Application Layer Protocols in Computer Network

FTP (File Transfer Protocol)

  • FTP is File Transfer Protocol.
  • It used to exchange files on the internet.
  • To enable the data transfer FTP uses TCP/IP, FTP is most commonly used to upload and download files from the internet.
  • FTP can be invoked from the command prompt or some graphical user interface.
  • FTP also allows to update (delete, rename, move, and copy) files at a server.
  • It uses a reserved port no 21.


  • Dynamic Host Configuration Protocol (DHCP) is used assigning IP addresses to computers in a network.
  • The IP addresses are assigned dynamically.
  • Certainly, using DHCP, the computer will have a different IP address every time it is connected to the network.
  • In some cases the IP address may change even when the computer is in network.
  • This means that DHCP leases out the IP address to the computer for sometime.
  • Clear advantage of DHCP is that the software can be used to manage IP address rather than the administrator.


  • The Hypertext Transfer Protocol (HTTP) is used to access the data on WWW(World Wide Web).
  • The functions of HTTP are the combination of FTP (File Transfer Protocol) and SMTP (Simple Mail Transfer Protocol).
  • HTTP is similar to FTP, because it uses only one TCP connection (data is transferred between Client and Sever).
  • In SMTP, the messages are stored and then forwarded to the destination, but the HTTP messages are delivered immediately.
  • HTTP uses the services of TCP on well-known port 80.


  • It is an application layer protocol, which can be used on the internet or LAN(Local Area Network).
  • It provides a bi-directional interactive text oriented communication service by using virtual terminal connection.
  • Telnet is basically a client server protocol, which is based on a reliable connection- oriented transport.
  • It uses a port number 23, to establish the connection with TCP (Transmission Control Protocol).

SMTP (Simple Mail Transport Protocol)

  • It is an internet standard for e-mail Transmission.
  • SMTP connections are secured with SSL (Secure Socket Layer).
  • In SMTP, the messages are stored and then forwarded to the destination.
  • SMTP uses a port number 25 of TCP.