Module Five: Computer Network (Notes)

A computer network is a number of computers (also known as nodes) connected by some communication lines in order of exchange information and resources.

Two computers can connected to the network can communicate with each other through other nodes if they are not directly connected.

Some of the nodes in the network may not be computers at all but they are network devices (like switches, routers, etc.) to facilitate communication

There are number of specialized terms that describe computer networks:-

Node – any device that is connected to a network . It could be a computer, printer, or data storage device.

Client – a node that requests and uses resources available from other nodes. Typically, a client is a user’s microcomputer.

Server – a node that shares resources with other nodes. Examples  Mail server, Communication Server, etc.

Hub – the center or central node for other nodes, simply a connection point for cables from other nodes.

Network Interface cards (NIC) - these are expansion cards located within the system unit that connect the computer to a network. Sometimes referred to as a LAN adaptor

Network Operating System (NOS): - controls and coordinates the activities of all computers and other devices on a network. These activities include electronic communication and the sharing information and resources.

Distributed processing - a system in which computing power is located and shared at different locations.

Network manager: - a computer specialist, also known as Network administrator, responsible for efficient network operations and implementation of new networks.

Network types

a) Local Area Network (LAN)

Networks that connects computers with devices in a limited geographical area such as a home, school computer lab, office building, or positioned group of buildings.

b) Metropolitan Area Network (MAN)

Some times is known as Regional network, span distances up to 100 miles. Unlike a LAN, a MAN is typically not owned by a single organization.

c) Wide Area Network (WAN)

Covers countrywide and worldwide networks. Of course, the widest of all WANs is the Internet, which span the entire globe.

Network architecture

Network Architecture describes how a computer Network is configured and what strategies are employed.

Configurations include star, bus, ring and hierarchical.

Strategies include terminal, client – server, and peer to peer.

Topologies

Topology - Physical and logical network layout

> Physical – actual layout of the computer cables and other network devices

> Logical – the way in which the network appears to the devices that use it.

The four principal network topologies are star, bus, ring and hierarchical. 

i. Star Network, a number of small computers or peripheral devices are linked to a central unit (hub or switch).

ii. Bus Network, each device in the network handles its own communications control. All communications travel along a common connecting cable called a Bus or Backbone

iii. Ring Network, each device is connected in the other , forming a ring. There is no central server or computer.

iv. The Hierarchical Network, also called a Hybrid network, it can consist more than one type of above networks. 

Strategies

Every network has a strategy, or way of coordinating the sharing information and resources.

The most common network strategies are terminal, Client or server, and Peer to peer.

1. Terminal Network System, processing power is centralized in one large computer, usually a mainframe.

The nodes connected to this host computer are either terminals, with little or no processing capabilities, or microcomputers  running special software that allows them to act as terminals.

2. Client or Server network systems use one computer to coordinate and supply services to other nodes on the network.

The server provides access to resources such as Webpages, databases, application software, and hardware. Server nodes coordinate and supply specialized services, and client nodes request the services.

3. Peer to peer Network  system, nodes have equal authority and can act as both clients and servers. For example, one microcomputer can obtain files located on another microcomputer and can also provide files to other microcomputers.

Organizational Internets

a) Intranet 

is a private network within an organization that resembles the Internet. Like the public Internet, intranets use browsers, websites, and Webpages. Intranets typically provide e–mail, mail lists, newsgroups, and FTP (File Transfer Protocol) services accessible only to those within the organization. Organizations use intranets to provide information to their employees.

b) Extranets

Is a private network that connects more than one organization. Many organizations use Internet technologies to allow suppliers and others limited access to their networks. The purpose is to increase efficiency and reduce costs.

c) Firewall

Organization have to be very careful to protect their information systems. A firewall is a security system designed to protect an organization’s network against external threats.

It consists of hardware and software that control access to a company’s intranet or other internal networks.

Typically organizational firewalls include a special computer called a proxy server. This computer is a gatekeeper. All communications between the company’s internal networks and the outside world  must pass through it.