COMPUTER NETWORKS

Computer Networks

A series of electronic devices connected together through copper cables, fiber optics, and radio waves.

There are many types of computer networks, including:

Local-Area Networks (LAN's): The computers are geographically close to each other (in the same building).

Wide-Area Networks (WAN's): The computers are farther apart and are connected by telephone lines or radio waves.

Metropolitan-Area Networks (MAN's): A MAN is usually not privately owned by the user or the company.

Computer Networks

Local-Area Networks (LAN's):

two buildings with 4 departments connected as a LAN.

Wide-Area Networks (WAN's):

                                             

A WAN would be most useful for large companies with offices or factories in widely separated areas

INTERNET – A type of WAN

                                                                                                                 

Computer Networks

In addition to these types, the following characteristics are also used to categorize different types of networks:

topology architecture protocol

topology : The geometric arrangement of

a computer system. Common topologies include a

mesh,star,bus, ring,tree.

Computer Networks

Topology refers to the shape of a network, or the network's layout.

Topologies are either physical or logical.

Physical TopologyThe physical layout of devices on a network.

Every LAN has a topology, or the way that the devices on a network are arranged and how they communicate with each other.

The way that the workstations are connected to the network through the actual cables that transmit data.

Logical Topology

The way that the signals act on the network media,

or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices.

Network Topology

The five most common network topologies. MeshStarBus Ring Tree

Mesh Topology

In a true mesh topology every node has a connection to every other node in the network.

Star Topology

Nodes communicate across the network by passing data through the hub.

All devices are

connected to a

central hub.

Bus Topology All devices are connected to a central cable, called the bus or backbone.

Ring Topology

All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it.

Tree Topology

A hybrid topology. Groups of star-configured networks are connected to a linear bus backbone.

Computer Networks

architecture

Networks can be broadly classified as using either a

peer-to-peer or client/server

Network Architecture

Sharing single computers  with

each other. peer-to-peer

peer-to-peer One individual can access and

save files to another individuals computer.

This can be slow when large files are being transferred.

client/server

A single computer is set aside to only save files and run programs.

Each computer in the network can run any program, or save files, to this single computer, which is named the server.

Computers on a network are sometimes called nodes, a processing location.

Every node has it's own unique network address.

Computers and devices that allocate resources for a network are called servers.

Computer Networks

protocolsFor two computers to talk to each other, they must agree on some kind of standard way of communicating.

Computer Networks

computers on a network will not be able to communicate unless they are able to speak the same "language."

The languages by which computers communicate over a network are called protocols.

protocol

Protocols tell computers how to send and receive data and what to do with the data after they receive it.

The protocol defines a common set of rules and signals that computers on the network use to communicate.

Computer Networks

Modern computer networks use standard protocol called Ethernet to communicate with one another.

Ethernet

One of the most popular protocols for LAN's is called Ethernet, a local-area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976.

Ethernet

Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps.

It is one of the most widely implemented LAN standards.

Another popular LAN protocol for PC's is the IBM token-ring network.

EthernetEthernet is a technology used to connect multiple devices together to form a "network", it consists of physical cables, connectors, and a protocol that allows clear communications between devices.

Ethernet run at either 10, 100 or 1000 megabits per second.

Cable and Hardware

Ethernet has several wiring standards that dictate the speed and the communications medium the computers will use.

Cable Type & Speed

Name

10Base-2

10Base-T

10Base-F

100Base-T (Fast Ethernet)

1000Base-T (Gigabit Ethernet)

Cable Type

Coaxial

CAT3 or CAT5

Twisted Pair

Fiber optic

CAT5 Twisted Pair

Fiber optic

Speed

10Mbps

10Mbps

10Mbps

100Mbps

1000Mbps

Network Channels

There are three main cable types:

Coaxial, which looks like TV antenna wire,

Twisted pair; which looks like phone wire; and

Fiber optic wire.

Types of cables

Coaxial Coaxial cable is

classified into two categories: baseband (uses

digital signals) and

broadband (uses analog signals) coaxial cable

Coaxial

A single insulated inner wire is surrounded by a cylindrical conductor which is covered with a shield; it transmits electromagnetic signals.

Types of cablesTwisted Pair

two insulated copper wires twisted together in a regular spiral pattern; one pair establishes one communication link; it transmits electromagnetic signals.

Twisted pair

Twisted pairs are distinguished between shielded (STP) & unshielded (UTP)twisted pairs according to their protection against electromagnetic fields

Types of cables

Fiber optic

transmits optical signals, which must be transformed to electromagnetic signals

consists of three concentric sections,the core (a fibre conducting optical rays), the cladding (reflecting optical rays) and the jacket (surrounding one or many fibres to protect them)

Fibre Optic

Wireless Networks Wireless networks are perfect when you don’t feel like stringing a bunch of cable over you floor. They also have the added advantage that your computer (or laptop) can be “on the go” anywhere in the house. However, they are quite expensive.

Other network hardware

Besides wire, you will need network cards for each machine on a network, and a hub

Hub

The most important piece of your network is the hub.

It is the heart of any 10/100 Base-T network.

All computers on the network are connected to the hub.

HubIt is the job of the hub to broadcast a signal send from one machine to all the machines on the network.

The hub also isolates a computer if it detects a cable fault.

HubHubs come in many sizes, ranging from 4 ports all the way up to 36 ports.

Each port can be used to connect a computer. The more ports, the more computers you can connect.

Obviously, the more ports, the higher the price.

The network card

The last piece of hardware you will need is network interface cards (or NICs) for each machine in your house.

The network card

This card is used to communicate on the network.

Some computers, such Macintoshes, already come pre-installed with network cards.

The network card

You can tell if your computer has a network card build in by looking in the rear of the case for a jack that looks kind of like a phone jack, only bigger.

Network cards come in three flavors: 10Base-T, 10/100Base-T 100Base-T.

The network card

10Base-T Ethernet

The primary type of Ethernet in use today is 10Base-T, which operates at 10 Mbps and follows a star topology using unshielded twisted-pair cabling.

10Base-T Ethernet networks are very easy to set up. This flavor of Ethernet relies on hubs.

The network card100Base-T cards cost only a little more than ones that operate at 10 Mbps, and give you much more flexibility for upgrading your network in the future.

Most 100Base-T hubs will automatically sense whether the card connected to each port is 10 or 100 Mbps and operate accordingly.

ARCNETShort for Attached Resource Computer network, ARCnet is one of the oldest, simplest, and least expensive types of local-area network.

ARCnet was introduced by Datapoint Corporation in 1977.

It uses a token-ring architecture, supports data rates of 2.5 Mbps, and connects up to 255 computers.

Token ringis a local area network (LAN) in which all computers are connected in a ring or star topology and a bit- or token-passing scheme is used.This prevents the collision of data between two computers that want to send messages at the same time. The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet.

ARCNET

A special advantage of ARCnet is that it permits various types of transmission media i.e twisted-pair wire, coaxial cable, and fibre optic cable

to be mixed on the same network.

Summary

Types of Networks:

LAN

WAN

MAN

Network Topology:

Mesh

Star

Bus

Ring

Tree

Channels:

Twisted pair

Coaxial

Fibre opticNetwork Interface Card:

Ethernet

Arcnet

Server

Nodes

Hubs