Computer Communications 24 (2001) 105±123 www.elsevier.com/locate/comcom Using dynamic con®guration to manage a scalable multimedia distribution systemq F. Kon*, R.H. Campbell, K. Nahrstedt Department of Computer Science, University of Illinois at Urbana-Champaign, 1304 West Spring®eld Avenue, Urbana, IL 61801-2987, USA1 Received 15 March 2000; accepted 4 September 2000 Abstract Multimedia applications and interfaces will change radically the way computer systems will look like in the coming years. Radio and TV broadcasting will assume a digital format and their distribution networks will be integrated to the Internet. Existing hardware and software infrastructures, however, are unable to provide all the scalability, ¯exibility, and quality of service (QoS) that these applications require. We present a framework for building scalable and ¯exible multimedia distribution systems that greatly improves the possibilities for the provision of quality of service in large-scale networks. We show how to use architectural-awareness, mobile agents, and a CORBA-based framework to support dynamic (re)con®guration, ef®cient code distribution, and fault-tolerance. This approach can be applied not only for multimedia distribution, but also for any QoS-sensitive distributed application. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Multimedia distribution; Dynamic con®guration; Middleware; CORBA; QoS-aware resource management 1. Introduction on architectures for distributing digital multimedia content through the Internet and intranet infrastructures. In particu- Multimedia interfaces will play a fundamental role in lar, researchers working on the technologies related to the human±computer interaction in next generation computer MBone [1,2] and to adaptive audiovisual streaming proto- systems. Applications will gradually abandon dull inter- cols [3,4] provided signi®cant contributions. We noticed, faces based on text and static graphics and move towards however, that existing MBone and unicast solutions do a more interesting look based on audio, video, and anima- not provide the degree of control, ¯exibility, and the possi- tions. Within one decade, there will probably be no distinc- bilities for QoS management that the next generation appli- tion among the telephone, radio, TV, and data networks; and cations require. In this article, we present an architecture for in future decades, no distinction between computer and scalable multimedia distribution that meets those require- dedicated radio and TV receivers. Everything will be inte- ments. The architecture combines modern technologies grated on an extension of today's Internet. from different Computer Science ®elds and extends them The Internet as we know today, however, is not suited for when necessary. the distribution of high-quality multimedia to a large We applied the ideas presented in this article to build an number of clients. A number of changes in the hardware object-oriented multimedia distribution system in C11 [5] and software that currently support the Internet will have and demonstrated that it is possible to use the existing Inter- to occur. We need systems to better control large numbers of net to distribute low and medium bandwidth multimedia to multimedia ¯ows, with support for Quality of Service (QoS) thousands of simultaneous users. Our early experiments, provision. though, pointed out dif®culties in managing such a large- In the past ten years, several research groups have worked scale system and keeping it available with an acceptable QoS. It showed the necessity for a better support for q This research is supported by the National Science Foundation, grants dynamic (re)con®guration, code distribution, and provision CCR 96-23867. 98-70736, 99-70139, and 99-72884EQ. Fabio Kon is of fault-tolerance. supported in part by a grant from CAPES, Brazil, proc. 1405/95-2. This article describes our most recent achievement in * Corresponding author. this area, i.e. an integrated software architecture addressing E-mail addresses: [email protected] (F. Kon), [email protected] (R.H. Campbell), [email protected] (K. Nahrstedt). the problems we encountered in the past. Our solution is 1 http://choices.cs.uiuc.edu/2K. based on an extensible Re¯ector system, mobile agents, 0140-3664/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0140-3664(00)00293-0 106 F. Kon et al. / Computer Communications 24 (2001) 105±123 ... Intermediate Public Reflector Reflector Capture Master Station Reflector Public Intermediate Reflector Reflector Public Reflector Intermediate . Reflector . Capture Master Station Public Reflector Intermediate Reflector Reflector Fig. 1. A Re¯ector network distributing two video streams. and a CORBA framework for dynamic con®guration and the system to the characteristics of the environment in which recon®guration. it executes. This property is known as dynamic con®gura- Section 2 presents an overview of the basic concepts tion. Also of extreme importance is the ability of a system to involved in scalable multimedia distribution. Section 3 change, on-the-¯y, its internal components and con®gura- describes our early design, discussing its limitations. tion parameters to adapt to changes in the environment. This Section 4 describes our new, enhanced architecture with is called dynamic recon®guration2. support for dynamic con®guration and explains the syner- (4) Quality of service (QoS). Multimedia applications gistic relationships between dynamic con®guration and have stringent requirements with respect to computational QoS. Section 5 presents a concrete implementation of our resources such as memory, CPU, and network [6]. If these architecture and Section 6 discusses performance evalua- requirements are not met, the quality of the multimedia tion. Finally, Section 7 discusses related work and Section service is degraded. This quality can be measured according 8 presents our conclusions and future work. to different metrics. A videoconference service, for exam- ple, can be evaluated according to the size and the number of colors of the video frames, the audio sampling rate, the 2. Basic concepts video frame rate and jitter, the synchronization of audio and video, the delay from the sender to the receiver, the number Before going into a more detailed description of our of frames that are lost or defective, and so on. architecture, we ®rst present a brief overview of the most (5) CORBA. The OMG Common Object Request Broker important concepts related to our approach to scalable Architecture is an architecture for distributed object multimedia distribution. communication that is both language-independent and (1) Re¯ector. It is the key element of our distribution platform-independent. It is based on a standard interface system. It acts as a relay, receiving input data packets de®nition language (IDL) and includes standard de®nitions from a list of trusted sources and forwarding these packets for interoperable distributed communication [7]. It also to other Re¯ectors or to programs executed by end-users. de®nes standard interfaces for services such as naming, The distribution system is composed of a network of Re¯ec- trading, real-time, persistence, and transactions [8]. tors that collaborate with each other to distribute the multi- media data over local-area, metropolitan-area, and wide- area networks. 3. Scalable distribution (2) Re¯ector administrator. A privileged user that is responsible for managing a Re¯ector network. Different Using traditional, centralized video-on-demand servers, it portions of the network may be managed by different is possible to stream video to hundreds of simultaneous administrators, making large systems more manageable clients [3]. Exploiting IP-Multicast [9], this number and helping to deal with different security domains. increases to several thousands or, maybe, a few millions. (3) Dynamic (re)con®guration. As computer environ- ments become more dynamic, a major requirement for 2 For simplicity, the term dynamic con®guration may be used to denote next generation computer systems is the ability to customize both dynamic con®guration and dynamic recon®guration. F. Kon et al. / Computer Communications 24 (2001) 105±123 107 IPMulticast/ Reflector local Ethernet F TCP/ TCP / longdistance fiber link interstate fiber WTCP Master Reflector Reflector IPMulticast/ A MBone Reflector TCP/ B phone dialup UDP/ TCP/ ISDN Capture Master Reflector transatlantic satellite link Station Reflector C TCP/ TCP / transatlantic satellite link longdistance fiber link Reflector Reflector VDP/ D E IPMulticast/ UDP/ phone dialup MBone LAN Fig. 2. A heterogeneous Re¯ector network. However, when using IP-Multicast to send video to a large news, or current stock values. Clients and administration number of clients, one has little control over the transmis- programs can connect to a Re¯ector in order to get informa- sion. It becomes dif®cult to provide support for a number of tion about available channels, Re¯ector load, bandwidth desired features such as QoS, security, accounting, and utilization, historical statistics, etc. reliability. To address this problem, we developed a scalable The Re¯ector network topology is determined by each multimedia distribution framework whose architecture is Re¯ector's con®guration. This information speci®es input described in this section. and output connections, access privileges, maximum allowed number of users, etc. The information is stored in 3.1. The Re¯ector a database controlled by the