Lecture2: Introduction to Multimedia...

Lecture2: Introduction to

Multimedia Networks

Instructor: Hamid R. Rabiee Spring 2013

Digital Media Lab - Sharif University of Technology 2

Outline

²  Media & Multimedia

²  Characteristics & Requirements

²  Applications

²  Networking principles

²  Multimedia Expectations

²  IP networks

²  Characteristics

²  Challenges

²  Wireless networks

²  Characteristics

²  Challenges

Definitions

²  Media: The form and technology used to communicate information [1]

²  A list of terms correlated with media

²  Multimedia:

diverse classes of media employed to represent information [2]

A better definition: The field concerned with the computer-controlled integration of text, graphics, drawings, still

and moving images (Video), animation, audio, and any other media where every type of information can be

represented, stored, transmitted and processed digitally [3]

²  Multimedia Traffic: The transmission of data representing diverse media over communication networks [2]

²  Multimedia App: An Application which uses a collection of multiple media sources e.g. text, graphics, images,

sound/audio, animation and/or video [3]

²  Multimedia System: a system capable of processing multimedia data and applications [3]

²  Multimedia Networking: the design of networks that can handle multiple media types with ease and deliver

scalable performance [2]


Multimedia Classifications

Classification From a content perspective: ² Text

²  Inherently digital

² Visuals ²  Analog or digital

²  Still or Moving

²  Extensions like BMP, JPG, GIF, TIF, PNG, …

²  Extensions like AVI, MOV, …

² Audio ²  sound/speech converted into digital form

using sampling and quantization

²  Analog or digital

²  Extensions like WAV, MP3, …


Fig. From [2]

Text

Visual Sound

• Formatted text

• Plain text

• Hypertext

• Phonetic transcripts

• Math • Tables

• Line Drawings

• Maps

• Images (Grayscale and Color)

• Animation • Simulation • Virtual Reality

• Music

• Speech (Natural & Synthetic)

• Voices (Animal) • File

• Video • Tele-Conf

Multimedia Classifications (Cont.)

Classification From a networking perspective:

²  Real-Time (RT)

² Hard or soft bounds on the end-to-end packet delay/jitter

²  Non Real-Time (NRT)

² No strict delay constraints

² Rigid constraints on error



²  Real-Time (RT) ²  Discrete media (DM): data is transmitted in discrete quantum as a file or message

²  MSN/Yahoo messengers

²  Continuous media (CM): data is transmitted continuously as a stream of messages with inter-

message dependency

²  delay tolerant: can tolerate higher amounts of delay without significant performance degradation

²  Streaming audio/video media

²  delay intolerant: can not tolerate higher amounts of delay

²  Video Conferencing

²  Non Real-Time (NRT)

²  Text, Data, and image.




Media Types

Continuous

Discrete

Delay Intolerant

Text chat, Instant

Messaging

Weather Updates

Remote Desktop

Applications

Interactive Audio/Video

Delay Tolerant

Streaming Audio/Video

Images Text, Data

Non-Real Time Real Time

Error Intolerant

Summary of QoS Principals [4]


Let’s next look at the mechanisms for achieving this …

Multimedia Quality Requirements

Media Type Example BW Usage error

requirements real-time nature Protocols/ Standards

Text

File transfer

Depends on size

Loss/error intolerant

No real-time (delay/jitter) constraints

FTP, HTTP, SMTP

Instant messaging Error /loss tolerant Some guarantees on the experienced delay

Audio

Two-way communication (Internet-Telephony)

Depends on dynamic range and/or spectrum

Loose requirements on packet loss/error

Bounds on end-to-end packet delay/jitter PCM, GSM,

CS-ACELP , ADPCM ,

MP3 Weaker bounds on delay/jitter

One-way communication (Internet webcast)

Graphics and

Animation

Static (image) Depends on

compression mode Error/loss tolerant No real-time

(delay/jitter) constraints

GIF. PNG, JPEG Dynamic (animation,

flash)

Video - Depends on the

spatial and temporal redundancy

Loose requirements on packet loss/error

Bounds on end-to-end packet delay/jitter

MPEG I, II, IV

H.263


Requirements on network BW/ bitrate


Application Speed Requirement Telephone Audio-conferencing CD-quality audio Digit music (QoS)

16 kbps 32 kbps

128-192 kbps 64-640 kbps

H. 261 H. 263 DVI video MPEG-1 video MPEG-2 video HDTV (compressed) HDTV (uncompressed)

64 kbps-2 Mbps <64 kbps

1.2-1.5 Mbps 1.2-1.5 Mbps 4-60 Mbps >20 Mbps >1 Gbps

MPEG-4 video-on-demand (QoS) Video conferencing (QoS)

250-750 kbps 384 kbps-2 Mbps

Tolerance of latency and jitter


Application Avg Latency

Tolerance (msec)

Avg Jitter Tolerance

(msec) Low-end videoconf. (64 kbps) Compressed voice (16 kbps)

300 30

130 130

MPEG NTSC video (1.5 Mbps) MPEG audio (256 kbps)

5 7

7 9

HDTV video (20 Mbps) 0.8 1

Requirements on Delay & Loss


Packet Loss

Delay (S) Zero Loss

0%

5%

100 (ms) 1(s) 10 (s) 100 (s)

Conversational Voice and video

Voice /video messaging

Streaming Audio/Video

Fax

Command/Control Interactive games

Transaction (E-Commerce, E-mail Access)

Messaging, Downloading

Background (eg: Use Net)

Performance Targets for Audio/Video Apps

Medium Application Degree of Symmetry

Typical Data Rate (Kb/s)

Key Performance Parameters and Target Values

One-Way Delay

Delay-Variation Information Loss

Audio Conversatio

nal Voice Two-Way 4-64

< 150 msec Preferred

<400 msec limit

< 1 msec < 3% Packet Loss

Ratio (PLR)

Audio Voice

Messaging Primarily One-Way

4-32

< 1 sec for playback <2 sec for

record

< 1 msec < 3% PLR

Audio

High Quality

Streaming Audio

Primarily One-Way

16-128 < 10 sec < 1 msec < 1% PLR

Video Video Phone

Two-Way 16-384

< 150 msec Preferred

<400 msec limit

< 1% PLR

Video One-Way One-Way 16-384 < 10 sec < 1% PLR


Performance Targets for Data Apps

Medium Application Degree of Symmetry

Typical amount of Data

(KB)

Key Performance Parameters and Target Values

One-Way Delay Delay-

Variation Information

Loss

Data Web-

browsing – HTML

Primarily One-Way

~ 10

Preferred < 2sec/ page

Acceptable < 4sec/page

N. A. 0

Data

Transaction Services –

High Priority e.g. e-

Commerce, ATM

Two-Way < 10

Preferred < 2sec

Acceptable < 4sec

N. A. 0

Data Command/

Control Two-Way ~ 1 < 250 msec N. A. 0

Data Interactive

Games Two-Way < 1 < 200 msec N. A. 0

Data Telnet Two-Way

(Asymmetric)

< 1 < 200 msec N. A. 0

Data E-mail (server access)

Primarily One-Way

< 10

Preferred < 2sec

Acceptable < 4sec

N. A. 0


How does Multimedia Networking Differ?

²  Data Formatting ²  the only universal data standard is ASCII …

²  Data Volume

²  many times there are several fat chunks …

²  Data Delivery Demands ²  synchronization & real-time requirements …

²  Interactive Data Exchange

²  user sensitive to response time …

²  Complex Communication Scenarios

²  additional meta-communication needed …


Classes of Multimedia Apps on the Network

²  Streaming stored media

²  Stored on server

²  Examples: pre-recorded songs, famous lectures, video-on-demand

²  Streaming live media

²  “Captured” from live camera, radio, T.V.

²  1-way communication, maybe multicast

²  Examples: concerts, radio broadcasts, lectures

²  Real-time interactive media

²  2-way communication

²  Examples: Internet phone, video conference


Multimedia Transmission Modes

²  Asynchronous

²  No temporal restriction in data delivery

²  Synchronous

²  Maximal end-to-end delivery delay

²  Isochronous ²  Maximal and minimal end-to-end delivery delay

²  Pseudo-Synchronous

²  Simulated or weakly bound end-to-end delivery delay


MM Communication Aspects

²  Type: Distribution

²  Audio/Video Broadcast, Web, Archives

²  Typical Aspects

²  Asynchronous or pseudo synchronous transmission

²  Client/Server Model, one to many (concurrent)

²  Unidirectional, low interactivity


MM Communication Aspects (Cont.)

²  Type: Exchange

²  Audio/Video Conferencing, Telelearning, Collaboration Tools

²  Typical Aspects ²  Synchronous or isochronous transmission

²  Peer-to-peer, one to one (or multipoint)

²  Bidirectional, high interactivity



²  Type: Production

²  Multimedia authoring, recording, (Email)

²  Typical Aspects ²  Synchronous or pseudo synchronous transmission

²  Client/Server Model, one to many (competitive)

²  Unidirectional, high interactivity



²  Type: Synchronization

²  Data synchronization, (synchronized) multi-archive retrieval, software distribution

²  Typical Aspects ²  Any mode of transmission

²  Client/Server Model, one to one or many

²  Uni or bidirectional, low interactivity


Multimedia over Network

²  Multimedia Expectations from a Communication Network

²  traffic requirements

²  limits on real-time parameters (delay, jitter), bandwidth and reliability

² Solutions: enhancements to the basic Internet Architecture

²  functional requirements

² support for multimedia services such as multicasting, security, mobility and

session management

² Solutions: introducing newer protocols over the TCP/IP networking stack

² Without these mechanisms, multimedia applications can operate with high

performance by incorporating the necessary functions into the application itself


Traffic Requirements over Network

²  Traffic requirements

²  Real-time Characteristics (Limits on Delay and Jitter)

² End-to-end delay: time taken by the packet to travel from the source to the destination

²  Jitter: variability in the inter-packet delay at the receiver

²  Need for Higher Bandwidth

² Compression techniques are not enough

²  Some times compression is not possible/allowable

²  Error Requirements

² When a packet is lost or damaged, error occurs


Functional Requirements over Network

²  Functional requirements ²  Multicasting Support

²  single source of communication with multiple simultaneous receivers

²  Need for distributed multimedia applications (multi-party audio/video conferencing)

²  Session Management

²  Media Description

²  Session information Distribution

²  Session Announcement

²  Announcement to participants about future sessions

²  Session Identification

²  Identification of separate/ integrated medias

²  Session Control

²  Multimedia Synchronization

²  Playback Controlling


Functional Requirements over Network (Cont.)

²  Security

²  Integrity (data cannot be changed in mid-flight)

²  Authenticity (Data comes from the right source)

²  Encryption (Data cannot be deciphered by any third party)

²  Copyrights

²  watermarking

²  Mobility Support

²  Wireless Networks


Networking Principles

²  Traditionally voice, video, and textual data have been handled by different

communication networks ²  Voice over telephone networks

²  Video over cable TV networks

²  Textual data over computer networks

²  Reasons for the separation: fundamental differences in the characteristics of

voice and video from textual data ²  Voice and video: real-time, requires bounded delay, tolerant to brief loss of information

²  Textual data: Tolerant to delay but cannot tolerate any transmission error or loss

²  Two fundamental mechanisms: circuit switching and packet switching


Circuit Switching

²  Characteristics: ²  Dedicated physical path from source to destination for the entire call duration

²  Fixed and dedicated bandwidth allocation

²  No data processing at intermediate nodes

²  Advantages: ²  Information delivery guaranteed to be sequenced

²  No overhead at intermediate nodes

²  Fixed end-to-end delay

²  Disadvantages: ²  Burst data may cause severe underutilization of network resources

²  Call setup requires round-trip latency

²  Short sessions are not cost effective

²  Unicast by nature


Packet Switching

²  Characteristics:

²  Dynamic allocation of bandwidth

²  Store-and-forward switching

²  Advantages:

²  Extremely flexible: supports both unicast and multicast transmission

²  Suitable for bursty traffic: permits network resources to be multiplexed among several

channels

²  Disadvantages:

²  Variable end-to-end delay due to queuing at switches

²  Information delivery may not be sequenced or reliable


IP Networks

²  IP network, especially Internet, is becoming a very attractive channel for

multimedia communications ²  Dedicated networks and ATM are not widely available

²  There are many applications for Internet multimedia:

² Internet telephone, Internet TV, video conferencing, network games, remote

colaboration, ….

²  IP is a best-effort communications technology, hard to provide QoS over IP by

current routing methods

²  Abundant bandwidth improves QoS, but unlikely to be available everywhere over

complex networks


Challenges of Transporting MM over IP Networks

²  IP uses packet switching ²  Suitable for unexpected burst of data without establishing an explicit connection.

²  Bandwidth is shared statistically, so data can be sent at any time.

²  IP is not reliable nor delay-bounded ²  Best effort

²  Internet cannot provide delay/jitter bounds.

²  Network failures can cause temporary packet loss.

²  Time critical applications cannot operate well due to large e-mail attachments and

web surfing

²  There is no delivery guarantee


Challenges of Transporting MM over IP Networks (Cont.)

²  TCP/IP networks such as the Internet provide two types of services to

applications ²  “connection-oriented” service – Transmission Control Protocol (TCP)

²  TCP is bundled with reliability, congestion control, and flow control

²  no guarantees on delay and jitter

²  “connectionless” service - User Datagram Protocol (UDP)

²  short playout delay (2-5 seconds) to compensate for network delay/jitter

²  No reliability

²  No congestion & flow control services

²  So, which one is proper for multimedia applications?

²  Today’s Internet multimedia applications use application-level techniques to mitigate (as best

as possible) effects of delay and loss


Proposed Service Models for the IP networks

²  We discuss about these mechanisms during this term


Wireless Networks

²  In wireless networks, multimedia transmission inherits all the

characteristics and constrains of the propagation in the free space.

²  Two main differences between wired and wireless networks

²  Packet Loss

²  Mobility


Challenges of Transporting MM on Wireless Networks

²  Link Failures

²  Packet Loss ²  Due to low Signal to Noise Ratio (SNR), the multi-path signal fading and the

interference from neighboring transmissions

²  Network Capacity

²  Maximum data rate varies from 11Mbps to 54Mbps for 802.11b and 802.11g

²  Network Latency

²  Hop-by-hop transmission

²  Single radio channel nature of networks


Challenges of Transporting MM on Wireless Networks (Cont.)

²  Hand off

²  It imposes delay, loss

²  Admission Control

²  The mobile device cannot recognize if sufficient QoS resources are available at a

new AP till after the handoff

²  Network Routing

²  QoS routing protocols are needed!


References

1.  http://www.webopedia.com

2.  Shashank Khanvilkar, Faisal Bashir, Dan Schonfeld, and Ashfaq Khokhar,

“Multimedia Networks and Communication”, University of Illinois,

Chicago, 2004.

3.  Dave Marshall, “Introduction to Multimedia”, Cardiff School of Computer

Science, Cardiff University , 2001.


Digital Media Lab - Sharif University of Technology

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