Application Layer - Seventh Layer in OSI Reference Model

Application Layer is the seventh layer in Open System Interconnection (OSI) Reference Model. Function of Application layer is to present data to users by enabling direct interaction between user and software applications. In simple words the major function of Application layer in OSI Reference Model is to provide user interface. User interface can be either command line based or GUI based. GUI based user interface is used in web browser and Command Line Interface(CLI) is used in Routers and Switches (IOS high end Routers and Switches).

Application Layer Protocols

A set of protocols are working on application layer. These application layer protocols are classified in to two.

  1. Common Application Specific Elements (CASE)
  2. Specific Application Specific Elements (SASE)

The major Application Layer protocols are:

  1. Telnet
  2. File Transfer Protocol (FTP)
  3. Simple Mail Transfer Protocol (SMTP)
  4. FTAM
  5. HTTP
  6. DHCP
  7. NFS
  8. POP3
  9. NNTP
  10. IRC

OSI Seven Layer Structure
  1. Physical layer

  2. Data link layer

  3. Network layer

  4. Transport layer

  5. Session layer

  6. Presentation layer

  7. Application layer

List of Application Layer Utilities

The major Application Layer utilities are.
  1. Address Resolution Protocol (ARP)

  2. Netstat

    Netstat works in application layer. To learn more about this application layer utility, visit the link below.
    Netstat -A Command Line Tool

  3. Ping

  4. Tracert

  5. FTP and TFTP

  6. Hostname

  7. Whois

Technology Guide

Presentation Layer - Sixth Layer in OSI Reference Model

Presentation Layer is the sixth layer in Open Systems Interconnection (OSI) Reference Model. Presentation layer is responsible for how data is presented to the user. Presentation of various forms of information like graphics, text, audio, video etc in various forms to user is the major duty of this layer. Data encryption is also one of the functions of presentation layer to ensure data security. Presentation layer is working as the intermediate between Application layer and Session layer in OSI Reference Model.

How Information is Presented in Presentation layer

Text information is presented in either ASCII or EBCDIC form to the user. In case of graphical information we can see various standards to present it to user. Some examples are JPEG, BMP, GIF etc.

Functions of Presentation Layer

Three functions of presentation layer are:

  1. Encryption and Decryption
  2. Compression
  3. Translation

As we can see presentation layer is responsible for data encryption and decryption. Forms of data presentation by presentation layer are in ASCII and EBCDIC.

Sub-layers in Presentation Layer

The Presentation Layer is composed of two sub-layers. They are:

  1. Common Application Service Element (CASE)
  2. Specific Application Service Element (SASE)

Presentation Layer Protocols

Major protocols in presentation layer are:

  1. Remote Desktop Protocol
  2. ASCII
  3. Network Data Representation
  4. External Data Representation

Further Reading

  1. Physical layer

  2. Data link layer

  3. Network layer

  4. Transport layer

  5. Session layer

  6. Presentation layer

  7. Application layer

Technology Guide