lecture2: introduction to multimedia...
TRANSCRIPT
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Lecture2:
Introduction to
Multimedia Networks
Instructor: Hamid R. Rabiee
Spring 2012
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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
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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]
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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, …
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Fig. From [2]
•Math
•Tables•Phonetic
transcripts
TEXT
VISUALS SOUND
•Formatted Text
•Plain Text •Hypertext
•Line Drawings
•Maps
•Images (Grayscale and
Color)•Animation
•Simulation
•Virtual Reality
•File
•Video
•Tele-Conference
•Music
•Speech
(Natural & Synthetic)
•Voices
(Animal)
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Multimedia Classifications
Classification From a 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
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Multimedia Classifications
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
Non Real-Time (NRT)
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
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Multimedia Classifications
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Summary of QoS Principals [4]
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Let’s next look at mechanisms for achieving this …
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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)
Video -
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.263
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Requirements on network BW/ bitrate
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Tolerance of latency and jitter
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Requirements on Delay & Loss
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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)
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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 Conversation
al 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
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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
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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 …
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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
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Multimedia Transmission Modes
Asynchronous
No temporal restriction in data delivery
Synchronous
Maximal end-to-end delivery delay
Isochronous
Maximal and minimal end-to-end delivery delay
Pseudo-Synchronous
Simulated or weakly bound end-to-end delivery delay
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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
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MM Communication Aspects (Cont…)
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
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MM Communication Aspects (Cont…)
Type: Production
Multimedia authoring, recording, (Email)
Typical Aspects
Synchronous or pseudo synchronous transmission
Client/Server Model, one to many (competitive)
Unidirectional, high interactivity
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MM Communication Aspects (Cont…)
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
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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
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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 nit enough
Some times compression is not possible/allowable
Error Requirements
When a packet is loss or damaged, error occurs
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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
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Functional Requirements over Network (Cont…)
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
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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
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Circuit Switching
Characteristics:
Dedicated physical path from source to destination for the entire call duration
Fixed and dedicated bandwidth allocation
No data processing at intermediate nodes
Advantages:
Information delivery guaranteed to be sequenced
No overhead at intermediate nodes
Fixed end-to-end delay
Disadvantages:
Burst data may yield severe underutilization of network resources
Call setup requires round-trip latency
short sessions are not cost effective
Unicast by nature
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Packet Switching
Characteristics:
Dynamic allocation of bandwidth
Store-and-forward switching
Advantages
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
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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
coloboration, ….
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
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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
There is no delivery guarantee
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Challenges of Transporting MM on IP Networks (Cont..)
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 as possible) effects of delay, loss
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Proposed Service Models for the IP networks
We discuss about these mechanisms during this term
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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
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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
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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 AP until after the handoff
Network Routing
QoS routing protocols are needed!
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Next Session
Audio
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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.
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Acknowledgement
The following graduate students have helped to prepare the slides for this
course:
Mostafa Salehi
Fatemeh Dabiran
Hoda Ayatollahi
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