Lecture2: Introduction to Multimedia Networksce.sharif.edu/courses/89-90/2/ce873-1/resources/root... · 2015-04-06 · Lecture2: Introduction to Multimedia Networks Hamid R. Rabiee

Lecture2:

Introduction to

Multimedia Networks

Hamid R. Rabiee

Mostafa Salehi, Fatemeh Dabiran, Hoda Ayatollahi

Spring 2011

Digital Media Lab - Sharif University of Technology2

Outlines

Media & Multimedia

Characteristics & Requirements

Applications

Networking principles

Multimedia Expectations

IP networks

Characteristics

Challenges

Wireless networks

Characteristics

Challenges

Definitions

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

A list of terms correlated with media

Multimedia: diverse classes of media employed to represent information [2]

Or a better definition:

Multimedia : 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]

Multimedia Traffic: The transmission of data representing diverse media over communication

networks [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]

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

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

deliver scalable performance [2]


Summary of QoS Principles [4]

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

Multimedia Classifications

Text

Inherently digital

Visuals

Analog or digital

Still or Moving

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

Extensions like AVI, MOV, …

Audio

sound/speech converted into digital form using sampling and quantization

Analog or digital

Extensions like WAV, MP3, …


Pic. From [2]


Classification From the networking perspective

Real-Time (RT)

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

Non Real-Time (NRT)

No strict delay constraints

Rigid constraints on error



Real-Time (RT)

Discrete media (DM): data is transmitted in discrete quantum as a file or message

MSN/Yahoo messengers

Continuous media (CM): data is transmitted continuously as a stream of messages

with inter-message dependency

Video Conferencing

Real-Time (RT)

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

degradation

Streaming audio/video media

delay intolerant: can not tolerate higher amounts of delay

Video Conferencing




Multimedia Quality Requirements

Media

TypeExample BW Usage

error

requirementsreal-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 tolerantsome 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/jitterPCM, GSM,

CS-ACELP ,

ADPCM ,

MP3weaker bounds on

delay/jitterone-way communication

(Internet webcast)

Graphics

and

Animation

Static (image)Depends on

compression modeError/loss tolerant

No real-time

(delay/jitter)

constraints

GIF. PNG,

JPEGDynamic (animation,

flash)

VideoVideo conferencing,

video multicasting

depend on the spatial

redundancy, temporal

redundancy

loose

requirements on

packet loss/error

bounds on end-to-end

packet delay/jitter

MPEG I, II,

IV, H.264,

H.263


Requirements on network BW/ bitrate


Tolerance of latency and jitter


Requirements on Delay & Loss


Performance Targets for Audio/Video Apps

Medium Application

Degree

of

Symmet

ry

Typical

Data

Rate

(Kb/s)

Key Performance Parameters and Target Values

One-Way

DelayDelay-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

Primaril

y One-

Way

4-32 < 1 sec for

playback

<2 sec for

record

< 1 msec < 3% PLR

Audio High Quality

Streaming

Audio

Primaril

y 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 ApplicationDegree of

Symmetry

Typical

amount

of Data

(KB)

Key Performance Parameters and Target Values

One-Way Delay Delay-VariationInformation

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?

Data Formatting

the only universal data standard is ASCII …

Data Volume

many times there are several fat chunks …

Data Delivery Demands

synchronization & real-time requirements …

Interactive Data Exchange

user sensitive to response time …

Complex Communication Scenarios

additional meta-communication needed …


Classes of Multimedia Apps on the Network

Streaming stored media

Stored on server

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

Streaming live media

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

1-way communication, maybe multicast

Examples: concerts, radio broadcasts, lectures

Real-time interactive media

2-way communication

Examples: Internet phone, video conference


Multimedia Transmission Modes

Asynchronous

No temporal restriction in data delivery (refers to processes in which data

streams can be broken by random intervals)

Synchronous

Maximal end-to-end delivery delay (in which data streams can be delivered

only at specific intervals)

Isochronous

Maximal and minimal end-to-end delivery delay (is not as rigid as

synchronous service, but not as lenient as asynchronous service)

Pseudo-Synchronous

Simulated or weakly bound end-to-end delivery delay


MM Communication Aspects

Type: Distribution

Audio/Video Broadcast, Web, Archives

Typical Aspects

Asynchronous or pseudo synchronous transmission

Client/Server Model, one to many (concurrent)

Unidirectional, low interactivity



Type: Exchange

Audio/Video Conferencing, Telelearning, Collaboration Tools

Typical Aspects

Synchronous or isochronous transmission

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

Bidirectional, high interactivity



Type: Production

Multimedia authoring, recording, (Email)

Typical Aspects

Synchronous or pseudo synchronous transmission

Client/Server Model, one to many (competitive)

Unidirectional, high interactivity



Type: Synchronization

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

distribution

Typical Aspects

Any mode of transmission

Client/Server Model, one to one or many

Uni- or bidirectional, low interactivity


Multimedia over Network

Multimedia Expectations from a Communication Network

traffic requirements

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

Solutions: enhancements to the basic Internet Architecture

functional requirements

support for multimedia services such as multicasting, security,

mobility and session management

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

Without these mechanisms, multimedia applications can operate with high

performance by incorporating the necessary functions into the application

itself


Traffic Requirements over Network

Traffic requirements

Real-time Characteristics (Limits on Delay and Jitter)

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

destination

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

Need for Higher Bandwidth

Compression techniques are not enough

Some times compression is not possible/allowable

Error Requirements

When a packet is loss or damaged, error occurs


Functional Requirements over Network

Functional requirements

Multicasting Support

single source of communication with simultaneous multiple receivers

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

Session Management

Media Description

Session information Distribution

Session Announcement

Announcement to participants about future sessions

Session Identification

Identification of separate/ integrated medias

Session Control

Multimedia Synchronization

Playback Controlling


Functional Requirements over Network

Functional requirements

Security

Integrity (Data cannot be changed in mid-flight)

Authenticity (Data comes from the right source)

Encryption (Data cannot be deciphered by any third party)

Copyrights

watermarking

Mobility Support

Wireless Networks


Networking Principles

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

communication networks

Voice over telephone networks

Video over cable TV networks

Textual data over computer networks

Reasons for the separation: fundamental differences in the characteristics of

voice and video from textual data

Voice and video: real-time, requires bounded delay, tolerant to brief loss of

information

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

Two fundamental mechanisms: circuit switching and packet switching


Circuit Switching

Characteristics:

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

Fixed and dedicated bandwidth allocation

Fixed end-to-end delay

No data processing at intermediate nodes

no overhead at intermediate nodes

Information delivery guaranteed to be sequenced

Disadvantages:

Bursty data may yield severe underutilization of network resources

Call setup requires round-trip latency

short sessions are not cost effective

Unicast by nature


Packet Switching

Characteristics:

Dynamic allocation of bandwidth

Store-and-forward switching

Extremely flexible: supports both unicast and multicast transmission

Suitable for bursty traffic, permits network resources to be multiplexed among

several channels

Disadvantages:

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

Information delivery may not be sequenced or reliable


IP Networks

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

for multimedia communications

Dedicated networks and ATM are not widely available

There are many applications for Internet multimedia:

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

corroboration, ….

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

over IP by current routing methods

Abundant bandwidth improves QoS, but unlikely to be available

everywhere over a complex networks


Challenges of Transporting MM on IP Networks

IP uses packet switching

Suitable for unexpected burst of data without establishing an explicit

connection.

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

IP is not reliable nor delay-bounded.

Best effort

Internet cannot provide delay/jitter bounds.

Network failures can cause temporary packet loss.

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

attachments and Web surfing

There is no delivery quarantine


Challenges of Transporting MM on IP Networks

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

applications

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

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

no guarantees on delay and jitter

“connectionless” service - User Datagram Protocol (UDP)

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

No reliability

No congestion & flow control services

So, which one is proper for multimedia applications?

Today’s Internet multimedia applications use application-level techniques to mitigate

(as best possible) effects of delay, loss


Proposed Service Models for the IP networks

We discuss about these mechanisms during this term


Wireless Networks

In wireless networks multimedia data transmission inherits also all the

characteristics and constrains related to the propagation to the free space.

2 main differences between wired and wireless network

Packet Loss

Mobility


Challenges of Transporting MM on Wireless Networks

Link Failures

Packet Loss

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

interference from neighboring transmissions

Network Capacity

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

Network Latency

Hop-by-hop transmission

Single radio channel nature of networks


Challenges of Transporting MM on Wireless Networks

Hand off

It imposes delay, loss

Admission Control

The mobile device cannot know if necessary QoS resources are available

at a new access point (AP) until after the handoff

Network Routing

QoS routing protocols are needed!


References

1. http://www.webopedia.com (accessed Feb. 2011)

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.

4. Jim Kurose, Keith Ross, “Computer Networking: A Top Down Approach

Featuring the Internet”, 2nd edition. Addison-Wesley, July 2002.


http://www.webopedia.com/

Documents

Lecture2: Introduction to Multimedia Networksce.sharif.edu/courses/89-90/2/ce873-1/resources/root... · 2015-04-06 · Lecture2: Introduction to Multimedia Networks Hamid R. Rabiee