multimedia communications
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Electrical Communication Engineering, Indian Institute of Science, Bangalore – 560012, India. Multimedia Communications. Objectives. To know the networking evolution. To understand the network types. To discuss multimedia requirements in the communication systems. - PowerPoint PPT PresentationTRANSCRIPT
E0262 - Multimedia Communications
Electrical Communication Engineering,Indian Institute of Science, Bangalore – 560012, India
Multimedia Communications
E0262 - Multimedia Communications
Objectives To know the networking evolution.
To understand the network types.
To discuss multimedia requirements in the
communication systems.
To understand the basics of a multimedia
communication system.
To illustrate multimedia networks.
To know the Internet protocol suite for multimedia
communications.
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The network formed by the co-operative
interconnection of a large number of computer
networks.
Every person who makes a connection owns a slice of the Internet.
The connected networks use the TCP/IP protocol.
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Application of Internet Telnet-Remote login
File Transfer Protocol (FTP)
Electronic Mail (Email)
Gopher
Internet Relay Chat (IRC)
Usenet News
World Wide Web (WWW)
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Computer Network
A communication system for connecting
computers / hosts
Why?
Better communication
Better sharing of resources
Bring people together
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Types of Computer NetworksLocal Area Network (LAN)
Connects hosts within a relatively small
geographical area.
Same room
Same building
Same campus
It is Faster: speeds- 10 Mbps to 10 Gbps
Cheaper-1 crore for a hundred node LAN (one-time
cost)
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Network Topologies Evolution LAN
Linear topology- Single segment LAN in linear
topology. Ethernets and token rings were cables
connecting each station
Star-wired-to avoid rewiring, Multistation access
units (MAUs) introduced. Hubs were used.
Multisegment-Bridges and routers connected
several LANs.
Backbone-connected-Backbone network
Switched-backbone-Replacement of backbone with
high bandwidth Switch.
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Internetworking Devices Hub- Extends the span of a single LAN.
Bridge / Layer-2 Switch
Connects two or more LANs together.
Works at data link layer level.
Router / Layer-3 Switch
Connects any combination of LANs and WANs.
Works at network layer level.
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Types of LANs
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WAN Wide Area Network (WAN)
Hosts may be widely dispersed
Across campuses
Across cities / countries/ continents
It is faster and cheaper
Typical speeds- 64 Kbps to 8 Mbps
Typical cost- 30 lakhs (recurring cost)
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Internet
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How to get connected to internet
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Gateway access- Level one connection, Access to
internet from a network that is not on internet. ISP
defines the limitations.
Good example of network with Level One connectivity within India is that of VSNL (Videsh
Sanchar Nigam Limited). All access to Internet from India are through VSNL gateway.
Dial up connection- Level two connection. Computer that provide
Connection to internet is called host and computer that receives the
Access is client. Also called remote modem access.
Leased connection-Direct internet access or level three connection.
Secure, dedicated expensive connection.Leased internet connections
Are connections limited to large corporations and universities that
Can afford the cost.
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Circuit Switching A dedicated communication path is required
between two stations. The path follows a fixed
sequence of intermediate links.
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In circuit switching, three steps are required for
communication:
Connection establishment
Required before data transmission.
Data transfer
Connection termination
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Drawbacks:
Channel capacity gets dedicated during the entire
duration of communication.
Acceptable for voice communication.
Very inefficient for bursty traffic.
There is an initial delay.
For connection establishment.
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Packet Switching Network resources are not dedicated.
A link can be shared.
Data are transmitted in short packets(~ Kbytes).
A longer message is broken up into smaller chunks.
The chunks are called packets.
Every packet contains a header.
Relevant information for routing, etc.
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Packet switching is based on store-and-forward
concept.
Each intermediate network node receives a whole
packet.
Decides the route.
Forwards the packet along the selected route.
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Advantages:
Links can be shared; so link utilization is better.
Suitable for computer-generated traffic.
Typically bursty in nature.
Buffering and data rate conversion can be performed
easily.
Some packets may be given priority over others, if
desired.
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How are the packets transmitted?
Two alternative approaches:
Virtual Circuits: Similar in concept to circuit
switching.
A route is established before packet transmission
starts.
All packets follow the same path.
The links comprising the path are not dedicated.
Datagram:No route is established beforehand.
Each packet is transmitted as an independent entity.
Does not maintain any history.
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Every intermediate node has to take routing
decisions dynamically.
Makes use of a routing table.
Every packet must contain source and destination
addresses.
Problems:
Packets may be delivered out of order.
If a node crashes momentarily, all of its queued
packets are lost.
Duplicate packets may also be generated.
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Advantages:
Faster than virtual circuit for smaller number of
packets.
No route establishment and termination.
More flexible.
Packets between two hosts may follow different
paths.
Can handle congestion/failed link.
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Three types of delays must be considered:
Propagation Delay: Time taken by a data signal to
propagate from one node to the next.
Transmission Time: Time taken to send out a
packet by the transmitter.
Processing Delay: Time taken by a node to
“process” a
packet.
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Multimedia Requirements For smooth running of multimedia applications over networks,
three issues need to be addressed.
To develop schemes for multi-access networks which can
provide performance guarantees.
To develop a distribute route-selection strategy for point-to-
point networks.
Real-time multimedia applications require guaranteed
performance communication services, such as throughput,
delay, delay jitter and loss rate.
The characteristics of a source, such as peak and average rate,
are known at channel establishment time.
Channel parameters have to be predicted in live continuous
video sources.
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Communication Service for Multimedia Quality-of-service (QoS) support and group communication
system:
establishment and take-down of appropriately configured
channels;
negotiation of QOS levels between end-systems, intermediate
systems, and network control; and
control of the agreed QOS level
bandwidth, delay, delay jitter (variance), and reliability.
Audio/Video groups can:
have static or dynamic memberships during their lifetime,
have centrally (typically sender) or distributively (typically receiver)
controlled membership,
consist of members with homogeneous or be heterogeneous
characteristics and requirements.
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Multimedia Communication System Multimedia Communication system (MCS) –
system that handles more than one media stream in
synchronized way from user's point of view.
Communication system-A system or facility capable
of providing information transfer between persons
and equipment.
It consist of collection of communication networks,
transmission system, relay stations, tributary
stations and terminal equipment.
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Multimedia Application Environment
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Terms and definitionsBandwidth-is a measurement of bit-rate of available or
consumed data communication resources expressed
in bits per second or multiples of it (bit/s, kbit/s,
Mbit/s, Gbit/s, etc.).
CD-ROM: “Compact disk read-only memory.” most
popular method of delivery of MM materials.
Client-Server Model: A client makes a request and a
server fulfills that request.
Composite Video: Analog video signals can be broken
down into parts such as luminance (Black & White)
and chrominance (color).
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Multimedia File types
Here are some examples of file types:
Text Files: .txt, .doc, .rtf
Audio Files: .au, .aif, .wav
Graphic
files: .jpg, .gif, .tif, .bmp, .pict, .pcx
Moving video files: .qt, .mov, .avi
Animation: .fli, .flc
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Multimedia Communication System
Interactive Multimedia Design- Interactive multimedia is becoming
increasingly popular in education, entertainment, and business.
Because of the capability of incorporating various media, and of
supporting interactivity and learner control, multimedia is often
used in delivering instruction.
Interleaved-synchronization of audio and video- lip
synchronization with audio.
Interlacing-A TV video signal is interlaced, meaning each full
screen of information is actually made up of two separate fields
—the odd field and the even field. First, the odd lines are
painted on the screen. Then, before the odd lines fade, the
even lines are painted in between the odd lines. This all
happens faster than the human eye can perceive
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Multimedia may be broadly divided into linear and non-
linear categories.
Linear active content progresses without any
navigation control for the viewer such as a cinema
presentation.
Non-linear content offers user interactivity to control
progress as used with a computer game or used in
self-paced computer based training. Hypermedia is
an example of non-linear content.
Presentation Multimedia-combination of digitized audio,
video, graphics, etc.
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Multimedia Communication System LAN Access Method
Routing
Frame and Packet Structures
Packet Discrimination
Identify packets that require special handling.
Be capable of accommodating those special
requirements.
Bandwidth Requirement, Reservation and
Conservation
High bandwidth and low latency
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Multimedia Communication System Architecture The ability to manage dynamically the achieved QoS of each service
component
The possibility for users to select some resources that best meet
their needs.
The possibility to interact with another user whose equipment has
differing characteristics.
The communications network must allow any user to select the
service components he/she wants:
The possibility for users to join in or withdraw from a communication
session according to certain policies, such as agreement of all
interacting partners before admitting a new user.
The possibility to set such quality of service parameters as the
synchronization tolerance between the service components, the echo
sensitivity, the burst sensitivity, and so on.
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Multimedia NetworksTechnical Issues
Network transmission is liable to errors and Data
loss. Excess of loss in video transmission affects
performance of video quality. Video quality can be
enhance by proper frame synchronization between
video and audio streams.
Admission control: takes into account resource reservation
request and available capacity whether to accept a new
request with its QoS requirements.
Scheduling: provides QoS by allocating resources depending
on the service requirements. This requires mapping of user
defined QoS requirement to resouce allocations for
providing the service.
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Resource management: Efficient resource management is a cost
effective solution for the provider and it ensures that
applications will get the specified QoS during the course of their
execution.
Congestion control: is required to avoid anything bad from
happening inside a network domain. Some applications may not
follow the standard protocol description and try to steal
resources, thereby deteriorating the QoS of other applications.
Policing/Shaping:Users might send traffic at a rate higher than
that agreed on. Policing is necessary to monitor these situations
and shaping makes the traffic smooth and reduces its
variations over time.
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Multimedia Network reference model• Hypothetical multimedia network reference model (MNRM). The
MNRM must have monitoring and real time control, management,
communication, and abstraction primitives that are organized and
real time control, management architecture, information transport
architecture and tele-base architecture respectively.
• Subdivision of MNRM based controls and communications
a. Management and traffic control architecture
b. Information transport architecture
• Reference model is organized into five planes :N plan, M- plane, C-
plan, U-plane.
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Multimedia Network Reference Model
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• N-plane: Management architecture resides in the network
management or N-plane and covers the functional areas of
network management- configuration, performance, fault,
accounting and security management, manager and agents.
• M-plane-comprises the entities and mechanism for resource
control such as cell scheduling, call admission, and call routing.
• C-plane- comprise the entities and mechanism responsible for
connection management and control.
• D-plane-Telebase architecture resides here and implements the
principles of data sharing for network monitoring, control and
communication primitives.
• U-plane- The information transport architecture is located in the
user transport or U plane and it models the protocols and
entities for transport of user information.
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Multimedia Hardware/Software Difference between steaming and non-streaming
media is streaming allow playback in RT. Non
streaming media require the whole file to be
downloaded before playback. Audio/Video Hardware
Digital Video (DV) Eliminates inefficient method of converting
analogue video to Digital by capturing video digitally.
Analog to Digital devices: Converts analoge video signals to
digital video.
Built-in Hardware:Most PCs come equipped with CD ROM drives
and microphones.
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Digital Video Software: Video format of widows computer is
AVI(audio video interleaved) files. Video file are compressed
using codecs so that they are small enough to deliver over the
internet.
Multimedia Software: combines various elements of
audio , graphics and video that allow creation of
shock-wave, director, quick-time(video format),
real-media etc.
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Comparison of Stacks
TCP/IP five layer reference model is a widely accepted model
For designing network protocols.
To single out the mm characteristics, we logically partition the
Five layer reference model into four layer mm design model that
Includes application layer, mm integration control and
synchronization layer (MICS) layer., the inter process
communication and synchronization layer (IPCS) and network
layer.
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Comparison of Stacks
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• IPCS layer-Consist of foundation of the MM communication
environment.
• Provides flexible set of communication and synchronization
primitives. It crates set of mechanisms that allow location
independent exchange of MM information between two
processes and provide the adequate tools for synchronization.
• MICS layer: Is responsible for integrating different types of
related communication media, preserving the timing relations.
Provides control operations required by supported applications.
• Application layer: provides set of user interaction functionality
to handle different types of user defined objects. This layer is
characterized by a coarse level of synchronization which has
direct implications on process scheduling and object
manipulation.
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Multimedia Internet Protocols
Multimedia over TCP: in mm application multicast
method used, TCP supports point to point. Reliable
connection, client has to wait for packets so delays.
Multimedia over UDP: connection less, best effort
delivery. Support Multi-casting and Best effort is
required for MM applications.
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RTP Real-time Transport Protocol (RTP) provides support
for the transport of real-time data such as video and
audio streams.
RTP needs support from lower layers that actually
have control over resources in switches and routers
RTP/RTCP provides functionality and control
mechanisms necessary for carrying real-time content.
RTP/RTCP itself is not responsible for the higher-level
tasks like assembly and synchronization. These have
to be done at application level.
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RTCP Real-Time Control Protocol extends RTP
In an RTP session, participants periodically send RTCP packets to
convey feedback on quality of data delivery and information of
membership.
Packets defined for carrying control information:
SR: Sender report, for transmission and reception statistics from
session participants that are
active senders.
RR: Receiver report, for reception statistics from session
participants, that are not active
senders.
SDES: Source description items, including CNAME
BYE: Indicates end of participation
APP: Application specific functions
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Multimedia Internet Protocols SAP & SDP-Session announcement protocol, Session
description protocol.
Peer to peer communication, the concept of session.
SIP
Signalling mechanisms that are necessary to establish
a session and to negotiate the parameters to be used
in it, such as codecs, media, location, etc.
MBONE Tools (Multicast Backbone)-allows us to
participate in different kinds of VC and meetings
using IP MultiCast as network technology
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• SDR-session directory tool -TV guide Shows all plans and
MBONE sessions.,
• VIC-Video conferencing tool used for video transmission with
great variety of codecs available. This can be used on every
platform and compatible with standards for capturing video.
• VAT and RAT-Video and Robust audio tool for video and audio
conferencing used in many platforms.
• WB- white board that can be used by participants and same
functionality as blackboard in classroom.
• NTE-Network text editor and offers the functionality of
distributed word processor. It supports tokens for asking
permission to write and quite comprehensions.
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Multimedia Internet Protocols RSVP (Resource Reservation Protocol)
Network control protocol
Allows data receiver to request a special end-to-end
quality of service for its data flows.
RTSP (Real Time Streaming Protocol)
A client-server multimedia presentation protocol to
enable controlled delivery of streamed multimedia
data over IP network.
Aims to provide the same services on streamed audio
and video just as HTTP does for text and graphics.
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Multimedia Communications High-Density File Transfers- Traffic include low resolution cartoon lie
images up to full colour , high resolution photographs.
Graphics File Transfers- graphics vary in size based on compression
algorithm. It have become readily accepted form for computing since the
advent of graphical user interfaces. eg. WWW.
Audio File Transfers -Pre recorded audio file can be encoded in several
different formats and may contain speech, sounds etc. files can be stored
in memory or disk. Temporary storage provides th time needed for
damaged or dropped packets to be identified and resent.
Video File Transfers- Recorded video files can be encoded in variety of
formats.
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Audio Communication-Can take three distinct forms- computer based telephony,
Audio conferencing, audio transmission.
Computer-Based Telephony-uses PCs and LANS/WANs to integrate voice telephony
Into data network.
Computer-Based Audio Conferencing- Used in sessions.
Streaming Audio-are unidirectional transmissions of stream of audio data. Such
transmission uses a host that either records audio in RT or uses pre-recorded
audio media
Video Communication-Required How power computer and bandwidth intensive.
Video Conferencing-RT bidirectional transmission between two or more points is
known as video conferencing.
Streaming Video-This is not bidirectional nor it have to live.Transmitted multicast
or broadcasted uni-directionally.