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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)

File and Message Transfer Overview and Application Categories 1 File Transfer Protocol (FTP)

As I mentioned in the preceding overview of file and message transfer protocols, they represent the most basic type of network communication: the simple movement of blocks of data. Of the many file and message transfer methods, the most fundamental application is what I call general file transfer. General file transfer protocols perform one main function: allowing files to be copied from one computer to another.

Since file transfer protocols move files from place to place without considering their contents much, they are relatively “unsophisticated” compared to certain message-processing applications. However, the idea of being able to move files around is so important that general file transfer protocols were one of the very first applications in internetworking. While many people now use electronic mail or Web browsers to perform the functions formerly performed exclusively using general file transfer, these older protocols are still very important and widely used, and important to understand.

In this section I take a look at the two TCP/IP general file transfer protocols. The first is called simply the File Transfer Protocol (FTP). The second is called the Trivial File Transfer Protocol (TFTP). Each is described in its own subsection.

The relationship between FTP and TFTP is similar to that of the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) at layer four. FTP is full-featured, session-oriented and somewhat complex. It is the more often-used of the two protocols, providing a full command interface and taking advantage of the reliability and stream transfer functions of TCP, over which it runs. TFTP, like the UDP it uses at the transport layer, is a “stripped down” version of FTP. It has far fewer commands and capabilities than FTP, but is ideal for cases where simplicity and small software program size is important, such as embedded software in devices.

File and Message Transfer Overview and Application Categories 1 File Transfer Protocol (FTP)