Multimedia Communications
Electrical Communication Engineering,
Indian Institute of Science,
Bangalore – 560012, India
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Objectives
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To know the networking evolution.
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To understand the network types.
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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
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Telnet-Remote login
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File Transfer Protocol (FTP)
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Electronic Mail (Email)
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Gopher
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Internet Relay Chat (IRC)
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Usenet News
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World Wide Web (WWW)
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Computer Network
A communication system for connecting computers / hosts
Why?
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Better communication
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Better sharing of resources
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Bring people together
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Types of Computer Networks
Local Area Network (LAN)
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Connects hosts within a relatively small geographical area.
Same room
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Same building
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Same campus
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It is Faster: speeds- 10 Mbps to 10 Gbps
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Cheaper-1 crore for a hundred node LAN (one-time
cost)
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Network Topologies Evolution
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LAN
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Linear topology- Single segment LAN in linear topology.
Ethernets and token rings were cables connecting each
station
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Star-wired-to avoid rewiring, Multistation access units
(MAUs) introduced. Hubs were used.
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Multisegment-Bridges and routers connected several
LANs.
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Backbone-connected-Backbone network
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Switched-backbone-Replacement of backbone with high
bandwidth Switch.
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Internetworking Devices
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Hub-
Extends the span of a single LAN.
Bridge / Layer-2 Switch
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Connects two or more LANs together.
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Works at data link layer level.
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Router / Layer-3 Switch
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Connects any combination of LANs and WANs.
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Works at network layer level.
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Types of LANs
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WAN
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Wide Area Network (WAN)
Hosts may be widely dispersed
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Across campuses
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Across cities / countries/ continents
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It is faster and cheaper
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Typical speeds- 64 Kbps to 8 Mbps
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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
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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:
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Connection establishment
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Required before data transmission.
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Data transfer
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Connection termination
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Drawbacks:
Channel capacity gets dedicated during the entire duration
of communication.
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Acceptable for voice communication.
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Very inefficient for bursty traffic.
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There is an initial delay.
For connection establishment.
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Packet Switching
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Network resources are not dedicated.
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A link can be shared.
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Data are transmitted in short packets(~ Kbytes).
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A longer message is broken up into smaller chunks.
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The chunks are called packets.
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Every packet contains a header.
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Relevant information for routing, etc.
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Packet switching is based on store-and-forward concept.
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Each intermediate network node receives a whole packet.
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Decides the route.
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Forwards the packet along the selected route.
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Advantages:
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Links can be shared; so link utilization is better.
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Suitable for computer-generated traffic.
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Typically bursty in nature.
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Buffering and data rate conversion can be performed easily.
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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.
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A route is established before packet transmission starts.
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All packets follow the same path.
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The links comprising the path are not dedicated.
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Datagram:No route is established beforehand.
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Each packet is transmitted as an independent entity.
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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:
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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.
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More flexible.
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Packets between two hosts may follow different paths.
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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:
the transmitter.
Time taken to send out a packet by
Processing Delay: Time taken by a node to “process” a
packet.
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Multimedia Requirements
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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
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Quality-of-service (QoS) support and group communication system:
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establishment and take-down of appropriately configured channels;
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negotiation of QOS levels between end-systems, intermediate
systems, and network control; and
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control of the agreed QOS level
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bandwidth, delay, delay jitter (variance), and reliability.
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Audio/Video groups can:
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have static or dynamic memberships during their lifetime,
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have centrally (typically sender) or distributively (typically receiver)
controlled membership,
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consist of members with homogeneous or be heterogeneous
characteristics and requirements.
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Multimedia Communication System
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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 definitions
Bandwidth-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
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Here are some examples of file types:
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Text Files: .txt, .doc, .rtf
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Audio Files: .au, .aif, .wav
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Graphic files: .jpg, .gif, .tif, .bmp, .pict, .pcx
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Moving video files: .qt, .mov, .avi
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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 nonlinear content.
Presentation Multimedia-combination of digitized audio, video,
graphics, etc.
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Multimedia Communication System
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LAN Access Method
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Routing
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Frame and Packet Structures
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Packet Discrimination
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Identify packets that require special handling.
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Be capable of accommodating those special requirements.
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Bandwidth Requirement, Reservation and Conservation
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High bandwidth and low latency
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Multimedia Communication System
Architecture
The ability to manage dynamically the achieved QoS of each service
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component
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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 Networks
Technical Issues
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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.
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Admission control: takes into account resource reservation request
and available capacity whether to accept a new request with its QoS
requirements.
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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
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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.
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Subdivision of MNRM based controls and communications
a. Management and traffic control architecture
b. Information transport architecture
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Reference model is organized into five planes :N plan, M- plane, C-plan, Uplane.
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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 managementconfiguration, 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
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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.
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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
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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
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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
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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:
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SR: Sender report, for transmission and reception statistics from session
participants that are
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active senders.
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RR: Receiver report, for reception statistics from session participants, that
are not active
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senders.
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SDES: Source description items, including CNAME
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BYE: Indicates end of participation
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APP: Application specific functions
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Multimedia Internet Protocols
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SAP & SDP-Session announcement protocol, Session
description protocol.
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SIP
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Peer to peer communication, the concept of session.
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.
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WB- white board that can be used by participants and same
functionality as blackboard in classroom.
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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
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RSVP (Resource Reservation Protocol)
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Network control protocol
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Allows data receiver to request a special end-to-end quality of
service for its data flows.
RTSP (Real Time Streaming Protocol)
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A client-server multimedia presentation protocol to enable
controlled delivery of streamed multimedia data over IP
network.
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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
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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.
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