The document provides an overview of application layer protocols in the OSI and TCP/IP models, highlighting their functions, such as remote logins, file management, and email services. It details common protocols like HTTP, HTTPS, DNS, FTP, and TFTP, explaining their roles in data communication, security features, and operational mechanisms. The application layer is essential as it directly interfaces with end-user applications, facilitating various types of network communication.

1. APPLICATION
LAYER PROTOCOLS
PRESENTED BY:
ROLIKA AGARWAL
SHIVI ARORA
SHRUTI SINGH
FLIP CLASS ON THE TOPIC

2. INTRODUCTION:
• The application layer in the OSI model and TCP/IP model is the
topmost and the closest layer to the end user which means that the
application layer and end user can interact directly with the software
application. The application layer programs are based on client and
servers.

3. SERVICES OF APPLICATION
LAYER
• Network Virtual terminal:
Application layer allows a user to log on to a remote host. To do so, the application
creates a software emulation of a terminal at the remote host. The user's computer
talks to the software terminal, which in turn, talks to the host. The remote host thinks
that it is communicating with one of its own terminals, so it allows the user to log on.
• File Transfer, Access, and Management (FTAM):
Application layer allows a user to access files in a remote computer, to retrieve files
from a computer and to manage files in a remote computer.
• Mail Services:
Application layer provides the basis for E-mail forwarding and storage.
• Directory Services:
An application contains a distributed database that provides access for global
information about various objects and services.

4. OVERVIEW: APPLICATION LAYER
PROTOCOLS
The Application layer protocols in computer networks are a set of standards and rules that
govern the communication between end-user applications over a network. These protocols
provide a specific services and functionality to support different types of application-level
communication, including file transfers, email, remote terminal connections, and web
browsing.
Some of the commonly used application layer protocols include:
• Hyper Text Transfer Protocol (HTTP)
• Hyper Text Transfer Protocol Secure (HTTPS)
• Domain Name System (DNS)
• File Transfer Protocol (FTP)
• Trivial File Transfer Protocol (TFTP)
• Simple Mail Transfer Protocol (SMTP)
• Post Office Protocol (POP3)

5. HYPERTEXT TRANSFER PROTOCOL
• HTTP is an application-level protocol that is widely used for transmitting data over the internet. It is used by
the World Wide Web, and it is the foundation of data communication for the web. This protocol is known as
HyperText Transfer Protocol because of its efficiency that allows us to use in a hypertext environment where
there are rapid jumps from one document to another document.
• HTTP works on client server model. When a user wants to access any HTTP page on the internet, the client
machine at user end initiates a TCP connection to server on port 80. When the server accepts the client
request, the client is authorized to access web pages.
• HTTP requests contain a method, a URI, and a set of headers, and they can also contain a payload, which is
the data being sent. HTTP responses contain a status code, a set of headers, and a payload, which is the
data being returned.
• HTTP is a connectionless stateless protocol, which means the The connection between client and server exist
only during the current request and response time onlyand the server maintains no information about earlier
requests by clients.

6. HYPERTEXT TRANSFER PROTOCOL
SECURE
• The HTTP protocol does not provide the security of the data, while HTTP ensures the
security of the data. Therefore, we can say that HTTPS is a secure version of the HTTP
protocol.
• HTTPS is encrypted in order to increase security of data transfer. This is particularly
important when users transmit sensitive data, such as by logging into a bank account,
email service, or health insurance provider.
• In modern web browsers such as Chrome, websites that do not use HTTPS are marked
differently than those that are.
• To provide encryption, HTTPS uses an encryption protocol known as Transport Layer
Security, and officially, it is referred to as a Secure Sockets Layer (SSL). This protocol
uses a mechanism known as asymmetric public key infrastructure, and it uses two
different keys which are given below:
• Private key: This key is available on the web server, which is managed by the owner of a
website.
• It decrypts the information which is encrypted by the public key.

7. DOMAIN NAME SYSTEM
• DNS stands for "Domain Name System," and it is an essential component of the internet that translates domain
names into IP addresses.
• A domain name is a human-readable string of characters, such as "google.com," that can be easily remembered,
while an IP address is a set of numbers and dots that computers use to communicate with each other over the
internet.
• The DNS system is a hierarchical, distributed database that maps domain names to IP addresses. When you
enter a domain name into your web browser, your computer sends a query to a DNS server, which then returns
the corresponding IP address. The browser can then use that IP address to send a request to the server hosting
the website you’re trying to access.
• DNS has several benefits:
• It makes it possible for humans to access websites and other internet resources using easy-to-remember
domain names, rather than having to remember IP addresses.
• It also allows website owners to change the IP address of their server without affecting the domain name,
making it easier to maintain and update their website.

8. FILE TRANSFER PROTOCOL
• FTP, or File Transfer Protocol, is a standard network protocol used for the transfer of files from one host to
another over a TCP-based network, such as the Internet. It is widely used for transferring large files or groups
of files, as well as for downloading software, music, and other digital content from the Internet.
• The systems involved in TCP-based network connections are heterogeneous, i.e. they differ in operating
systems, directories, structures, character sets, etc the FTP shields the user from these differences and
transfers data efficiently and reliably.
• FTP operates in a client-server architecture and has two communication channels, command channel for
conversation control and data channel for file content, where a client establishes a connection to an FTP
server and can then upload or download files from the server. The client and server exchange messages to
initiate transfers, manage data transfers, and terminate the connection. It supports both active and passive
modes, which determine the way the data connection is established between the client and the server.

9. TRIVIAL FILE TRANSFER PROTOCOL
• TFTP is defined as a protocol that is used to transfer a file from a client to a server and from a server to a
client. It is majorly used when no complex interactions are required by the client and server.
• It is implemented on top of the UDP/IP protocols using well-known port number 69.
• TFTP does not provide security features ,therefore, it is not used in communications that take place over the
Internet. It is used only for the systems that are set up on the Local Area Networks(LANs).
• TFTP requires less amount of memory and is intended for applications that do not need the sophisticated
interactions that FTP provides.
• TFTP only reads and writes files from or to a remote server. It cannot list, delete, or rename files or directories
and it has no provisions for user authentication.