2.1.1 network topology

Topic 3

INTERNET TECHNOLOGY

3.1 Network Basics
3.1.1 Network Topology

1

Learning Outcome

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

• Explain types of network topology.

2

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.

3

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.

4

Communication Devices

Cable modem

Hubs & Switches
5

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.
6

Physical Transmission Media
Twisted-pair cable

Fiber-optic cable

Coaxial cable

7

Wireless Transmission Media

Cellular Radio

Communication Satellite

Microwaves 8

Define Network…cont.

 Advantages of a network include:

Facilitating Sharing Sharing data
communications hardware and information

Sharing Transferring
software funds

9

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.
10

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.

11

Computer Network Terms

Terms Definition
Node 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.
12

Computer Network Terms
Terms Definition
Switch 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 Expansion cards located within the system
Interface unit that connect the computer to a network.
Cards (NIC)
Token Special series of bits that functions like a ticket.

Packets Small pieces into which messages are divided.
13

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

14

Basic type of network topology:
 Bus Network.

15

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).

Terminator

T-Connector Backbone

16

Bus Network Topology…cont.

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

Terminator


17

 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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 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.

Terminator


19


 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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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.

21


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.

22

 Ring Network.

23

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.

24

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. 25


 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.

26

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

27

 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. 28


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.

29


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.

30

 Star Network.

31

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

32

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.
33


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.

34


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.

35

2.1.1 network topology

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