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UNIT I Computer Networks and the Internet

What Is the Internet? The Network Edge, The Network Core, Delay, Loss, and Throughput in
Packet Switched Networks, Reference Models, Example Networks, Guided Transmission Media,
Wireless Transmission

Internet:
 The internet is a global network of interconnected computers, servers, phones, and smart
appliances that communicate with each other using the transmission control protocol (TCP)
standard to enable a fast exchange of information and files, along with other types of
services.

computer network
 A computer network is a system that connects multiple computers and other electronic
devices to facilitate communication and resource sharing. This network allows devices to
transmit, exchange, and access data and information efficiently.

Key components and characteristics of a computer network include:

Nodes: These are the devices like computers, servers, printers, and other equipment that are
connected in the network.
Communication Media: Networks use various media for communication, such as wired
connections (Ethernet cables, coaxial cables) and wireless connections (Wi-Fi, Bluetooth).
Data Transmission: Data is transferred in the form of packets and signals. Protocols like TCP/IP
govern how data is transmitted and received.
Network Topologies: The arrangement of a network can vary. Common topologies include bus,
star, ring, mesh, and tree, each with its unique layout and communication style.
Network Types: Depending on the scale and range, networks can be categorized as Local Area
Networks (LAN), Wide Area Networks (WAN), Metropolitan Area Networks (MAN), and
Personal Area Networks (PAN).
Internet: The largest and most well-known computer network, connecting millions of computers
globally.
Security: Networks implement various security measures to protect data and maintain privacy.
Firewalls, encryption, and access control are some common security practices.
Protocols: Set of rules and conventions for communication. Protocols like HTTP, FTP, and SMTP
are used for specific types of data transmission.
Network Hardware: Includes routers, switches, hubs, and bridges that help in directing and
controlling network traffic.
Applications: Networks enable numerous applications, such as email, file sharing, online gaming,
and video conferencing.
There are different categories in which various networks can be classified, according to their size,
capabilities, and the geographical distance they cover. A network is normally a group of multiple
computer systems linked together in some manner so that they can share information and data
between them.

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Edge Network

 An edge network contains fewer hops to its adjacent network than a core network. In other
words, the edge network has few or no layer 3 devices. According to the OSI model, layer
3 represents the network layer. Hence, the devices used in the network layer are known as
layer 3 devices. Example of level 3 devices includes routers and switches.
 Additionally, we place the edge network close to the end users. A typical example of an
edge network would be a data center network. Another example of an edge network is a
branch office network that connects to the core network via IP routing protocols such
as Virtual Router Redundancy Protocol (VRRP) and policy-based routing (PBR).
 An edge network is ideal for connecting devices near the end users, such as a branch office
or remote site.

Core Network

 A core network contains more hops to its adjacent network than an edge network. In other
words, the core network has more layer 2 and 3 devices and is the center of the enterprise
network. It’s also known as the backbone network. Furthermore, we design core networks
to transfer network traffic at high speeds. A core network uses both wide-area networks
(WAN) and local area networks (LAN).
 A typical example of a core network would be a central office network connecting to the
edges via Multiprotocol Label Switching (MPLS) such as Open Shortest Path First
(OSPF) and Border Gateway Protocol (BGP).
 A core network generally has a larger number of layer 2 and 3 devices
 A core network is better suited to connect devices away from the end users, such as a
central office or data center.

Delays in Computer Network

The delays, here, means the time for which the processing of a particular packet takes place. We
have the following types of delays in computer networks:
1.TransmissionDelay:
The time taken to transmit a packet from the host to the transmission medium is called
Transmission delay.

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For example, if bandwidth is 1 bps (every second 1 bit can be transmitted onto the transmission
medium) and data size is 20 bits then what is the transmission delay? If in one second, 1 bit can
be transmitted. To transmit 20 bits, 20 seconds would be required.
Let B bps is the bandwidth and L bit is the size of the data then transmission delay is,
Tt = L/B
This delay depends upon the following factors:
If there are multiple active sessions, the delay will become significant.
Increasing bandwidth decreases transmission delay.
MAC protocol largely influences the delay if the link is shared among multiple devices.
Sending and receiving a packet involves a context switch in the operating system, which takes a
finite time.

2.Propagationdelay:

After the packet is transmitted to the transmission medium, it has to go through the medium to
reach the destination. Hence the time taken by the last bit of the packet to reach the destination
is called propagation delay.

Factors affecting propagation delay:

Distance – It takes more time to reach the destination if the distance of the medium is longer.
Velocity – If the velocity(speed) of the medium is higher, the packet will be received faster.
Tp = Distance / Velocity

3.Queueingdelay:

Let the packet is received by the destination, the packet will not be processed by the destination
immediately. It has to wait in a queue in something called a buffer. So, the amount of time it
waits in queue before being processed is called queueing delay.
In general, we can’t calculate queueing delay because we don’t have any formula for that.
This delay depends upon the following factors:
If the size of the queue is large, the queuing delay will be huge. If the queue is empty there will
be less or no delay.
If more packets are arriving in a short or no time interval, queuing delay will be large.
The less the number of servers/links, the greater is the queuing delay.

4.Processingdelay:

Now the packet will be taken for the processing which is called processing delay.
Time is taken to process the data packet by the processor that is the time required by intermediate
routers to decide where to forward the packet, update TTL, perform header checksum
calculations.

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It also doesn’t have any formula since it depends upon the speed of the processor and the speed
of the processor varies from computer to computer.

LOSS:

 Packet loss describes lost pieces of data traveling through a network, but failing to reach
its destination. Packet loss occurs when network congestion, hardware issues, software
bugs, and a number of other factors cause dropped packets during data transmission.
 Packet loss sits alongside the trio of two other major network performance
complications: latency, and jitter.
 In any network environment, data is sent and received via different devices across the
network in small units called packets. This applies to everything you do on the internet,
from emailing, uploading or downloading images or files, browsing, streaming, gaming –
to voice and video communication.
 Your network's Transmission Control Protocol (TCP) divides data files into efficiently
sized pieces for routing, then each piece is separately numbered and identified with the
destination’s internet address. Each individual packet may travel a different route, and
when they have arrived, they are restored to the original file by the TCP at the receiving
end.

Data communication comprises two words: Data and Communication. Data can be anything text,
images, audio, videos and multimedia whereas communication is an act of sending and receiving
data. Data communication refers to the exchange of data between two or more networked or
connected devices.

Reasons for packet loss

Network congestion - The primary cause of network packet loss is congestion.

Think of the queues on the road at certain times of the day, like early mornings and the end of the
working day. Too much traffic crowding onto the same road can become bottle-necked when it
tries to merge, and the result is that it doesn’t reach its destination on time.

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When your network's traffic hits its maximum limit, packets are discarded, and those packets lost
have to queue and wait to be delivered. Fortunately, most software is designed to either
automatically retrieve and resend those discarded packets or slow down transfer speed.
Network hardware problems - The speed with which hardware becomes outdated or redundant
these days is another major problem for your network. Hardware such as firewalls, routers, and
network switches consume a lot of power, and can considerably weaken network signals.
Sometimes organizations overlook the need to update hardware during expansions or mergers and
this can contribute to packet loss or connectivity outages.
Software bugs - Closely related to faulty hardware is a buggy software running on the network
device. Bugs or glitches in your system can sometimes be responsible for disrupting network
performance and preventing the delivery of packets. Hardware reboots and patches may fix bugs.
Overtaxed devices - When a network is operating at a higher capacity than it was designed to
handle, it weakens and becomes unable to process packets, and drops them. Most devices have
built-in buffers to assign packets to holding patterns until they can be sent.
Wi-fi packet loss vs wireless packet loss - Your internet connection has a significant effect on
packet loss. As a rule, wireless networks experience more issues with packet loss than wired
networks. Radio frequency interference, weaker signals, distance and physical barriers like walls
can all cause wireless networks to drop packets. With wired networks, faulty cables can be the
culprit, impeding signal flow through the cable.
Security threats - If you’re noticing unusually high rates of packet drop, the problem could be a
security breach. Cybercriminal’s hack into your router and instruct it to drop packets. They can
also execute a denial-of-service attack (DoS), preventing legitimate users from accessing files,
emails, or online accounts by flooding the network with too much traffic to handle. Packet loss
can be difficult to fix during a full-blown security.
Deficient infrastructure - This highlights the importance of a comprehensive network monitoring
solution. Some out-of-packet monitoring tools were not engineered for the job they’ve been
assigned to do and have limited functionality.

How to Fix Packet Loss:

It is important to note that there is no options for 100% prevention of packet loss, meaning there can only
be a reduction of packet loss stemming from preventative measures, but zero packet loss is impossible. This
is because the causes of packet loss, such as an overloaded system, can never be completely eliminated.
Systems and networks keep growing larger and larger, so engineers and IT staff can only do their best to
address the increasing problem.

1. Restart your system

Rebooting not just employee devices or endpoints but also the routers can help. Often, when a system
reboots, software is updated, temporary files are deleted, and additional memory becomes available.
2. Check network connections
Make sure that your network is configured properly. Even a single cable that is not plugged in correctly can
cause packet loss. Further, another look at the network's multiprotocol label switching (MPLS), which
is a protocol designed to get data packets to their destinations quickly, might be necessary.
3. Use cable connections instead of Wi-Fi
Since packets are more likely to get lost via Wi-Fi, check whether a wired, Ethernet connection will fix
the issue, but it's a temporary solution at best.
4. Update or upgrade your software

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Updating your operating system (OS) and your most used programs will also help. The most recent version
of an OS is less likely to have bugs, which means there is a lower likelihood of packet loss. Lean on the
hard work of the dozens, if not hundreds, of engineers working for software vendors such as Apple,
Microsoft, and Mozilla, who fix errors on an ongoing basis to improve your computing experience.
5. Replace old hardware
Sometimes older hardware can be an issue. This goes for employee endpoints as well as the firewalls,
network switches, and routers that make up your network infrastructure. Determine whether an older and
possibly faulty piece of hardware on the network is causing packet loss and replace it with a new one.
6. Use QoS settings
Quality of service (QoS) settings help manage packet loss by organizing network resources. QoS
settings will assign more network traffic to the places that can best accommodate more resource-intensive
data, such as voice and video.

Switch:
 A switch is a hardware device in a network that connects other devices, like computers
and servers. It helps multiple devices share a network without their data interfering with
each other.
 A switch works like a traffic cop at a busy intersection.
 When a data packet arrives, the switch decides where it needs to go and sends it through
the right port.
 Some data packets come from devices directly connected to the switch, like computers
or VoIP phones. Other packets come from devices connected through hubs or routers.
 switching is the process of transferring data packets from one device to another in a
network, or from one network to another, using specific devices called switches.
 Switching takes place at the Data Link layer of the OSI Model. This means that after the
generation of data packets in the Physical Layer, switching is the immediate next process
in data communication

Message Switching: This is an older switching technique that has become obsolete. In message
switching technique, the entire data block/message is forwarded across the entire network thus,
making it highly inefficient.

Circuit Switching: In this type of switching, a connection is established between the source and
destination beforehand. This connection receives the complete bandwidth of the network until
the data is transferred completely.
This approach is better than message switching as it does not involve sending data to the entire
network, instead of its destination only.

Packet Switching
Packet switching is a method of transferring data over a network in the form of packets. For better
efficiency and for a faster transfer of information we break the data into small pieces, or small
“packets” of variable length using store and forward operations.

Each time when a device sends a file to another device, the information is broken down into packets
to determine the most efficient route for sending the data across the required network over a time
period.
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Example: 5 MB file is divided into small packets with a packet header which has an origin IP
address and a destination IP address with the entire data file and sequence number.

Types of Packets Switching:

There are two types of packets switching:

 Connection-Oriented Packet Switching
 Connectionless Packet Switching (datagram)

Connection-Oriented Packet Switching

Connection-Oriented Packet Switching is also known as virtual switching or circuit switching.
 Here, the data packets are first assembled and then numbered.
 They already have a predefined route and travel sequentially.
 Address is not required in circuit switching.
 All the packets are in a sequence.

Connectionless Packet Switching (datagram)

This is one of the most basic types of packets switching where multiple packets are individually
routed. Here, each packet does carry complete routing information but has different paths of
transmission. Packets belonging to one flow can take different routes to arrive at different
destinations, which can result in the packets arriving at the destination being out of order. It has
no connection set up hence reliable delivery has to be provided by end systems with additional
protocols. Connectionless packet switching is also known as Datagram switching.

Connectionless packet switching contains the following information:

 It always has a source address.
 Contains a destination address.
 Contains a sequence number for reorientation.
 Upon packets reaching the destination, the devices which receive them reassemble the
packet to form the original message.

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Difference Between Packet Switching and Circuit Switching

Packet Switching Circuit Switching

There is no predetermined path, data packets are The route is determined in advance for the
received by the routers. transfer of info.
There is no fixed bandwidth, it provides the flexibility This setup works within a fixed bandwidth.
to work in different frequencies.
During the transfer of information, the order of data is During the transfer of information, the order
not maintained. Data packets are arranged by the of data is maintained.
receiving routers.
It exists in a network layer. It exists in the physical layer.
This kind of method is ideal for data transmission. This kind of method is ideal for voice
transmission or delay connections.

Some main advantages and disadvantages of packet switching are as follows.

Advantages
 This type of switching has improved efficiency and has less bandwidth network wastage.
 Works at an optimal speed with a less latency factor.
 Improved fault tolerance of the circuit.
 They are more reliable.
Disadvantages
 Sequence numbers are required for each packet since they are not ordered.
 Can be a bit more complex.
 Rerouting can cause transmission delay.
 It is beneficial for small messages or small data.

Different Types of Computer Networks

 A computer network can be defined as a group of computers that utilize a set of common
communication protocols over digital interconnections to share resources over the network.
A network can be a small one including a handful of systems to a one with millions of
devices spread all across the world.

Types of Computer Networks

1. Local Area Network (LAN)
- Definition: A network that connects computers and devices in a limited geographic area, such
as a home, school, office building, or closely positioned group of buildings.
- Examples: A home Wi-Fi network, office Ethernet network.
2. Wide Area Network (WAN)
- Definition: A network that covers a broad area (e.g., any network whose communications links
cross metropolitan, regional, or national boundaries). The Internet is the largest WAN.
- Examples: The Internet, a company network with offices in different cities.
3. Metropolitan Area Network (MAN)
- Definition: A network designed to cover a metropolitan area, typically a city or a large campus.
It is larger than a LAN but smaller than a WAN.
- Examples: A network covering a university campus or a city's public Wi-Fi network.

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4. Personal Area Network (PAN)

- Definition: A network for interconnecting devices centered around an individual person's
workspace, typically within a range of a few meters.
- Examples: Bluetooth-connected devices, such as a phone connected to a wireless headset.
5. Wireless Local Area Network (WLAN)
- Definition: A LAN that uses wireless communication technology to connect devices within a
limited area.
- Examples: Home Wi-Fi networks, Wi-Fi in coffee shops.
6. Storage Area Network (SAN)
- Definition: A specialized high-speed network that provides block-level network access to
storage.
- Examples: Networks in data centers designed for connecting servers to storage devices.
7. Virtual Private Network (VPN)
- Definition: A secure network that uses encryption and other security mechanisms to connect
remote users or sites to a private network over a public network like the Internet.
- Examples: Employees connecting to their company's network from home.
Local Area Network (LAN)
This is one of the original and very basic types of networks, and also one of the simplest. LAN
networks group computers together over comparatively small distances, such as within a single
building or a small group of buildings, schools, offices, colleges, universities, etc to share resources
such as printers, file servers, scanners, and the internet.

Often they do not contain more than one subnet and are generally controlled by a single
administrator. The communication medium used for LAN is twisted pair, coaxial cable, etc, and
is build with less costly or inexpensive hardware such as hubs, network adapters, and ethernet
cables.
The data is carried at an extremely accelerated rate in the Local Area Network with added higher
security. It principally works on private IP addresses and does not include heavy routing. LAN can
be wired, wireless, or in both styles at once.

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Personal Area Network (PAN)

 The smallest and most primary type of network, a PAN is composed of a wireless modem,
a computer or two, phones, laptops, Bluetooth-enabled devices or infrared-enabled devices,
media player, printers, tablets, etc., and revolves around one individual in one building.
 This may also incorporate a wireless computer keyboard and mouse, Bluetooth-enabled
headphones, wireless printers, and TV remotes.
 These types of networks are typically observed in small offices or residences and are
controlled by one person or organization from a single device.
 PAN possesses a connectivity span of up to 10 meters. There are two types of Personal
Area Network: Wired Personal Area Network and Wireless Personal Area Network.
Metropolitan Area Network (MAN)
 MAN is a kind of network which is bigger than a LAN but smaller than a WAN and
incorporates properties of both. It typically covers a town or city and is controlled by a
single person or company, such as a local council or a large company. It has a longer range
than Local Area Network (LAN).
 This type of network can be applied to connect citizens with various Organizations for
example communication between the banks in a city, employed in college within a city,
Government and private organizations use MAN to connect all its offices within the city.

Wide Area Network (WAN)

 This is another kind of the original category of network and is Slightly more complex than
a LAN. WAN networks encapsulate computers together over huge physical distances,
remotely connecting them over a network and allowing them to communicate even when
far apart.
 The Internet is an example of WAN which connects computers all around the world
together. WANs are generally too large to be controlled by one administrator, and so
generally have collective ownership, or in the case of the internet, is publicly owned. WAN
is a general connection between LANs and MANs, that is not restricted to a single location.
 A Wide Area Network is extensively applied in the field of business, government, and
education. The data communication is slowest in WAN due to the largest distance. The
installation cost of WAN is very high and utilizes advanced technologies such as
Asynchronous Transfer Mode (ATM), Frame Relay, and Synchronous Optical Network
(SONET).

Campus Area Network (CAN)

 This is a network that is bigger as compared to a LAN, but smaller than a MAN. This is
very common in areas like a university, large school, or small business. CAN spread over
several buildings which are reasonably local to each other. It can have an internal Ethernet
along with the capability of connecting to the internet. It’s also referred to as a “Corporate
Area Network”.
Wireless Local Area Network (WLAN)
This is a LAN that is implemented with the use of wireless network technology such as Wi-Fi.
This kind of network is becoming more popular these days as wireless technology is further
developed and is used commonly in the home and small businesses. In other words, devices do not

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need to be dependent on physical cables and wires as much and can organize their spaces more
effectively.

System Area Network (SAN)

System area network combines computers on an especially high-speed connection, in a
configuration known as a cluster (server-to-server applications). It means computers that are linked
in a group to work as a single system, and can be implemented as a result of very high-speed
computers and new low-cost microprocessors. They are generally used to enhance performance
and for cost-effectiveness.

Reference models

In computer networks, reference models give a conceptual framework that standardizes

communication between heterogeneous networks.
The two popular reference models are −
OSI Model
TCP/IP Protocol Suite
TCP/IP Model

OSI Model
 OSI or Open System Interconnection model was developed by International Standards
Organization (ISO). It gives a layered networking framework that conceptualizes how
communication should be done between heterogeneous systems. It has seven
interconnected layers.
 The seven layers of the OSI Model are a physical layer, data link layer, network layer,
transport layer, session layer, presentation layer, and application layer.
The hierarchy is depicted in the following figure −

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TCP / IP MODEL
TCP stands for Transmission Control Protocol, while IP stands for Internet Protocol. It is a suite
of protocols for communication structured in four layers. It can be used for communication over
the internet as well as for private networks.
The four layers are application layer, transport layer, internet layer and network access layer, as
depicted in the following diagram −

OSI Model Layers:

Each layer in the OSI model performs a defined function essential to maintain smooth data flow
in a network. It communicates and works with layers above and below it to allow physical and
virtual data communication across a networking architecture. Let’s understand each layer in
greater detail. We start with the uppermost layer 7 and move to layer 1.
7. Application layer
 The application layer is the topmost layer in the OSI model. The layer establishes
communication between the application on the network and the end user using it by
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defining the protocols for successful user interaction. An excellent example of this layer is
that of web browsers.
 Application layer protocols allow the software to direct data flow and present it to the user.
Some of the known protocols include Hypertext Transfer Protocol (HTTP), Simple Mail
Transfer Protocol (SMTP), and File Transfer Protocol (FTP).

Key functions:
The application layer provides user interfaces (UI) that are key to user interaction
Supports a variety of applications such as e-mail and remote file transfer
In summary, layer 7 ensures effective communication between applications on different computing
systems and networks.
6. Presentation layer
 The presentation layer is often referred to as a syntax or translation layer as it translates the
application data into a network format. This layer also encrypts and decrypts data before
transmitting it over the network.
 For instance, layer 6 encrypts data from the application and decrypts it at the recipient’s
end, ensuring secure data transmission. Moreover, this layer is known to compress data
received from layer 7 to reduce the overall size of the data transferred.

Key functions:
 Performs data translation based on the application’s data semantics
 Encrypts and decrypts sensitive data transferred over communication channels
 Performs data compression to reduce the number of bits in exchanged data
 In summary, layer 6 ensures that the communicated information is in the desired format as
required by the receiving application.
5. Session layer
 The session layer establishes a communication session between communicating entities.
The session is maintained at a sufficient time interval to ensure efficient data transmission
and avoid wasting computing resources.

 This OSI layer is also responsible for data synchronization to maintain smooth data flow.
This implies that in situations where large volumes of data are sent at once, layer 5 can
break down the data into smaller chunks by adding checkpoints.

 For example, let’s say you want to send a 500-page document to another person. In this
case, this layer can add checkpoints at 50 or 100 pages. This is in case a document transfer
is interrupted due to network or system failure. Once the system failure issue is resolved,
the document transfer resumes from the last checkpoint. Such a system saves time by not
restarting the file transfer from the beginning.
Key functions:
 Opens maintains, and closes communication sessions
 Enables data synchronization by adding checkpoints to data streams
 In summary, layer 5 establishes, maintains, synchronizes, and terminates sessions between
end-user applications.

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4. Transport layer
 The transport layer allows safe message transfer between the sender and the receiver. It
divides the data received from the layer above into smaller segments. It also reassembles
the data at the receiver side to allow the session layer to read it.
 Layer 4 performs two critical functions: flow control and error control. Flow control
implies regulating data transfer speeds. It ensures that the communicating device with a
good network connection does not send data at higher rates, which is difficult for devices
with slower connections to handle.
 Error control refers to the error-checking functionality to ensure the completeness of data.
In incomplete data cases, this layer requests the system to resend the incomplete data.
 Examples of transport layer protocols include transmission control protocol (TCP) and user
datagram protocol (UDP).
Key functions:
 Ensures completeness of each message exchanged between source and destination
 Maintains proper data transmission through flow control and error control
 Performs data segmentation and reassembling of data
 In summary, layer 4 is responsible for transmitting an entire message from a sender
application to a receiver application.

3. Network layer
 The network layer enables the communication between multiple networks. It receives data
segments from the layer above, further broken down into smaller packets at the sender side.
On the receiver side, this layer reassembles the data together.
 The network layer also handles routing functionality, wherein the data transmission is
accomplished by choosing the best possible route or path that connects different networks
and ensures efficient data transfer. This network layer uses internet protocol (IP) for data
delivery.
Key functions:
 Handles routing to recognize suitable routes from sender to receiver
 Performs logical addressing that assigns unique names to each device operating over the
network
 In summary, layer 3 is responsible for dividing segmented data into network packets,
reassembling them at the recipient’s side, and identifying the shortest yet most suitable and
secure path for transmitting data packets.
2. Data link layer
 The data link layer transmits data between two nodes that are directly connected or are
operating over the same network architecture. Typically, this layer takes data packets from
layer 3 and breaks them down into frames before sending them to the destination.
 Layer 2 is divided into two sub-layers: media access control (MAC) and logical link control
(LLC). The MAC layer encapsulates data frames transmitted through the network

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connecting media such as wires or cables. In situations where such data transmission fails,
LLC helps manage packet retransmission.
 The well-known data link layer protocol includes the Address Resolution Protocol (ARP)
that translates IP addresses to MAC addresses to establish communication between systems
whose addresses vary in bit length (32 bits vs. 48 bits).

Key functions:
 Detects damaged or lost frames and retransmits them
 Performs framing where data received from layer 3 is further subdivided into smaller units
called frames
 In summary, layer 2 is responsible for setting up and terminating physical connections
between participating network nodes.
1. Physical layer
The last OSI layer is the physical layer that manages physical hardware and network components
such as cables, switches, or routers that transmit data.
In the context of data, layer 1 transmits data in the form of ones and zeros. Technically, this layer
picks up bits from the sender end, encodes them into a signal, sends the signal over the network,
and decodes the signal at the receiver end. Thus, without layer 1, communicating data bits across
network devices through physical media is not possible.
Key functions:
 Synchronizes data bits
 Enables modulation (conversion of a signal from one form to another for data transmission)
 Defines data transmission rate (bits/sec)

Advantages of OSI Model

 The OSI Model defines the communication of a computing system into 7 different layers.
Its advantages include:
 It divides network communication into 7 layers which makes it easier to understand and
troubleshoot.
 It standardizes network communications, as each layer has fixed functions and protocols.
 Diagnosing network problems is easier with the OSI model.
 It is easier to improve with advancements as each layer can get updates separately.
Disadvantages of OSI Model
Complexity: The OSI Model has seven layers, which can be complicated and hard to understand
for beginners.
Not Practical: In real-life networking, most systems use a simpler model called the Internet
protocol suite (TCP/IP), so the OSI Model isn’t always directly applicable.
Slow Adoption: When it was introduced, the OSI Model was not quickly adopted by the
industry, which preferred the simpler and already-established TCP/IP model.

Types of Transmission Media

Transmission media refer to the physical pathways through which data is transmitted from one
device to another within a network. These pathways can be wired or wireless. The choice of

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medium depends on factors like distance, speed, and interference. In this article, we will discuss
the transmission media.
Transmission Media is broadly classified into the following types:

1. Guided Media
Guided Media is also referred to as Wired or Bounded transmission media. Signals being
transmitted are directed and confined in a narrow pathway by using physical links.
Features:
High Speed
Secure
Used for comparatively shorter distances

There are 3 major types of Guided Media:

Twisted Pair Cable

It consists of 2 separately insulated conductor wires wound about each other. Generally, several
such pairs are bundled together in a protective sheath. They are the most widely used
Transmission Media. Twisted Pair is of two types:
Unshielded Twisted Pair (UTP): UTP consists of two insulated copper wires twisted around
one another. This type of cable has the ability to block interference and does not depend on a
physical shield for this purpose. It is used for telephonic applications.

Advantages of Unshielded Twisted Pair

Least expensive
Easy to install
High-speed capacity
Disadvantages of Unshielded Twisted Pair
Susceptible to external interference
Lower capacity and performance in comparison to STP
Short distance transmission due to attenuation

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Shielded Twisted Pair (STP): This type of cable consists of a special jacket (a copper braid
covering or a foil shield) to block external interference. It is used in fast-data-rate Ethernet and
in voice and data channels of telephone lines.
Advantages of Shielded Twisted Pair
Better performance at a higher data rate in comparison to UTP
Eliminates crosstalk
Comparatively faster
Disadvantages of Shielded Twisted Pair
Comparatively difficult to install and manufacture
More expensive
Bulky
Coaxial Cable
It has an outer plastic covering containing an insulation layer made of PVC or Teflon and 2
parallel conductors each having a separate insulated protection cover. The coaxial
cable transmits information in two modes: Baseband mode (dedicated cable bandwidth) and
Broadband mode (cable bandwidth is split into separate ranges). Cable TVs and analog television
networks widely use Coaxial cables.

Advantages of Coaxial Cable

 Coaxial cables support high bandwidth.
 It is easy to install coaxial cables.
 Coaxial cables have better cut-through resistance so they are more reliable and durable.
 Less affected by noise or cross-talk or electromagnetic inference.
 Coaxial cables support multiple channels
Disadvantages of Coaxial Cable
 Coaxial cables are expensive.
 The coaxial cable must be grounded in order to prevent any crosstalk.
 As a Coaxial cable has multiple layers it is very bulky.
Optical Fiber Cable
Optical Fibre Cable uses the concept of refraction of light through a core made up of glass or
plastic. The core is surrounded by a less dense glass or plastic covering called the cladding. It is
used for the transmission of large volumes of data. The cable can be unidirectional or
bidirectional. The WDM (Wavelength Division Multiplexer) supports two modes, namely
unidirectional and bidirectional mode.

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Advantages of Optical Fibre Cable

Increased capacity and bandwidth
Lightweight
Disadvantages of Optical Fibre Cable
Difficult to install and maintain
High cost
Applications of Optical Fibre Cable
 Medical Purpose: Used in several types of medical instruments.
 Defense Purpose: Used in transmission of data in aerospace.
 For Communication: This is largely used in formation of internet cables.
 Industrial Purpose: Used for lighting purposes and safety measures in designing the
interior and exterior of automobiles.
2. Unguided Media
It is also referred to as Wireless or Unbounded transmission media. No physical medium is
required for the transmission of electromagnetic signals.
Features of Unguided Media
The signal is broadcasted through air
Less Secure
Used for larger distances
There are 3 types of Signals transmitted through unguided media:
Radio Waves
Radio waves are easy to generate and can penetrate through buildings. The sending and receiving
antennas need not be aligned. Frequency Range:3KHz – 1GHz. AM and FM radios and cordless
phones use Radio waves for transmission.

Further Categorized as Terrestrial and Satellite.

Microwaves

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It is a line-of-sight transmission i.e., the sending and receiving antennas need to be properly
aligned with each other. The distance covered by the signal is directly proportional to the height
of the antenna. Frequency Range:1GHz – 300GHz. Micro waves are majorly used for mobile
phone communication and television distribution.

Infrared
Infrared waves are used for very short distance communication. They cannot penetrate through
obstacles. This prevents interference between systems. Frequency Range:300GHz – 400THz. It
is used in TV remotes, wireless mouse, keyboard, printer, etc.

Difference between Radio Waves Vs Micro Waves Vs Infrared Waves

Basis Radio wave Microwave Infrared wave

These are These are

These are omni-
Direction unidirectional in unidirectional in
directional in nature.
nature. nature.

At low frequency, At low frequency,

they can penetrate they can penetrate They cannot
through solid objects through solid objects penetrate through
Penetration
and walls but high and walls. at high any solid object and
frequency they bounce frequency, they walls.
off the obstacle. cannot penetrate.

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Basis Radio wave Microwave Infrared wave

Frequency range:
Frequency range: 3 Frequency range: 1
Frequency range 300 GHz to 400
KHz to 1GHz. GHz to 300 GHz.
GHz.

These offers poor These offers medium These offers high

Security
security. security. security.

Attenuation is
Attenuation Attenuation is high. Attenuation is low.
variable.

Some frequencies in Some frequencies in

There is no need of
Government the radio-waves the microwaves
government license
License require government require government
to use these waves.
license to use these. license to use these.

Setup and usage Cost Setup and usage Cost Usage Cost is very
Usage Cost
is moderate. is high. less.

These are used in long These are used in long These are not used
Communication distance distance in long distance
communication. communication. communication.

Types of Wireless Transmission Media

When we talk about a Headset or Earphones, there are wired regular earphones that we physically
connect to our phones, and there are wireless Bluetooth headsets that we connect via
Bluetooth. Transmission via Bluetooth is one of the simplest and most prominent examples of
wireless transmission media.
Wireless data transmission is also called "Unguided Transmission" or "Unbounded
Transmission" because of the absence of physical boundaries. When we turn on the Bluetooth on
our phone and connect a headset, our phone and the device communicate with each other
using ultra high-frequency Radio waves-one of the wireless transmission media.
This tutorial explains about three major wireless transmission media in details with examples
around us.
1. Infrared Transmission
 IR or Infrared radiation is a part of electromagnetic radiation. These rays have
a wavelength greater than visible light, making them invisible to the human eye. We
cannot see Infrared light but feel the rays in the form of heat. Frequency range: 300 GHz
to 400 THz.

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 When we look at a fire, we can feel the heat from it and see it because it emits visible light
and Infrared energy. The human body also emits heat but only in the form of Infrared light.
Instruments such as night-vision goggles and Infrared cameras can capture Infrared light.
 Sun is the biggest source of Infrared radiation. Hence, it causes a lot of interference in
Infrared communication. One most important point about Infrared rays is that these rays
cannot penetrate through walls. Hence, the applications of Infrared rays lie within a
contained space.
 So, how does the data transfer take place use this Infrared light?
 Let us apply for Infrared data transfer and see how it is happening. The most used
application is the "TV Remote control". When we press a button on the remote, how is it
changing the channel on the TV?
 An Infrared Light emitting diode is embedded into the TV remote and an IR detector is
inserted into the TV. This detector converts the Infrared light signal from the remote
and converts it into an electrical signal. Hence, the remote acts as a transmitter and the TV
as a receiver.

All the buttons on a TV remote are connected to a microprocessor which generates a unique
binary code for each button pressed. All these codes will be of the same length. The LED flashes
on and off according to the generated pattern of the pressed button.
The detector on the TV will be pre-programmed to interpret the binary codes and perform the
requested actions. These binary codes vary from company to company and device to device, which
is why we can't control a TV with a remote that doesn't belong to it. Although, a universal remote
has all the codes programmed into it, which is why it can control any TV.

If there is some object between your remote and the TV, the detector on the TV might not be able
to get the Infrared rays from the remote as these rays can't penetrate through objects. New
technology led to various changes in Remote control, like using Radio waves instead of Infrared,
mobile apps, voice control, etc.

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Applications of Infrared transmissions:

 Laptops to printers
 Development of high-speed LANs
 microphones, headsets
Advantages of Infrared communication:
 Large bandwidth
 Simple and inexpensive to implement
 The best medium for short-range communication
 Secure transmission
 Power usage is efficient
Disadvantages of Infrared communication:
 Only short-range communication is supported.
 It can't propagate through obstructions like walls, wood, and other opaque objects.

2. Radio waves
Like Infrared radiation, Radio waves are also a part of electromagnetic radiation. These waves
have the longest wavelengths, from 1mm to 100km in the spectrum. The name itself has Radio.
A Radio is one of the thousands of wireless technologies that use Radio waves for communication.
A Radio is the simplest example of Radio wave communication. Other examples Bluetooth
headsets, TV Broadcasts. Frequency range: 300GHz to 3kHz.
Like in Infrared communication, there will be a Radio wave transmitter and a receiver. The
information can be from audio, video, sound, and textual data. Suppose a person is using Radio,
sine waves are transmitted from it, and if another person uses a TV, it also broadcasts sine waves.
Every single Radio signal will have a different frequency for the sine waves.
This is the flow:
Transmitter (Sender's side):
Information -> Sine waves -> Radio waves -> Antenna
The information in any form is encoded into sine waves and is transmitted into the air by radiating
the waves through an Antenna.
Receiver (Destination):
Antenna -> Radio waves -> Sine waves
The Antenna on the receiver's side captures the Radio waves and decodes the information from
the sine waves.
To transmit Radio signals, there is a need for a transmitting antenna on the transmitter's side and a
receiving antenna at the receiver's side.
Advantages:
Radio waves are the best choice for large-distance communications.
These waves can also penetrate through obstacles.
These waves are Omnidirectional which means they can be transmitted in all directions.
Low cost.
Disadvantages:
Not very secure due to the large distances
Interference with other Radio signals

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Not very effective in bad weather conditions.

3. Microwaves
These waves are also a part of electromagnetic radiation. The micro indicates that these waves
have short wavelengths from 1 meter to 1 millimeter. These are high-frequency waves->
Frequency range: 300MHz to 300GHz. These waves fall between Radio waves and Infrared
waves.
These waves are used for point-to-point communication as it only transmits data in one direction.
These can transmit all kinds of data, from audio to video. These waves can be used to transmit
thermal energy too.

Applications:
 Cooking food in Microwave ovens, Popcorn machines.
 TV distributions
 Capturing the speed of the vehicle
 Phone channels to a mobile phone
 RADAR, Satellite communications

Advantages:
 The speed of transmission is very fast
 We can reduce antenna size due to high frequency
 Lower power consumption
 Supports larger bandwidth
 Can easily pass through the Ionosphere.
Disadvantages:
 Expensive
 Not effective in bad weather conditions
 Occupies more space
 Interference
 Harmful radiation

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