Introduction to data communication and networking

Introduction to data communication and networking 1
1.0 INTRODUCTION
Data communications and networking may be the fastest growing technologies in
our culture today. One of the ramifications of that growth is a dramatic increase in the
number of professions where an understanding of these technologies is essential for
success and a proportionate increase in the number and types of students taking courses
to learn about them.
Data communications and networking are changing the way we do business and
the way we live. Business decisions have to be made ever more quickly, and the decision
makers require immediate access to accurate information. Why wait a week for that
report from Germany to arrive by mail when it could appear almost instantaneously
through computer networks? Businesses today rely on computer networks and
internetworks. But before we ask how quickly we can get hooked up, we need to know
how networks operate, what types of technologies are available, and which design best
fills which set of needs.
The development of the personal computer brought about tremendous changes for
business, industry, science, and education. A similar revolution is occurring in data
communications and networking. Technological advances are making it possible for
communications links to carry more and faster signals. As a result, services are evolving
to allow use of this expanded capacity.
Research in data communications and networking has resulted in new
technologies. One goal is to be able to exchange data such as text, audio, and video from
all points in the world. We want to access the Internet to download and upload
information quickly and accurately and at any time.
This part addresses four issues: data communications, networks, the Internet, and
protocols and standards. First we give a broad definition of data communications. Then
we define networks as a highway on which data can travel. The Internet is discussed as a
good example of an internetwork (a network of networks). Finally, we discuss different
types of protocols, the difference between protocols and standards, and the organizations
that set those standards.
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Networks exist so that data may be sent from one place to another- the basic
concept of data communications. To fully grasp this project, we must understand the data
communication components, how different types of data can be represented, and how to
create a data flow.
Data communications between remote parties can be achieved through a process
called networking, involving the connection of computers, media, and networking
devices.
Protocols and standards are vital to the implementation of data communications
and networking. Protocols refer to the rules; a standard is a protocol that has been
adopted by vendors and manufacturers.
Network models serve to organize, unify, and control the hardware and software
components of data communications and networking. Although the term “network
model” suggests a relationship to networking, the model also encompasses data
communications.
The two dominant networking models are the Open System Interconnection
(OSI) and the Internet model (TCP/IP). The first is a theoretical framework; the second is
the actual model used in today’s data communications. So, we will discuss the OSI model
to give a general background. We then concentrate on the Internet model.
1.1 DATA COMMUNICATIONS
When we communicate, we are sharing information. This sharing can be local or
remote. Between individuals, local communications usually occurs face to face, while
remote communication takes place over distance. The term telecommunication, which
includes telephony, telegraphy, and television, means communication at distance (tele is
Greek for “far”).
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. For data communications to occur, the
communicating devices must be part of a communication system made up of a
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combination of hardware (physical equipment) and software (programs). The
effectiveness of a data communications system depends on four fundamental
characteristics: delivery, accuracy, timeliness, and jitter.
? Delivery. The system must deliver data to the correct destination. Data must be
received by the intended device or user and only by that device or user.
? Accuracy. The system must deliver the data accuracy. Data that have been altered
in transmission and left uncorrected are unusable.
? Timeliness. The system must deliver data in a timely manner. Data delivered late
are useless. In the case of video and audio, timely delivery means delivering data
as they are produced, in the same order that they are produced, and without
significant delay. This kind of delivery is called real-time transmission.
? Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay
in the delivery of audio or video packets. For example, let us assume that video
packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and
others with 40-ms delay, an uneven quality in the video is the result.
Components. A data communications system has five components:
? Message. The message is the information (data) to be communicated. Popular
forms of information include text, numbers, pictures, audio, and video.
? Sender. The sender is the device that sends the data message. It can be a
computer, workstation, telephone handset, video camera, and so on.
? Receiver. The receiver is the device that receives the message. It can be a
computer, workstation, telephone handset, television, and so on.
? Transmission medium. The transmission medium is the physical path by which
a message travels from sender to receiver. Some examples of transmission media
include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
? Protocols. A protocol is a set of rules that govern data communications. It
represents an agreement between the communicating devices. Without a protocol,
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two devices may be connected but not communicating, just as a person speaking
French cannot be understood by a person who speaks only Japanese.
Data Flow. Communication between two devices can be simplex, half-duplex, or fullduplex.
? Simplex. In simplex mode, the communication is unidirectional, as on a one-way
street. Only one of the two devices on a link can transmit; the other can only
receive.
Keyboards and traditional monitors are examples of simplex devices. The
keyboard can only introduce input; the monitor can only accept output. The
simplex mode can use the entire capacity of the channel to send data in one
direction.
? Half-Duplex. In half-duplex mode, each station can both transmit and receive, but
not at the same time. When one device is sending, the other can only receive, and
vice versa.
The half-duplex mode is like a one-lane road with traffic allowed in both
directions. When cars are travelling in one direction, cars going the other way
must wait. In a half-duplex transmission, the entire capacity of a channel is taken
over by whichever of the two devices is transmitting at the time.
The half-duplex mode is used in cases where there is no need for communication
in both directions at the same time; the entire capacity of the channel can be
utilized for each direction.
? Full-Duplex. In full-duplex mode (also called duplex), both stations can transmit
and receive simultaneously. The full-duplex mode is like a two-way street with
traffic flowing in both directions at the same time. In full-duplex mode, signals
going in one direction share the capacity of the link with signals going in other
direction. The sharing can occur in two ways: Either the link must contain
physically separate transmission paths, one for sending and the other for
receiving; or the capacity of the channel is divided between signals travelling in
both directions.
One common example of full-duplex communication is the telephone network.
When two people are communicating by a telephone line, both can talk and listen
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at the same time. The full-duplex mode is used when communication in both
directions is required all the time. The capacity of the channel, however, must be
divided between the two directions.
1.2 NETWORKS
A network is a set of devices (often referred as nodes) connected by
communication link(s). A node can be a computer, printer, or any other device capable of
sending and/or receiving data generated by other nodes on the network.
Distributed Processing. Most networks use a distributed processing, in which a task is
divided among multiple computers. Instead of one single large machine being responsible
for all aspects of a process, separate computers (usually a personal computer or
workstation) handle a subset.
Network Criteria. A network must be able to meet a certain number of criteria. The
most important of these are performance, reliability, and security.
? Performance. Performance can be measured in many ways, including transit time
and response time. Transit time is the amount of time required for a message to
travel from one device to another. Response time is the elapsed time between an
inquiry and a response. The performance of a network depends on a number of
factors, including the number of users, the type of transmission medium, the
capabilities of the connected hardware, and the efficiency of the software.
Performance is often evaluated by two networking metrics: throughput and delay.
We often need more throughput and less delay. However, these two criteria are
often contradictory. If we want to send more data to the network, we may increase
throughput but we increase the delay because of traffic congestion in the network.
? Reliability. In addition to accuracy of delivery, network reliability is measured by
the frequency of failure, the time it takes a link to recover from a failure, and the
network’s robustness in a catastrophe.
? Security. Network security issues include protecting data from unauthorized
access, protecting data from damage and development, and implementing policies
and procedures for recovery from breaches and data losses.