Multimedia Networking - Computer Network Systems - Lecture Slides, Slides of Computer Networks

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Lecture 18

Multimedia Networking

slides are modified from Dave Hollinger Docsity.com

Multimedia and Quality of Service: What is it?

7: Multimedia Networking 7-

multimedia applications: network audio and video (“continuous media”)

network provides

application with level of

performance needed for

application to function.

QoS

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Chapter 7 outline

7.1 multimedia networking applications

7.2 streaming stored audio and video

7.3 making the best out of best effort service

7.4 protocols for real-time interactive applications RTP,RTCP,SIP

7.5 providing multiple classes of service 7.6 providing QoS guarantees

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MM Networking Applications

Fundamental characteristics:

• loss tolerant : infrequent losses cause minor glitches
• typically delay sensitive
  • end-to-end delay
  • delay jitter
• antithesis of data, which are loss intolerant but delay tolerant.

Classes of MM applications:

1. stored streaming

2. live streaming

3. interactive, real-time

7: Multimedia Networking 7-

Jitter is the variability of packet delays within the same packet stream

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Streaming Stored Multimedia:

What is it?

7: Multimedia Networking 7-

1. video recorded
   2. video sent (^) 3. video received, played out at client

streaming: at this time, client playing out early part of video, while server still sending later part of video

network delay (^) time

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Streaming Stored Multimedia:

Interactivity

7: Multimedia Networking 7-

• VCR-like functionality: client can pause, rewind, FF, push slider bar - 10 sec initial delay OK - 1-2 sec until command effect OK
• timing constraint for still-to-be transmitted data: in time for playout

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Real-Time Interactive Multimedia

• 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? 7: Multimedia Networking 7-
• applications: IP telephony, video conference, distributed interactive worlds

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Multimedia Over Today’s Internet

TCP/UDP/IP: “best-effort service”

• no guarantees on delay, loss

7: Multimedia Networking 7-

Today’s Internet multimedia applications use application-level techniques to mitigate (as best possible) effects of delay, loss

But multimedia apps require QoS and level of performance to be effective!

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A few words about audio

compression

• analog signal sampled at constant rate - telephone: 8,000 samples/sec - CD music: 44, samples/sec
• each sample quantized, i.e., rounded - e.g., 2 8 =256 possible quantized values
• each quantized value represented by bits - 8 bits for 256 values - example: 8, samples/sec, 256 quantized values --> 64,000 bps - receiver converts bits back to analog signal: - some quality reduction Example rates - CD: 1.411 Mbps - MP3: 96, 128, 160 kbps - Internet telephony: 5.3 kbps and up

7: Multimedia Networking (^) Docsity.com7-

A few words about video

compression

• video: sequence of images displayed at constant rate - e.g. 24 images/sec
• digital image: array of pixels - each pixel represented by bits
• redundancy
  • spatial (within image)
  • temporal (from one image to next)

Examples:

• MPEG 1 (CD-ROM) 1.5 Mbps
• MPEG2 (DVD) 3-6 Mbps
• MPEG4 (often used in Internet, < 1 Mbps) Research:
• layered (scalable) video
  • adapt layers to available bandwidth

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Streaming Stored Multimedia

application-level streaming techniques for making the best out of best effort service:

• client-side buffering
• use of UDP versus TCP
• multiple encodings of multimedia - jitter removal - decompression - error concealment - graphical user interface w/ controls for interactivity

7: Multimedia Networking 7-

Media Player

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Internet multimedia: simplest

approach

• audio or video stored in file

• files transferred as HTTP

object

• received in entirety at client
• then passed to player

7: Multimedia Networking 7-

audio, video not streamed:

• no “pipelining,”
• long delays until playout! Docsity.com

Streaming from a streaming

server

• allows for non-HTTP protocol between server, media player
• UDP or TCP for step (3)

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Streaming Multimedia: Client

Buffering

client-side buffering, playout delay

compensate for network-added delay, delay

jitter 7: Multimedia Networking^ 7-

constant bit rate video transmission

time

variable network delay

client video reception

constant bit rate video playout at client

client playout delay

bufferedvideo

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