TCP/IP and the OSI Model – The Application (Process) Layer

The Application/Process Layer is where TCP/IP applications and services reside. You’re more than likely familiar with many of these, since you probably interact with many TCP/IP applications on a daily basis – a web browser using HTTP, or your email client connecting to a POP3 server are but two simple examples.

The list below outlines some of the more common Application layer protocols that you should be familiar with.

  • Telnet. Telnet is used to create a terminal session with a remote host, providing command-line access to the target system running a telnet server (daemon).
  • FTP. The File Transfer Protocol is used to reliably transfer files between an FTP client and server using TCP.
  • SMTP. The Simple Mail Transfer Protocol is used for the exchange of email between systems.
  • DNS. The Domain Name Service is a distributed database that is queried to resolve (or translate) names such as to an IP address.
  • SNMP. The Simple Network Management Protocol is a lightweight network protocol that allows information to be gathered about network devices. Examples include information about utilization, hardware configuration, and so forth.
  • TFTP. The Trivial File Transfer Protocol is used to transfer files between a client and a TFTP server over UDP. You’ll learn more about TFTP later, since it’s the protocol used to transfer files to and from a Cisco router.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.