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Table Of Contents  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)

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TFTP General Operation, Connection Establishment and Client/Server Communication
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TFTP Options and Option Negotiation
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TFTP Detailed Operation and Messaging
(Page 2 of 3)

TFTP Read Process Steps

Let's use an example to see how TFTP messaging works. Suppose the client wants to read a particular file that is 1,200 bytes long. Here are the steps in simplified form (also displayed in Figure 293):

  1. The client sends a read request to the server, specifying the name of the file.

  2. The server sends back a data message containing block #1, carrying 512 bytes of data.

  3. The client receives the data, and sends back an acknowledgment for block #1.

  4. The server sends block #2, with 512 bytes of data.

  5. The client receives block #2, and sends back an acknowledgment for it.

  6. The server sends block #3, containing 176 bytes of data. It waits for an acknowledgment before terminating the logical connection.

  7. The client receives the data, sends an acknowledgment for block #3. Since this data message had fewer than 512 bytes, it knows the file is complete.

  8. The server receives the acknowledgment, and knows the file was received successfully.

    Figure 293: TFTP Read Process

    In this example, the client starts the process of reading a file by sending a request for it to the server. The server acknowledges this request by immediately sending a DATA message carrying block #1, containing the first 512 bytes of the file. The client acknowledges this with an ACK message for block #1. The server then sends block #2, containing bytes 513 to 1,024, which the client acknowledges. When the client receives block #3, it realizes it has only 176 bytes, which marks it as the last block of the file.

     



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TFTP General Operation, Connection Establishment and Client/Server Communication
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TFTP Options and Option Negotiation
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