1 Computer Networking - Introduction

What is a network?

A network is 2 or more connected computers for information exchange or resource sharing. These can be connected with electric cables, fibre optic cables or wireless network.

Building blocks of a network

Client computers: Used  by end users to access the resources of the network.

Server computers: These computers provide shared resources and network services to client computers. Run a specialised network operating system such as Windows Server along with special software like MS-Exchange, Apache Web Server etc.

Network Interface:This interface (sometime called a network port) is installed on a computer to enable it to communicate over a network. In old times, you needed to install a network interface card on a computer, nowadays all computers come with it installed (NIC).

Cable: for physically connecting computers. Twisted pair cable most common. It's official name is 10BaseT.

Switch: Each computer is connected to a central switch which connects to the rest of the network. Each switch has a certain number of ports, typically 8 or 16.

Wireless networks: Radio transmitters used for networking. Less secure than cabled networks.

Network software: Network operating system (NOS) and configuration of servers and clients.

Benefits of network

Sharing information - e-mail, chat, video conference etc.
Sharing resources - file server, printers etc.
Sharing applications - special applications which can be accessed simultaneously through workstations

Dedicated servers and peers

Dedicated server: A server that does the job of a server alone. Such a network is called a client-server network
Peer-to-peer network: Same computer can be both server and client. Built in all operating systems since Windows 95.

Networks Big and Small

LAN: networks within same office or building
WAN: spans city, region or country. Geographic distance is the criteria here.
MAN: Typically connects LANs within the same city.

Network Topology

Topology refers to the shape of how computers and other network components are connected to each other.

Node: is a term used to refer to a device connected to a network

Packet: Message sent over network from one node to another. Each packet contains address of sending and receiving nodes along with data.

Types of topology

Bus: Nodes are strung together in a line. Every node can see every packet sent on a cable.

Star: Each network node is connected to a central device - a hub or a switch. Only networks that use switches have a true star topology. (Hub - does not know about computers connected to each of its ports, so when a node sends a packet for another node, hub sends it to all of its ports. Switch however sends the packet only to the intended recipient).

Expanding stars: More complex topology. Backbone (bus that connects the switches is called a backbone) and daisy-chaining (switch connected to another switch as if it were one of the nodes in the star).

Ring: Packets are sent around the circle from computer to computer.

Mesh: Has multiple connections between each node on the network.