severely underutilize the forward path throughput. Use of multicast further complicates the problem; TCP-like frequent feedback from each receiver to the sender in a large scale multicast session cause well-known scalability limitations (e.g. acknowledgment implosion). We have developed a new flow control approach for multimedia streaming, called TCP emulation at receivers (TEAR). TEAR shifts most of flow control mechanisms to receivers. In TEAR, a receiver does not send to the sender the congestion signals detected in its forward path but rather processes them immediately to determine its own appropriate receiving rate. TEAR can determine this rate using congestion signals observed at the receiver. These signals are used to emulate the TCP sender’s flow control functions at receivers.The emulation allows receivers to estimate a TCP-friendly rate for the congestion conditions observed in their forward paths. TEAR also allows receivers to adjust their receiving rates to a TCP-friendly rate without actually modulating the rates to probe for spare bandwidth, or to react to packet losses directly. Thus, the perceived rate fluctuations at the application are much more smooth than in TCP. A unicast version of TEAR is implemented. This report describes the implementation of TEAR, examine the performance of this TEAR implementation from the NS simulation and Internet experiments, and compare it with that of other TCP-friendly flow control techniques. Our preliminary tests indicate that TEAR shows superior fairness to TCP with significantly lower rate fluctuations than TCP. TEAR’s sensitivity to feedback interval is very low, so that even under high feedback latency, TEAR flows exhibit acceptable performance in terms of fairness, TCP-friendliness, and rate fluctuations. Finally, I will discuss the future extension of TEAR for multicast environments. This work is supported in part by NSF CAREER ANI-9875651.

TEAR: TCP emulation at receivers – flow control for multimedia streaming

A method is provided for ensuring that specific traffic flows are adequately prioritized in a public packet communication network even when the network is heavily congested. Per-flow QoS capability is added to VPN tunnels. Connection requests are routed through a specific port in an access provider's network to designated VPN gateway. Deep packet inspection is performed on traffic through the port in an attempt to determine whether the connection request was accepted. If the connection request was accepted, the traffic flows associated with that session may be given a specific priority of QoS level when transiting a packet access network.

System and method for prioritization of traffic through internet access network

Layered Video Multicast with Retransmissions (LVMR) is a system for distributing video content using layered coding over the Internet. The two key contributions of the system are (1) improving the quality of reception within each layer by retransmitting lost packets given an upper bound on recovery time and applying an adaptive playback point scheme to help achieve more successful retransmission, and (2) adapting to network congestion and heterogeneity using a hierarchical rate control mechanism. A hierarchical rate control system and method is disclosed for regulating the flow of video information in a network by establishing subnet agents for each subnet, and by establishing intermediate agents for each domain. The subnet agents gather information concerning add-layer experiments conducted by receivers in a subnet, and the information is provided to intermediate agents of the domains for regulating data traffic.

Hierarchical rate control of receivers in a communication system transmitting layered video multicast data with retransmission (LVMR)

A method and for establishing a virtual private network (VPN) session for a priority request. The method and apparatus includes identifying a priority request from a plurality of VPN session request classes. Reserved bandwidth is allocated to the priority request if a nominally allocated bandwidth is insufficient to satisfy the priority request. Once the allocated bandwidth is assigned, admission control is applied to the priority request.

Class-based bandwidth allocation and admission control for virtual private networks with differentiated service

In a video multicast session, the receivers may possess different capabilities or be connected to the network through avariety of different access speeds. Multicasting video traffic at any one rate to all of the receivers can be unfair as some receivers may experience high losses while others find that their full reception capacity is not fully utilized. Layeredvideo multicast protocols have been developed to address this intra-session fairness problem. In such protocols (e.g., RLM and LVMR) , video is multicast in multiple layers over separate multicast groups. Receivers join as manylayers as they can handle. While protocols such as RLM and LVMR have been shown to successfully address theintra-session fairness issue in video multicast, they do not address the issue of inter-session fairness, i.e., fair sharingbetween multiple video sessions and TCP sessions. In this paper, we demonstrate and develop insight into theinter-session fairness problem through a set of simulation experiments. We then propose a novel idea to improveinter-session fairness for layered video multicast protocol: layer-based congestion sensitivity mechanism, and finallyevaluate it with some other end-to-end schemes designed to promote inter-session fairness when used to augment

Xue Li

Papers

Hierarchical rate control of receivers in a communication system transmitting layered video multicast data with retransmission (LVMR)

Class-based bandwidth allocation and admission control for virtual private networks with differentiated service

Multisession rate control for layered video multicast