This work addresses the challenge of providing seamless multimedia services to mobile users by proposing a proxy-assisted multicast architecture for delivery of video streams. We propose a hybrid system of streaming proxies, interconnected by an application-layer multicast tree, where each proxy acts as a cluster head to stream out content to its stationary and mobile users. The architecture is based on our previously proposed Enhanced-NICE protocol, which uses an application-layer multicast tree to deliver layered video streams to multiple heterogeneous receivers. We targeted the study on placements of streaming proxies to enable efficient delivery of live and on-demand video, supporting both stationary and mobile users. The simulation results are evaluated and compared with two other baseline scenarios: one with a centralized proxy system serving the entire population and one with mini-proxies each to serve its local users. The simulations are implemented using the J-SIM simulator. The results show that even though proxies in the hybrid scenario experienced a slightly longer delay, they had the lowest drop rate of video content. This finding illustrates the significance of task sharing in multiple proxies. The resulted load balancing among proxies has provided a better video quality delivered to a larger audience.
This work address two important challenges in congestion control for reliable multicast: (1) Provably TCP-fairness and (2) Providing scalable feedback. We first present a simple, rate-based, flat-structured scheme, RMCC (Reliable Multicast Congestion Control), that does not rely on router assistance and is readily deployable at end hosts. It is enhanced from a generic scheme originally proposed by Whetten and Cohan. Detailed design of source and receiver mechanisms is described. Next we propose three scalable feedback schemes for RMCC over heterogeneous wired/wireless/mobile networks. Using sampling techniques, these feedback schemes adapt their feedback generation frequency according to network dynamics including congestion status, end host mobility, and packet losses. The RMCC algorithm and the three feedback methods are carefully evaluated through simulation experiments using various network configurations and traffic scenarios. We found that RMCC multicast flow co-exists well with TCP traffic and is TCP-fair. The three feedback schemes are effective in reducing acknowledgments, yet are able to promptly communicate significant network changes.
Proc. SPIE. 3530, Performance and Control of Network Systems II
KEYWORDS: Internet, Switches, Control systems, Computer simulations, Local area networks, Optical character recognition, Americium, Asynchronous transfer mode, Received signal strength, Virtual colonoscopy
Multipoint communication has been an increasingly focused topic in computer communication networks, including both the Internet and the ATM networks. We have previously presented, analyzed, and evaluated new point-tomultipoint ABR flow control algorithms. In this paper, we focus on multipoint-to-point flow control. As the major objective of ABR service is to provide minimum-loss, fair service to data traffic, an effective merge-point scheme for multipoint-to-point flow control should guarantee some suitable fairness. In this paper, we first examine the "essential fairness" concept proposed by Wang and Schwartz for point-to-multipoint flow control in the Internet. We extend and enhance the concept to the multipoint-to-point ABR flow control. A general algorithm guaranteeing essential fairness is presented, with a detailed implementation on top of the ERICA unicast algorithm proposed by Jam, et. al. The general algorithm may be used for a wide range of fairness specifications to accommodate various bandwidth requirement from unicast or multicast sources of different application streams. Three major variations of the general algorithm are presented. These three schemes are simulated and evaluated, and compared with an existing scheme proposed by Ren, Siu, and Suzuki. Simulation results show that the proposed merge-point algorithm achieves, within short transient time, max-mm fairness based on different weights given to individual sources or sessions, or according to various specifications of fairness. The fairness concept and the general algorithm presented here may be readily applied to other high-speed networks such as the Next Generation Internet and Wireless ATM, and to different multicast settings such as point-to-multipoint and multipoint-to-multipoint.
Keywords: ATM network, ABR traffic, flow control, multicast
One major function of the ATM (Asynchronous Transfer Mode) networks is to provide real-time, low-loss, and minimum- delay transmission of VBR (variable bit rate) video traffic. The Leaky Bucket (LB) mechanism has been proposed and adopted at the ATM Forum to police network traffic. In this work, we enhance and integrate the ideas of (1) soft multiplexing and (2) multi-level rate policing, to design an advanced traffic policing mechanism: the Multi-Level Leaky Bucket with Token Passing. The new mechanism has an efficient mechanism to estimate the current bit-rate and burst-duration of a VBR source. Based on the estimation, it allows sources to transmit at different bit rates for restricted amounts of time. It also allows interactions among the Leaky Buckets of the input streams of the same virtual path. We use simulation to evaluate the performance of the new mechanism and to compare it with three existing methods. Two VBR traffic source models are used: (1) Markov Modulated Poisson Process with parameters set according to a HDTV model, and (2) an Autoregressive Markovian model of order 2, AR. We compare bandwidth utilization, cell-loss probability, and queuing delay for all methods, by varying the offered traffic load and the size of cell buffers and token buckets. We found that, due to different traffic characteristics possessed by different VBR sources, using token passing or multi-rate policing alone does not improve the original LB on certain VBR sources. We found that the new mechanism achieves better performance than the three existing schemes in all the scenarios.
The ATM Forum has adopted rate-based congestion control for ABR (available bit rate) traffic. Much of the existing work evaluating ABR congestion control schemes has used some threshold value on buffer queue length to indicate congestion. On the other hand, many ER (explicit rate) algorithms calculate their 'fair-share' values based on utilization level, with the assumption that ER switches are able to measure the current utilization level of ABR traffic. If one would use the same mechanism -- measuring utilization level -- to indicate congestion, then the same switch could easily implement both binary and ER ABR control algorithms. Based on the above observations, in this paper we study the effect of using two different congestion indication methods: (1) buffer queue length (the most commonly used method); and (2) utilization level (the new method). We evaluate two binary ABR control schemes: EFCI (explicit forward congestion indication) and CI (congestion indication) using backward notification, using the two different congestion methods. We also evaluate and compare two ER algorithms: the ERICA (explicit rate indication for congestion avoidance) algorithm proposed by Jain and the CAPC-2 (congestion avoidance with proportional control - 2) algorithm proposed by Barnhart. Performance evaluation are carried out by computer simulation. We simulate two ABR switches connected by an OC-3 link, with each switch connecting five end-systems. The distance between the two switches are 20 km for LAN and 1,000 km for WAN, based on ATM forum specification. For each simulation run, we measure average queuing delay, maximum queue length, and network utilization. Traces of ACR (allowed cell rate) and buffer queue length are also examined. We found that using the new congestion method indication dramatically reduces the maximum queue length and average queuing delay, with a slight decrease in utilization. Both ER schemes show smooth buffer occupancy and attain high utilization.