How networks communicate ?

LEVEL – 3 (1) SHWE YEE MYA WIN
1
Types of networks
There are several different types of computer networks. These computer networks can be
classified based on various factors. One such classification factor is geographical area the
networks occupy. Networks can span from a handful of devices within a single room to millions
of devices spread across the entire world. The following table shows some of the different types
of networks based on their size.
Local Area Network (LAN)
A system of interconnected computers located in a small
area, such as within the same office or building. Cost of
setting up and maintaining this type of network is usually low
and normally owned, controlled, and managed by a single
administrative system.
Wide Area Network (WAN)
A complex network system that spans over a large
geographic area, such as an entire city, region, or even an
entire country. It is used to connect many different networks
that are relatively far apart. Internet is the world largest
WAN.
Metropolitan Area Network (MAN)
This network size falls between LANs and WANs which is
larger than a LAN but smaller than a WAN. It network is
normally formed by connecting multiple LANs which are far
apart.
What is computer network?
Two or more computing devices connected to each other so that they can
exchange data, information and resources.

2
Network Technologies
Workstations in any type of networks may use a wired, wireless or both technologies to
create a connection between workstations and allow them communicate with each other.
Wired Network
It connects all the workstations and devices in the network
using electrical cables.
Data travel form one workstation to another over a cable in the
form of electrical signals.
Each data is first converted into binary digits and these binary
digits are then encoded into an electrical signals that can be
transmitted over the cables.
Building Blocks of wired network
 Network Interface Card (NIC)
A card installed in a computer that enables it to connect
with other workstations in the network. NIC contains a
transceiver that convert binary digits to electrical signals
when transmitting data and convert incoming electrical
signals to binary digits. It also supports a network port
that a cable can plugged in.
 Cables
Computers in wired network are physically connected to
each other using electrical cable. There are several types
of cable available such as coaxial cables, twisted pair
cables: UTP and STP, and fiber optic cables. The most
common used cable today is twisted pair. For high-speed
network connections, fiber-optic cable is used.
Fig 1.3: UTP Cable Fig 1.4: Coaxial Cable Fig 1.5: Fiber Optic Cable
I n f o
Although two computers can be
directly connected to each other
using a cable, wired network
generally requires central devices
like hubs, switches, or routers to
connect more computers.
FIGURE 1.1: Wired Network
FIGURE 1.2

3
 Bus Topology
Figure 1.7: Network connected in Bus Topology
Every notes communicates with each other through the
backbone cable.
When one node sends a data, signal travels to all nodes
connected to the cable and each node looks at each packet to
determine whether the packet is intended for it and the only
intended node can accepts the signal.
This way, nodes communicate with each other by responding
to data sent to it and ignoring data sent to other nodes on the
network.
Since every data is sent out to every node, other nodes have
to wait until it finishes broadcasting.
Network Topologies
In order to have network communication in wired network, it requires a network topology. The
way that the data travels from one device to another are different according to the topology that
the network has implemented. The common topologies in use today are bus, star, and ring.
Info
Terminators are added at
the both ends of the
backbone cable. The
purpose of the terminator
is to catch signals so that
they do not reflect back
down the line.

4
 Star Topology
All the nodes communicates with each other through central
device using a point-to-point connection.
All the data passes through the central device before reaching
the intended destination. The central device can be a hub or a
switch.
If a switch is used as a central device, each node sees only
those packets that were sent specifically to it. A switch knows
which node is connected to its ports so when it receives a
packet intended for a particular node, it sends the packet only
to the port that the recipient is connected to. Moreover, it can
send and receive data at the same time.
But if a hub is used as a central device, every data that arrives
to the hub from any of its port will automatically be
broadcasted to all other nodes, not just to the intended node
since it does not know which device is connected to which port,
just like in a bus topology.
Thus, only networks that use switches have a true star
topology but using hub would physical look like star topology
while network communicates logically in bus topology.
FIGURE 1.8: Network
Connected in Star Topology
Key Terms
 Physical Topology
Physical layout of devices in a
network.
 Logical Topology
Layout of how data actually
transfers in a network.
 Ring Topology
Data travels around the network in one direction from node
to node, until it reaches its destination.
Sending and receiving of data takes place by the help of
TOKEN.
At the start, an empty token is circulating on the ring for
transporting data. To send a data, a node first has to capture
the free token and writes its data and the recipient's address
onto the Token. This token passes to next node, checks if the
signal is intended to it. If yes, it receives it and passes the
empty token to the network. If not, token passes along with
the data to next node until the signal reaches its intended
destination.
FIGURE 1.9: Network Connected
in Ring Topology

5
Wireless Network
In a wireless network, data travels through the air eliminating
the need for cables. Wireless network rely on high-frequency
radio transmissions to connect nodes within a specific range.
Since wireless networks transmit data over radio waves, it is
subjected to unintentional electromagnetic interference from the
environment so the data transfer rate is usually slower than in
wired network and it is easy to hack data on wireless data
transmissions.
Therefore, many protocols are used to allow access and control
of the medium, to avoid collisions and to create more secure
network.
Building Blocks of wireless network
 Wireless Network adapter
A device installed in a computer to gain access to the
wireless network without the use of network cables. It is
responsible for translating binary digits to radio
frequency when transmitting data and converting radio
frequency to binary digits for receiving incoming data.
Info
Although devices can connect to each other wirelessly just by
installing wireless network adapter, you will need an interconnecting
device called wireless access point (WAP) to connect these wireless
devices to a wired network.
Key Term
Protocols is a set of rules used
to define a method of exchanging
data over a computer network.
FIGURE 2.1: WIRELESS NETWORK
FIGURE 2.2: WIRELESS NETWORK using WAP

6
Network Services
When exchanging data in a network, a variety of network services have been used to allow
network devices to efficiently communicate with each other.
Packet Switching
Packet switching is the technology of dividing a data into small chunks of formatted units called
packets for fast and efficient data transfer over the network.
All the processes of sending and receiving data from node to node in a computer network are
done through packet switching.
When a computer tries to send a file to another computer in a network, that file is broken into
packets so that it can be sent across the network in the most efficient way.
It also attaches information that identifies the sending computer and intended recipient, total
number to pieces and sequence number needed to reassembly at the other end. Using these
information, network switches and routers determine the best path to transfer these packets to
its destination.
FIGURE 3.1: Packet routing through the network

7
Access Methods
In a network, devices cannot communicate with each other whenever they like. This is because
problems like data collision arise when multiple devices attempt to send data at the same time
if every device in a network can send data anytime they want. To overcome such kind of
problem, a system called access control method is used to control which devices may use and
access the network for communication. There are three different access methods to control the
data transmission in a network: CSMA/CD, CSMA/CA and token passing methods.
Multiplexing
Multiplexing is the networking technique that transmits several
different signals or information streams on a single carrier so
that multiple communications can take place at the same time.
These complex signals are then converted into separate signals
at the receiving end. These processes are done by multiplexer
and de-multiplexer.
A good example of multiplexing would be phone calls in
telecommunications where more than one phone call is
transmitted over a single medium.
Key Terms
 Multiplexer
A device that selects and
combines input signals and
transmits it over a single
channel.
 De-multiplexer
A device that converts
multiplexed signals from a
single transmission line into
separate signals at the receiving
end.
Info
Normally, a multiplexer and
de-multiplexer are combined
into a single device capable of
processing both outgoing and
incoming signals.
FIGURE 3.2: Channel Multiplexing

8
CSMA/CD
CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is a set of rules that defines
how network devices respond when two devices encounter a data collision by trying to use a
data channel at the same time. CSMA/CD access method is used in Ethernet network to monitor
the network traffic.
Every host on the network has equal access to the wire but it can place data on the wire only
when the wire is free from traffic.
 Every host will check the wire to find whether another host is already using the medium
before placing its data on the wire.
 If no transmission is taking place at that time, the host can transmit its data.
 If there is traffic already in the medium, the host will need to wait until the traffic is clear.
 But, if two hosts try to place data on the medium at the same time, they will collide with
each other, destroying the data.
 After collision, each host needs to wait a random amount of time to avoid collision again
and the data will be retransmitted.

9
CSMA/CA
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is also the access method used
to monitor the network traffic. Unlike CSMA/CD which deals with transmissions after a collision
has occurred, CSMA/CA acts to avoid data collisions.
 Before any real data is transmitted by a host, it sends a piece of “dummy” data onto
the network to check if the traffic is clear.
 If the channel is clear, then the real data is transmitted.
 If it collides with any other data, it broadcast other hosts not to transmit any data.
 Then the host waits a random amount of time and checks again to see if the traffic is
clear.
 The process is repeated until the traffic is clear.

10
Token Passing
A communications network access method that uses a continuously repeating signal called token
for managing access to the transmission medium.
Different token passing access methods work differently. Token Ring networks allow only one
token on the cable at a time while FDDI networks can have multiple tokens circulating
simultaneously.
The token is circling from one host to another
around the network orderly in a very high
speed.
When a host wants to send a data, it has to
wait for an empty token to transmit its
data.
When an empty token reached to the host,
it fills the token with its data, the address of
the destination station and mark the token as
being used and place the token
back to the network.
Destination host grabs the token,
reads the data and resets the token status
to empty.
In CSMA/CD and CSMA/CA access methods, the chances of collisions increases as the number of
hosts in the network increases. But there can be no collisions on a token passing network since
each host will get its turn of sending data only when the empty token reached to them so they
have no change of sending data simultaneously avoiding the possibilities of data collisions.
1 2
3 4

11
As a conclusion, I am going to explain how all the things I have mentioned above take
place in allowing a communication to take place in a network.
First of all, it is important to identify the overall structure of network. Is the type of network
LAN, MAN or WAN? Because the way they communicate differ from each type of network. For
example, LANs can be connected through wire or wireless technology using simple topology while
it requires both wire and wireless technology with a mixture of topologies for WANs.
Then, to understand how networks communicate you need to know what technologies is
used to implement the network. Is the connection between workstations is made through wired
or wireless? If it is wired network, then the workstations are connected with each other using
cables in the form of electrical signals. If it is wireless then the radio frequency are used to
connect the workstations. Since workstations are physically connected to each other in wired
network, the way communicate are different according to the arrangement of the devices.
Thirdly, the main purpose of using network is to communicate with other network devices.
Communication in a network means exchanging information with each other no matter what type
of network it is and what technologies and topologies they used. While exchanging information,
network service ensure that data are efficiently transferred in a network. Network services take
place when a data is transmitted from the source and that data is reached to the destination.
Last of all, access methods are used to control the access and data flow of the whole
network to avoid data collision.
References:
 (2010) ' Communication Technologies’, in Anderson, K., Jarvis, A., Kaye, A., Lawson, J.,
McGill, R., Phillips, J. and Smith, A. BTEC Level 3 Information Technology Book 1. Person
Education Limited. pp. 304-310.
 Lowe, D. (2005) Networking All-in-One Desk Reference for Dummies, 2nd edin. Indianapolis,
Indiana: Wiley Publishing, Inc. pp. 9, 14, 15 – 17.
 (no date) Token Ring , Available at:
http://www.datacottage.com/nch/troperation.htm#.VYZJavmqqkp (Accessed : 13th June
2015)
 (no date) Multiplexing Definition , Available at:
http://searchnetworking.techtarget.com/definition/multiplexing (Accessed : 13th June 2015)
 (no date) multiplexor , Available at: http://www.webopedia.com/TERM/M/multiplexor.html
(Accessed : 20th June 2015)
 Thomas, J. (no date) Network Access Methods - CSMA/CD, CSMA/CA and Token Passing ,
Available at: http://www.omnisecu.com/basic-networking/network-access-methods.php

12
 Beal, V. (no date) CSMA/CA - Carrier Sense Multiple Access/Collision Avoidance , Available
at: http://www.webopedia.com/TERM/C/CSMA_CA.html (Accessed : 13th June 2015)
 (no date) CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) Definition , Available
at: http://searchnetworking.techtarget.com/definition/CSMA-CA (Accessed : 13th June
2015)
 (no date) Access Methodologies , Available at:
http://www.technologyuk.net/telecommunications/networks/access_methodologies.shtml
 (no date) CSMA/CD, Available at: http://www.computerhope.com/jargon/c/csmacd.htm
 (no date) Definition of: token passing , Available at:
http://www.pcmag.com/encyclopedia/term/52962/token-passing (Accessed : 13th June
2015)

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