Mario Baldi

Interactive Multimedia Networking

Outline

Applications that require real-time interaction among their users are gaining importance and diffusion as computer networks become increasingly powerful and ubiquitous. Many such applications impose very stringent requirements on the network; among the applications today widely deployed, videoconferencing is most demanding.

In order for the participants in a videoconference call to interact naturally, the end-to-end delay should be below human perception; even though an objective and unique figure cannot be set, 100 ms is widely recognized as the desired one way delay requirement for interaction. Since the global propagation delay alone can be about 100 ms, the actual end-to-end delay budget available to the system designer (excluding propagation delay) is very limited (e.g., no more than 10 ms).

We identify the components of the end-to-end delay in various configurations with the objective of understanding how it can be kept below the desired 100 ms bound.

After an overview of the distinctive features of interactive multimedia applications, their requirements on the network are discussed and limited delay and delay variation (Jitter) identified as the most demanding requirements. The most common techniques for controlling service quality are presented and the two major frameworks for their deployment within IP networks, i.e., Integrated Services (IntServ) and Differentiated Services (DiffServ), outlined. The tutorial also studies the implications of the architecture of packet switches on delay bounds.

Then the tutorial delves into more detail by analyzing the end-to-end delay components of a videoconferencing system step-by-step, through six system configurations obtained by combining three generic network architectures with two video encoding schemes: the transmission of raw video and variable bit rate (VBR) MPEG video encoding over (i) circuit switching, (ii) synchronous packet switching, and (iii) asynchronous packet switching.

Various queuing and scheduling algorithms for asynchronous and synchronous packet networks will be analyzed and compared.

The tutorial finally shows that having a global common time reference, together with an innovative queuing and scheduling scheme called time-driven priority (TDP) and VBR MPEG video encoding, provides adequate end-to-end delay, which is

1. below 10 ms (excluding propagation delay),
2. independent of the network instant load, and
3. independent of the connection rate.

The participants are expected to have basic knowledge on packet switching and the Internet Protocol Suite. Depending on the background of the audience on multimedia, the first part of the tutorial can be organized as a quick overview of the general context to which the remainder, or as an in-depth discussion.

Contents

• Multimedia networking: distinctive features and requirements of interactive multimedia applications
• Analysis of delay components in multimedia communications systems
• Controlling the network delay

• statistical multiplexing and delay
• queuing and scheduling algoriths
• Fixed Priority
• Round Robin
• Class based queuing
• Weighted fair queuing
• Time driven priority
• Switch architectures for controlled delay
• Quality of service in the Internet
• Integrated Services
• Differentiated Services
• Encoding and transmission of MPEG video: a closer look
• video over circuit switched networks
• video over asynchronous packet switching
• CBR video
• VBR video
• VBR video with time-driven priority

Course Material

• Introduction (black&white for printing)
• First part: multimedia applications (black&white for printing)
• Second part: delay analysis of videoconference (2 slides per page)
• M. Baldi, Y. Ofek, "End-to-end Delay Analysis of Videoconferencing over Packet Switched Networks," IEEE/ACM Transactions on Networking, Vol. 8, No. 4, Aug. 2000, pp. 479-492.

• M. Baldi, F. Risso, "Efficiency of Packet Voice with Deterministic Delay," IEEE Communications Magazine, Vol. 38, No. 5, May 2000, pp. 170-177. (earlier version in gzipped postscript and PDF format)

Last Update in August 2006