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

The major Application Layer utilities are.

1. Address Resolution Protocol (ARP)
2. Netstat
3. Ping
4. Tracert
5. FTP and TFTP
6. Hostname
7. Whois

Technology Guide