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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)

TFTP Detailed Operation and Messaging 1 2 3 4 TFTP Message Formats

TFTP Read Process With and Without Option Negotiation

The initial message exchange for a normal read (without option negotiation), as shown in Figure 293:

1. Client sends Read Request.
   
   
2. Server sends Data block #1.
   
   
3. Client acknowledges data block #1.

And so on…

And now, a read with option negotiation (Figure 295):

1. Client sends Read Request with options.
   
   
2. Server sends Option Acknowledgment.
   
   
3. Client sends regular acknowledgment for “block #0”, that is, it acknowledges the OACK.
   
   
4. Server sends data block #1.
   
   
5. Client acknowledges data block #1.

Etc…

Figure 295: TFTP Read Process With Option Negotiation

This diagram shows the same example illustrated in Figure 293, but with one added message exchange used for option negotiation (purple background). The client’s initial Read Request here includes options that it wants to use for this transfer. The server responds not immediately with the first data block, but with an Option Acknowledgment. The client indicates receipt of the OACK by sending an acknowledgment using block #0. The server sends data block #1 and the rest of the exchange proceeds as normal.

TFTP Detailed Operation and Messaging 1 2 3 4 TFTP Message Formats

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Version 3.0 - Version Date: September 20, 2005

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