IETF RFC 7440 PDF

The "Trivial File Transfer Protocol" (RFC 1350) is a simple, lockstep, file transfer protocol that allows a client to get or put a file onto a remote host. One of its primary uses is in the early stages of nodes booting from a Local Area Network (LAN). TFTP has been used for this application because it is very simple to implement. The employment of a lockstep scheme limits throughput when used on a LAN.

This document describes a TFTP option that allows the client and server to negotiate a window size of consecutive blocks to send as an alternative for replacing the single‐block lockstep schema. The TFTP option mechanism employed is described in "TFTP Option Extension" (RFC 2347).