Have a number of standard TCP/IP applications such as
- Simple Mail Transfer Protocol (SMTP)
- File Transfer Protocol (FTP)
- Telnet
A number of applications have been standardized to operate on top of TCP. We mention three of the most common here.
The Simple Mail Transfer Protocol (SMTP) provides a basic electronic mail transport facility for transferring messages among separate hosts. The SMTP protocol does not specify the way in which messages are to be created; some local editing or native electronic mail facility is required. The target SMTP module will store the incoming message in a user's mailbox.
The File Transfer Protocol (FTP) is used to send files from one system to another under user command. Both text and binary files are accommodated. FTP sets up a TCP connection to the target system for the exchange of control messages. Once a file transfer is approved, a second TCP data connection is set up for the data transfer, without the overhead of any headers or control information at the application level. When the transfer is complete, the control connection is used to signal the completion and to accept new file transfer commands.
TELNET provides a remote logon capability, which enables a user at a terminal or personal computer to logon to a remote computer and function as if directly connected to that computer. The protocol was designed to work with simple scroll-mode terminals. Terminal traffic between User and Server TELNET is carried on a TCP connection.
Some TCP/IP Protocols
Each layer in the TCP/IP protocol suite interacts with its immediate adjacent layers. This use of each individual layer is not required by the architecture. As Stallings DCC8e Figure 2.5 suggests, it is possible to develop applications that directly invoke the services of any one of the layers. Most applications require a reliable end-to-end protocol and thus make use of TCP. Some special-purpose applications do not need the services of TCP. Some of these applications, such as the Simple Network Management Protocol (SNMP), use an alternative end-to-end protocol known as the User Datagram Protocol (UDP); others may make use of IP directly. Applications that do not involve internetworking and that do not need TCP have been developed to invoke the network access layer directly.