1. Tema 0: Transmisión de Datos Multimedia
Clases de aplicaciones multimedia
Redes basadas en IP y QoS
Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.

2. What is multimedia? Definition of multimedia
Hard to find a clear-cut definition
In general, multimedia is an integration of text, graphics, still and moving images, animation, sounds, and any other medium where every type of information can be represented, stored, transmitted and processed digitally
Characteristics of multimedia
Digital – key concept
Integration of multiple media type, usually including video or/and audio
May be interactive or non-interactive

3. Various Media Types
Text, Graphics, image, video, animation, sound, etc.
Classifications of various media types
Captured vs. synthesized media
Captured media (natural) : information captured from the real world
Example: still image, video, audio
Synthesized media (artificial) : information synthesize by the computer
Example: text, graphics, animation
Discrete vs. continuous media
Discrete media: space-based, media involve the space dimension only
Text, Image, Graphics
Continuous media: time-based, media involves both the space and the time dimension
Video, Sound, Animation

4. Classification of Media Type
Sound
Video
Image
Animation
Text
Graphics
Captured
From real world
Synthesized
By computer
Discrete
Continuous

5. Text Plain text Rich text Unformatted Characters coded in binary form
ASCII code
All characters have the same style and font
Rich text
Formatted
Contains format information besides codes for characters
No predominant standards
Characters of various size, shape and style, e.g. bold, colorful

6. Plain Text vs. Rich Text
An example of Plain text
Example of Rich text

7. Graphics Revisable document that retains structural information
Consists of objects such as lines, curves, circles, etc
Usually generated by graphic editor of computer programs
Example of graphics (FIG file)

8. Images 2D matrix consisting of pixels Have no structural information
Pixel—smallest element of resolution of the image
One pixel is represented by a number of bits
Pixel depth– the number of bits available to code the pixel
Have no structural information
Two categories: scanned vs. synthesized still image
Computer
software
Capture and
A/D conversion
Digital still image
Synthesized
image
Scanned
Camera

9. Images (cont.) Examples of images Binary image – pixel depth 1
Gray-scale – pixel depth 8
Color image – pixel depth 24
Gray-scale image
color image
Binary image

10. Video vs. Animation
Both images and graphics can be displayed as a succession of view which create an impression of movement
Video – moving images or moving pictures
Captured or Synthesized
Consists of a series of bitmap images
Each image is called a frame
Frame rate: the speed to playback the video (frame per second)
Animation – moving graphics
Generated by computer program (animation authoring tools)
Consists of a set of objects
The movements of the objects are calculated and the view is updated at playback

11. Sound 1-D time-based signal Speech vs. non-speech sound
Speech – supports spoken language and has a semantic content
Non-speech – does not convey semantics in general
Natural vs. structured sound
Natural sound – Recorded/generated sound wave represented as digital signal
Example: Audio in CD, WAV files
Structured sound – Synthesize sound in a symbolic way
Example: MIDI file

12. Networked Multimedia Local vs. networked multimedia Image server
Local: storage and presentation of multimedia information in standalone computers
Sample applications: DVD
Networked: involve transmission and distribution of multimedia information on the network
Sample applications: videoconferencing, web video broadcasting, multimedia , etc.
Image server
A scenario of multimedia networking
Internet
Video server

13. Consideration of Networked Multimedia
Requirements of multimedia applications on the network
Typically delay sensitive
end-to-end delay
delay jitter:
Jitter is the variability of packet delays within the same packet stream
Quality requirement
Satisfactory quality of media presentation
Synchronization requirement
Continuous requirement (no jerky video/audio)
Can tolerant some degree of information loss

14. Technologies of Multimedia Networking
Challenges of multimedia networking
Conflict between media size and bandwidth limit of the network
Conflict between the user requirement of multimedia application and the best-effort network
How to meet different requirements of different users?
Media compression – reduce the data volume
Address the 1st challenge
Image compression
Video compression
Audio compression
Multimedia transmission technology
Address the 2nd and 3rd challenges
Protocols for real-time transmission
Rate / congestion control
Error control

15. Multimedia Networking Systems
Live media transmission system
Capture, compress, and transmit the media on the fly (example?)
Send stored media across the network
Media is pre-compressed and stored at the server. This system delivers the stored media to one or multiple receivers. (example?)
Differences between the two systems
For live media delivery:
Real-time media capture, need hardware support
Real-time compression– speed is important
Compression procedure can be adjusted based on network conditions
For stored media delivery
Offline compression – better compression result is important
Compression can not be adjusted during transmission

16. Classes of multimedia applications
Streaming stored audio and video
Streaming live audio and video
Real-time interactive audio and video

17. Streaming Stored Multimedia: What is it?
100%
streaming: at this time, client
playing out early part of video,
while server still sending later
part of video
3. video received,
played out at client
Cumulative data
2. video
sent
1. video
recorded
network
delay
time

18. Streaming vs. Download of Stored Multimedia Content
Download: Receive entire content before playback begins
High “start-up” delay as media file can be large
~ 4GB for a 2 hour MPEG II movie
Streaming: Play the media file while it is being received
Reasonable “start-up” delays
Reception Rate >= playback rate. Why?

19. Streaming Stored Multimedia: Interactivity
VCR-like functionality: client can pause, rewind, FF, push slider bar
10 sec initial delay OK
1-2 sec until command effect OK
RTSP often used (more later)
timing constraint for still-to-be transmitted data: in time for playout

20. Streaming Multimedia: Client Buffering
constant bit
rate video
transmission
variable
network
delay
client video
reception
constant bit
rate video
playout at client
client playout
delay
Cumulative data
buffered
video
time
Client-side buffering, playout delay compensate for network-added delay, delay jitter

21. Streaming Multimedia: Client Buffering
Client-side buffering, playout delay compensate for network-added delay, delay jitter
constant
drain
rate, d
variable fill
rate, x(t)
buffered
video

22. Interactive, Real-Time Multimedia
applications: IP telephony, video conference, distributed interactive worlds
end-end delay requirements:
audio: < 150 msec good, < 400 msec OK
includes application-level (packetization) and network delays
higher delays noticeable, impair interactivity
session initialization
how does callee advertise its IP address, port number, encoding algorithms?

23. Internet multimedia: simplest approach
audio or video stored in file
files transferred as HTTP object
received in entirety at client
then passed to player
audio, video not streamed:
no, “pipelining,” long delays until playout!

24. Progressive Download browser GETs metafile
browser launches player, passing metafile
player contacts server
server downloads audio/video to player

25. Streaming from a streaming server
This architecture allows for non-HTTP protocol between server and media player
Can also use UDP instead of TCP.

26. Multimedia Over Today’s Internet
TCP/UDP/IP: “best-effort service”
no guarantees on delay, loss
But multimedia apps requires QoS and level of performance to be effective!
Today’s Internet multimedia applications use application-level techniques to mitigate (as best possible) effects of delay, loss

27. Streaming Multimedia: UDP or TCP?
server sends at rate appropriate for client (oblivious to network congestion!)
often send rate = encoding rate = constant rate
then, fill rate = constant rate - packet loss
short playout delay (2-5 seconds) to compensate for network delay jitter
error recover: time permitting
TCP
send at maximum possible rate under TCP
fill rate fluctuates due to TCP congestion control
larger playout delay: smooth TCP delivery rate
HTTP/TCP passes more easily through firewalls

28. Multimedia, Quality of Service: What is it?
Multimedia applications: network audio and video
(“continuous media”)
network provides application with level of performance needed for application to function.
QoS

29. Improving QOS in IP Networks
Thus far: “making the best of best effort”
Future: next generation Internet with QoS guarantees
RSVP: signaling for resource reservations
Differentiated Services: differential guarantees
Integrated Services: firm guarantees
simple model for sharing and congestion studies:

30. Principles for QOS Guarantees
Example: 1Mbps IPphone, FTP share 1.5 Mbps link.
bursts of FTP can congest router, cause audio loss
want to give priority to audio over FTP
Principle 1
packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly

31. Principles for QOS Guarantees (more)
what if applications misbehave (audio sends higher than declared rate)
policing: force source adherence to bandwidth allocations
marking and policing at network edge:
similar to ATM UNI (User Network Interface)
Principle 2
provide protection (isolation) for one class from others

32. Principles for QOS Guarantees (more)
Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation
Principle 3
While providing isolation, it is desirable to use resources as efficiently as possible

33. Principles for QOS Guarantees (more)
Basic fact of life: can not support traffic demands beyond link capacity
Principle 4
Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs

34. Summary of QoS Principles