Computer Communications & Networking
Week 1 - Introduction
By: Faiza Tariq
29th August, 2012
Recommended Text Books
1. Data Communications And Networking
2. ( Text book )
By: Behrouz Forouzan
Publisher: McGraw Hill International
Computer Networks (Additional Reading)
By: Andrew S. Tanenbaum
Publisher: Prentice Hall International
By communicating information is shared
Local sharing or Remote
Individuals can communicate locally face to face
Remote communication can take place over
Telecommunication is used for remote
communication e.g. telephone, fax, radio,
Tele is Greek word means “far”.
1-1 DATA COMMUNICATIONS
The term telecommunication means communication
at a distance. The word data refers to information
presented in whatever form is agreed upon by the
parties creating and using the data. Data
communications are the exchange of data between
two devices via some form of transmission medium
such as a wire cable.
It involves the transmission of data through
conducted or radiated communication media
In computer information system data are
represented by binary information units (or bits)
produced and consumed in form of 0 and 1.
Data communication is exchange of data (in the
form of 0 and 1) between two devices via some
form of transmission medium (wire or wireless).
Data communication is considered local if the
communicating devices are same building or
restricted geographical area
Remote if communicating devices are far away.
Aim & Objectives of DC
To provide an insight into the basic concepts of
To introduce the various communication equipment
that are used and their functions.
To develop an appreciation of the various
techniques and protocols used in data
transmission, the relevant network topologies and
data transmission channels.
To provide an understanding of the differences in
LANs and WANs and the protocols used.
To introduce the standards used in networking and
in particular the basic principles of the ISO-OSI
Aim & Objectives of DC
Describe the functions and operations of data
communications hardware in a typical network
Describe the various means of data transmission,
error control and line control procedures.
Illustrate the need for protocols and give examples of
existing protocols used.
Illustrate the various types of network topologies used
in LANs and WANs and the
advantages/disadvantages of each implementation.
Explain briefly the purpose of layering and the
functions of each layer in the ISO-OSI reference
Effectiveness of Data Communication
Delivery: Deliver to intended recipient (It must
be delivered to correct device or user).
Accuracy: Data must be delivered unaltered
as modified data (modified during
transmission) may be unusable or may lead
to incorrect result.
Timeliness: Delayed delivery of data may not
Advantages of Distributed Processing
Security/Encapsulation: System designer
may limit the kind of interactions that a given
user may have with the entire system. Limited
access to information
For example a bank can allow users access
to their own account through ATM without
allowing access to the bank’s entire
Distributed Databases: WWW gives access
to distributed data through URL.
Set of devices (normally called nodes)
connected by media links (called channels).
Network systems use distributed processing
Network Criteria – Performance
To be effective and efficient network, network
must meet criteria as mentioned below
Number of users: Design of network is
based on an assessment of the average
number of users that will be communicating
at any one time.
Type of Transmission Medium: It defines
the speed at which data can travel through a
Hardware: The type of hardware in a network
affect both the speed and capacity of
Network Criteria – Security
Unauthorized Access: At lower level user id
and passwords. At higher level encryption
Viruses & Trojan Horses: Serious threat to
network. Must used trusted OS and
application software to protect virus and
Trojan Horse attacks. E.g. Network
(Message, Sender, Receiver, Medium and Protocol)
(simplex, half-duplex, and full-duplex)
Types of connections: point-to-point and multipoint
Figure 1.4 Categories of topology
Figure 1.5 A fully connected mesh topology (five devices)
Figure 1.6 A star topology connecting four stations
Figure 1.7 A bus topology connecting three stations
Figure 1.8 A ring topology connecting six stations
Figure 1.9 A hybrid topology: a star backbone with three bus networks
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet
Figure 1.11 WANs: a switched WAN and a point-to-point WAN
A heterogeneous network made of four WANs and
Without standard difficulties arise
A Steering wheel from one make or model of car
will not fit into another model.
A standard provides a model for development that
makes it possible for product to work regardless of
individual manufacturer. E.g. IBM compatible PC;
3.5” 1.44 MB Diskette
No widely accepted definition
“ A prescribed set of rules, conditions or requirements
concerning definition of terms; classification of components;
specification of materials; performance or operations;
measurement of quantity and quality in describing materials;
products; systems; service or practices” [ National
Standards Policy Advisory Committee, US 1979]
As companies realized the money they could save
and the productivity they could gain by using
networking technology, they added networks and
expanded existing networks almost as rapidly as
new network technologies and products could be
Proprietary systems are privately developed,
owned, and controlled. In the computer industry,
proprietary is the opposite of open, meaning that
one or a small group of companies controls all
usage of the technology. Open means that free
usage of the technology is available to the public.
Advantage of standardization
A standard assures that there will be a large
market for a particular piece of equipment,
h/w or s/w’ which encourages mass
A standard allows products from multiple
vendors to communicate, giving the
purchasers more flexibility in equipment
selection and use.
RFC (Request for comments)
Document that contains information about a
proposed new standard and asks users to
look at the document and make any
RFC is registered by The Internet
Engineering Task Force (IETF).
For more information visit http://www.ietf.org/
Voluntary (De facto) Standards
Developed by standards organization like ISO
Manufacturer voluntarily implement a product that
conforms to a standard for their own interest, as there
is no legal requirement.
Purpose is to cause the market to prefer a standard
Regulatory (De jure) Standards
Developed by Government Regulatory Agency to
meet some public objectives such as economics,
These standards have force of law behind them and
must be compiled with
Data Communication Standards
De facto: Means “By fact” or “By convention”
Proprietary: standards are those originally
invented by a commercial organization as a
basis for the operation of its product.
The are owned by the inventing company
Non-proprietary: Those originally developed
by those groups or committees that have
passed them in public domain.
De jure: those that have been legislated by
an officially recognized body
Standards are developed by cooperation
among standards creation committees,
forums and regulatory agencies.
There are many standards organization.
Some of popular standards organizations are:
The International Standards
This voluntary organization was created in 1947 –
dedicated to world wide agreement on international
Aim to facilitate the international exchange of goods
and services by providing models for compatibility,
improved quality, increased productivity and
More than 70 % of ISO member bodies are from
governmental standard agencies.
Open System Interconnection (OSI) seven layers
model for network communication was designed by ISO.
USA is represented in ISO by ANSI
Pakistan is represented in ISO by Pakistan Standards and
Quality Control Authority
Union – Telecommunication
Standard Sector (ITU – T)
Formerly called Consultative Committee for International
Telegraphy and Telephony (CCITT)
International organization related to UN that develops
standards for telecommunication.
The best known ITU – T standards are the V series
(v.32, v.33, v.42) which define data transmission over
ITU – T
X – series (X.25, X.400, X.500) which define
transmission over public digital networks: email and the Integrated Services Digital
ITU-T's mission is to ensure an efficient and
on-time production of high quality standards
covering all fields of telecommunications.
Standards Institute (ANSI)
An American NGO – aim serving the national
coordinating institution for voluntary standardization in
It represents US in ISO and ITU – T
ANSI members include professional societies, industry
associations, state regulatory bodies and consumer
Institute of Electrical and Electronics
Largest professional engineering society in the world
responsible for standards in field of electrical engineering ,
electronics and radio as well as related engineering.
One of its goal – development and adoption of international
standards for computing and communication.
It has a special committee for local area networks (LANs).
European Conference on
Postal & Telecommunications
The European Conference of Postal and
Telecommunications Administrations - CEPT was established in 1959 by 19 countries
expanded to 26 during its first ten years.
CEPT's activities included co-operation on
commercial, operational, regulatory and
technical standardisation issues.
Administrations from the following 44 countries
are members of CEPT:
Albania, Andorra, Austria, Azerbaijan, Belgium,
Bosnia and Herzegovina, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Great Britain,
Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Liechtenstein, Lithuania, Luxembourg, Malta,
Moldova, Monaco, Netherlands, Norway,
Poland, Portugal, Romania, Russian Federation,
San Marino, Slovakia, Slovenia, Spain, Sweden,
Switzerland, The former Yugoslav Republic of
Macedonia, Turkey, Ukraine, Vatican.
Internet Engineering Task
Concerned with speeding the growth and
evolution of Internet Communication.
Standard body for Internet, reviews Internet
Software & Hardware
Important contribution include development of
Simple Network Management Protocol
(SNMP) and the review of performance
standards for bridges, routers and routers
International Standards Bodies:
The Internet Engineering Task Force (IETF)
is the protocol engineering and development
arm of the Internet.
The IETF is a large open international
community of network designers, operators,
vendors, and researchers concerned with the
evolution of the Internet architecture and the
smooth operation of the Internet.
It is open to any interested individual.
ATM Forum and
Deals with standardization of services to
ATM Consortium is made up of vendors of
hardware and software that support ATM.
International Standards Bodies:
Forums: ATM Forum
The Asynchronous Transfer Mode Forum is a
worldwide organization, aimed at promoting ATM
within the industry and the end user community.
Formed in October 1991, with four (4) members,
the ATM Forum membership currently includes
more than 700 companies representing all
sectors of the communications and computer
industries, as well as a number of government
agencies, research organizations and users.
(Definition taken directly from ATM Forum WWW home-page)
All communications technology is subject to
regulation by government agencies such as
Federal Communications Commission (FCC)
in US and Pakistan Telecommunication
Authority (PTA) in Pakistan.
Whether you are listening to the radio,
watching TV, talking on the phone, or
using your pager, you’re involved in
All these regulations are governed by the
FCC in USA
The Act specifies the Functions of the Authority.
Section 4 (1) of the Act says:
"The Authority shall...
regulate the establishment, operation and maintenance
of telecommunication systems and the provision of
telecommunication services in Pakistan;
receive and expeditiously dispose of applications for the
use of radio-frequency spectrum;
promote and protect the interests of users of
telecommunication services in Pakistan;
promote the availability of a wide range of high
quality, efficient, cost effective and competitive
telecommunication services throughout Pakistan;
promote rapid modernization of telecommunication
systems and telecommunication services;
investigate and adjudicate on complaints and other
claims made against licensees arising out of alleged
contravention of the provisions of this Act, the rules
made and licenses issued thereunder and take
make recommendations to the Federal Government
on policies with respect to international
telecommunications, provision of support for
participation in international meetings and
agreements to be executed in relation to the routing
of international traffic and accounting settlements;
perform such other functions as the Federal
Government may from time to time, assign to it."
• Any process that permits the passage from a
sender to one or more receivers of
information of any nature, delivered in any
easy to use form (printed copy, fixed or
moving pictures, visible or audible signals) by
any electromagnetic system (electrical
transmission, guided waves) which includes
telegraphy, telephony, video-telephony, data
transmission and others.
The object or element which originates (or
transmits) the message
The object or element which obtains or is the
destination of the message
The means of transmitting the message
Set of rules that govern DC. Without protocol
computers can not communicate even if physical
network has been established. Different
languages or different way to attend calls
What’s a protocol?
a human protocol and a computer network protocol:
Q: Other human protocol?
Protocol and Standards
Two nodes can not just send information to
each other and expect to be understood.
For communication to occur, the nodes must
agree to a protocol.
A protocol is a set of rules that govern the
A protocol defines what is communicated,
how it is communicated and when it is
A standard or set of rules that govern data communication &
communication on a network more efficient
Telephone call – “Hello” The person answering the phone should
English call protocol – Urdu
A protocol defines how the computers should identify each other on
The form that the data should take in transit, and how the
information should be reconstructed once it reaches its final
Protocols also define how to handle damaged transmissions.
TCP/IP, AppleTalk, SPX/IPX and NetBEUI are examples of network
Elements of the Protocol
Structure of format of the data i.e. order in
which presented e.g.
First eight bits reserved for sender address,
2nd eight bits reserved for the receiver
address, rest of the bits for message
Refers to the meaning of section of bits
How different fields be interpreted
When data should be sent
At what speed data can be sent
Elements of the Protocol
Actual Data (Message)
Error detection bits
History Of Data Communication
Manual work, stored
in paper files.
Introduction of computers,
used as electronic storage
Problems of sharing data.
Various branches had own
Link computers together to
centralise the data (hence,
Data Communications Applications
For n devices in a network, what is the
number of cable links required for: