Application Layer Definition

The application layer is the top layer of both the seven-layer OSI (open systems interconnection) model and the five-layer TCP/IP (transmission control protocol/Internet protocol) model. It provides services to connect application programs to communications protocols and to ensure effective communication with other application programs over a network.

These services include (1) confirming that necessary communication resources exist (e.g.,that there a functioning modem in the sender's computer), (2) ensuring identification of the destination host, (3) authenticating either or both the message sender and recipient, (4) determining protocol rules at the application level and (5) ensuring agreement at both ends about error recovery procedures, data integrity and privacy.

Some of the most popular application layer protocols include DHCP (dynamic host configuration protocol), FTP (file transfer protocol), HTML (hypertext markup language), HTTP (hypertext transfer protocol), IRC (Internet relay chat), NFS (network file system), NNTP (network news transfer Protocol), POP3 (post office protocol 3), SMTP (simple mail transfer protocol), SNMP (simple network management protocol) and telnet.

Created November 16, 2005.
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