2.1.1 network topology

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INTERNET TECHNOLOGY

3.1 Network Basics3.1.1 Network Topology

Topic 3

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Learning Outcome

At the end of this topic, students should be able to:

• Explain types of network topology.

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Define Network

A network is a collection of computers and devices connected together via communications devices and transmission media.

A computer network is a communication system that connects two or more computers, and their peripheral devices to exchange information and share resources.

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Network Terms

Communications devices. Hardware component that enables a computer

to send (transmit) and receive data, instructions, and information to and from one or more computers.

Examples: cable modem, wireless modem, network cards, hubs & switches.

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Communication Devices

Cable modem

Hubs & Switches

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Network Terms

Transmission media. Materials or substances capable of carrying one or

more signals in a communications channel. There are two types of transmission media: physical and wireless.

Example of physical transmission media: twisted-pair cable, coaxial cable & fiber-optic cable.

Example of wireless transmission media: Infrared, broadcast radio, cellular radio, microwave radio & communication satellite.

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Physical Transmission Media

Twisted-pair cable

Coaxial cable

Fiber-optic cable

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Wireless Transmission Media

Communication Satellite

Cellular Radio

Microwaves

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Define Network…cont.

Advantages of a network include:

Facilitating communications

Sharing hardware

Sharing data and information

Sharing software

Transferring funds

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Network Topology

What is a network topology?i. A network topology refers to the layout of the

computers and devices in a communications network, or

ii. A network topology refers to the configuration of a network that consists of cables, computers, and other peripherals.

It describes the physical and logical layout of the network.

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Network Topology…cont.

What is a physical topology? The physical topology of a network refers to the configuration of cables, computers, and other peripherals.

What is a logical topology? The logical topology of a network refers to the architecture, that is the way in which the network appears to the devices that use it.

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Computer Network Terms

Terms DefinitionNode Any device that is connected to a network

such as computer, printer, or data storage device.

Client A node that requests and uses resources available from other nodes.

Server A node that share resources with other nodes.

Host Any computer that provides services and connections to other computers on a network.

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Computer Network TermsTerms DefinitionSwitch Central node that coordinates the flow of data

by sending messages directly between sender and receiver nodes.

Hub The device that provides a common central connection point for nodes on network.

Network Interface Cards

(NIC)

Expansion cards located within the system unit that connect the computer to a network.

Token Special series of bits that functions like a ticket.

Packets Small pieces into which messages are divided.

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Types of Network Topology

Three (3) basic types of network topology: Bus Network. Star Network. Ring Network.

Bus Network

Star Network

Ring Network

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Types of Network Topology

Basic type of network topology: Bus Network.

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Bus Network Topology

Bus Network Topology: A bus network consists of a single central cable

(backbone/trunk), to which all computers and other devices connect (nodes).

T-Connector

Terminator

Backbone

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Bus Network Topology…cont.

The bus is the physical cable that connects the computers and other devices.

T-Connector

Terminator

Backbone

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Bus Network Topology…cont.

The bus in a bus network transmit data, instructions, and information as a series of signal.

Those signals are sent as electrical pulses that travel along the length of the cable in both directions.

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Bus Network Topology…cont.

Each device is connected to the single bus cable through T-Connector.

A terminator is required at each end of the bus cable to prevent the signal from bouncing back and forth on the bus cable.

T-Connector

Terminator

Backbone

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Bus Network Topology…cont.

When a sending device transmits data, the address of the receiving device is included with the transmission.

If the device address does not match the intended address for the data, the device ignores the data.

If the data match the device address, the data is accepted.

Thus, each computer examines EVERY data to determine who the data is for and accepts only messages addressed to them.

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Bus Network Topology

Advantages of Bus Network:

i. Bus networks are inexpensive and easy to install.

ii. Computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network.

iii. Failure of one device usually does not affect the rest of the bus network.

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Bus Network Topology

Disadvantages of Bus Network:

i. Network disruption might occur when computer or other devices are added or removed.

ii. Because all systems on the network connect to a single cable or backbone, a break in the cable will prevent all systems from accessing the network.

iii. It is difficult to identify the problem if the entire network shut down.

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Types of Network Topology

Basic type of network topology: Ring Network.

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Ring Network Topology

Ring Network Topology: On a ring network, a cable forms a closed loop

(ring) with all computers and devices arranged along the ring.

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Ring Network Topology…cont.

Data transmitted on a ring network travels from device to device around the entire ring, in one direction (clockwise or counterclockwise).

When a computer or device sends data, the data travels to each computer on the ring until it reaches its destinations.

Token passing is one method for sending data around a ring.

Each device takes a turn sending and receiving information through the use of a token.

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Ring Network Topology…cont.

The token along with any data is sent from the first device to the second device which extracts the data addressed to it and adds any data it wishes to send.

Then second device passes the token and data to the third device, etc. until it comes back around to the first device again.

Only the device with the token is allowed to send data. All other devices must wait for the token to come to them.

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Ring Network Topology…cont.

Data transmitted on a ring network travels from device to device around the entire ring, in one direction.

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Ring Network Topology…cont.

Machine 1 wants to send some data to machine 4, so it first has to capture the free Token. It then writes its data and the recipient's address onto the Token (represented by the yellow flashing screen).

The packet of data is then sent to machine 2 who reads the address, realizes it is not its own, so passes it on to machine 3. Machine 3 does the same and passes the Token on to machine 4.

This time it is the correct address and so machine 4 reads the message (represented by the yellow flashing screen). It cannot, however, release a Token on to the ring, it must first send the message back to machine 1 with an acknowledgement to say that it has received the data (represented by the purple flashing screen).

The receipt is then sent to machine 5 who checks the address, realizes that it is not its own and so forwards it on to the next machine in the ring, machine 6.

Machine 6 does the same and forwards the data to machine 1, who sent the original message.

Machine 1 recognizes the address, reads the acknowledgement from machine 4 (represented by the purple flashing screen) and then releases the free Token back on to the ring ready for the next machine to use.

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Ring Network Topology

Advantages of Ring Network:

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

ii. Cable faults are easily located, making troubleshooting easier.

iii. The uses of token passing enables all devices in a ring topology to share the network resources fairly.

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Ring Network Topology

Disadvantages of Ring Network:

i. A failure in any cable or device breaks the loop and can take down the entire network.

ii. Data packets must pass through every computer therefore, this makes it slower.

iii. A ring network can span a larger distance than a bus network, but it is more difficult to install.

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Types of Network Topology

Basic type of network topology: Star Network.

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Star Network Topology

Star Network Topology: Two types of devices that provide a common

central connection point for nodes on the network are a hub and a switch.

Hub / Switch

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Star Network Topology…cont.

Hub or Switch: A device that provides a common central connection

point for other devices on a network. All data that transfer from one device to another passes

through the hub or switch.

The difference between a hub and a switch: The hub takes a signal that comes from any device and

passes it along to all the other devices in the network. Whenever a node sends a message, it is routed to the

switch, which then passes the message to the intended recipient.

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Star Network Topology

Advantages of Star Network:

i. If one device fails, only that device is affected.

ii. Devices can be added to or removed from network with little or no disruption.

iii. Easy to troubleshoot and isolate problem.

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Star Network Topology

Disadvantages of Star Network:

i. If the hub or switch fails, the entire network will be inoperable.

ii. Requires more cable than most of the other topologies.

iii. More expensive because the cost of the hub/switch.