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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):
- The client sends a read request to
the server, specifying the name of the file.
- The server sends back a data message
containing block #1, carrying 512 bytes of data.
- The client receives the data, and sends
back an acknowledgment for block #1.
- The server sends block #2, with 512
bytes of data.
- The client receives block #2, and sends
back an acknowledgment for it.
- The server sends block #3, containing
176 bytes of data. It waits for an acknowledgment before terminating
the logical connection.
- 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.
- 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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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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