Network Topology

Overview

CraigNDave

https://www.youtube.com/watch?v=Fzho2mQQEuU&list=PLCiOXwirraUDvVsza-xO2mMwW9QBIa_FG&index=0

Computer Science Tutor

https://www.youtube.com/watch?v=iiU06wkTAuY&list=PL04uZ7242_M6O_6ITD6ncf7EonVHyBeCm&index=28

Star Topology

Nodes are connected to a host computer or hub that controls communication between devices. the hub or host computer regenerates any signal that it receives and passes it on. Only the intended recipient computer acts on the message.

All nodes have independent connections to the host. A cable failure on one branch of the network will continue to function normally and the failure will be easy to isolate.

Advantages	Disadvantages
· Adding new devices is easy and doesn't disrupt the rest of the network.	· It requires a lot of cables.
· There are no data collisions.	· It is expensive to install.
· There is less traffic on the network.	· Needs professionals to maintain and up keep.
· A cable failure on one branch of the network will be easy to isolate.

Bus Topology

When the bus (or line) topology is used each workstation is connected to a single cable (or backbone) which links all of the workstations.

The servers are connected to the main bus for data distribution to all the workstations.

Data can be transmitted in either directed along the main cable and workstations can communicate with other workstations.

A range of peripherals can also be connected to the main bus for shared usage. This could be a printer for example.

Advantages	Disadvantages
·Is cheaper to install as it used the least cable as the cost of network cabling (particular fibre optic), and the cost of the network cable installation can be significant	·If there is heavy traffic the system performance will fall off dramatically
.	·Data collisions due to shared cable
.	.Problems can be difficult to isolate

Data Collisions - CSMA/CD

CSMA/CD stands for Carrier Sense Multiple Access/Collision Detection. It is the protocol for carrier transmission access in ethernet networks. If two devices try to send a frame at the same time, a collision occurs and the frames are discarded. Each devices then waits a random amount of time and retries until the transmission is successfully sent.

Logical Bus Topology

A network could be wired using a star topology, but could act like a bus topology if all data traffic is sent to all machines.

Switches vs Hubs

A switch and a hub are network components used to connect multiple devices to a network. They essentially have a given number of ports at the front, a single device can be plugged into a single port. They both use a Twisted Pair cable, which uses a dedicated pair of wires for sending and a dedicated pair of wires for recieving.

A hub takes the transmission from one device and passes it to the receiving wire for every other device connected to the hub.

A switch is semi intelligent, because it will take the transmission from one device and check its destination. If it knows the destination, the switch will only pass the transmission to that device. A switch will pass the transmission to all devices if the destination is unknown. It will maintain a list of known devices.

Revision Questions

1. What is bus Topology?

	Multiple Nodes are connected to a host computer
→	thats a star topology not a bus
	Each computer is connected to 1 main linear cable.
→	that is correct
	Its the customer service in the bus station
→	Not that bus silly.
	A host computer that controls all devices
→	it is a star topology where this happens you boomer

2. In a bus topology, all devices use different cables for connection.

	False.
→	Woop woop you got it right!
	True.
→	Nah, that's a star network.
	Idk.
→	Umm why are you on this course??

3. What is a bus topology?

	Uses may cables to transmit data
→	This is incorrect, a bus topology uses a single main cable as a backbone
	Uses one main cable as a backbone to transmit data
→	This is correct
	Connected devices in a network where each workstation has a dedicated cable to a central computer or switch
→	This is a star topology. A bus network uses one main cable as a backbone to transmit data
	A wire with a bus in it
→	This is very wrong, a bus topology uses a single main cable as a backbone to transmit data

4. What network topology connects all nodes via a central device?

	Mesh Topology.
→	Incorrect, mesh topologies have no central device.
	Bus Topology.
→	Incorrect, bus topologies utilise a main cable rather than a central device.
	Ring Topology.
→	Incorrect, ring topologies use no central device, instead connecting each device consecutively.
	Star Topology.
→	Correct, star topologies utilise a central hub or switch.

5. Which one of these is an advantage of star topologies?

	Adding new devices is easy and doesn't disrupt the rest of the network.
→	Correct answer
	It requires a lot of cables.
→	The correct answer was "Adding new devices is easy and doesn't disrupt the rest of the network."
	It is expensive to install.
→	The correct answer was "Adding new devices is easy and doesn't disrupt the rest of the network."
	Needs professionals to maintain and up keep.
→	The correct answer was "Adding new devices is easy and doesn't disrupt the rest of the network."

6. State one advantage of the bus topology over the star topology network:

	Uses the least amount of cables
→	Incorrect: All nodes are connected by their own wire to the hub
	No data collision
→	Correct: Because all nodes don't use one wire for the backbone of transferring data
	it is scalable
→	Incorrect: can become unmanageable
	Multiple devices can communicate at any one time
→	Incorrect: it is a single cable, therefore only one device can transmit at any one time

7. can a network with a physical bus topology have a logical star topology

	true
→	this cannot be done as collisions would be prominent and functionality isn't that of star
	false

8. A switch regenerates any signal that it receives and passes it on to all machines.

	TRUE.
→	Incorrect as a switch maintains a list of known devices and will pass a transmission to only one known device
	FALSE.
→	A Hub regenerates any signal that it receives and passes it on to all machines

9. What are the differences between a switch and a hub?

	A hub sends signals to the switch.
→	No
	Switches maintain a list of devices that it has encountered before.
→	If a device is on the list and is the intended recipient of a message, the message will only be transmitted to the device.
	A hub contains all of your favourite shows for only £9.99 paid bi-monthly, what a steal.
→	Not a hub.
	A switch prevents data collisions.
→	Both hubs and switches prevent data collisions.
	A hub will transmit data to all devices
→	Yes
	A switch will never transmit to all devices
→	A switch will transmit to all devices if it hasn't ever encountered the intended recipient of the data.

10. Bus networks uses CSMA/CD (carrier sense multiple access with collision detection), what does it do when a collision is detected?

	stops sending data from all included devices and produces an error message
→	doesn't just just sending
	stops sending data all devices wait a random ammount of time then retry
→	correct
	keeps retrying until sent
→	incorrect this would not work and will stop the computer
	data is transfered through the air instead
→	this cannot be done with this protocol or possible in these systems

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