Application Layer in OSI Model
The Application Layer of OSI (Open System Interconnection) model, is the top layer in this model and takes care of network communication. The application layer provides the functionality to send and receive data from users. It acts as the interface between the user and the application. The application provides services like file transmission, mail service, and many more.
Application Layer in OSI Model
Functions of Application Layer
The Application Layer, being topmost layer in OSI model, performs functions required in any kind of application or communication process. Let’s have a look into the functions:
Working of Application Layer
- At first, client sends a command to server and when server receives that command, it allocates port number to client.
- Thereafter, the client sends an initiation connection request to server and when server receives request, it gives acknowledgement (ACK) to client through client has successfully established a connection with the server.
- Therefore, now client has access to server through which it may either ask server to send any types of files or other documents or it may upload some files or documents on server itself.
Services Provided by Application Layer Protocols
The following are some of the services which are provided by Application layer protocols-
- The Application Layer protocol defines process for both parties which are involved in communication.
- These protocols define the type of message being sent or received from any side (either source host or destination host).
- These protocols also define basic syntax of the message being forwarded or retrieved.
- These protocols define the way to send a message and the expected response.
- These protocols also define interaction with the next level.
Read in detail about Services Provided by Application Layer.
Protocols of the Application Layer
The application layer provides several protocols which allow any software to easily send and receive information and present meaningful data to its users. The following are some of the application layer protocols.
- HTTP: HTTP stands for Hyper Text Transfer Protocol. It is the foundation of the World Wide Web (WWW). HTTP works on the client server model. This protocol is used for transmitting hypermedia documents like HTML. This protocol was designed particularly for the communications between the web browsers and web servers, but this protocol can also be used for several other purposes. HTTP is a stateless protocol (network protocol in which a client sends requests to server and server responses back as per the given state), which means the server is not responsible for maintaining the previous client’s requests. HTTP uses port number 80.
- DNS: DNS stands for Domain Name System. The DNS service translates the domain name (selected by user) into the corresponding IP address. For example- If you choose the domain name as www.abcd.com, then DNS must translate it as 192.36.20.8 (random IP address written just for understanding purposes). DNS protocol uses the port number 53.
- TELNET: Telnet stands for Telecommunications Network. This protocol is used for managing files over the Internet. It allows the Telnet clients to access the resources of Telnet server. Telnet uses port number 23.
- DHCP: DHCP stands for Dynamic Host Configuration Protocol. It provides IP addresses to hosts. Whenever a host tries to register for an IP address with the DHCP server, DHCP server provides lots of information to the corresponding host. DHCP uses port numbers 67 and 68.
- FTP: FTP stands for File Transfer Protocol. This protocol helps to transfer different files from one device to another. FTP promotes sharing of files via remote computer devices with reliable, efficient data transfer. FTP uses port number 20 for data access and port number 21 for data control.
- SMTP: SMTP stands for Simple Mail Transfer Protocol. It is used to transfer electronic mail from one user to another user. SMTP is used by end users to send emails with ease. SMTP uses port numbers 25 and 587. .
- NFS: NFS stands for Network File System. This protocol allows remote hosts to mount files over a network and interact with those file systems as though they are mounted locally. NFS uses the port number 2049.
- SNMP: SNMP stands for Simple Network Management Protocol. This protocol gathers data by polling the devices from the network to the management station at fixed or random intervals, requiring them to disclose certain information. SNMP uses port numbers 161 (TCP) and 162 (UDP).
Read in detail about Protocols in Application Layer.
Frequently Asked Questions on Application Layer in OSI Model – FAQ’s
What is the Function of the Application Layer?
The function of application layer is to provide an interface to send and receive data from user.
Which is an Application Layer Service?
The application layer services are remote login, email services and file transmission.
How does the Application Layer ensure data integrity?
It uses protocols and error-checking mechanisms to detect and correct transmission errors.
Can the Application Layer handle multiple protocols simultaneously?
Yes, it supports concurrent protocols like HTTP, FTP, SMTP, and DNS for seamless network operations.
How does the Application Layer interact with other OSI model layers?
It requests data formatting from the Presentation Layer and relies on lower layers for connection and data transmission.
