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: spaced-based, media involve the space dimension only
• Continuous media: time-based, media involves both the space and the
time dimension
4. 4
Classification of Media Type
Sound Video
Image
Animation
Text Graphics
Captured
From real world
Synthesized
By computer
Discrete Discrete
Continuous Continuous
5. Text
• Plain 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. 6
Plain Text vs. Rich Text
An example of Plain text Example of Rich text
7. 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
-4
-2
0
2
4
-4
-2
0
2
4
-10
-5
0
5
10
Example of
graphics (FIG file)
8. 8
Images
• 2D matrix consisting of pixels
– 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
image
Camera
9. 9
Sound
• 1-D time-based signal
• Speech vs. non-speech sound
– Speech – supports spoken language and has a semantic content
– Non-speech – does no
– t 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
0 100 200 300 400 500 600 700 800 900 1000
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
10. EE442 Multimedia Networking 10
Networked Multimedia
• Local vs. networked multimedia
– 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 Email, etc.
Internet
Video server
Image serverA scenario of multimedia networking
11. Consideration of Networked Multimedia
• Characteristics of multimedia information
– Large data volume
Exercise: What is the size of a video clip of 60 minutes if the frame size is
640*480, the pixel depth is 24, and the frame rate is 24 fps?
– Real-time property
• Continuous display
• Delay requirement of multimedia applications
• Properties of current Internet
– Limitation of bandwidth
– Best effort network, cannot guarantee quality of multimedia applications
– Heterogeneity
• Different user requirements
• Different user network conditions
12. Consideration of Networked
Multimedia
• Requirements of multimedia applications on the network
– Delay requirement
– Quality requirement
• Satisfactory quality of media presentation
• Synchronization requirement
• Continuous requirement (no jerky video/audio)
• Can tolerant some degree of information loss
• 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?
13. Technologies of Multimedia
Networking
• Media compression – reduce the data volume
Address the1st 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
14. 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
15. 15
Generic Media Streaming System
Video
Encoder
Input video
Compressed
Video
Streaming
Server
Internet
ReceiverVideo
Decoder
Video Display
Error control, rate
control can be done
here to improve QoS
Error control, provide
feedback to the sender
Compressed Video
Video Packets
16. Synchronous Time Division
Multiplexing
• Data rate of medium exceeds data rate of
digital signal to be transmitted
• Multiple digital signals interleaved in time
• May be at bit level of blocks
• Time slots preassigned to sources and fixed
• Time slots allocated even if no data
• Time slots do not have to be evenly
distributed amongst sources
19. TDM Link Control
• No headers and trailers
• Data link control protocols not needed
• Flow control
– Data rate of multiplexed line is fixed
– If one channel receiver can not receive data, the others must carry on
– The corresponding source must be quenched
– This leaves empty slots
• Error control
– Errors are detected and handled by individual channel systems
22. ATM
• By the mid 1980s, three types of communication
networks had evolved.
• The telephone network carries voice calls, television
network carries video transmissions, and newly
emerging computer network carries data.
• Telephone companies realized that voice
communication was becoming a commodity service
and that the profit margin would decrease over time.
• They realized that data communication was
increasing.
• The telecommunication industry decided to expand
its business by developing networks to carry traffic
other than voice.
23. Goal of ATM (extremely ambitious)
• Universal Service
• Support for all users
• Single, unified infrastructure
• Service guarantees
• Support for low-cost Devices
24. ATM
• The phone companies created Integrated Service
Digital Network (ISDN) and Asynchronous Transfer
Mode (ATM).
• ATM is intended as a universal networking
technology that handles voice, video, and data
transmission.
• ATM uses a connection-oriented paradigm in which
an application first creates a virtual channel (VC),
uses the channel for communication, and then
terminates it.
• The communication is implemented by one or more
ATM switches, each places an entry for the VC in its
forwarding table.
25. ATM
• There are two types of ATM VCs: a PVC is
created manually and survive power failures,
and an SVC is created on demand.
• When creating a VC, a computer must specify
quality of service (QoS) requirements.
• The ATM hardware either reserves the
requested resources or denies the request.
26. Development of ATM
• ATM designers faced a difficult challenge because the
three intended uses (voice, video, and data) have
different sets of requirements.
• For example, both voice and video require low delay
and low jitter (i.e. low variance in delay) that make it
possible to deliver audio and video smoothly with
gaps or delays in the output.
• Video requires a substantially higher data rate than
audio.
• Most data networks introduce jitter as they handle
packets.
27. Development of ATM
• To allow packet switches to operate at high
speeds and to achieve low delay, low jitter, and
echo cancellation, ATM technology divides all
data into small, fixed-size packets called cells.
• Each ATM cell contains exactly 53 octets.
• 5 octets for header
• 48 octets for data
28. ATM Cell Structure
Flow Control VPI (First 4 bits)
VPI (Last 4 bits) VCI (First 4 bits)
VCI (Middle 8 bits)
VCI (Last 4 bits) Payload
type
PRIO
Cyclic Redundancy Check
Bits: 0 7
48 Data Octets start here
29. ATM design and cells
• ATM was designed to be completely general. We will
large cell for data and small cell for voice.
• In ATM, cell size is chosen as a compromise between
large cells and small cells.
• Header is 10% of the payload area.
• In Ethernet: data => 1500 octets
header => 14 octets
cell tax =>1%
• In ATM: data => 48 octets
header => 5 octets
cell tax => 10%
30. ATM : Connection oriented
• After the establishment of a connection
between sender and receiver, the network
hardware returns a connection identifier (a
binary value) to each of the two computers.
• When sender sends cells, it places the
connection identifier in each cell header.
• When it receives a cell, an ATM switch
extracts the connection identifier and consults
a table to determine how to forward the cell.
31. VPI/VCI
• Formally, an ATM connection is known as a virtual
channel (VC).
• ATM assigns each VC a 24-bit identifier that is
divided into 2 parts to produce a hierarchy.
• The first part, a virtual path identifier (VPI), specifies
the path the VC follows through the network.
• A VPI is 8 bits long.
• The second part, a Virtual Channel Identifier (VCI),
specifies a single VC within the path.
• A VCI is 16 bits long.
33. ATM Protocol Layer
• Physical Layer: The lowest layer in the ATM protocol. It
describes the physical transmission media. We can use
shielded and unshielded twisted pair, coaxial cable, and fiber-
optic cable.
• ATM Layer: It performs all functions relating to the routing
and multiplexing of cells over VCs. It generates a header to the
segment streams generated by the AAL. Similarly, on receipt
of a cell streams, it removes the header from the cell and pass
the cell contents to the AAL protocol. To perform all these
functions, the ATM layer maintains a table which contains a
list of VCIs.
34. ATM Protocol Layer
• ATM Adaptation Layer: Top layer in the ATM protocol
Model. It converts the submitted information into streams of
48-octet segments and transports these in the payload field of
multiple ATM cells. Similarly, on receipt of the stream of cells
relating to the same call, it converts the 48-octet information
field into required form for delivery to the particular higher
protocol layer. Currently five service types have been defined.
They are referred to as AAL1-5. AAL1 and AAL2 are
connection oriented. AAL1 provides a constant bit rate (CBR)
service, where as AAL2 provides a variable bit rate (VBR)
service. Initially, AAL 3 was defined to provide connection
oriented and VBR service. Later, this service type was dropped
and it is now merged with AAL 4. Both AAL ¾ and AAL 5
provide a similar connectionless VBR service.
35. Disadvantages
• ATM has not been widely accepted. Although
some phone companies still use it in their
backbone networks.
• The expense, complexity and lack of
interoperability with other technologies have
prevented ATM from becoming more
prevalent.
36. Disadvantages
• Expense: ATM technology provides a comprehensive lists of
services, even a moderate ATM switch costs much more than
inexpensive LAN hardware. In addition, the network interface
card needed to connect a computer to an ATM network is
significantly more expensive than a corresponding Ethernet
NIC.
• Connection Setup Latency: ATM’s connection-oriented
paradigm introduces significant delay for distant
communication. The time required to set up and tear down the
ATM VC for distant communication is significantly larger than
the time required to use it.
37. Disadvantages
• Cell Tax: ATM cell headers impose a 10% tax on all data
transfer. In case of Ethernet, cell tax is 1%.
• Lack of Efficient Broadcast: Connection-oriented networks
like ATM are sometimes called Non Broadcast Multiple
Access (NBMA) networks because the hardware does not
support broadcast or multicast. On an ATM network, broadcast
to a set of computers is ‘simulated’ by arranging for an
application program to pass a copy of the data to each
computer in the set. As a result, broadcast is in efficient.
38. Disadvantages
• Complexity of QoS: The complexity of the
specification makes implementation
cumbersome and difficult. Many
implementations do not support the full
standard.
• Assumption of Homogeneity: ATM is designed
to be a single, universal networking system.
There is minimal provision for interoperating
with other technologies
