The original TCP/IP specification described a number of different applications that fit into the top layer of the protocol stack. These applications include Telnet, FTP, SMTP and DNS.
Telnet is a program that supports the TELNET [13] protocol over TCP. TELNET is a general two-way communication protocol that can be used to connect to another host and run applications on that host remotely.
FTP (File Transfer Protocol) [14] is a protocol that was originally designed to promote the sharing of files among computer users. It shields the user from the variations of file storage on different architectures and allows for a reliable and efficient transfer of data.
SMTP (Simple Mail Transport Protocol) [15] is the protocol used to transport electronic mail from one computer to another through a series of other computers along the route.
DNS [10] (Domain Name System) resolves the numerical address of a network node into its textual name or vice-versa. It would translate www.yahoo.com to 204.71.177.71 to allow the routing protocols to find the host that the packet is destined for.