Tag - Application Layers

Application Layer

Application Layer enable the user, whether human or software, to access the network. It provides user interfaces and support for services such as electronic mail,file access and transfer, access to system resource, surfing the world wide web, and network management.

Application layer is Responsible for Providing Services to the user.

  • Application Layer is a term used in categorizing protocols and methods in architectural models of computer networking. Both the OSI model and the Internet Protocol Suite (TCP/IP) define application layers.
  • In TCP/IP, the Application Layer contains all protocols and methods that fall into the realm of process-to-process communications via an Internet Protocol (IP) network using the Transport Layer protocols to establish underlying host-to-host connections.
  • Provides a means for the user to access information on the network through an application. This layer is the main interface for the user to interact with the application and therefore the network.
  • The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model. Application layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication. When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit. When determining resource availability, the application layer must decide whether sufficient network resources for the requested communication exist. In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer.


Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP).

                                                                                                OSI  Model


  • Application Layer do¬†Interaction (Providing Services to the user)
  • 80% Application on internet do interact
  • i.e ¬†google.com —–> will auto —–> ¬†www.google.com ——> Here www intract ¬†on port 80
  • i.e ¬†for buy house property dealer do interact

Application Layer Protocols

What is Firewall

A firewall is a software or hardware appliance that is used as a line of defense between your computer and the external threats from the internet.  Firewall technologies have evolved to meet the security requirements of the IT infrastructure. In a computer network, a firewall solution is usually implemented at the gateway computer to block the threats like intruders, hackers, viruses and unauthorized access.  There are different types of the firewall techniques and the implementation methods and the most commonly used techniques are packet filtering, proxy server, application gateway and the circuit-level gateway.


There are many companies that produce the firewall products and the most commonly used firewall products are manufactured by Zone Alarm, Microsoft Windows Firewall, Comodo, F-Secure, Kaspersky, LavaSoft, McAfee, Symantec, R-Firewall, AShampoo and Trend Micro PC-cillin.

Firewall works very closely to a router program by examining each packet of the data.  A properly configured firewall prevent your computer form the internal and external threats. Most business class firewall products offer application layer filtering.  Application filtering is required to prevent the spam, viruses and the application layers threats. Performance is very important in the busy networks and the firewall throughput can range from 150 mpbs to 1 gbps.  Configuring the firewall requires the detailed understating of the network applications and the overall IT infrastructure. To select the best firewall product, you need to know your IT infrastructure and the level of security you require.  Most of the firewall products posses the following features.

Firewall Features

  • Monitoring inbound and outbound traffic.
  • User‚Äôs authentication.
  • Ports blocking
  • Bandwidth management
  • Logging
  • NAT (Network Address Translation)
  • Antivirus
  • Spam Filtering
  • URL Screening
  • Web caching
  • Centralized management
  • SSL
  • VPN
  • Email Security
  • IP Spoofing
  • Blocks Intrusion attempts
  • Blocks viruses, spyware and other web threats.
  • HTTP Filtering
  • MAC Address filtering
  • Remote administration
  • Ports Scanning
  • Application monitoring
  • IP Address ban list
  • Application Layer Filtering


Before selecting a firewall product you should consider the following things

  • Do you prefer software firewall or hardware?
  • How many concurrent connections you require.
  • Do you need high availability?
  • What VPN protocols do you want to use.
  • Which level of security does your network require?
  • How many VPN tunnels do you need to run concurrently?
  • What type of user interface do you prefer?
  • Authentication features.

what is Connection oriented and Connectionless

Difference Between Connection oriented vs Connection less 

Connection-oriented means that a connection (a virtual link) must be established before data can be exchanged. This can guarantee that data will arrive, and in the same order it was sent. It guarantees delivery by sending acknowledgements back to the source when messages are received.


TCP is an example of an connection-oriented transport protocol.

A common example of connection-oriented communication is a telephone call: you call, the ‘destination’ picks up the phone and acknowledges and you start talking (sending data). When a message or a piece of it doesn’t arrive, you say: “What!?” and the sender will retransmit the data.

Connectionless is the opposite of connection-oriented; the sender does not establish a connection before it sends data, it just sends without guaranteeing delivery.


UDP is an example of an connectionless transport protocol.

Application Layers

Host A————————————Host B

Application layer——-data————Application layer

Presentation layer—–data————Presentation layer

Session layer———–data————Session layer

Transport layer—–segments——–Transport layer

Network layer¬†¬† ——packets———-Network layer

Data-link layer——-frames———–Data-link layer

Physical layer———–bits————-Physical layer


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