Download Data Communications Basics

Data Communications Basics
• Define telecommunications
• Define data communications
• Understand the data communication's
requirements
• List the characteristics of cluster and distributed
networks
• List different network topologies
• Understand the evolution of communications
network
Data communications and
networking concepts
Communications: by definition refers to the
transfer of information from one place to
another between two individuals using
agreed symbols, signs or even human
behaviour.
• Talking to your friend over a phone
• Writing a mail to overseas relative
• Lecturing a course
Types of information:
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Voice through radio or telephone
Video picture seen on TV screen
Digital Data between modem and PC
Image received by FAX
Communication System
• A very simple communication system may
include a sender (originator or caller), a
receiver and the medium.
Telecommunications
• Telecommunications: refers to the
transmission of information between
distant locations by some electromagnetic
means.
Data Communications
• Data communications: defined as the
interchange and processing encoded
information between distant locations
using Telecommunications. Encoded
information refers to digital information.
Why Data Communications?
• It is beneficial if computers can exchange data
through the common links.
• tasks of distributed nature can be processed by
distributed computers.
• A way to link hardware, software, and data bases
among computer systems.
• Increased computation power
• Cheaper mass storage, Increased data
management and Reduction in cost.
Computer Network
• Network by definition refers to a group of
interconnected devices
• communicating with each other. The device
could be telephone exchange.
If the device is a computer, it is called
computer network.
• Clustered : Computers are grouped together
• Distributed: This is the current trend for computer
communications.
Examples of Clustered Network
Advantages of computer
Networks
• Resource sharing including program, data
base, hardware etc.
• Graceful degradation of system upon
component failure. One of computer node's
failure will affect part of the network only.
Cluster Network
• A cluster network is a simple
communication system with a single host
processor or a few grouped processors at
the same location.
Distributed networks
The network is characterized by connecting
multiple processors geographically
distributed within the network.
• Flexibility for future growth and expansion.
• Versatile and reliable in terms of system
down time
• Cost effective in terms of system growth
and maintenance
Example of distributed networks
Network Topologies
• Network topology refers to the way of
grouping/linking the communication
nodes to serve particular need.
Communication Sub-network
• Arrangement of the computers and the
interconnections between them.
• DTE: data terminating equipment
• DCE: data circuit equipment
Network Topology
• Network topology is broadly classified into
point-to-point or multi-point.
Point-to-point
Message has to be transferred between two adjacent nodes
linking up by various transmission media
• Star ( A central node is required to relay messages)
• Loop ( A message has to pass through several nodes in the
system prior to be received by the targeted node.
• Tree (A top node irrespective of topology is still required.)
• Complete (Direct connection between two nodes are
formed.)
• Irregular or Mesh (Irregular shape).
Broadcast
• Message is sent to all nodes within the
network by means of common bus.
• Bus topology like broadcasting radio or
Ethernet network.
• Ring topology like IBM Token Ring
Network Applications
• There are numerous applications using
networked computers such as:• A central host computer with networked stations.
• Access to remote program by use of IBM LU 6.2 in
local machine.
• Access to the remote database (Library
cataloging system)
• Financial information (Hong Kong Stock Exchange
provided by Reuters)
• E-commerce, Web-shopping and Electronic Data
Interchange (EDI)
Commercial Networks
• ARPANET, As created by the Defense Advanced Research
Projects Agency whose project started in 1969.
• The Internet, refers to the National Science Foundation
Internet (NSFNet).
• Telenet , Is the commercial public service offshoot of
ARPANET
• CYBERNET, Is the commercial time-sharing network of
Control
• Data Corporation with Centers located around the
world.MARK III, Information
• DDX, Is the Japanese packet switched network.
• Datapak, Is a packet switching network offered by Hong
Kong Telephone company using a protocol based on X.25.
• DATAPAC, Is a Canadian packet switched network using a
protocol based on X.25
Vendor Network
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HP, Distributed Systems Network (DSN).
IBM, Systems Network Architecture (SNA).
DEC, Distributed Network Architecture (DNA). .
Honeywell, Honeywell Distributed Systems
Environment (DSE).
• UNIVAC, Distributed Communications
Architecture (DCA).
• Datapoint, Attached Resource Computer (ARC)
• NCR, Distributed Network Architecture (DNA)
Communication Organisations
• ITU , International Telecommunication Union,, a
treaty organization formed in 1865..
• EIA, This refers to Electronics Industries
Association
• ISO, International Standards Organization (ISO),
• IEEE , The Institute of Electrical and Electronic
Engineers.
• Telecommunications Authority, A HKSAR
government based organisation
Network Evolution
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Telephone network
Terminal-based Distributed System
Large Terminal-based Distributed System
PSDN-based Distributed System
LAN-based Distributed System
The Internet