Network Topologies

Instructor: Shahzad Alishahzadali039@gmail.com

Lec#2Friday, 30th Oct, 2015

Punjab Group of Colleges, Pakpattan Campus

Network topologies

Contents Description of network What is Topology Different Topologies Advantages and Disadvantages of different

Topologies

What is a Network?• Networks means Interconnection• Interconnection of People

Computer Network• A collection of computing devices that are

connected in various ways in order to communicate and share resources

• In information technology, a network is a series of points or nodes interconnected by communication paths.

• Networks can interconnect with other networks and contain sub networks.

• Example:o Two computers connecting together is an example of a network.

How so many computers are

connected together?

Network TopologyTopology Design of Network Or refers to the layout of connected devices

Network Topology Topology refers to the layout of connected devices

on a network. The pattern of interconnection of nodes in a

network is called the Topology. This layout also determines the manner in which

information is exchanged within the network.

Why we use network topologies?• Network topology is used initially for planning the

best way to design your network to get maximum performance.

Network TopologyTopologies can be either physical or logical.

• Physicalo Actual layout of the computer cables and other

network deviceso Physical topologies describe how the cables are run.

• Logicalo The way in which the network appears to the

devices that use ito Logical topologies describe how the network

messages travel

Considerations while choosing a Topology

The factors while selecting a Topology1. Cost2. Flexibility 3. Reliability

Different Network Topologies

Mesh TopologyStar TopologyBus TopologyRing TopologyTree TopologyHybrid Topology

Mesh Topology• Computers in mesh topologies

are connected directly to every other device with cables.

• Create point to point connection to every device on network.

• If one cable fail data always has alternative path to get to its destination.

• This type topology generally use in military area.

cont.• This topology is rarely found in LANs, mainly because

of the complexity of the cabling. • If there are n computers, there will be (n × (n–1)) ÷

2 cables in the network. For example, if you have five computers in a mesh network, it will use 5 × (5 – 1) ÷ 2, which equals 10 cables. This complexity is compounded when you add another workstation.

• For example, your five-computer, 10-cable network will jump to 15 cables just by adding one more computer.

• Imagine how the person doing the cabling would feel if you told them you had to cable 50 computers in a mesh network—they’d have to come up with 50 × (50 – 1) ÷ 2 = 1225 cables!

Mesh TopologyAdvantages

• Data can be transmitted from different devices simultaneously. This topology can withstand (face) high traffic.

• Even if one of the components fails there is always an alternative present. So data transfer doesn’t get affected.

• Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages• Connections not fully utilized.• Overall cost of this network is

way too high as compared to other network topologies.

• Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.

Star Topology• In a star topology all

computers are connected to a central device known as hub or switch.

• All the computers share data through the Hub or Switch

Star TopologyAdvantages

• A new node can be easily connected to the existing network by connecting it with unused port of hub.

• If there is fault in cable connected with computer, only the particular computer get affected.

• Less cables required than Mesh Topology. That’s why it is affordable by small organisations also.

Disadvantages• If Hub or switch get

faulty, all computer connected to it will be get affected.

• Traffic increased when computers are simultaneously sending data to each other.

Bus Topology• In bus topology computers are connected via a single

cable known as a Trunk or Backbone cable.• Trunk cable was then connected to the branch cables

which were further connected to the PCs. • Each computer shares the same data and address path.

With a logical bus topology, messages pass through the trunk, and each workstation checks to see if the message is addressed to itself. If the address of the message matches the workstation’s address, the network adapter copies the message to the card’s on-board memory.

• Normally coaxial cable is used.• Terminators at both end of BUS absorb signal, removing it

from BUS.• Popular on LANs because they are inexpensive and easy

to install.

cont.

Bus TopologyAdvantages

• Easy to connect computer or peripheral to a linear bus.

• Uses less cables than mesh topology

• Don’t need any special device like Hub or Switch.

Disadvantages• Entire network shuts

down if there is a break in the main cable.

• Difficult to identify the problem if the entire network shuts down.

• Terminators are required at both ends of the backbone cable.

Ring Topology In ring topology all the nodes are connected to each-other

in such a way that they make a closed loop. Data travels around the network, in one direction. Sending

and receiving of data takes place by the help of TOKEN. Token Passing: Token contains a piece of information

which along with data is sent by the source computer. This token then passes to next node, which checks if the signal is intended to it. If yes, it receives it and passes the empty to into the network, otherwise passes token along with the data to next node. This process continues until the signal reaches its intended destination.

Single ring – All the devices on the network share a single cable

Dual ring – The dual ring topology allows data to be sent in both directions.

cont.

Ring TopologyAdvantages

• Each node gets to send the data when it receives an empty token. This helps to reduces chances of collision.

• The transmission of data is relatively simple as packets travel in one direction only.

• Every computer serves as a repeater to boost signals and send it to the next node along with the token and data.

Disadvantages• Each packet of data must pass

through all the computers between source and destination. This makes it slower.

• If one workstation or port goes down, the entire network gets affected

• Difficult to add and remove devices once the network has been set up.

• Data sharing accomplished through one direction only. It takes more time to send or receive data.

Tree Topology• Integrates the

characteristics of star and bus topology.

• In tree topology number of star network connected using bus. The backbone cable is called as Bus.

Tree TopologyAdvantages

• Expansion of Network is possible and easy.

• Networks divided into segments, that can be easily maintained.

• Each segment is provided with dedicated point-to-point wiring to the central hub.

• If one segment is damaged, other segments are not affected.

Disadvantages• Relies heavily on the

main bus cable, if it breaks whole network is crippled.

• As more and more nodes and segments are added, the maintenance becomes difficult.

• Heavy traffic cause the network and make it slow.

Hybrid Topology• The hybrid topology can be a combination of two

or more basic topologies, such as bus, ring, star, mesh, or tree.

• Hybrid networks combine more than two topologies, which, in turn, enable  you to get advantages of the constituent topologies.

cont.

Differentiation between the three most common types of Network Topologies…!

BUS TOPOLOGY

DEFINITION•All computers and devices connected to central cable

ADVANTAGE•Easy to connect a computer or peripheral to a linear bus.

•Requires less cable length than a star topology.

DISADVANTAGE

•Entire network shuts down if there is a break in the main cable. •Terminators are required at both ends of the backbone cable. •Difficult to identify the problem if the entire network shuts down.

Summary

RING TOPOLOGY

DEFINITION•Cable forms closed ring or loop, with all computers and devices arranged along ring.

ADVANTAGE•Data is quickly transferred without a ‘bottle neck’. •The transmission of data is relatively simple as packets travel in one direction only.

DISADVANTAGE

•Data packets must pass through every computer between the sender and recipient therefore, this makes it slower. •If any of the nodes fail then the ring is broken and data cannot be transmitted successfully. •It is difficult to troubleshoot the ring.

cont.

DEFINITION•All devices connect to a central device, called hub.

ADVANTAGE•Easy to install and wire. •Security can be implemented in the hub/switch.

DISADVANTAGE•Requires more cable length than a linear topology. If the hub or concentrator fails, nodes attached are disabled. More expensive than linear bus topologies because of the cost of the concentrators.

STAR TOPOLOGY

•Easy to detect faults and to remove parts

cont.

1.Provide redundant path between device.

DEFINITION•In the mesh topology each computer are connected with each other by separate cable..

ADVANTAGE•1.Provide redundant path between device.. The network can be expanded without disruption to current user..

DISADVANTAGERequire more cable then other topology .

Complicated implementations.

MESH TOPOLOGY

cont.

31

Network Topologies

Q&A

?

EXERCISE

2)On a __________, all of the computers and devices (nodes) on the network connect to a central device.

A. Bus network.B. Ring network.C. Star network.D. All of above.

EXERCISE

3)On a star network, the central device that provides a common

connection point for nodes on the network is called the __________.

A. Hub.B. Personal computer.C. Printer.D. File server.

EXERCISE

4) On a bus network, such as that illustrated in the accompanying figure, if one node fails ________.

A. Only that node is affected.B. Only the nodes before that node are

affected.C. Only the nodes after that node

are affected.D. All the nodes are affected.

EXERCISE

The transmission of data is relatively simple as packets travel in one direction only. 5) The statement above is correctly refer to the ______.

A. Bus network.B. Ring network.C. Star network.D. All of the above.

EXERCISE

6) All the statements true about ring topology except

A. Data is quickly transferred without a ‘bottle neck’.

B. The transmission of data is relatively simple as packets travel in one direction only.

C. If any of the nodes fail then the ring is broken and data cannot be transmitted successfully.

D. Security can be implemented in the hub/switch.

EXERCISE

7) The statement true about star topology is

A. Difficult to identify the problem if the entire

network shuts down.B. Terminators are required at both ends

of the backbone cable. C. The transmission of data is relatively

simple as packets travel in one direction only. D. Easy to detect faults and to remove

parts.