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Unformatted text preview: ogin to the server, the client FTP automatically sends the SYST command,
which the server responds to with its system type. If the reply begins with the string "215
UNIX Type: L8", and if the client is running on a Unix system with 8 bits per byte,
binary mode (image) is used for all file transfers, unless changed by the user. file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (16 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol When we fetch the file hello.c the client automatically sends the command TYPE I to
set the file type to image. Only 38 bytes are transferred across the data connection.
The Host Requirements RFC says an FTP server must support the SYST command (it was an option in
RFC 959). But the only systems used in the text (see inside front cover) that support it are BSD/386 and
AIX 3.2.2. SunOS 4.1.3 and Solaris 2.x reply with 500 (command not understood). SVR4 has the
extremely unsocial behavior of replying with 500 and closing the control connection! Aborting A File Transfer: Telnet Synch Signal
We now look at how the FTP client aborts a file transfer from the server. Aborting a file
transfer from the client to the server is easy - the client stops sending data across the data
connection and sends an ABOR to the server on the control connection. Aborting a
receive, however, is more complicated, because the client wants to tell the server to stop
sending data immediately. We mentioned earlier that the Telnet synch signal is used, as
we'll see in this example.
We'll initiate a receive and type our interrupt key after it has started. Here is the interactive
session, with the initial login deleted:
ftp> get a.out
---> TYPE I fetch a large file
client and server are both 8-bit byte Unix
systems 200 Type set to I.
---> PORT 140,252,13,66,4,99
200 PORT command successful.
---> RETR a.out
150 Opening BINARY mode data connection for a.out (28672
type our inte...
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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