NETWORK TOPOLOGIES

There are three basic

configurations used to connect

computers they are the

Bus

Ring

Star

Bus topology

This type of network was widely used in the 1980’s

In this configuration every computer (node) shares the networks total bus capacities.

In this configuration adding more computers will reduce the access speed on the network.

Each computer communicates to other computers on the network independently this is referred to as

PEER-TO-PEER networking

How a Bus Peer to Peer

Network Works

All computers on a network have a distinct

address just like your house does

a message would be send from one

computer with the address of another

computer attached to the message

The message is broadcasted to all the

computers on the network until the

addressed PC accepts the message

How it worked

The type of wires used for Bus Networks in the 80’s were called Thicknet and Thinnet

A Thicknet cable (very large about 1 inch in diameter usually yellow was hung around a room)

Thinnet cables were connected to the PC’s NIC and a Transceiver. The Transceiver was tapped into the Thicknet cable

To stop the message from bouncing back and forward down the wire (known as signal bounce) both ends of the network are terminated with 50Ω resistors

Problems

One of the main problems with this type of

network is that it is not very fault tolerant, a

break or defect in the bus would affect the

whole network

Ring Topology

In Ring topology each node is connected to the

two nearest nodes so the entire network forms a

circle

Data only travels in one direction on a Ring

network

How this Topology works

a node has information to send to another computer on the network so it sends the information out on the network to the PC it is connected to, if the information is for this PC (the recipients NIC address is attached to the message, which is like putting an address on an envelope) then the PC accepts the data

otherwise it passes the information on to the next PC by repeating the data back out on the line

This method of repeating the data helps keep the integrity of the data readable by other computers

How it Works

As it is better to have computers take turns using the connecting Data cable, Ring topologies incorporated a system called Token passing

In this topology, to transmit on the wire your computer must have control of the token or wait for the token to be free

Larger Token Ring networks use multiple tokens

Problems and Solutions

The drawback to this type of topology is that a single malfunctioning workstation can disable the whole network

To make sure all the information is sent the receiving PC sends the token back to the sending PC after it has received all the data

If the sending PC is finished sending it passes the token to the next PC

This type of network was also widely used in the 1980’s

This type of network used Thinnet cable joining nodes.

In the mid 1980’s Thinnet cable was replaced by

Category 3 Ethernet cable capable of handling up to 10Mbps

Star topology

In a Star topology every node is connected

through a central device such as a Hub,

Switch or Router

Compared to a Ring or Bus topology a Star

topology requires that more thought be put

into its setup

HUB

The Good and Bad of a

Star Network

The upside of a star network is that if any

one cable fails then only the node

connected on that cable would be affected

Another positive point to this type of network

is that it is very simple to join two star

networks together by connecting their

central devices to each other

The Good and Bad of a

Star Network

As each computer is connected to a central

device (Hub) the location of the Hub must

be made as central as possible, so as to

reduce cable lengths

The drawback to this type of topology is if a

central device was to fail then all computers

connected to that device would not be able

to see the network

What is a Hub?

A hub is usually a small rectangular box,

often made of plastic, which receives its

power from an ordinary wall outlet

A hub joins multiple computers (or other

network devices) together to form a single

network segment

On this network segment, all computers can

communicate directly with each other

What is a Hub?

Ethernet hubs are by far the most common

type, but hubs for other types of networks

such as USB also exist

A hub includes a series of ports that each

accepts a network cable

Small hubs can network four computers

together

They contain four or sometimes five ports

What is a Hub?

Many times the fifth port is reserved for

"uplink" which is the connecting of one hub

to another hub or similar device (joining two

segments together).

Larger hubs contain eight, 12, 16, and even

24 ports

Key Features of Hubs

Hubs classify as Layer 1 devices in the OSI model

OSI stands for :

The Open Systems Interconnection Basic Reference

Model

At the physical layer, hubs can support little in the

way of sophisticated networking

Hubs do not read any of the data passing through

them and are not aware of their source or

destination

Key Features of Hubs

Essentially, a hub simply receives incoming

packets, possibly amplifies the electrical

signal, and broadcasts these packets out to

all devices on the network - including the

one that originally sent the packet!

a packet is a formatted block of data carried

by a computer network

Different Types of Hubs

Technically speaking, three different types

of hubs exist

Passive

Active

Intelligent

Passive hubs

Passive hubs do not amplify the electrical

signal of incoming packets before

broadcasting them out to the network

Active hubs

amplify the electrical signal of incoming

packets back to their original level before

broadcasting them back out on the network

Intelligent hubs

add extra features to an active hub that are

of particular importance to businesses

An intelligent hub is typically stackable (built

in such a way that multiple units can be

placed one on top of the other to conserve

space).

Intelligent hubs

It also typically includes remote

management capabilities via SNMP and

virtual LAN (VLAN) support (You can

configure or check it from a computer that is

connected to it).

SNMP-Simple Network Management

Protocol

What is a Network Switch?

A network switch is a small hardware

device that joins multiple computers

together within one local area network (LAN)

Technically, network switches operate at

layer two (Data Link Layer) of the OSI model

Network Switch

Network switches appear nearly identical to network hubs, but a switch generally contains more "intelligence" (and a slightly higher price tag) than a hub

Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately

Network Switch

By delivering each message only to the

connected device it was intended for, a

network switch conserves network

bandwidth and offers generally better

performance than a hub

What is a Router?

Routers are physical devices that join multiple wired or wireless networks together

Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks together

A Gateway is a device that acts like a security guard and only allows data in or out if it has the right network headers

Routers

Home “networkers” often use an Internet Protocol

(IP) wired or wireless router

IP is the most common OSI network layer protocol

Protocols are the rules governing the transfer of

data information, it can also be compared to how

humans use languages (to get your point across

you must talk in the same language as the person

you are speaking to).

Routers

An IP router such as a DSL or cable modem

are broadband routers and joins the home's

local area network (LAN) to the wide-area

network (WAN) of the Internet

A Broadband Router is a device that allows

multiple PC’s to access the Internet using

only one address.