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BIT 2108 computer Networks
Lesson 1
Introduction to Computer networks
General objective
By the end of the semester the learner should be able to explain why Computer Networks are so vital in the society
Specific objectives
✓ To appreciate the need for Computer Networks
✓ To define Computer Networks terminologies
✓ To distinguish the different types of Computer Networks
✓ To describe the technologies that drive Computer Networks
Definition: a computer network consists of two or more computers that are linked in order to share resources such as printers, CD ROMs, exchange files or allow electronic communication.
The computers are linked through a transmission media such as cables, radio waves, satellites or infrared light beam.
Definition of terms:
✓ Simplex/Half duplex
✓ Full duplex
✓ Parallel transmission mode
✓ Serial transmission mode
✓ Asynchronous transmission mode
✓ Synchronous transmission mode
✓ Bit, bit rate
✓ Baud rate/modulation rate
Advantages of installing networks:
✓ Speed- they provide rapid method of sharing and transferring files.
✓ Cost-software licenses are cheaper, easier to upgrade and propagate changes
✓ Security- we can use “copy inhibit” for files and programs; security can also be a disadvantage.
✓ Centralized software management- software are usually loaded into servers as opposed to individual workstations
✓ Resource sharing-can share printers , scanners, faxes, CD ROMs and writers, MODEMs etc
✓ Communication- E-mails are easy to manage
✓ Flexibility- provides flexible access to files, remote access to resources ie one can work at home
✓ Workgroup computing- people can work at a common project from different continents
Disadvantages of networks:
✓ High initial cost- expensive to install initially as it requires hardware such a s cables, communication devices like servers, computers, routers etc, soft- wares like Network Operating systems and application soft-wares
✓ Administrative time- requires a lot of time and support expertise
✓ Server may fail – The central controller may fail leading to total network failure
✓ Network cable break – A failure in the backbone cable may lead to total network failure, this can be minimized by the use of good Network topology.
✓ Spreading of virus- viruses and other unethical material are easy to spread using networks
Major components of Computer Networks
✓.1.Standards/Protocols
✓.2.Hardware
- Communicating Devices
- (^) Transmission Media
- Networking Devices
✓.3.Software
- Application Software
- Network Operating System.
Types of networks
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• The flow of message and which node are allowed to “see” the message for security reasons
• Ability to use a node as a repeater
• Physical size of the network
• Amount of cable
Types of topologies
• The physical topology – what we see physical
• Logical topology – how information flows at times the two are different.
Physical topologies
• Point - to – point topology
Connects two nodes directly, eg via a MODEM. Addressing may not be required
• Multipoint topologies
Common uses of the Internet
E-mail
The concept of sending electronic text messages between parties in a way analogous to mailing
letters or memos predates the creation of the Internet.
The World Wide Web
Many people use the terms Internet and World Wide Web (or just the Web ) interchangeably, but
the two terms are not synonymous.
The World Wide Web is a huge set of interlinked documents, images and other resources, linked
by hyperlinks and URLs. These hyperlinks and URLs allow the web server and other machines
that store originals, and cached copies, of these resources to deliver them as required using
HTTP (Hypertext Transfer Protocol).
Remote access
The Internet allows computer users to connect to other computers and information stores easily,
wherever they may be across the world. They may do this with or without the use of security,
authentication and encryption technologies, depending on the requirements.
Collaboration
The low cost and nearly instantaneous sharing of ideas, knowledge, and skills has made
collaborative work dramatically easier. Not only can a group cheaply communicate and test, but
the wide reach of the Internet allows such groups to easily form in the first place, even among
niche interests. Examples are Internet "chat" instant messaging
File sharing: A computer file can be e-mailed to customers, colleagues and friends as an
attachment.
Streaming media
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Many existing radio and television broadcasters provide Internet "feeds" of their live audio and
video streams (for example, the BBC). They may also allow time-shift viewing or listening such
as Preview, Classic Clips and Listen Again features. These providers have been joined by a range
of pure Internet "broadcasters" who never had on-air licenses. This means that an Internet-
connected device, such as a computer or something more specific, can be used to access on-line
media in much the same way as was previously possible only with a television or radio receiver.
Voice telephony (VoIP)
VoIP stands for Voice over IP, where IP refers to the Internet Protocol that underlies all Internet
communication.
Internet access
Common methods of home access include dial-up, landline broadband (over coaxial cable, fiber
optic or copper wires), Wi-Fi, satellite and 3G technology cell phones.
Social impact
The Internet has made possible entirely new forms of social interaction, activities and
organizing, thanks to its basic features such as widespread usability and access.
Social networking websites such as Facebook and MySpace have created a new form of
socialization and interaction.
Political organization and censorship
Many political groups use the Internet to achieve a whole new method of organizing, in order to
carry out Internet activism.
Leisure activities
Today, many Internet forums have sections devoted to games and funny videos;
Complex architecture
The Internet is extremely heterogeneous. (For instance, data transfer rates and physical
characteristics of connections vary widely.)
Marketing
The Internet has also become a large market for companies; some of the biggest companies
today have grown by taking advantage of the efficient nature of low-cost advertising and
commerce through the Internet, also known as e-commerce. It is the fastest way to spread
information to a vast number of people simultaneously. The Internet has also subsequently
revolutionized shopping—for example; a person can order a CD online and receive it in the mail
within a couple of days, or download it directly in some cases. The Internet has also greatly
facilitated personalized marketing which allows a company to market a product to a specific
person or a specific group of people more so than any other advertising medium.
