CN:Unit 1

Fundamentals of Computer Networking

What is a Computer Network?
"A Computer Network is defined as a set of two or more computers
that are linked together?either via wired cables or wireless
networks i.e., WiFi?with the purpose of communicating, exchanging,
sharing or distributing data, files and resources."

Computer Networks are built using a collection of hardware (such

as routers, switches, hubs, and so forth) and networking software (such
as operating systems, firewalls, or corporate applications).

Though one can also define the computer networks based on their
geographic location, a LAN (local area network) connects computers in a
definite physical dimension, such as home or within an office.

In contrast, a MAN (Metropolitan area network) connects computers ranging

between multiple buildings in a city.

The Internet is the most significant example of WAN (Wide Area

Network), connecting billions of networking devices across the world.

One can also describe the concept of computer networking by its communicating protocols, the
physical arrangement of its networking elements, how it manages network traffic, and it's
functioning.

Computer networks are globally used by businesses, the entertainment industry, education in the
research field for communication and transferring their data from source to destination node.

All the other technologies, including the internet, Google search, instant
messaging apps, online video streaming, social media, email, cloud
kitchen, cloud data storage, etc., all exist because of computer networks.

Computer Network Types

Below are the most common computer network types that are frequently
used these days:

o LAN [Local Area Network}

 o WLAN [Wireless local area network]
o CAN [Campus Area Network]
o MAN [Metropolitan Area Network]
o PAN [Personal Area Network]
o SAN [Storage Area Network]
o VPN [Virtual Private Network]
o WAN [ Wide Area Network]

LAN

LAN or Local Area Network is a group of devices connecting the

computers and other devices such as switches, servers, printers, etc.,
over a short distance such as office, home. The commonly used LAN
is Ethernet LAN. This network is used as it allows the user to transfer or
share data, files, and resources.

2. WLAN

WLAN or Wireless local area network is similar to LAN with the

difference that it uses wireless communication between devices instead of
wired connections. WLAN typically involves a Wi-Fi router or wireless
access point for devices, unlike smartphones, laptops, desktops, etc.

3. CAN
CAN or Campus Area Network is a closed corporate communication
network. A CAN is a mobile network that may contain a private or public part.
CANs are widely used colleges, academies, and corporate sites.

4. MAN
MAN or Metropolitan Area Network is typically a more extensive network
when compared to LANs but is smaller than WANs. This network ranges
between several buildings in the same city. Man networks are connected via
fiber optic cable (usually high-speed connection). Cities and government
bodies usually manage MANs.

5. PAN
PAN or Personal Area Network is a type of network used personally and
usually serves one person. This network usually connects devices unlike your
smartphones, laptop, or desktop to sync content and share small files, unlike
songs, photos, videos, calendars, etc. These devices connect via wireless
networks such as Wi-Fi, Bluetooth, Infrared, etc.

6. SAN
SAN or Storage Area Network is a specialized high-speed network that
stores and provides access to block-level storage. It is a dedicated shared
network that is used for cloud data storage that appears and works like a
storage drive.

SAN consists of various switches, servers, and disks array. One of the
advantages of SAN is that it is fault-tolerant, which means if any switch or
server goes down, the data can still be accessed.

7. VPN
VPN or Virtual Private Network is a secure tool that encrypts point-to-
point Internet connection and hides the user's IP address and virtual location.
It determines an encrypted network to boost user's online privacy so as their
identity and data are inaccessible to hackers.

8. WAN
WAN or Wide Area Network is the most significant network type
connecting computers over a wide geographical area, such as a country,
continent. WAN includes several LANs, MANs, and CANs. An example of
WAN is the Internet, which connects billions of computers globally.

Networking terms and concepts

Some of the most commonly used terms in day-to-day networking life are as
discussed below:

1. IP address
An IP address or Internet Protocol is a unique number that represents
the address where you live on the Internet. Every device that is
connected to the network has a string of numbers or IP addresses unlike
house addresses.

You won't find two devices connected to a network with an identical IP

address. When your computer sends data to another different, the sent data
contains a 'header' that further contains the devices' IP address, i.e., the
source computer and the destination device.

2. Nodes
A node refers to a networking connection point where a connection
occurs inside a network that further helps in receiving, transmitting,
creating, or storing files or data.

Multiple devices could be connected to the Internet or network using wired or

wireless nodes. To form a network connection, one requires two or more
nodes where each node carries its unique identification to obtain access,
such as an IP address. Some examples of nodes are computers, printers,
modems, switches, etc.

3. Routers
A router is a physical networking device, which forwards data packets
between networks. Routers do the data analysis, perform the traffic
directing functions on the network, and define the top route for the data
packets to reach their destination node. A data packet may have to surpass
multiple routers present within the network until it reaches its destination.

4. Switches
In a computer network, a switch is a device that connects other devices
and helps in node-to-node communication by deciding the best way
of transmitting data within a network (usually if there are multiple
routes in a more extensive network).

Though a router also transmits information, it forwards the information only

between networks, whereas a switches forwards data between nodes
present in a single network.

Switching is further classified into three types, which are as follows:

o Circuit Switching
o Packet Switching
o Message Switching

o Circuit Switching: In this switching type, a secure communication path is

established between nodes (or the sender and receiver) in a network. It
 establishes a dedicated connection path before transferring the data, and this
path assures a good transmission bandwidth and prevents any other traffic
from traveling on that path. For example, the Telephone network.
o Packet Switching: With this technique, a message is broken into
independent components known as packets. Because of their small size, each
packet is sent individually. The packets traveling through the network will
have their source and destination IP address.
o Message Switching: This switching technique uses the store and forward
mechanism. It sends the complete unit of the message from the source node,
passing from multiple switches until it reaches its intermediary node. It is not
suitable for real-time applications.

5. Ports
A port allows the user to access multiple applications by identifying
a connection between network devices. Each port is allocated a set of
string numbers. If you relate the IP address to a hotel's address, you can
refer to ports as the hotel room number. Network devices use port numbers
to decide which application, service, or method is used to forward the
detailed information or the data.

6. Network cable types

Network cables are used as a connection medium between different
computers and other network devices. Typical examples of network
cable types are Ethernet cables, coaxial, and fiber optic. Though the
selection of cable type usually depends on the size of the network, the
organization of network components, and the distance between the network
devices.

Computer Networks and the Internet

The Internet is the major example of a WAN, which connects billions of
computers globally. Internet follows standard protocols that facilitate
communication between these network devices. Those protocols include:

1. HTTP (Hypertext Transfer Protocol)

2. IP (Internet protocol or IP addresses)
3. TCP (Transmission Control Protocol)
 4. UDP (User Datagram Protocol)
5. FTP (File Transfer Protocol)

ISPs (Internet Service Providers) NSPs (Network Service

Providers) effectively support the internet infrastructure. The infrastructure
allows the transportation of data packets to the recipient device over the
Internet.

Internet is a giant hub of information, but this information is not sent to

every computer connected to the Internet. The protocols and infrastructure
are responsible for managing to share the precise information the user has
requested.

How do they work?

1. The Computer networks are formed by connecting multiple
nodes such as computers, desktops, routers, hubs, and switches with the
help of either wired cables (Ethernet, data cables, fiber optics) or wireless
networks (Bluetooth, Wi-Fi). This network connection enables the nodes to
communicate and exchange data over the network.
2. Networks follow communication protocols to send, receive, create or
forward data. Each note connected with a network is allocated a unique IP
(Internet Protocol), the IP address used to identify a device and enables the
other devices to identify it.
3. Routers and Switches are the virtual or physical medium that
supports and manages the communications between networks. Routers
examine the data packets to conclude the best route, following which the
data can easily reach its destination node. In contrast, Switches connect the
devices if there are multiple routes in a more extensive network and facilitate
node-to-node communication, ensuring that the data packets traveling across
the network reach their destination node.

Network Topology
"Network topology is defined as the arrangement of computers or
nodes of a computer network to establish communication among
all."
A node refers to a device that can transmit, receive, create, or store
information. The nodes are connected via a network link that could be either
wired (cables, Ethernet) or wireless (Bluetooth, Wi-Fi).

To help build a successful network in different situations, topologies are

further classified into several types.
Though there are several topologies but in this tutorial, we will discuss the
commonly used ones, which are as follows:

1. Bus Topology

o A Bus network topology supports a common transmission medium where

each node is directly connected with the main network cable.
o The data is transmitted through the main network cable and is received by all
nodes simultaneously.
o A signal is generated through the source machine, which contains the
address of the receiving machine. The signal travels in both the direction to
all the nodes connected to the bus network until it reaches the destination
node.
o Bus topology is not fault-tolerant and has a limited cable length.

2. Ring Topology
 o A Ring topology is a modified version of bus topology where every node is
connected in a closed-loop forming peer-to-peer LAN topology.
o Every node in a ring topology has precisely two connections. The Adjacent
node pairs are connected directly, whereas the non-adjacent nodes are
indirectly connected via various nodes.
o Ring topology supports a unidirectional communication pattern where
sending and receiving of data occurs via TOKEN.

3. Star Topology
 o In a Star network topology, every node is connected using a single central
hub or switch.
o The hub or switch performs the entire centralized administration. Each node
sends its data to the hub, and later hub shares the received information to
the destination device.
o Two or more-star topologies can be connected to each other with the help of
a repeater.

4. Mesh Topology
o In a Mesh topology, every node in the network connection is directly
connected to one other forming overlapping connections between the nodes.
o This topology delivers better fault tolerance because if any network device
fails, it won't affect the network, as other devices can transfer information.
o The Mesh networks self-configure and self-organize, finding the quickest,
most secure way to transmit the data.
o One can form a full mesh topology by connecting every single node to
another node in the network. Full mesh is expensive and is only used in the
networks, which demands high data redundancy.
o Another type of mesh topology is partial mesh topology, where only a few
devices are connected, and few are connected to the devices with which they
share the most information. This mesh type is applicable in the networks,
requiring less redundancy or a cost-effective network topology that is easy to
execute.
IP Address Format and Table
IP address is a short form of "Internet Protocol Address." It is a unique
number provided to every device connected to the internet network, such as
Android phone, laptop, Mac, etc. An IP address is represented in an integer
number separated by a dot (.), for example, 192.167.12.46.

Types of IP Address
An IP address is categorized into two different types based on the number of
IP address it contains. These are:

o IPv4 (Internet Protocol version 4)

o IPv6 (Internet Protocol version 6)

What is IPv4?
IPv4 is version 4 of IP. It is a current version and the most commonly
used IP address. It is a 32-bit address written in four numbers separated by a
dot (.), i.e., periods. This address is unique for each device. For example,
66.94.29.13

What is IPv6?
IPv4 produces 4 billion addresses, and the developers think that these
addresses are enough, but they were wrong. IPv6 is the next generation of IP
addresses. The main difference between IPv4 and IPv6 is the address size of
IP addresses. The IPv4 is a 32-bit address, whereas IPv6 is a 128-bit
hexadecimal address. IPv6 provides a large address space, and it contains a
simple header as compared to IPv4.

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To know more about the difference between IPv4 and IPv6, look at our
article ipv4 vs. ipv6.

IP Address Format
Originally IP addresses were divided into five different categories
called classes. These divided IP classes are class A, class B, class C, class D,
and class E. Out of these, classes A, B, and C are most important. Each
address class defines a different number of bits for its network prefix
(network address) and host number (host address). The starting
address bits decide from which class an address belongs.

Network Address: The network address specifies the unique number which
is assigned to your network. In the above figure, the network address takes
two bytes of IP address.

Host Address: A host address is a specific address number assigned to

each host machine. With the help of the host address, each machine is
identified in your network. The network address will be the same for each
host in a network, but they must vary in host address.

Address Format IPv4

The address format of IPv4 is represented into 4-octets (32-bit), which is
divided into three different classes, namely class A, class B, and class C.
The above diagram shows the address format of IPv4. An IPv4 is a 32-bit
decimal address. It contains four octets or fields separated by 'dot,' and each
field is 8-bit in size. The number that each field contains should be in the
range of 0-255.

Class A
Class A address uses only first higher order octet (byte) to identify the
network prefix, and remaining three octets (bytes) are used to define the
individual host addresses. The class A address ranges between 0.0.0.0 to
127.255.255.255. The first bit of the first octet is always set to 0 (zero), and
next 7 bits determine network address, and the remaining 24 bits determine
host address. So the first octet ranges from 0 to 127 (00000000 to
01111111).

Class B
Class B addresses use the initial two octets (two bytes) to identify the
network prefix, and the remaining two octets (two bytes) define host
addresses. The class B addresses are range between 128.0.0.0 to
191.255.255.255. The first two bits of the first higher octet is always set to
10 (one and zero bit), and next 14 bits determines the network address and
remaining 16 bits determines the host address. So the first octet ranges from
128 to 191 (10000000 to 10111111).

Class C
Class C addresses use the first three octets (three bytes) to identify the
network prefix, and the remaining last octet (one byte) defines the host
address. The class C address ranges between 192.0.0.0 to 223.255.255.255.
The first three bit of the first octet is always set to 110, and next 21 bits
specify network address and remaining 8 bits specify the host address. Its
first octet ranges from 192 to 223 (11000000 to 11011111).

Class D
Class D IP address is reserved for multicast addresses. Its first four bits of
the first octet are always set to 1110, and the remaining bits determine the
host address in any IP address. The first higher octet bits are always set to
1110, and the remaining bits specify the host address. The class D address
ranges between 224.0.0.0 to 239.255.255.255. In multicasting, data is not
assigned to any particular host machine, so it is not require to find the host
address from the IP address, and also, there is no subnet mask present in
class D.

Class E
Class E IP address is reserved for experimental purposes and future use. It
does not contain any subnet mask in it. The first higher octet bits are always
set to 1111, and next remaining bits specify the host address. Class E
address ranges between 240.0.0.0 to 255.255.255.255.

In every IP address class, all host-number bits are specified by a power of 2

that indicates the total numbers of the host's address that can create for a
particular network address. Class A address can contain the maximum
number of 224 (16,777,216) host numbers. Class B addresses contain the
maximum number of 216 (65, 536) host numbers. And class C contains a
maximum number of 28 (256) host numbers.

Subnet address of IP address, understand with an example:

Suppose a class A address is 11.65.27.1, where 11 is a network prefix

(address), and 65.27.1 specifies a particular host address on the network.
Consider that a network admin wants to use 23 to 6 bits to identify the
subnet and the remaining 5 to 0 bits to identify the host address. It can be
represented in the Subnet mask with all 1 bits from 31 to 6 and the
remaining (5 to 0) with 0 bits.

Subnet Mask (binary): 11111111 11111111 11111111 11000000

IP address (binary): 00001011 01000001 00011011 00000001

Now, the subnet can be calculated by applying AND operation (1+1=1,

1+0=0, 0+1=0, 0+0=0) between complete IP address and Subnet mask.
The result is:

00001011 01000001 00011011 00000000 = 11.65.27.0 subnet address

IP Address Format IPv6

All IPv6 addresses are 128-bit hexadecimal addresses, written in 8 separate
sections having each of them have 16 bits. As the IPv6 addresses are
represented in a hexadecimal format, their sections range from 0 to FFFF.
Each section is separated by colons (:). It also allows to removes the starting
zeros (0) of each 16-bit section. If two or more consecutive sections 16-bit
contains all zeros (0 : 0), they can be compressed using double colons (::).

IPv6 addresses are consist of 8 different sections, each section has a 16-bit
hexadecimal values separated by colon (:). IPv6 addresses are represented
as following format:

xxxx : xxxx : xxxx : xxxx : xxxx : xxxx : xxxx : xxxx

Each "xxxx" group contains a 16-bit hexadecimal value, and each "x" is a 4-
bit hexadecimal value. For example:

FDEC : BA98 : 0000 : 0000 : 0600 : BDFF : 0004 : FFFF

You can also remove the starting zeros (0) of each 16-bit section. For
example, the above IPv6 can be rewritten by omitting starting zeros (0) as
follow:

FDEC : BA98 : 0 : 0 : 600 : BDFF : 4 : FFFF

You can also compress the consecutive sections 16-bit zeros (0 : 0) using
double colons (::). But keep in mind that you can do it only once per IP
address.

FDEC : BA98 : : 600 : BDFF : 4 : FFFF

IP Address Table
On the basis of ranges, IP addresses are categorized into five address classes
which are given below.

Clas Higher Network Host No. of No.of hosts Range

s bits address bits address bits networks per network

A 0 8 24 27 224 0.0.0.0 t
125.255.255.2
5

B 10 16 16 214 216 128.0.0.0 t

191.255.255.2
5

C 110 24 8 221 28 192.0.0.0 t

223.255.255.2
5

D 1110 Not defined Not defined Not defined Not defined 224.0.0.0 t
and reserved and and reserved and reserved 239.255.255.2
 for future reserved for for future for future 5
future

E 1111 Not defined Not defined Not defined Not defined 240.0.0.0 t
and reserved and and reserved and reserved 255.255.255.2
for future reserved for for future for future 5
future

TCP/IP model
o The TCP/IP model was developed prior to the OSI model.
o The TCP/IP model is not exactly similar to the OSI model.
o The TCP/IP model consists of five layers: the application layer, transport layer,
network layer, data link layer and physical layer.
o The first four layers provide physical standards, network interface,
internetworking, and transport functions that correspond to the first four
layers of the OSI model and these four layers are represented in TCP/IP model
by a single layer called the application layer.
o TCP/IP is a hierarchical protocol made up of interactive modules, and each of
them provides specific functionality.

Here, hierarchical means that each upper-layer protocol is supported by two

or more lower-level protocols.
Functions of TCP/IP layers:

Network Access Layer

o A network layer is the lowest layer of the TCP/IP model.
o A network layer is the combination of the Physical layer and Data Link layer
defined in the OSI reference model.
o It defines how the data should be sent physically through the network.
o This layer is mainly responsible for the transmission of the data between two
devices on the same network.
o The functions carried out by this layer are encapsulating the IP datagram into
frames transmitted by the network and mapping of IP addresses into physical
addresses.
o The protocols used by this layer are ethernet, token ring, FDDI, X.25, frame
relay.

Internet Layer
o An internet layer is the second layer of the TCP/IP model.
 o An internet layer is also known as the network layer.
o The main responsibility of the internet layer is to send the packets from any
network, and they arrive at the destination irrespective of the route they
take.

Following are the protocols used in this layer are:

IP Protocol: IP protocol is used in this layer, and it is the most significant

part of the entire TCP/IP suite.

Following are the responsibilities of this protocol:

o IP Addressing: This protocol implements logical host addresses known as IP

addresses. The IP addresses are used by the internet and higher layers to
identify the device and to provide internetwork routing.
o Host-to-host communication: It determines the path through which the
data is to be transmitted.
o Data Encapsulation and Formatting: An IP protocol accepts the data from
the transport layer protocol. An IP protocol ensures that the data is sent and
received securely, it encapsulates the data into message known as IP
datagram.
o Fragmentation and Reassembly: The limit imposed on the size of the IP
datagram by data link layer protocol is known as Maximum Transmission unit
(MTU). If the size of IP datagram is greater than the MTU unit, then the IP
protocol splits the datagram into smaller units so that they can travel over
the local network. Fragmentation can be done by the sender or intermediate
router. At the receiver side, all the fragments are reassembled to form an
original message.
o Routing: When IP datagram is sent over the same local network such as
LAN, MAN, WAN, it is known as direct delivery. When source and destination
are on the distant network, then the IP datagram is sent indirectly. This can
be accomplished by routing the IP datagram through various devices such as
routers.

ARP Protocol
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o ARP stands for Address Resolution Protocol.

o ARP is a network layer protocol which is used to find the physical address
from the IP address.
o The two terms are mainly associated with the ARP Protocol:
o ARP request: When a sender wants to know the physical address of
the device, it broadcasts the ARP request to the network.
o ARP reply: Every device attached to the network will accept the ARP
request and process the request, but only recipient recognize the IP
address and sends back its physical address in the form of ARP reply.
The recipient adds the physical address both to its cache memory and
to the datagram header

ICMP Protocol

o ICMP stands for Internet Control Message Protocol.

o It is a mechanism used by the hosts or routers to send notifications regarding
datagram problems back to the sender.
o A datagram travels from router-to-router until it reaches its destination. If a
router is unable to route the data because of some unusual conditions such
as disabled links, a device is on fire or network congestion, then the ICMP
protocol is used to inform the sender that the datagram is undeliverable.
o An ICMP protocol mainly uses two terms:
o ICMP Test: ICMP Test is used to test whether the destination is
reachable or not.
o ICMP Reply: ICMP Reply is used to check whether the destination
device is responding or not.
o The core responsibility of the ICMP protocol is to report the problems, not
correct them. The responsibility of the correction lies with the sender.
o ICMP can send the messages only to the source, but not to the intermediate
routers because the IP datagram carries the addresses of the source and
destination but not of the router that it is passed to.
Transport Layer
The transport layer is responsible for the reliability, flow control, and
correction of data which is being sent over the network.

The two protocols used in the transport layer are User Datagram protocol
and Transmission control protocol.

o User Datagram Protocol (UDP)

o It provides connectionless service and end-to-end delivery of
transmission.
o It is an unreliable protocol as it discovers the errors but not specify the
error.
o User Datagram Protocol discovers the error, and ICMP protocol reports
the error to the sender that user datagram has been damaged.
o UDP consists of the following fields:
Source port address: The source port address is the address of the
application program that has created the message.
Destination port address: The destination port address is the
address of the application program that receives the message.
Total length: It defines the total number of bytes of the user
datagram in bytes.
Checksum: The checksum is a 16-bit field used in error detection.
o UDP does not specify which packet is lost. UDP contains only
checksum; it does not contain any ID of a data segment.
 o Transmission Control Protocol (TCP)
o It provides a full transport layer services to applications.
o It creates a virtual circuit between the sender and receiver, and it is
active for the duration of the transmission.
o TCP is a reliable protocol as it detects the error and retransmits the
damaged frames. Therefore, it ensures all the segments must be
received and acknowledged before the transmission is considered to
be completed and a virtual circuit is discarded.
o At the sending end, TCP divides the whole message into smaller units
known as segment, and each segment contains a sequence number
which is required for reordering the frames to form an original
message.
o At the receiving end, TCP collects all the segments and reorders them
based on sequence numbers.

Application Layer
o An application layer is the topmost layer in the TCP/IP model.
o It is responsible for handling high-level protocols, issues of representation.
o This layer allows the user to interact with the application.
o When one application layer protocol wants to communicate with another
application layer, it forwards its data to the transport layer.
 o There is an ambiguity occurs in the application layer. Every application
cannot be placed inside the application layer except those who interact with
the communication system. For example: text editor cannot be considered in
application layer while web browser using HTTP protocol to interact with the
network where HTTP protocol is an application layer protocol.

Following are the main protocols used in the application layer:

o HTTP: HTTP stands for Hypertext transfer protocol. This protocol allows us to
access the data over the world wide web. It transfers the data in the form of
plain text, audio, video. It is known as a Hypertext transfer protocol as it has
the efficiency to use in a hypertext environment where there are rapid jumps
from one document to another.
o SNMP: SNMP stands for Simple Network Management Protocol. It is a
framework used for managing the devices on the internet by using the TCP/IP
protocol suite.
o SMTP: SMTP stands for Simple mail transfer protocol. The TCP/IP protocol
that supports the e-mail is known as a Simple mail transfer protocol. This
protocol is used to send the data to another e-mail address.
o DNS: DNS stands for Domain Name System. An IP address is used to identify
the connection of a host to the internet uniquely. But, people prefer to use
the names instead of addresses. Therefore, the system that maps the name
to the address is known as Domain Name System.
o TELNET: It is an abbreviation for Terminal Network. It establishes the
connection between the local computer and remote computer in such a way
that the local terminal appears to be a terminal at the remote system.
o FTP: FTP stands for File Transfer Protocol. FTP is a standard internet protocol
used for transmitting the files from one computer to another computer.

OSI Model
o OSI stands for Open System Interconnection is a reference model that
describes how information from a software application in
 one computer moves through a physical medium to the software application
in another computer.
o OSI consists of seven layers, and each layer performs a particular network
function.
o OSI model was developed by the International Organization for
Standardization (ISO) in 1984, and it is now considered as an architectural
model for the inter-computer communications.
o OSI model divides the whole task into seven smaller and manageable tasks.
Each layer is assigned a particular task.
o Each layer is self-contained, so that task assigned to each layer can be
performed independently.

Characteristics of OSI Model:

 o The OSI model is divided into two layers: upper layers and lower layers.
o The upper layer of the OSI model mainly deals with the application related
issues, and they are implemented only in the software. The application layer
is closest to the end user. Both the end user and the application layer interact
with the software applications. An upper layer refers to the layer just above
another layer.
o The lower layer of the OSI model deals with the data transport issues. The
data link layer and the physical layer are implemented in hardware and
software. The physical layer is the lowest layer of the OSI model and is
closest to the physical medium. The physical layer is mainly responsible for
placing the information on the physical medium.

7 Layers of OSI Model

There are the seven OSI layers. Each layer has different functions. A list of
seven layers are given below:

1. Physical Layer
2. Data-Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer
1) Physical layer

o The main functionality of the physical layer is to transmit the individual bits
from one node to another node.
o It is the lowest layer of the OSI model.
o It establishes, maintains and deactivates the physical connection.
o It specifies the mechanical, electrical and procedural network interface
specifications.

Functions of a Physical layer:

o Line Configuration: It defines the way how two or more devices can be
connected physically.
o Data Transmission: It defines the transmission mode whether it is simplex,
half-duplex or full-duplex mode between the two devices on the network.
o Topology: It defines the way how network devices are arranged.
o Signals: It determines the type of the signal used for transmitting the
information.
2) Data-Link Layer

o This layer is responsible for the error-free transfer of data frames.

o It defines the format of the data on the network.
o It provides a reliable and efficient communication between two or more
devices.
o It is mainly responsible for the unique identification of each device that
resides on a local network.
o It contains two sub-layers:
o Logical Link Control Layer
o It is responsible for transferring the packets to the Network layer
of the receiver that is receiving.
o It identifies the address of the network layer protocol from the
header.
o It also provides flow control.
o Media Access Control Layer
o A Media access control layer is a link between the Logical Link
Control layer and the network's physical layer.
o It is used for transferring the packets over the network.
Functions of the Data-link layer
o Framing: The data link layer translates the physical's raw bit stream into
packets known as Frames. The Data link layer adds the header and trailer to
the frame. The header which is added to the frame contains the hardware
destination and source address.

o Physical Addressing: The Data link layer adds a header to the frame that
contains a destination address. The frame is transmitted to the destination
address mentioned in the header.
o Flow Control: Flow control is the main functionality of the Data-link layer. It
is the technique through which the constant data rate is maintained on both
the sides so that no data get corrupted. It ensures that the transmitting
station such as a server with higher processing speed does not exceed the
receiving station, with lower processing speed.
o Error Control: Error control is achieved by adding a calculated value CRC
(Cyclic Redundancy Check) that is placed to the Data link layer's trailer which
is added to the message frame before it is sent to the physical layer. If any
error seems to occurr, then the receiver sends the acknowledgment for the
retransmission of the corrupted frames.
o Access Control: When two or more devices are connected to the same
communication channel, then the data link layer protocols are used to
determine which device has control over the link at a given time.
3) Network Layer

o It is a layer 3 that manages device addressing, tracks the location of devices

on the network.
o It determines the best path to move data from source to the destination
based on the network conditions, the priority of service, and other factors.
o The Data link layer is responsible for routing and forwarding the packets.
o Routers are the layer 3 devices, they are specified in this layer and used to
provide the routing services within an internetwork.
o The protocols used to route the network traffic are known as Network layer
protocols. Examples of protocols are IP and Ipv6.

Functions of Network Layer:

o Internetworking: An internetworking is the main responsibility of the
network layer. It provides a logical connection between different devices.
o Addressing: A Network layer adds the source and destination address to the
header of the frame. Addressing is used to identify the device on the internet.
 o Routing: Routing is the major component of the network layer, and it
determines the best optimal path out of the multiple paths from source to the
destination.
o Packetizing: A Network Layer receives the packets from the upper layer and
converts them into packets. This process is known as Packetizing. It is
achieved by internet protocol (IP).

4) Transport Layer

o The Transport layer is a Layer 4 ensures that messages are transmitted in the
order in which they are sent and there is no duplication of data.
o The main responsibility of the transport layer is to transfer the data
completely.
o It receives the data from the upper layer and converts them into smaller units
known as segments.
o This layer can be termed as an end-to-end layer as it provides a point-to-
point connection between source and destination to deliver the data reliably.

The two protocols used in this layer are:

o Transmission Control Protocol

 o It is a standard protocol that allows the systems to communicate over
the internet.
o It establishes and maintains a connection between hosts.
o When data is sent over the TCP connection, then the TCP protocol
divides the data into smaller units known as segments. Each segment
travels over the internet using multiple routes, and they arrive in
different orders at the destination. The transmission control protocol
reorders the packets in the correct order at the receiving end.
o User Datagram Protocol
o User Datagram Protocol is a transport layer protocol.
o It is an unreliable transport protocol as in this case receiver does not
send any acknowledgment when the packet is received, the sender
does not wait for any acknowledgment. Therefore, this makes a
protocol unreliable.

Functions of Transport Layer:

o Service-point addressing: Computers run several programs
simultaneously due to this reason, the transmission of data from source to
the destination not only from one computer to another computer but also
from one process to another process. The transport layer adds the header
that contains the address known as a service-point address or port address.
The responsibility of the network layer is to transmit the data from one
computer to another computer and the responsibility of the transport layer is
to transmit the message to the correct process.
o Segmentation and reassembly: When the transport layer receives the
message from the upper layer, it divides the message into multiple
segments, and each segment is assigned with a sequence number that
uniquely identifies each segment. When the message has arrived at the
destination, then the transport layer reassembles the message based on their
sequence numbers.
o Connection control: Transport layer provides two services Connection-
oriented service and connectionless service. A connectionless service treats
each segment as an individual packet, and they all travel in different routes
 to reach the destination. A connection-oriented service makes a connection
with the transport layer at the destination machine before delivering the
packets. In connection-oriented service, all the packets travel in the single
route.
o Flow control: The transport layer also responsible for flow control but it is
performed end-to-end rather than across a single link.
o Error control: The transport layer is also responsible for Error control. Error
control is performed end-to-end rather than across the single link. The sender
transport layer ensures that message reach at the destination without any
error.

5) Session Layer

o It is a layer 3 in the OSI model.

o The Session layer is used to establish, maintain and synchronizes the
interaction between communicating devices.

Functions of Session layer:

o Dialog control: Session layer acts as a dialog controller that creates a dialog
between two processes or we can say that it allows the communication
between two processes which can be either half-duplex or full-duplex.
o Synchronization: Session layer adds some checkpoints when transmitting
the data in a sequence. If some error occurs in the middle of the transmission
 of data, then the transmission will take place again from the checkpoint. This
process is known as Synchronization and recovery.

6) Presentation Layer

o A Presentation layer is mainly concerned with the syntax and semantics of

the information exchanged between the two systems.
o It acts as a data translator for a network.
o This layer is a part of the operating system that converts the data from one
presentation format to another format.
o The Presentation layer is also known as the syntax layer.

Functions of Presentation layer:

o Translation: The processes in two systems exchange the information in the
form of character strings, numbers and so on. Different computers use
different encoding methods, the presentation layer handles the
interoperability between the different encoding methods. It converts the data
from sender-dependent format into a common format and changes the
common format into receiver-dependent format at the receiving end.
 o Encryption: Encryption is needed to maintain privacy. Encryption is a
process of converting the sender-transmitted information into another form
and sends the resulting message over the network.
o Compression: Data compression is a process of compressing the data, i.e.,
it reduces the number of bits to be transmitted. Data compression is very
important in multimedia such as text, audio, video.

7) Application Layer

o An application layer serves as a window for users and application processes

to access network service.
o It handles issues such as network transparency, resource allocation, etc.
o An application layer is not an application, but it performs the application layer
functions.
o This layer provides the network services to the end-users.

Functions of Application layer:

o File transfer, access, and management (FTAM): An application layer
allows a user to access the files in a remote computer, to retrieve the files
from a computer and to manage the files in a remote computer.
o Mail services: An application layer provides the facility for email forwarding
and storage.
 o Directory services: An application provides the distributed database sources
and is used to provide that global information about various objects.

In the world of technology, there are vast numbers of users' communicating with
different devices in different languages. That also includes many ways in which they
transmit data along with the different software they implement. So, communicating
worldwide will not be possible if there were no fixed 'standards' that will govern the way
user communicates for data as well as the way our devices treat those data. Here we
will be discussing these standard set of rules.

Yes, we're talking about "protocols" which are set of rules that help in governing the way
a particular technology will function for communication. In other words, it can be said
that the protocols are digital languages implemented in the form of networking
algorithms. There are different networks and network protocols, user's use while surfing.

Types of Protocols
There are various types of protocols that support a major and compassionate role in
communicating with different devices across the network. These are:

1. Transmission Control Protocol (TCP)

2. Internet Protocol (IP)
3. User Datagram Protocol (UDP)
4. Post office Protocol (POP)
5. Simple mail transport Protocol (SMTP)
6. File Transfer Protocol (FTP)
7. Hyper Text Transfer Protocol (HTTP)
8. Hyper Text Transfer Protocol Secure (HTTPS)
9. Telnet
10. Gopher
Let's discuss each of them briefly:

1. Transmission Control Protocol (TCP): TCP is a popular communication protocol which is

used for communicating over a network. It divides any message into series of packets
that are sent from source to destination and there it gets reassembled at the destination.
2. Internet Protocol (IP): IP is designed explicitly as addressing protocol. It is mostly used
with TCP. The IP addresses in packets help in routing them through different nodes in a
network until it reaches the destination system. TCP/IP is the most popular protocol
connecting the networks.
3. User Datagram Protocol (UDP): UDP is a substitute communication protocol to
Transmission Control Protocol implemented primarily for creating loss-tolerating and
low-latency linking between different applications.
4. Post office Protocol (POP): POP3 is designed for receiving incoming E-mails.
 5. Simple mail transport Protocol (SMTP): SMTP is designed to send and distribute
outgoing E-Mail.
6. File Transfer Protocol (FTP): FTP allows users to transfer files from one machine to
another. Types of files may include program files, multimedia files, text files, and
documents, etc.
7. Hyper Text Transfer Protocol (HTTP): HTTP is designed for transferring a hypertext
among two or more systems. HTML tags are used for creating links. These links may be
in any form like text or images. HTTP is designed on Client-server principles which allow
a client system for establishing a connection with the server machine for making a
request. The server acknowledges the request initiated by the client and responds
accordingly.
8. Hyper Text Transfer Protocol Secure (HTTPS): HTTPS is abbreviated as Hyper Text
Transfer Protocol Secure is a standard protocol to secure the communication among two
computers one using the browser and other fetching data from web server. HTTP is
used for transferring data between the client browser (request) and the web server
(response) in the hypertext format, same in case of HTTPS except that the transferring
of data is done in an encrypted format. So it can be said that https thwart hackers from
interpretation or modification of data throughout the transfer of packets.
9. Telnet: Telnet is a set of rules designed for connecting one system with another. The
connecting process here is termed as remote login. The system which requests for
connection is the local computer, and the system which accepts the connection is the
remote computer.
10. Gopher: Gopher is a collection of rules implemented for searching, retrieving as well as
displaying documents from isolated sites. Gopher also works on the client/server
principle.

Some Other Protocols

Some other popular protocols act as co-functioning protocols associated with these
primary protocols for core functioning. These are:

 ARP (Address Resolution Protocol)

 DHCP (Dynamic Host Configuration Protocol)
 IMAP4 (Internet Message Access Protocol)
 SIP (Session Initiation Protocol)
 RTP (Real-Time Transport Protocol)
 RLP (Resource Location Protocol)
 RAP (Route Access Protocol)
 L2TP (Layer Two Tunnelling Protocol)Advertisements
 PPTP (Point To Point Tunnelling Protocol)
 SNMP (Simple Network Management Protocol)
 TFTP (Trivial File Transfer Protocol)

Interior and exterior routing gateways

Interior gateways are gateways that belong to the same autonomous
system. They communicate with each other using the Routing Information
Protocol (RIP), Routing Information Protocol Next Generation
(RIPng), Intermediate System to Intermediate System protocol, Open
Shortest Path First (OSPF) protocol, or the HELLO Protocol (HELLO).
Exterior gateways belong to different autonomous systems. They use
the Exterior Gateway Protocol (EGP), the Border Gateway Protocol
(BGP), or BGP4+.

For example, consider two autonomous systems. The first is all the networks
administered by the Widget Company. The second is all the networks
administered by the Gadget Company. The Widget Company has one
machine, called apple, which is Widget's gateway to the Internet. The Gadget
Company has one machine, called orange, which is Gadget's gateway to the
Internet. Both companies have several different networks internal to the
companies. The gateways connecting the internal networks are interior
gateways. But apple and orange are exterior gateways.

Each exterior gateway does not communicate with every other exterior
gateway. Instead, the exterior gateway acquires a set of neighbors (other
exterior gateways) with which it communicates. These neighbors are not
defined by geographic proximity, but rather by their established
communications with each other. The neighboring gateways, in turn, have
other exterior gateway neighbors. In this way, the exterior gateway routing
tables are updated and routing information is propagated among the exterior
gateways.

The routing information is sent in a pair, (N,D), where N is a network and D is

a distance reflecting the cost of reaching the specified network. Each
gateway advertises the networks it can reach and the costs of reaching
them. The receiving gateway calculates the shortest paths to other networks
and passes this information along to its neighbors. Thus, each exterior
gateway is continually receiving routing information, updating its routing
table and then passing that information to its exterior neighbors.

TCP/IP routing gateways

Last Updated: 2023-03-24
Gateways are a type of router. Routers connect two or more networks and
provide the routing function. Some routers, for example, route at the
network interface level or at the physical level. Gateways, however, route at
the network level.

Gateways receive IP datagrams from other gateways or hosts for delivery to

hosts on the local network, and route IP datagrams from one network to
another. For example, a gateway connecting two Token-Ring networks has
two Token-Ring adapter cards, each with its own Token-Ring network
interface. To pass on information, the gateway receives datagrams through
one network interface and sends them out through the other network
interface. Gateways periodically verify their network connections through
interface status messages.

Gateways route packets according to the destination network, not according

to the destination host. That is, a gateway machine is not required to keep
track of every possible host destination for a packet. Instead, a gateway
routes packets according to the network of the destination host. The
destination network then takes care of sending the packet to the destination
host. Thus, a typical gateway machine requires only limited disk storage
capacity (if any) and limited main memory capacity.

The distance a message must travel from originating host to destination host
depends upon the number of gateway hops it must make. A gateway is zero
hops from a network to which it is directly attached, one hop from a network
that is reachable through one gateway, and so on. Message distance is
usually expressed in the number of gateway hops required, or hop
counts (also called the metric).

 Interior and exterior routing gateways

Interior gateways are gateways that belong to the same autonomous system.
They communicate with each other using the Routing Information
Protocol (RIP), Routing Information Protocol Next Generation
(RIPng), Intermediate System to Intermediate System protocol, Open
Shortest Path First (OSPF) protocol, or the HELLO Protocol (HELLO).
Exterior gateways belong to different autonomous systems. They use
the Exterior Gateway Protocol (EGP), the Border Gateway Protocol
(BGP), or BGP4+.
 Gateway protocols
All gateways, whether interior or exterior, use protocols to communicate with
each other. Here are brief descriptions of the more commonly
used TCP/IP gateway protocols:

TCP/IP routing
Last Updated: 2023-03-24
A route defines a path for sending packets through the Internet network to
an address on another network.

A route does not define the complete path, only the path segment from one
host to a gateway that can forward packets to a destination (or from one
gateway to another). There are five types of routes:
Item Description

host
Defines a gateway that can forward packets to a specific host on another network.
route

networ
Defines a gateway that can forward packets to any of the hosts on a specific network.
k route

default
Defines a gateway to use when a host or network route to a destination is not otherwise d
route

loopba
ck Default route for all packets sent to local network addresses. The loopback route IP is alw
route

broadc
Default route for all broadcast packets. Two broadcast routes are automatically assigned
ast
network has an IP (one to the subnet address and one to the broadcast address of the sub
route

Routes are defined in the kernel routing table. The route definitions include
information on networks reachable from the local host and on gateways that
can be used to reach remote networks. When a gateway receives a
datagram, it checks the routing tables to find out where next to send the
datagram along the path to its destination.

You can add multiple routes for the same destination in the kernel routing
table. A routing lookup evaluates all routes that match the request then
chooses the route with the lowest distance metric. If multiple matching
routes have equal distance, a lookup chooses the most specific route. If both
criteria are equal for multiple routes, routing lookups alternate choices of
matching routes.

 Static and dynamic routing

In TCP/IP, routing can be one of two types: static or dynamic.
 TCP/IP routing gateways
Gateways are a type of router. Routers connect two or more networks and
provide the routing function. Some routers, for example, route at the network
interface level or at the physical level. Gateways, however, route at the
network level.
 Gateway considerations
Take these actions before configuring your gateway.
 Configuring a gateway
To configure a machine to act as a gateway, use these instructions.
 Route use restrictions
Routes can be restricted so they can be used only by some users. The
restrictions are based on the primary group IDs of users.
  Dead gateway detection
A host can be configured to detect whether a gateway it is using is down, and
can adjust its routing table accordingly.
 Route cloning
Route cloning allows a host route to be created for every host that a system
communicates with.
 Dynamic route removal
If you are using the routed daemon, a manually deleted route is not replaced
by incoming RIP information (because ioctl's are used).
 Configuring the routed daemon
Follow these steps to configure the routed daemon.
 Configuring the gated daemon
When configuring the gated daemon, you must decide which gateway
protocols are most appropriate for your system.
 Autonomous system numbers
If you use EGP or BGP, you should obtain an official autonomous system
number for your gateway.

Dynamic Host Configuration Protocol

Dynamic Host Configuration Protocol (DHCP) is a network management
protocol used to dynamically assign an IP address to nay device, or node, on
a network so they can communicate using IP (Internet Protocol). DHCP
automates and centrally manages these configurations. There is no need to
manually assign IP addresses to new devices. Therefore, there is no
requirement for any user configuration to connect to a DHCP based network.

DHCP can be implemented on local networks as well as large enterprise

networks. DHCP is the default protocol used by the most routers and
networking equipment. DHCP is also called RFC (Request for comments)
2131.

DHCP does the following:

o DHCP manages the provision of all the nodes or devices added or dropped
from the network.
o DHCP maintains the unique IP address of the host using a DHCP server.
o It sends a request to the DHCP server whenever a client/node/device, which
is configured to work with DHCP, connects to a network. The server
acknowledges by providing an IP address to the client/node/device.
DHCP is also used to configure the proper subnet mask, default gateway and
DNS server information on the node or device.

There are many versions of DCHP are available for use in IPV4 (Internet
Protocol Version 4) and IPV6 (Internet Protocol Version 6).

How DHCP works

DHCP runs at the application layer of the TCP/IP protocol stack to
dynamically assign IP addresses to DHCP clients/nodes and to allocate TCP/IP
configuration information to the DHCP clients. Information includes subnet
mask information, default gateway, IP addresses and domain name system
addresses.

DHCP is based on client-server protocol in which servers manage a pool of

unique IP addresses, as well as information about client configuration
parameters, and assign addresses out of those address pools.

The DHCP lease process works as follows:

o First of all, a client (network device) must be connected to the internet.

o DHCP clients request an IP address. Typically, client broadcasts a query for
this information.
o DHCP server responds to the client request by providing IP server address
and other configuration information. This configuration information also
includes time period, called a lease, for which the allocation is valid.
o When refreshing an assignment, a DHCP clients request the same
parameters, but the DHCP server may assign a new IP address. This is based
on the policies set by the administrator.

Components of DHCP
When working with DHCP, it is important to understand all of the
components. Following are the list of components:

o DHCP Server: DHCP server is a networked device running the DCHP service
that holds IP addresses and related configuration information. This is typically
a server or a router but could be anything that acts as a host, such as an SD-
WAN appliance.
 o DHCP client: DHCP client is the endpoint that receives configuration
information from a DHCP server. This can be any device like computer,
laptop, IoT endpoint or anything else that requires connectivity to the
network. Most of the devices are configured to receive DHCP information by
default.
o IP address pool: IP address pool is the range of addresses that are available
to DHCP clients. IP addresses are typically handed out sequentially from
lowest to the highest.
o Subnet: Subnet is the partitioned segments of the IP networks. Subnet is
used to keep networks manageable.
o Lease: Lease is the length of time for which a DHCP client holds the IP
address information. When a lease expires, the client has to renew it.
o DHCP relay: A host or router that listens for client messages being
broadcast on that network and then forwards them to a configured server.
The server then sends responses back to the relay agent that passes them
along to the client. DHCP relay can be used to centralize DHCP servers
instead of having a server on each subnet.

Benefits of DHCP
There are following benefits of DHCP:

Centralized administration of IP configuration: DHCP IP configuration

information can be stored in a single location and enables that administrator
to centrally manage all IP address configuration information.

Dynamic host configuration: DHCP automates the host configuration

process and eliminates the need to manually configure individual host. When
TCP/IP (Transmission control protocol/Internet protocol) is first deployed or
when IP infrastructure changes are required.

Seamless IP host configuration: The use of DHCP ensures that DHCP

clients get accurate and timely IP configuration IP configuration parameter
such as IP address, subnet mask, default gateway, IP address of DND server
and so on without user intervention.

Flexibility and scalability: Using DHCP gives the administrator increased

flexibility, allowing the administrator to move easily change IP configuration
when the infrastructure changes.
Bootstrap Protocol (BOOTP)
What is Protocol?
In networking, protocol means the set of rules which determines how data
will be transmitted on a network and how device nodes will be managed. In
this article, we will explain about the Bootstrapping protocol and how much it
is important in managing the nodes in a network. The Bootstrap protocol is
the set of rules which assigns the IP (Internet Protocol) address to each
node/member which participates in the network to communicate with others
or to the central server.

Features of Bootstrap Protocol (BOOTP)

o As soon as a device connects to the network, the Bootstrap Protocol (BOOTP)
immediately provides each member in the connection a distinct IP address for
authentication and identification purposes. This aids the server in
accelerating connection requests and data transfers.
o BOOTP employs a special IP address method to instantly assign a fully
distinct IP address to each system connected to the network. BOOTP is a
broadcast protocol since it must transmit messages to all of the network's
active hosts in order to receive responses or resources. The name BOOTP
refers to the Bootstrap procedure that occurs when a computer first starts up.
o The connection time between the server and the client is reduced as a result.
Even with very little information, it begins the process of downloading and
updating the source code.
o BOOTP servers generally use bootpd daemon to give the response of the
requests received from the clients and which has the data for the clients
using BOOTP gateway and without any broadcasting. The server's file
/etc/inet/bootptab contains the BOOTP configuration database.
o In BOOTP, devices or clients use the combination of Dynamic Host
Configuration Protocol (DHCP) and User Datagram Protocol (UDP) to transmit,
 receive and manage the data/information from the various other nodes
connected to the network.
o The server and client only require an IP address and a gateway address to
successfully connect in a BOOTP connection. The server and client often
share the same LAN in a BOOTP network, and the routers that are used in the
network must enable BOOTP bridging.
o The Bootstrap Protocol network is a wonderful illustration of a network using
a TCP/IP configuration. BOOTP uses its individual IP address whenever a
computer on the network sends a specific request to the server in order to
swiftly resolve it.

Difference between Bootstrap protocol and DHCP

protocol
As compared to BOOTP network servers, DHCP network servers are
significantly more widely used. It could be used for the reason when a user
requests information about a specific IP address from the server, and the
server only responds with information about that specific IP address, saving
time from having to monitor additional addresses.

Each network user is identified and authenticated by BOOTP using the UDP
(User Datagram Protocol) over an IPv4 address connection. Additionally, a
BOOTP connection contains a reliable static database of IP addresses that
provides the client with the needed IP address right away.

Working of Bootstrap Protocol

o Each member of the network does not initially have an IP address. The
network manager then uses the IPv4 protocol to assign each computer on the
network a special IP address.
o To build the compatibility with all other nodes on a network, the client
immediately installs the BOOTP protocol using TCP/IP intervention on their
system.
o An appropriate unicast address is then included in a message that is sent by
the BOOTP network administrator. The master server then forwards this
unicast address to the BOOTP client.
Uses of Bootstrap Protocol
o When you first turn on your computer, Bootstrap (BOOTP) is primarily needed
to assess the system on a network.
o On the network, each node/computer has a record of its own BIOS cycle,
which makes it easier for the motherboard and network manager to
efficiently transmit the data on the particular device as it starts booting up.
o Since all data is saved in the network cloud for effective usage, BOOTP is
primarily employed in a diskless setting and requires no media.
o A client and a server exchange data over BOOTP in order to transmit and
receive requests and the networking server's appropriate responses.
o We need not require any kind of external storage because BOOTP supports
the motherboards so that we can use them, and there is no need for other
storage devices except the cloud network.

Asynchronous Transfer Mode (ATM) in

Computer Network
We use an Asynchronous Transfer Mode (ATM) network because it is driven
by the integration of performance and service, which is the requirement for
both data network and telephony. It also provides network support for the
single quality of the service, and these services are very expensive. It is very
cheap and flexible. It also supports some ranges of services at a reasonable
cost.

Asynchronous Transfer Mode (ATM)

Asynchronous Transfer Mode (ATM) is an International Telecommunication
Union- Telecommunications Standards Section (ITU-T) that is very efficient
for the relay of calling. Also, it is used to transfer all the services like voice,
data, or video. These services can be conveyed in a small fixed-sized packet
called the cell. These cells are connected in a network that transmits the
data asynchronously.

Asynchronous transfer mode (ATM) is a technology that was developed in the

year between 1970 and 1980. This was considered the revolution in packet
switching. Each cell consists of 53 bytes longs. Further, the 53 bytes long can
be divided into 5 bytes header and 48 bytes payload. Before making an ATM
call, we need to send a message to set up the connection.
All the cells follow the same path connected to the destination. The cell can
also handle both variable and constant rate traffic. Thus it has multiple types
of traffic with end-to-end encryption. Asynchronous transfer mode (ATM)
does not depend on the transmission medium. Asynchronous transfer mode
(ATM) uses cell or packet switching and virtual circuits to switch the
transmission medium. The main purpose of designing the Asynchronous
transfer mode (ATM) is to help implement high-performance multimedia
networking.

ATM Cell Format

In Asynchronous transfer mode (ATM), the data are transmitted through a
fixed-size unit called cells. As we know, each cell has 53 bytes long. There
are two types of Asynchronous transfer modes (ATM). These are as follows:

1. UNI header

This is used in the private connection in the Asynchronous transfer mode

(ATM) network between ATM switches and ATM endpoints.

2. NNI header

It communicates between the Asynchronous Transfer Mode (ATM) switches.

Working of ATM
Two types of connection use the Asynchronous transfer mode (ATM). A
virtual path can be created end-to-end across an ATM network, as it does not
route the cells to a particular virtual circuit. In case of major failure, all cells
belonging to a particular virtual path are routed the same way through the
ATM network, thus helping faster recovery.

Switches connected to subscribers use both VPIs and VCIs to switch the cells,
which are Virtual Path and Virtual Connection switches that can have
different virtual channel connections between them, serving the purpose of
creating a virtual trunk between the switches, which can be handled as a
single entity. Its basic operation is straightforward looking up the connection
value in the local translation table, determining the outgoing port of the
connection, and the new VPI/VCI value of the connection on that link.

ATM vs. DATA Networks (Internet)

o ATM is a "virtual circuit" based: Here, the path is reserved before
transmission. While Internet Protocol (IP) is connectionless, end-to-end
 resource reservations are impossible. RSVP is a new signaling protocol on the
internet.
o ATM Cells: Fixed or small, and the Tradeoff is between voice or data. At the
same time, IP packets are of variable size.
o Addressing: ATM uses 20-byte global NSAP addresses for signaling and 32-
bit locally assigned labels in cells. At the same time, IP uses 32-bit global
addresses in all packets.

ATM Applications
1. ATM WANs

To send the data over a long distance, we use WAN and a router to connect
ATMs and other networks.

2. Multimedia virtual private networks and managed services

It helps manage ATM, LAN, voice, and video services and is capable of full-
service virtual private networking, including integrated multimedia access.

3. Frame relay backbone

Frame relay services are a networking infrastructure for a range of data

services and enable frame-relay ATM service to Internetworking services.

4. Residential broadband networks

ATM by choice provides the networking infrastructure for establishing

residential broadband services in search of highly scalable solutions.

5. Carrier infrastructure for telephone and private line networks

To make more effective use of SONET/SDH fiber infrastructures we build the

ATM infrastructure to carry out the telephonic and private-line traffic.

Switching techniques
In large networks, there can be multiple paths from sender to receiver. The
switching technique will decide the best route for data transmission.

Switching technique is used to connect the systems for making one-to-one

communication.
Classification Of Switching Techniques

Circuit Switching
o Circuit switching is a switching technique that establishes a dedicated path
between sender and receiver.
o In the Circuit Switching Technique, once the connection is established then
the dedicated path will remain to exist until the connection is terminated.
o Circuit switching in a network operates in a similar way as the telephone
works.
o A complete end-to-end path must exist before the communication takes
place.
o In case of circuit switching technique, when any user wants to send the data,
voice, video, a request signal is sent to the receiver then the receiver sends
back the acknowledgment to ensure the availability of the dedicated path.
After receiving the acknowledgment, dedicated path transfers the data.
o Circuit switching is used in public telephone network. It is used for voice
transmission.
o Fixed data can be transferred at a time in circuit switching technology.
Communication through circuit switching has 3 phases:

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o Circuit establishment
o Data transfer
o Circuit Disconnect

Circuit Switching can use either of the two technologies:

Space Division Switches:

 o Space Division Switching is a circuit switching technology in which a single
transmission path is accomplished in a switch by using a physically separate
set of crosspoints.
o Space Division Switching can be achieved by using crossbar switch. A
crossbar switch is a metallic crosspoint or semiconductor gate that can be
enabled or disabled by a control unit.
o The Crossbar switch is made by using the semiconductor. For example, Xilinx
crossbar switch using FPGAs.
o Space Division Switching has high speed, high capacity, and nonblocking
switches.

Space Division Switches can be categorized in two ways:

o Crossbar Switch
o Multistage Switch

Crossbar Switch

The Crossbar switch is a switch that has n input lines and n output lines. The
crossbar switch has n2 intersection points known as crosspoints.

Disadvantage of Crossbar switch:

The number of crosspoints increases as the number of stations is increased.

Therefore, it becomes very expensive for a large switch. The solution to this
is to use a multistage switch.

Multistage Switch

o Multistage Switch is made by splitting the crossbar switch into the smaller
units and then interconnecting them.
o It reduces the number of crosspoints.
o If one path fails, then there will be an availability of another path.

Advantages Of Circuit Switching:

o In the case of Circuit Switching technique, the communication channel is

dedicated.
 o It has fixed bandwidth.

Disadvantages Of Circuit Switching:

o Once the dedicated path is established, the only delay occurs in the speed of
data transmission.
o It takes a long time to establish a connection approx 10 seconds during which
no data can be transmitted.
o It is more expensive than other switching techniques as a dedicated path is
required for each connection.
o It is inefficient to use because once the path is established and no data is
transferred, then the capacity of the path is wasted.
o In this case, the connection is dedicated therefore no other data can be
transferred even if the channel is free.

Message Switching
o Message Switching is a switching technique in which a message is transferred
as a complete unit and routed through intermediate nodes at which it is
stored and forwarded.
o In Message Switching technique, there is no establishment of a dedicated
path between the sender and receiver.
o The destination address is appended to the message. Message Switching
provides a dynamic routing as the message is routed through the
intermediate nodes based on the information available in the message.
o Message switches are programmed in such a way so that they can provide
the most efficient routes.
o Each and every node stores the entire message and then forward it to the
next node. This type of network is known as store and forward network.
o Message switching treats each message as an independent entity.
Advantages Of Message Switching

o Data channels are shared among the communicating devices that improve
the efficiency of using available bandwidth.
o Traffic congestion can be reduced because the message is temporarily stored
in the nodes.
o Message priority can be used to manage the network.
o The size of the message which is sent over the network can be varied.
Therefore, it supports the data of unlimited size.

Disadvantages Of Message Switching

o The message switches must be equipped with sufficient storage to enable

them to store the messages until the message is forwarded.
o The Long delay can occur due to the storing and forwarding facility provided
by the message switching technique.

Packet Switching
o The packet switching is a switching technique in which the message is sent in
one go, but it is divided into smaller pieces, and they are sent individually.
o The message splits into smaller pieces known as packets and packets are
given a unique number to identify their order at the receiving end.
o Every packet contains some information in its headers such as source
address, destination address and sequence number.
o Packets will travel across the network, taking the shortest path as possible.
 o All the packets are reassembled at the receiving end in correct order.
o If any packet is missing or corrupted, then the message will be sent to resend
the message.
o If the correct order of the packets is reached, then the acknowledgment
message will be sent.

Approaches Of Packet Switching:

There are two approaches to Packet Switching:

Datagram Packet switching:

o It is a packet switching technology in which packet is known as a datagram, is

considered as an independent entity. Each packet contains the information
about the destination and switch uses this information to forward the packet
to the correct destination.
o The packets are reassembled at the receiving end in correct order.
o In Datagram Packet Switching technique, the path is not fixed.
o Intermediate nodes take the routing decisions to forward the packets.
o Datagram Packet Switching is also known as connectionless switching.

Virtual Circuit Switching

o Virtual Circuit Switching is also known as connection-oriented switching.

 o In the case of Virtual circuit switching, a preplanned route is established
before the messages are sent.
o Call request and call accept packets are used to establish the connection
between sender and receiver.
o In this case, the path is fixed for the duration of a logical connection.

Let's understand the concept of virtual circuit switching through a

diagram:

o In the above diagram, A and B are the sender and receiver respectively. 1
and 2 are the nodes.
o Call request and call accept packets are used to establish a connection
between the sender and receiver.
o When a route is established, data will be transferred.
o After transmission of data, an acknowledgment signal is sent by the receiver
that the message has been received.
o If the user wants to terminate the connection, a clear signal is sent for the
termination.
Differences b/w Datagram approach and Virtual Circuit approach
Datagram approach Virtual Circuit approach

Node takes routing decisions to forward Node does not take any routing decision.
the packets.

Congestion cannot occur as all the Congestion can occur when the node is busy, and
packets travel in different directions. does not allow other packets to pass through.

It is more flexible as all the packets are It is not very flexible.

treated as an independent entity.

Advantages Of Packet Switching:

o Cost-effective: In packet switching technique, switching devices do not

require massive secondary storage to store the packets, so cost is minimized
to some extent. Therefore, we can say that the packet switching technique is
a cost-effective technique.
o Reliable: If any node is busy, then the packets can be rerouted. This ensures
that the Packet Switching technique provides reliable communication.
o Efficient: Packet Switching is an efficient technique. It does not require any
established path prior to the transmission, and many users can use the same
communication channel simultaneously, hence makes use of available
bandwidth very efficiently.

Disadvantages Of Packet Switching:

o Packet Switching technique cannot be implemented in those applications that

require low delay and high-quality services.
o The protocols used in a packet switching technique are very complex and
requires high implementation cost.
o If the network is overloaded or corrupted, then it requires retransmission of
lost packets. It can also lead to the loss of critical information if errors are nor
recovered.