Unformatted text preview: omenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (9 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol ftp> quit
---> QUIT 221 Goodbye. we're done When the FTP client prompts us for a login name, it prints the default (our login name on
the client). When we type the RETURN key, this default is sent.
Asking for a directory listing of a single file causes a data connection to be established and
used. This example follows the procedure we showed in Figures 27.4 and 27.5. The client
asks its TCP for an ephemeral port number for its end of the data connection, and sends
this port number (1174) to the server in a PORT command. We can also see that a single
interactive user command (dir) becomes two FTP commands (PORT and LIST).
Figure 27.6 is the time line of the packet exchange across the control connection. (We
have removed the establishment and termination of the control connection, along with all
the window size advertisements.) We note in this figure where the data connection is
opened, used, and then closed. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (10 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol Figure 27.6 Control connection for FTP example.
Figure 27.7 is the time line for the data connection. The times in this figure are from the
same starting point as Figure 27.6. We have removed all window advertisements, but have
left in the type-of-service field, to show that the data connection uses a different type-ofservice (maximize throughput) than the control connection (minimize delay). (The TOS
values are in Figure 3.2.) Figure 27.7 Data connection for FTP example.
In this time line the FTP server does the active open of the data connection, from port 20
(called ftp-data), to the port number from the PORT command (1174). Also in this
example, where the server writes to the data connection, the server does the active close of
the data connection, which tells the client when the listing is complete. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (11 of...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12