Computer Network

is a collection of computing devices that are connected in various ways to communicate and share resources.

• • Email ,instant messaging and web pages all rely on communication that occurs across an underlying computer network

  • Connections between computers in a network are made using physical wires and cables or wireless.

Role of the client and server in the context of networked system

• • Client

    • A piece of computer hardware or software that accesses a service made available by a server / 

    • The role of a client is to access a service made available by a server by sending a request for service;

  • Server

    • A program/host computer that awaits and fulfills requests from client programs (in the same or other computers) /

    • The role of a server is to fulfill requests from client programs (which can reside in the same or in other computers)

Computer as a network client

• • Is at the receiving end of a service in a client/server model networking system.

  • Can be categorized as either a thin client or a thick client:

(1) Thin client

• • • A client system with minimum functions that uses the resources provided by a host computer. 

    • Relies on a server to do most or all of its processing.

    • Applications are run on the server and only interacts with the thin client for input and output.

(2) Thick/fat client

• • • A client system that runs its own applications and only relies on a server for data storage.

    • Is more expensive than a thin client as it needs a faster processor and more resources e.g. money.

Types of computer networks

Local-Area Networks (LANs): 

• • The computers are geographically close together (e.g. they are in the same building).

Wide-Area Networks (WANs): 

• • The computers and LANs are spread over greater distances within the same city or local region. They are connected by telephone lines or radio waves.

Metropolitan-Area Networks (MANs): 

• • A data network designed to provide coverage for an entire town or city.

Home-Area Networks (HANs): 

• • A network contained within a user’s home that connects the digital devices of its residents.

Computer as a server

• A server is a computer that is dedicated to managing network resources.

• Servers are referred to as “dedicated” because they carry out hardly any other tasks apart from their server tasks.

Server categories

• • Print servers;

  • Email servers;

  • File servers;

  • Web servers; 

  • Network servers (e.g. DNS);

  • Database servers.

File Server

• • A computer dedicated to storing and managing files of network users

Web server

• • A computer dedicated to responding to requests for web pages/web content

Email server

• • Is an application, usually installed on dedicated hardware, that stores incoming mail for distribution to local users and sends out outgoing messages.

  • Run software that is built around standardized messaging protocols, usually Simple Mail Transfer Protocol (SMTP).

DNS server

• • The most basic function is to translate a domain name into its respective IP address.

Print server

• • Is a computer that can process print-related jobs for a network of computers.

  • This allows users in a computer network to print without having to move files to the specific computer connected directly to the printer.

Other technologies used in a network

Router

• • Is a device that analyzes the content of data packets transmitted within a network to determine whether the source and destination are on the same network or whether data must be transferred from one network type to another.

Firewall

• • Blocks unauthorized access from external public or private networks.

  • Are implemented to prevent unauthorized internet users or illicit software services from gaining access to private networks.

NAS

• • A type of server that provides in-house or remotely connected users with a broader external network and/or internet. 

  • It centrally manages and gives connected users the ability to receive a suite of network-enabled services, while serving as the single point of access or gateway to network resources. 

Switch

• • A device that handles data and knows the specific addresses to send the message. It can decide which computer is the message intended for and send the message directly to the right computer

Hub

• • Network connection point for devices. Data arriving at a this point is copied and send to all the devices on the network.

  • It passes data packets from input channels;  To all output channels; 

Repeater/Extender

• • A network device that strengthens and propagates a signal along a long communication line