While the OSI model separates the individual application, presentation, and session function, most widely known and implemented TCP/IP applications incorporate the functionality of all three layers.
The TCP/IP application protocols specify the format and control information necessary for many common Internet communication functions. Among these TCP/IP protocols are:
- Domain Name System (DNS) - This protocol resolves Internet names to IP addresses.
- Telnet - This is used to provide remote access to servers and networking devices.
- Simple Mail Transfer Protocol (SMTP) - This protocol transfers mail messages and attachments.
- Dynamic Host Configuration Protocol (DHCP) - A protocol used to assign an IP address, subnet mask, default gateway, and DNS server addresses to a host.
- Hypertext Transfer Protocol (HTTP) - This protocol transfers files that make up the web pages of the World Wide Web.
- File Transfer Protocol (FTP) - A protocol used for interactive file transfer between systems.
- Trivial File Transfer Protocol (TFTP) - This protocol is used for connectionless active file transfer.
- Bootstrap Protocol (BOOTP) - This protocol is a precursor to the DHCP protocol. BOOTP is a network protocol used to obtain IP address information during bootup.
- Post Office Protocol (POP) - A protocol used by email clients to retrieve email from a remote server.
- Internet Message Access Protocol (IMAP) - This is another protocol for email retrieval.
Application layer protocols are used by both the source and destination devices during a communication session. For the communications to be successful the application layer protocols implemented on the source and destination host must be compatible.