Chapter 4.1-Multimedia Communications

8/9/2019 Chapter 4.1-Multimedia Communications

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Multimedia Communications


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Network Topologies Evolution

LAN: Local Area Network

WAN: Wide Area Network

WLAN: Wireless Local Area Network


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Network Topologies Evolution LAN

A LAN is a high-speed data network that covers arelatively small geographic area. eg. home, office etc

LANs offer computer users many advantages,including shared access to devices and applications,

file exchange between connected users, andcommunication between users via electronic mail andother applications.

LAN data transmissions fall into three classifications:

unicast, multicast, and broadcast. LAN Topologies: bus, ring, star, and tree.


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BUS TOPOLOGY

Bus networks: A bus network topology is a network

architecture in which a set of clients are connected via a shared

communications line, called a bus.

Bus networks are the simplest way to connect multiple clients,but often have problems when two clients want to transmit at

the same time on the same bus.

Thus systems which use bus network architectures normally

have some scheme of collision handling or collision avoidance

for communication on the bus, quite often using Carrier Sense

Multiple Access


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BUS NETWORK


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Ring networks,

A ring network is a network topology inwhich each node connects to exactly twoother nodes, forming a circular pathway forsignals: a ring. Data travels from node to

node, with each node handling every packet. Because a ring topology provides only one

pathway between any two nodes, ringnetworks may be disrupted by the failure of asingle link. A node failure or cable breakmight isolate every node attached to the ring.


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Ring network


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Tree topology

Tree Topology is a combination of the bus and the Star Topology. The

tree like structure allows you to have many servers on the network andyou can branch out the network in many ways.


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Circuit Switching

Switched circuits allow data connections that can be

initiated when needed and terminated when

communication is complete. This works much like a

normal telephone line works for voice communication


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Packet SwitchingPacket switching is a WAN technology in which users

share common carrier resources.


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Wireless LANA wireless LAN or WLAN is a wireless local area

network, which is the linking of two or more computerswithout using wires.WLAN utilizes radio waves to enable communication

between devices in a limited area, also known as the

basic service set.This gives users the mobility to move around within a

broad coverage area and still be connected to the

network.


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Interactive Learning System for Conceptualization


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Interlace is a technique of improving the picture quality

of a video signal by removing flicker without consumingany extra bandwidth.

This animation demonstrates the interline twitter

effect. The two interlaced images use half the bandwidth

of the progressive one.


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Interleaving in disk storage

The primary purpose of interleaving was to adjust the timing

differences between when the computer was ready to transfer data,

and when that data was actually arriving at the drive head to be read.

Interleaving was used to arrange the sectors in the most efficient

manner possible, so that after reading a sector, time would be

permitted for processing, and then the next sector in sequence is ready

to be read just as the computer is ready to do so.

Interleaving is used in digital data transmission technology to protect

the transmission against burst errors. These errors overwrite a lot of

bits in a row, so a typical error correction scheme that expects errors

to be more uniformly distributed can be overwhelmed. Interleaving is

used to help stop this from happening.


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Linear Multimedia

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 computergame or used in self-paced computer based training.

Non-linear content is also known as hypermedia content.


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If the sequence and timing of the multimedia elements

can be controlled by the user, then one can name it asNon-Interactive Multimedia.Streaming AudioRealPlayerStreaming Videoquick time

Non-Interactive Multimedia.


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Multimedia Networks Technical Issues

Admission control:Admission control is a network Quality ofService (QoS) procedure.

Admission control determines how bandwidth and latency are

allocated to streams with various requirements.

An application that wishes to use the network to transport traffic

with QoS must first request a connection, which involves

informing the network about the characteristics of the traffic and

the QoS required by the application.

This information is stored in a traffic contract. The network

judges whether it has enough resources available to accept the

connection, and then either accepts or rejects the connection

request. This is known as Admission Control.


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Multimedia Networks Scheduling: Scheduling is a key concept in computer

multitasking and multiprocessing operating system design,

and in real-time operating system design. It refers to the way

processes are assigned priorities in a priority queue. This

assignment is carried out by software known as a scheduler.

Different computer operating systems implement differentscheduling schemes. Unix implementations use a scheduler

with multilevel feedback queues.

Windows 3.1 and Macintosh OS 9 use a simple non-

preemptive scheduler which requires programmers to

instruct their processes to "yield" in order for other processes

to gain some CPU time. Windows NT 4.0-based operating

systems use a multilevel feedback queue.


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Multimedia Networks Congestion Control: A congestion control system

typically monitors various factors like CPUoccupancy, link occupancy and messaging delay.

Based on these factors it takes a decision if the

system is overloaded. If the system is overloaded, it

initiates actions to reduce the load by asking front

end processors to reject traffic.


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Multimedia Networks Resource management

resource management is the efficient and effectivedeployment of an organization's resources when

they are needed.

Resource Management and Scheduling Strategiescollectively addresses multiple issues including

QoS, throughput, responsiveness and efficiency.


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INTERNET

The Internet is a global network of interconnectedcomputers, enabling users to share information alongmultiple channels.


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Internetworking

Despite the incompatibilities among networktechnologies, researchers devised a schemefor providing universal service amongheterogeneous technologies calledinternetworking.

Hardware is used to interconnect a set ofphysical networks and common software on

all the attached computers provides universalservice. The resultant system is known as aninternetwork or internet.


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Connection to Internet

There are many ways to connect to the Internet from a personal


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There are many ways to connect to the Internet from a personal

workstation:

1. Dial-Up:With a dial-up connection, the Internet user can

connect to the Internet via his or telephone line and an Internetservice provider.

Broadband connections offer another way to connect to the

Internet. In this category are cable and DSL connections.

cable connection, the user must subscribe to a cable-television/Internet service.

DSL (Digital Subscriber Line): DSL offers much faster speeds

than those available with dial-up modems.

Satellite Internet service is another form of high-speed

Internet connection .It employs telecommunications satellites to

allow users to connect to the Internet

4.

M lti di I t t P t l


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Multimedia Internet Protocols Multimedia over TCP: TCP in connection-oriented protocol that is

reliable including flow control and supports byte-stream in full

duplex mode.

The multicast method to send data to more than one client is

not supported by the TCP protocol.

Delays is exactly what we do not want in real-time data

transmissions.

For example in a video transmission, we just drop the lost

packet and display the previous packet a second time. For the

human eye this little trick does not affect the quality. So

reliable transmission on transport layer is not exactly what we

need for multimedia transmissions.

TCP is not a good basis to transport multimedia real-time data

over a network, to summarize the usability of TCP.


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Multimedia over UDP

UDP is a connectionless protocol that triesbest effort delivery with no flow-control andincluded message support.UDP is not reliable and that is one of thekey advantages for real-timetransmissions.UDP also supports multicast methods.

This protocol does not support flow-control and that is actually veryimportant for real-time applications.

RTP


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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 mechanismsnecessary 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


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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: Session Announcement Protocol:used to assist the advertisement of

multicast multimedia conferences and other multicast sessions, and to

communicate the relevant session setup information to prospective

participants.

SDP: Session Description Protocol protocol for multimedia sessions. A

common mode of usage is for a client to announce a conference session by

periodically multicasting an announcement packet to a well known

multicast address and port using the Session Announcement Protocol

MBONE Tools:MBONE stands for "Multicast Backbone", a virtual

network. The network originated from an effort to multicast audio and

video from the "Internet Engineering Task Force" (IETF) meetings.

MBONE today is used by several hundred researchers for developing

protocols and applications for group communication

SDR(Sesion directory tool), VIC(Video Tool), VAT (Audio tool)and

RAT(Robust audio tool).



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Multimedia Internet Protocols RSVP:The Resource ReSerVation Protocol designed to reserve resources

across a network for an integrated services Internet.

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 which allows a client to remotely

control a streaming media server, issuing VCR-like commands such as

"play" and "pause", and allowing time-based access to files on a server.

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


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Multimedia Communications High-Density File Transfers .

Graphics File Transfers: using ftp Audio File Transfers

Video File Transfers

Audio Communication

Computer-Based Telephony

Computer-Based Audio Conferencing

Streaming Audio

Video Communication

Video Conferencing

Streaming Video

Documents

Chapter 4.1-Multimedia Communications