Session 1: Networked Multimedia Systems
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What is a multimedia system?
A multimedia system is characterized by procession, storage, generation, transport, and synchronization of multimedia information.
What is the difference between continuous media and static media?
Continuous media (audio and video) are time dependent. Statis media (text and images) is static with no element of time. Coninuous media is sensitive to delay, but can tolerate 10 to 20% packet loss.
What are some of the architectural elements of a distributed multimedia system?
All the following connect thru a WAN: Database server, video server, web server, PC, set top box, HDTV.
What are the 3 classes of continuous media applications?
Streaming, unidirectional real time, interactive real time.
Can you explain streaming media applications?
Characterized by stored media requested by a client. These can be interactive. Characterized by delay of 1 to 10 seconds on start up. Examples: RealNetworks, MS Windows media.
Can you explain real-time interactive applications?
Examples: phone and video conferences. More stringent delay requirements than streaming. Video requires < 150 msec response. Audio can tolerate up to 400 msec response.
What is latency?
How long it takes to deliver media.
What is quality of service?
Made up of delay, jitter, and packet loss metrics.
What is synchronization?
the requirement for simultaneous retrieval of multiple media segments and dynamic composition at the client.
What is scalability?
The number of users supported in an application and how well the application supports all those users.
What is reliability?
A measure of how often system components fail.
What are the design issues related to networking?
High utilization and shared resources creates problems with respect to timely delivery of video and audio.
What are the design issues related to protocols?
TCP/IP does not guarantee delivery, delay, or jitter (variance in delay). New protocols were developed for this (RSP, STP, RSVP).
What are the design issues related to compression?
Uncompressed data too large for network. Efficient delivery requires a careful choice of codecs.
What are the design issues related to databases?
Media must be stored, queried, and retrieved efficiently.
What are the design issues related to information retrieval?
There must be efficient search algorithms. Videos must be indexed somehow. Videos/audio must be broken into smaller clips somehow. Audio must be transcribed. Images must be indexed somehow.
What are the design issues related to media servers?
Media must be continuous at a constant rate once is starts. Servers must be scalable. Clients must be able to all access same media. Striping across RAID arrays complicated this.
What is admission control?
if sufficient resources are not available to service a request then that request is rejected.
What is media caching?
Store the data close to the end user to reduce bandwidth needs.
What are the system software design issues?
These apps are I/O sensitive. Typically have large columes that are time sensitive. Requires real time OS support for scheduling of tasks.