Multimedia Communications

E0262 - Multimedia Communications

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.

To understand the basics of a multimedia

communication system.

To illustrate multimedia networks.

To know the Internet protocol suite for multimedia

communications.


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.


Application of Internet Telnet-Remote login

File Transfer Protocol (FTP)

Electronic Mail (Email)

Gopher

Internet Relay Chat (IRC)

Usenet News

World Wide Web (WWW)


Computer Network

A communication system for connecting

computers / hosts

Why?

Better communication

Better sharing of resources

Bring people together


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)


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.


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.


Types of LANs


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)



Internet


How to get connected to internet


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.


Circuit Switching A dedicated communication path is required

between two stations. The path follows a fixed

sequence of intermediate links.


In circuit switching, three steps are required for

communication:

Connection establishment

Required before data transmission.

Data transfer

Connection termination


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


Multimedia Application Environment


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).


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


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



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.


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


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.


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.


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.


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.


Multimedia Network Reference Model


• 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.


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.


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.


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.


Comparison of Stacks


• 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.


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.


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.


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


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


• 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.


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.


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.


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.

Documents

Multimedia Communications