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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)                 9  TCP/IP General File Transfer Protocols (FTP and TFTP)                      9  Trivial File Transfer Protocol (TFTP)

Trivial File Transfer Protocol (TFTP) 1 2 3 TFTP General Operation, Connection Establishment and Client/Server Communication

Overview of TFTP Operation

Communication and messaging in TFTP is very different than it is in FTP because of the different transport layer protocols used by each. FTP makes use of TCP's rich functionality, including its stream data orientation, to allow it to send bytes of data directly over the FTP data connection. TCP also takes care of reliable delivery of data for FTP, ensuring files are received correctly. In contrast, since TFTP uses UDP, it must package data into individual messages for both protocol control and data communication. TFTP must also take care of timing transmissions to detect lost datagrams and then retransmitting as needed.

TFTP servers allow connections from TFTP clients to perform file send and receive operations. Many hosts that run FTP servers will also run a separate TFTP server module as well. TFTP users initiate connections by starting a TFTP client program, which generally uses a command-line interface similar to that of many FTP clients; the main difference is the much smaller number of commands in TFTP.

The basic operation of TFTP has not changed since RFC 1350 was published, but a new feature was added to the protocol in 1995. RFC 1782, TFTP Option Extension, defines a mechanism by which a TFTP client and TFTP server can negotiate certain parameters that will control a file transfer prior to the transfer commencing. This allows more flexibility in how TFTP is used, adding a slight amount of complexity to TFTP, but not a great deal.

The option extension is backwards-compatible with regular TFTP, and is only used if both server and client support it. Two subsequent RFCs define the actual options that can be negotiated: RFC 1783, TFTP Blocksize Option and RFC 1784, TFTP Timeout Interval and Transfer Size Options. This set of three RFCs (1782, 1783 and 1784) was replaced in 1998 by updated versions in RFCs 2347, 2348 and 2349.

Trivial File Transfer Protocol (TFTP) 1 2 3 TFTP General Operation, Connection Establishment and Client/Server Communication