DATA COMMUNICATION AND NETWORKING
DISCUSSION INFO:
Direction of data flow (simplex, half duplex, full duplex), Topology design, categories of network (LAN,
MAN, WAN, WLAN), Reference models: OSI reference model, TCP/IP reference model, their comparative
study. Network Devices.
Transmission Modes in Computer Networks (Simplex, Half-Duplex
and Full-Duplex)
Transmission mode means transferring of data between two devices. It is also known as
communication mode. Buses and networks are designed to allow communication to occur
between individual devices that are interconnected. There are three types of transmission
mode:
These are explained as following below.
1. Simplex Mode:
In Simplex mode, the communication is unidirectional, as on a one-way street. Only
one of the two devices on a link can transmit, the other can only receive. The simplex
mode can use the entire capacity of the channel to send data in one direction.
Example: Keyboard and traditional monitors. The keyboard can only introduce input,
the monitor can only give the output.
2. Half Duplex Mode:
In half-duplex mode, each station can both transmit and receive, but not at the same time.
When one device is sending, the other can only receive, and vice versa. The half-duplex mode
is used in cases where there is no need for communication in both direction at the same time.
The entire capacity of the channel can be utilized for each direction.
Example: Walkie- talkie in which message is sent one at a time and messages are sent in both
the directions.
Channel capacity=Bandwidth * Propagation Delay
3. Full Duplex Mode:
In full-duplex mode, both stations can transmit and receive simultaneously. In full_duplex
mode, signals going in one direction share the capacity of the link with signals going in other
direction, this sharing can occur in two ways:
• Either the link must contain two physically separate transmission paths, one for
sending and other for receiving.
• Or the capacity is divided between signals traveling in both directions.
Full-duplex mode is used when communication in both direction is required all the time. The
capacity of the channel, however must be divided between the two directions.
Example: Telephone Network in which there is communication between two persons by a
telephone line, through which both can talk and listen at the same time.
Channel Capacity=2* Bandwidth*propagation Delay
END....
What Is Network Topology?
Network topology refers to how various nodes, devices, and connections on your network are
physically or logically arranged in relation to each other. Think of your network as a city, and
the topology as the road map. Just as there are many ways to arrange and maintain a city—
such as making sure the avenues and boulevards can facilitate passage between the parts of
town getting the most traffic—there are several ways to arrange a network. Each has
advantages and disadvantages and depending on the needs of your company, certain
arrangements can give you a greater degree of connectivity and security.
There are two approaches to network topology: physical and logical. Physical network
topology, as the name suggests, refers to the physical connections and interconnections
between nodes and the network—the wires, cables, and so forth. Logical network topology
is a little more abstract and strategic, referring to the conceptual understanding of how and
why the network is arranged the way it is, and how data moves through it.
Why Is Network Topology Important?
The layout of your network is important for several reasons. Above all, it plays an essential
role in how and how well your network functions. Choosing the right topology for your
company’s operational model can increase performance while making it easier to locate
faults, troubleshoot errors, and more effectively allocate resources across the network to
ensure optimal network health. A streamlined and properly managed network topology can
increase energy and data efficiency, which can in turn help to reduce operational and
maintenance costs.
The design and structure of a network are usually shown and manipulated in a software
created network topology diagram. These diagrams are essential for a few reasons, but
especially for how they can provide visual representations of both physical and logical layouts,
allowing administrators to see the connections between devices when troubleshooting.
The way a network is arranged can make or break network functionality, connectivity, and
protection from downtime. The question of, “What is network topology?” can be answered
with an explanation of the two categories in the network topology.
1. Physical – The physical network topology refers to the actual connections
(wires, cables, etc.) of how the network is arranged. Setup, maintenance, and
provisioning tasks require insight into the physical network.
2. Logical – The logical network topology is a higher-level idea of how the
network is set up, including which nodes connect to each other and in which
ways, as well as how data is transmitted through the network. Logical network
topology includes any virtual and cloud resources.
Effective network management and monitoring require a strong grasp of both the physical
and logical topology of a network to ensure your network is efficient and healthy.
What’s the Most Common Type of Network Topology?
Building a local area network (LAN) topology can be make-or-break for your business, as you
want to set up a resilient, secure, and easy-to-maintain topology. There are several different
types of network topology and all are suitable for different purposes, depending on the
overall network size and your objectives.
What Is Star Topology?
A star topology, the most common network topology, is laid out so every node in the network
is directly connected to one central hub via coaxial, twisted-pair, or fiber-optic cable. Acting
as a server, this central node manages data transmission—as information sent from any node
on the network has to pass through the central one to reach its destination—and functions
as a repeater, which helps prevent data loss.
Advantages of Star Topology
Star topologies are common since they allow you to conveniently manage your entire network
from a single location. Because each of the nodes is independently connected to the central
hub, should one go down, the rest of the network will continue functioning unaffected,
making the star topology a stable and secure network layout.
Additionally, devices can be added, removed, and modified without taking the entire network
offline.
On the physical side of things, the structure of the star topology uses relatively little cabling
to fully connect the network, which allows for both straightforward setup and management
over time as the network expands or contracts. The simplicity of the network design makes
life easier for administrators, too, because it’s easy to identify where errors or performance
issues are occurring.
Disadvantages of Star Topology
On the flipside, if the central hub goes down, the rest of the network can’t function. But if the
central hub is properly managed and kept in good health, administrators shouldn’t have too
many issues.
The overall bandwidth and performance of the network are also limited by the central node’s
configurations and technical specifications, making star topologies expensive to set up and
operate.
What Is Bus Topology?
A bus topology orients all the devices on a network along a single cable running in a single
direction from one end of the network to the other—which is why it’s sometimes called a
“line topology” or “backbone topology.” Data flow on the network also follows the route of
the cable, moving in one direction.
Advantages of Bus Topology
Bus topologies are a good, cost-effective choice for smaller networks because the layout is
simple, allowing all devices to be connected via a single coaxial or RJ45 cable. If needed, more
nodes can be easily added to the network by joining additional cables.
Disadvantages of Bus Topology
However, because bus topologies use a single cable to transmit data, they’re somewhat
vulnerable. If the cable experiences a failure, the whole network goes down, which can be
time-consuming and expensive to restore, which can be less of an issue with smaller
networks.
Bus topologies are best suited for small networks because there’s only so much bandwidth,
and every additional node will slow transmission speeds.
Furthermore, data is “half-duplex,” which means it can’t be sent in two opposite directions at
the same time, so this layout is not the ideal choice for networks with huge amounts of traffic.
What Is Ring Topology? Single vs. Dual
Ring topology is where nodes are arranged in a circle (or ring). The data can travel through
the ring network in either one direction or both directions, with each device having exactly
two neighbours.
Pros of Ring Topology
Since each device is only connected to the ones on either side, when data is transmitted, the
packets also travel along the circle, moving through each of the intermediate nodes until they
arrive at their destination. If a large network is arranged in a ring topology, repeaters can be
used to ensure packets arrive correctly and without data loss.
Only one station on the network is permitted to send data at a time, which greatly reduces
the risk of packet collisions, making ring topologies efficient at transmitting data without
errors.
By and large, ring topologies are cost-effective and inexpensive to install, and the intricate
point-to-point connectivity of the nodes makes it relatively easy to identify issues or
misconfigurations on the network.
Cons of Ring Topology
Even though it’s popular, a ring topology is still vulnerable to failure without proper network
management. Since the flow of data transmission moves unidirectionally between nodes
along each ring, if one node goes down, it can take the entire network with it. That’s why it’s
imperative for each of the nodes to be monitored and kept in good health. Nevertheless, even
if you’re vigilant and attentive to node performance, your network can still be taken down by
a transmission line failure.
The question of scalability should also be taken into consideration. In a ring topology, all the
devices on the network share bandwidth, so the addition of more devices can contribute to
overall communication delays. Network administrators need to be mindful of the devices
added to the topology to avoid overburdening the network’s resources and capacity.
Additionally, the entire network must be taken offline to reconfigure, add, or remove nodes.
And while that’s not the end of the world, scheduling downtime for the network can be
inconvenient and costly.
What Is Dual-Ring Topology?
A network with ring topology is half-duplex, meaning data can only move in one direction at
a time. Ring topologies can be made full-duplex by adding a second connection between
network nodes, creating a dual ring topology.
Advantages of Dual-Ring Topology
The primary advantage of dual ring topology is its efficiency: because each node has two
connections on either side, information can be sent both clockwise and counter clockwise
along the network. The secondary ring included in a dual-ring topology setup can act as a
redundant layer and backup, which helps solve for many of the disadvantages of traditional
ring topology. Dual ring topologies offer a little extra security, too: if one ring fails within a
node, the other ring is still able to send data.
What Is Tree Topology?
The tree topology structure gets its name from how the central node functions as a sort of
trunk for the network, with nodes extending outward in a branch-like fashion. However,
where each node in a star topology is directly connected to the central hub, a tree topology
has a parent-child hierarchy to how the nodes are connected. Those connected to the central
hub are connected linearly to other nodes, so two connected nodes only share one mutual
connection. Because the tree topology structure is both extremely flexible and scalable, it’s
often used for wide area networks to support many spread-out devices.
Pros of Tree Topology
Combining elements of the star and bus topologies allows for the easy addition of nodes and
network expansion. Troubleshooting errors on the network is also a straightforward process,
as each of the branches can be individually assessed for performance issues.
Cons of Tree Topology
As with the star topology, the entire network depends on the health of the root node in a tree
topology structure. Should the central hub fail, the various node branches will become
disconnected, though connectivity within—but not between—branch systems will remain.
Because of the hierarchical complexity and linear structure of the network layout, adding
more nodes to a tree topology can quickly make proper management an unwieldy, not to
mention costly, experience. Tree topologies are expensive because of the sheer amount of
cabling required to connect each device to the next within the hierarchical layout.
What Is Mesh Topology?
A mesh topology is an intricate and elaborate structure of point-to-point connections where
the nodes are interconnected. Mesh networks can be full or partial mesh. Partial mesh
topologies are mostly interconnected, with a few nodes with only two or three connections,
while full-mesh topologies are—surprise! —fully interconnected.
The web-like structure of mesh topologies offers two different methods of data transmission:
routing and flooding. When data is routed, the nodes use logic to determine the shortest
distance from the source to destination, and when data is flooded, the information is sent to
all nodes within the network without the need for routing logic.
Advantages of Mesh Topology
Mesh topologies are reliable and stable, and the complex degree of interconnectivity
between nodes makes the network resistant to failure. For instance, no single device going
down can bring the network offline.
Disadvantages of Mesh Topology
Mesh topologies are incredibly labour-intensive. Each interconnection between nodes
requires a cable and configuration once deployed, so it can also be time-consuming to set up.
As with other topology structures, the cost of cabling adds up fast, and to say mesh networks
require a lot of cabling is an understatement.
What Is Hybrid Topology?
Hybrid topologies combine two or more different topology structures—the tree topology is a
good example, integrating the bus and star layouts. Hybrid structures are most commonly
found in larger companies where individual departments have personalized network
topologies adapted to suit their needs and network usage.
Advantages of Hybrid Topology
The main advantage of hybrid structures is the degree of flexibility they provide, as there are
few limitations on the network structure itself that a hybrid setup can’t accommodate.
Disadvantages of Hybrid Topology
However, each type of network topology comes with its own disadvantages, and as a network
grows in complexity, so too does the experience and know-how required on the part of the
admins to keep everything functioning optimally. There’s also the monetary cost to consider
when creating a hybrid network topology.
Which Topology Is Best for Your Network?
No network topology is perfect, or even inherently better than the others, so determining the
right structure for your business will depend on the needs and size of your network. Here are
the key elements to consider:
• Length of cable needed
• Cable type
• Cost
• Scalability
Cable Length
Generally, the more cable involved in network topology, the more work it’ll require to set up.
The bus and star topologies are on the simpler side of things, both being fairly lightweight,
while mesh networks are much more cable- and labour-intensive.
Cable Type
The second point to consider is the type of cable you’ll install. Coaxial and twisted-pair cables
both use insulated copper or copper-based wiring, while fiber-optic cables are made from
thin and pliable plastic or glass tubes. Twisted-pair cables are cost-effective but have less
bandwidth than coaxial cables. Fiber-optic cables are high performing and can transmit data
far faster than twisted-pair or coaxial cables, but they also tend to be far more expensive to
install, because they require additional components like optical receivers. So, as with your
choice of network topology, the wiring you select depends on the needs of your network,
including which applications you’ll be running, the transmission distance, and desired
performance.
Cost
As I’ve mentioned, the installation cost is important to account for, as the more complex
network topologies will require more time and funding to set up. This can be compounded if
you’re combining different elements, such as connecting a more complex network structure
via more expensive cables (though using fiber-optic cables in a mesh network is overdoing it,
if you ask me, because of how interconnected the topology is). Determining the right topology
for your needs, then, is a matter of striking the right balance between installation and
operating costs and the level of performance you require from the network.
Scalability
The last element to consider is scalability. If you anticipate your company and network
expanding—or if you’d like it to be able to—it’ll save you time and hassle down the line to use
an easily modifiable network topology. Star topologies are so common because they allow
you to add, remove, and alter nodes with minimal disruption to the rest of the network. Ring
networks, on the other hand, have to be taken entirely offline for any changes to be made to
any of the nodes.
Computer Network Types
A computer network is a group of computers linked to each other that enables the computer
to communicate with another computer and share their resources, data, and applications.
A computer network can be categorized by their size. A computer network is mainly of four
types:
o LAN(Local Area Network)
o PAN(Personal Area Network)
o MAN(Metropolitan Area Network)
o WAN(Wide Area Network)
LAN(Local Area Network)
o Local Area Network is a group of computers connected to each other in a small area
such as building, office.
o LAN is used for connecting two or more personal computers through a communication
medium such as twisted pair, coaxial cable, etc.
o It is less costly as it is built with inexpensive hardware such as hubs, network adapters,
and ethernet cables.
o The data is transferred at an extremely faster rate in Local Area Network.
o Local Area Network provides higher security.
PAN(Personal Area Network)
o Personal Area Network is a network arranged within an individual person, typically
within a range of 10 meters.
o Personal Area Network is used for connecting the computer devices of personal use is
known as Personal Area Network.
o Thomas Zimmerman was the first research scientist to bring the idea of the Personal
Area Network.
o Personal Area Network covers an area of 30 feet.
o Personal computer devices that are used to develop the personal area network are
the laptop, mobile phones, media player and play stations.
There are two types of Personal Area Network:
o Wired Personal Area Network
o Wireless Personal Area Network
Wireless Personal Area Network: Wireless Personal Area Network is developed by simply
using wireless technologies such as WiFi, Bluetooth. It is a low range network.
Wired Personal Area Network: Wired Personal Area Network is created by using the USB.
Examples of Personal Area Network:
o Body Area Network: Body Area Network is a network that moves with a person. For
example, a mobile network moves with a person. Suppose a person establishes a
network connection and then creates a connection with another device to share the
information.
o Offline Network: An offline network can be created inside the home, so it is also
known as a home network. A home network is designed to integrate the devices such
as printers, computer, television but they are not connected to the internet.
o Small Home Office: It is used to connect a variety of devices to the internet and to a
corporate network using a VPN
MAN(Metropolitan Area Network)
o A metropolitan area network is a network that covers a larger geographic area by
interconnecting a different LAN to form a larger network.
o Government agencies use MAN to connect to the citizens and private industries.
o In MAN, various LANs are connected to each other through a telephone exchange line.
o The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3,
ADSL, etc.
o It has a higher range than Local Area Network(LAN).
Uses of Metropolitan Area Network:
o MAN is used in communication between the banks in a city.
o It can be used in an Airline Reservation.
o It can be used in a college within a city.
o It can also be used for communication in the military.
WAN(Wide Area Network)
o A Wide Area Network is a network that extends over a large geographical area such
as states or countries.
o A Wide Area Network is quite bigger network than the LAN.
o A Wide Area Network is not limited to a single location, but it spans over a large
geographical area through a telephone line, fibre optic cable or satellite links.
o The internet is one of the biggest WAN in the world.
o A Wide Area Network is widely used in the field of Business, government, and
education.
Examples of Wide Area Network:
o Mobile Broadband: A 4G network is widely used across a region or country.
o Last mile: A telecom company is used to provide the internet services to the
customers in hundreds of cities by connecting their home with fiber.
o Private network: A bank provides a private network that connects the 44 offices. This
network is made by using the telephone leased line provided by the telecom company.
Advantages of Wide Area Network:
Following are the advantages of the Wide Area Network:
o Geographical area: A Wide Area Network provides a large geographical area. Suppose
if the branch of our office is in a different city then we can connect with them through
WAN. The internet provides a leased line through which we can connect with another
branch.
o Centralized data: In case of WAN network, data is centralized. Therefore, we do not
need to buy the emails, files or back up servers.
o Get updated files: Software companies work on the live server. Therefore, the
programmers get the updated files within seconds.
o Exchange messages: In a WAN network, messages are transmitted fast. The web
application like Facebook, WhatsApp, Skype allows you to communicate with friends.
o Sharing of software and resources: In WAN network, we can share the software and
other resources like a hard drive, RAM.
o Global business: We can do the business over the internet globally.
o High bandwidth: If we use the leased lines for our company then this gives the high
bandwidth. The high bandwidth increases the data transfer rate which in turn
increases the productivity of our company.
Disadvantages of Wide Area Network:
The following are the disadvantages of the Wide Area Network:
o Security issue: A WAN network has more security issues as compared to LAN and MAN
network as all the technologies are combined together that creates the security
problem.
o Needs Firewall & antivirus software: The data is transferred on the internet which
can be changed or hacked by the hackers, so the firewall needs to be used. Some
people can inject the virus in our system so antivirus is needed to protect from such a
virus.
o High Setup cost: An installation cost of the WAN network is high as it involves the
purchasing of routers, switches.
o Troubleshooting problems: It covers a large area so fixing the problem is difficult.
Internetwork
o An internetwork is defined as two or more computer network LANs or WAN or
computer network segments are connected using devices, and they are configured by
a local addressing scheme. This process is known as internetworking.
o An interconnection between public, private, commercial, industrial, or government
computer networks can also be defined as internetworking.
o An internetworking uses the internet protocol.
o The reference model used for internetworking is Open System Interconnection(OSI).
Types of Internetwork:
1. Extranet: An extranet is a communication network based on the internet protocol such
as Transmission Control protocol and internet protocol. It is used for information sharing.
The access to the extranet is restricted to only those users who have login credentials. An
extranet is the lowest level of internetworking. It can be categorized as MAN, WAN or other
computer networks. An extranet cannot have a single LAN, atleast it must have one
connection to the external network.
2. Intranet: An intranet is a private network based on the internet protocol such
as Transmission Control protocol and internet protocol. An intranet belongs to an
organization which is only accessible by the organization's employee or members. The main
aim of the intranet is to share the information and resources among the organization
employees. An intranet provides the facility to work in groups and for teleconferences.
Intranet advantages:
o Communication: It provides a cheap and easy communication. An employee of the
organization can communicate with another employee through email, chat.
o Time-saving: Information on the intranet is shared in real time, so it is time-saving.
o Collaboration: Collaboration is one of the most important advantage of the intranet.
The information is distributed among the employees of the organization and can only
be accessed by the authorized user.
o Platform independency: It is a neutral architecture as the computer can be connected
to another device with different architecture.
o Cost effective: People can see the data and documents by using the browser and
distributes the duplicate copies over the intranet. This leads to a reduction in the cost
OSI Vs TCP / IP Reference Models
Similarities between OSI and TCP / IP Reference Models
• Both the reference models are based upon layered architecture.
• The layers in the models are compared with each other. The physical layer and the
data link layer of the OSI model correspond to the link layer of the TCP/IP model. The
network layers and the transport layers are the same in both the models. The session
layer, the presentation layer and the application layer of the OSI model together form
the application layer of the TCP/IP model.
• In both the models, protocols are defined in a layer-wise manner.
• In both models, data is divided into packets and each packet may take the individual route from the source to the destination.
Differences between OSI and TCP / IP Reference Models
• OSI model is a generic model that is based upon functionalities of each layer. TCP/IP
model is a protocol-oriented standard.
• OSI model distinguishes the three concepts, namely, services, interfaces, and
protocols. TCP/IP does not have a clear distinction between these three.
• OSI model gives guidelines on how communication needs to be done, while TCP/IP
protocols layout standards on which the Internet was developed. So, TCP/IP is a more
practical model.
• In OSI, the model was developed first and then the protocols in each layer were
developed. In the TCP/IP suite, the protocols were developed first and then the model
was developed.
• The OSI has seven layers while the TCP/IP has four layers.
The following diagram shows the corresponding layers of OSI and TCP/IP models −
Network Devices (Hub, Repeater, Bridge,
Switch, Router, Gateways and Brouter)
1. Repeater – A repeater operates at the physical layer. Its job is to regenerate
the signal over the same network before the signal becomes too weak or
corrupted so as to extend the length to which the signal can be transmitted
over the same network. An important point to be noted about repeaters is that
they do not amplify the signal. When the signal becomes weak, they copy the
signal bit by bit and regenerate it at the original strength. It is a 2-port device.
2. Hub – A hub is basically a multiport repeater. A hub connects multiple wires coming from
different branches, for example, the connector in star topology which connects different
stations. Hubs cannot filter data, so data packets are sent to all connected devices. In other
words, collision domain of all hosts connected through Hub remains one. Also, they do not
have the intelligence to find out best path for data packets which leads to inefficiencies and
wastage.
Types of Hub
• Active Hub:- These are the hubs which have their own power supply and can clean,
boost, and relay the signal along with the network. It serves both as a repeater as
well as wiring centre. These are used to extend the maximum distance between
nodes.
• Passive Hub :- These are the hubs which collect wiring from nodes and power
supply from active hub. These hubs relay signals onto the network without
cleaning and boosting them and can’t be used to extend the distance between
nodes.
• Intelligent Hub :- It work like active hubs and include remote management
capabilities. They also provide flexible data rates to network devices. It also
enables an administrator to monitor the traffic passing through the hub and to
configure each port in the hub.
3. Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the
functionality of filtering content by reading the MAC addresses of source and
destination. It is also used for interconnecting two LANs working on the same protocol.
It has a single input and single output port, thus making it a 2-port device.
Types of Bridges
• Transparent Bridges: - These are the bridge in which the stations are completely
unaware of the bridge’s existence i.e., whether or not a bridge is added or deleted
from the network, reconfiguration of the stations is unnecessary. These bridges
make use of two processes i.e., bridge forwarding and bridge learning.
• Source Routing Bridges: - In these bridges, routing operation is performed by
source station and the frame specifies which route to follow. The host can discover
frame by sending a special frame called discovery frame, which spreads through
the entire network using all possible paths to destination.
4. Switch – A switch is a multiport bridge with a buffer and a design that can boost its
efficiency (a large number of ports imply less traffic) and performance. A switch is a data link
layer device. The switch can perform error checking before forwarding data, that makes it
very efficient as it does not forward packets that have errors and forward good packets
selectively to correct port only. In other words, switch divides collision domain of hosts,
but broadcast domain remains same.
5. Routers – A router is a device like a switch that routes data packets based on their IP
addresses. Router is mainly a Network Layer device. Routers normally connect LANs and
WANs together and have a dynamically updating routing table based on which they make
decisions on routing the data packets. Router divide broadcast domains of hosts connected
through it.
6. Gateway – A gateway, as the name suggests, is a passage to connect two networks together
that may work upon different networking models. They basically work as the messenger
agents that take data from one system, interpret it, and transfer it to another system.
Gateways are also called protocol converters and can operate at any network layer. Gateways
are generally more complex than switch or router.
7. Brouter – It is also known as bridging router is a device which combines features of both
bridge and router. It can work either at data link layer or at network layer. Working as router,
it is capable of routing packets across networks and working as bridge, it is capable of filtering
local area network traffic.
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