NETWORK TOPOLOGIESNETWORK TOPOLOGIES

There are three basic There are three basic configurations used to connect configurations used to connect

computers they are the computers they are the Bus Bus Ring Ring Star Star

Bus topologyBus topology This type of network was widely used in the 1980’s This type of network was widely used in the 1980’s In this configuration every computer (node) shares In this configuration every computer (node) shares

the networks total bus capacities. the networks total bus capacities. In this configuration adding more computers will In this configuration adding more computers will

reduce the access speed on the network. reduce the access speed on the network. Each computer communicates to other computers Each computer communicates to other computers

on the network independently this is referred to as on the network independently this is referred to as PEER-TO-PEER networking PEER-TO-PEER networking

Bus (continued)

How it workedHow it worked

All computers on a network have a distinct All computers on a network have a distinct address just like your house doesaddress just like your house does

a message would be send from one a message would be send from one computer with the address of another computer with the address of another computer attached to the messagecomputer attached to the message

The message is broadcasted to all the The message is broadcasted to all the computers on the network until the computers on the network until the addressed PC accepts the message addressed PC accepts the message

How it worked (cont,,)How it worked (cont,,)

The type of wires used for Bus Networks in the The type of wires used for Bus Networks in the 80’s were called Thicknet and Thinnet80’s were called Thicknet and Thinnet

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

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

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

Advantages of Bus Topology

Works well for small networks Relatively inexpensive to implement Easy to add to it

Disadvantages ofBus Topology

Management costs can be high Potential for congestion with network

traffic It is not very fault tolerant, a break or It is not very fault tolerant, a break or

defect in the bus would affect the whole defect in the bus would affect the whole networknetwork

Ring TopologyRing Topology

In Ring topology each node is connected to the In Ring topology each node is connected to the two nearest nodes so the entire network forms a two nearest nodes so the entire network forms a circle circle

Data only travels in one direction on a Ring Data only travels in one direction on a Ring network network

Ring

How this Topology worksHow this Topology works

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

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

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

How it WorksHow it Works

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

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

Larger Token Ring networks use multiple Larger Token Ring networks use multiple tokens tokens

Problems and SolutionsProblems and Solutions

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

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

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

This type of network was also widely used in the 1980’s This type of network was also widely used in the 1980’s This type of network used Thinnet cable joining nodes.This type of network used Thinnet cable joining nodes. In the mid 1980’s Thinnet cable was replaced by In the mid 1980’s Thinnet cable was replaced by

Category 3 Ethernet cable capable of handling up to Category 3 Ethernet cable capable of handling up to 10Mbps10Mbps

Advantages of Ring Topology

Easier to manage; easier to locate a defective node or cable problem

Well-suited for transmitting signals over long distances on a LAN

Handles high-volume network traffic Enables reliable communication

Disadvantages ofRing Topology

Expensive Requires more cable and network

equipment at the start Not used as widely as bus topology

– Fewer equipment options– Fewer options for expansion to high-speed

communication

Star topologyStar topology

• Star topology– Every node on the network is connected through

a central device

The Good and Bad of a The Good and Bad of a Star NetworkStar Network

The upside of a star network is that if any The upside of a star network is that if any one cable fails then only the node one cable fails then only the node connected on that cable would be affected connected on that cable would be affected

Another positive point to this type of network Another positive point to this type of network is that it is very simple to join two star is that it is very simple to join two star networks together by connecting their networks together by connecting their central devices to each other central devices to each other

Advantages of Star Topology

Good option for modern networks Low startup costs Easy to manage reduce cable lengthsreduce cable lengths If one cable fails then only the node If one cable fails then only the node

connected on that cable would be affectedconnected on that cable would be affected

Disadvantages ofStar Topology

if a central device was to fail then all if a central device was to fail then all computers connected to that device would computers connected to that device would not be able to see the network not be able to see the network

Requires more cable than the bus

What is a Hub?What is a Hub?

A hub is usually a small rectangular box, A hub is usually a small rectangular box, often made of plastic, which receives its often made of plastic, which receives its power from an ordinary wall outlet power from an ordinary wall outlet

A hub joins multiple computers (or other A hub joins multiple computers (or other network devices) together to form a single network devices) together to form a single network network segment

On this network segment, all computers can On this network segment, all computers can communicate directly with each other communicate directly with each other

What is a Hub?What is a Hub?

Many times the fifth port is reserved for Many times the fifth port is reserved for "uplink" which is the connecting of one hub "uplink" which is the connecting of one hub to another hub or similar device (joining two to another hub or similar device (joining two segments together). segments together).

Larger hubs contain eight, 12, 16, and even Larger hubs contain eight, 12, 16, and even 24 ports 24 ports

Key Features of HubsKey Features of Hubs

Hubs classify as Layer 1 devices in the Hubs classify as Layer 1 devices in the OSI model Hubs do not read any of the data passing through Hubs do not read any of the data passing through

them and are not aware of their source or them and are not aware of their source or destination destination

Key Features of HubsKey Features of Hubs

Essentially, a hub simply receives incoming Essentially, a hub simply receives incoming packets, possibly amplifies the electrical , possibly amplifies the electrical signal, and broadcasts these packets out to signal, and broadcasts these packets out to all devices on the network - including the all devices on the network - including the one that originally sent the packet! one that originally sent the packet!

a a packetpacket is a formatted block of data carried is a formatted block of data carried by a computer by a computer networknetwork

Different Types of HubsDifferent Types of Hubs

Technically speaking, three different types Technically speaking, three different types of hubs exist of hubs exist

PassivePassive

ActiveActive

IntelligentIntelligent

Passive hubsPassive hubs Passive hubsPassive hubs do not amplify the electrical do not amplify the electrical

signal of incoming packets before signal of incoming packets before broadcasting them out to the networkbroadcasting them out to the network

Active hubsActive hubs

amplify the electrical signal of incoming amplify the electrical signal of incoming packets back to their original level before packets back to their original level before broadcasting them back out on the network broadcasting them back out on the network

Intelligent hubsIntelligent hubs

add extra features to an active hub that are add extra features to an active hub that are of particular importance to businessesof particular importance to businesses

An intelligent hub is typically stackable (built An intelligent hub is typically stackable (built in such a way that multiple units can be in such a way that multiple units can be placed one on top of the other to conserve placed one on top of the other to conserve space). space).

What is a Network Switch?What is a Network Switch?

A A network switchnetwork switch is a small hardware is a small hardware device that joins multiple computers device that joins multiple computers together within one together within one local area network (LAN)

Technically, network switches operate at Technically, network switches operate at layer two (Data Link Layer) of the layer two (Data Link Layer) of the OSI model

Network SwitchNetwork Switch

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

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

Network SwitchNetwork Switch

By delivering each message only to the By delivering each message only to the connected device it was intended for, a connected device it was intended for, a network switch conserves network switch conserves network bandwidth and offers generally and offers generally better performance than a hub better performance than a hub

What is a Router?What is a Router?

RoutersRouters are physical devices that join are physical devices that join multiple wired or wireless networks togethermultiple wired or wireless networks together

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

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