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<tr><td width="100%" colspan="2" height="100" align="center" valign="top"><br><p align="center">[<a href="index.htm">回到开始</a>][<a href="288.htm">上一层</a>][<a href="295.htm">下一篇</a>]
<hr><p align="left"><small>发信人: tianxing (天行健，君子自强不息), 信区: Winsock <br>
标 题: Telnet Protocol(英文版一) <br>
发信站: 武汉白云黄鹤站 (Thu Jun 29 19:10:53 2000), 站内信件 <br>
<br>
<br>
<br>
Network Working Group Jon Postel <br>
Request for Comments: 318 UCLA-NMC <br>
NIC: 9348 April 3, 1972 <br>
References: RFC 139, 158, and NIC 7104 <br>
Telnet Protocol <br>
At the October 1971 Network Working Group Meeting, I promised to <br>
promptly produce a document which clearly and succinctly specified <br>
and explained the Official Telnet Protocol. This document fails to <br>
meet any part of that promise. This document was not produced <br>
promptly. This document is neither clear nor succinct. There is NO <br>
Official Telnet Protocol. <br>
The following pages present my understanding of the ad hoc Telnet <br>
protocol. There are some who have serious questions about this <br>
protocol. The proposed changes to the protocol are given in Section <br>
IV. <br>
Any comments should be promptly directed to me via the Network <br>
Information Center (Ident = JBP) or by phone (213) 825-2368 or by <br>
mail. <br>
Jon Postel <br>
SPADE Group <br>
3804 Boelter Hall <br>
UCLA <br>
Los Angeles, California 90024 <br>
Postel [Page 1] <br>
RFC 318 Telnet Protocol April 1972 <br>
I. DEFINITION OF THE NETWORK VIRTUAL TERMINAL <br>
The Network Virtual Terminal (NVT) is a bi-directional character <br>
device. The characters are represented by 8 bit codes. The NVT has <br>
no timing characteristics. The character codes 0 through 127 are the <br>
USASCII codes. (Note all code values are given in decimal.) The <br>
codes 128 through 255 are used for special control signals. The NVT <br>
is described as having a printer and a keyboard. The printer <br>
responds to incoming data and the keyboard produces outgoing data. <br>
The Printer <br>
The NVT printer has an unspecified carriage width (common values are <br>
40, 72, 80, 120, 128, 132). The printer can produce representations <br>
of all 95 USASCII graphics (codes 32 through 126). Of the 33 USASCII <br>
control codes (0 through 31 and 127) the following 8 have specific <br>
meaning to the NVT printer. <br>
NAME CODE MEANING <br>
NULL (NUL) 0 A no operation. <br>
BELL (BEL) 7 Produces an audible or visible signal. <br>
Back Space (BS) 8 Backspaces the printer one character <br>
position. <br>
Horizontal Tab (HT) 9 Moves the printer to next horizontal <br>
tab stop. <br>
Line Feed (LF) 10 Moves the printer to next line (keeping <br>
the same horizontal position). <br>
Vertical Tab (VT) 11 Moves the printer to the next vertical <br>
tab stop. <br>
Form Feed (FF) 12 Moves the printer to the top of the <br>
next page. <br>
Carriage Return (CR) 13 Moves the printer to the left margin <br>
of the current line. <br>
The remaining USASCII codes (1 through 6, 14 through 31, and 127) do <br>
not cause the NVT printer to take any action. <br>
Postel [Page 2] <br>
RFC 318 Telnet Protocol April 1972 <br>
The Keyboard <br>
The NVT Keyboard has keys or key combinations or key sequences for <br>
generating all of the 128 USASCII codes. Note that although there <br>
are codes which have no effect on the NVT printer, the NVT Keyboard <br>
is capable of generating these codes. <br>
The End of the Line Convention <br>
The end of a line of text shall be indicated by the character <br>
sequence Carriage Return Line Feed (CR, LF). This convention applies <br>
to both the sending (Keyboard) and receiving (Printer) (virtual) <br>
mechanisms. <br>
Break and Reverse Break <br>
The Telnet control signals provide a BREAK signal which can be used <br>
to simulate the use of the break or attention or interrupt button <br>
found on most terminals. This signal has no effect on the NVT. When <br>
the BREAK Telnet control signal is used from server to user it is <br>
sometimes called "reverse break". Such a reverse break has no effect <br>
on the NVT. <br>
II. DEFINITION OF TELNET PROTOCOL <br>
The purpose of Telnet Protocol is to provide a standard method of <br>
interfacing terminals devices at one site to processes at another <br>
site. <br>
The Telnet Protocol is built up from three major substructures, first <br>
the Initial Connection Protocol (ICP), second the Network Virtual <br>
Terminal (NVT), and third the Telnet control signals described <br>
herein. <br>
herein. <br>
Telnet user and server processes follow the ICP to establish <br>
connections. The term "Logger" has been associated with the set of <br>
processes in the serving system which respond to the ICP and perform <br>
the initial interactions e.g. obtain a name and password. The ICP is <br>
defined and the initial socket number and byte size parameters are <br>
defined in "Current Network Protocols" (NIC #7104). <br>
The data transmitted between the user and server programs (and vice <br>
versa) is treated as a character stream with embedded control <br>
signals. <br>
Note that all code values are given in decimal. <br>
Postel [Page 3] <br>
RFC 318 Telnet Protocol April 1972 <br>
TELNET CONTROL SIGNALS <br>
NAME CODE MEANING <br>
DATA MARK 128 Used to mark a point in the data stream. <br>
Used in conjunction with INS. See SYNCH. <br>
BREAK 129 User-to-Server: Has the same meaning to <br>
the server as the "Break," "Interrupt," or <br>
"Attention" button found on many terminals. <br>
Server-to-User: Has the same meaning to <br>
to use as the "reverse break" used with <br>
some terminals. <br>
NOP 130 No Operation. <br>
NO ECHO 131 User-to-Server: Asks the server not to <br>
return Echos of the transmitted data. <br>
Server-to-User: States that the server is <br>
not sending echos of the transmitted data. <br>
Sent only as a reply to ECHO or NO ECHO, <br>
or to end the hide your input. <br>
ECHO 132 User-to-Server: Asks the server to send <br>
Echos of the transmitted data. <br>
Server-to User: States that the server is <br>
sending echos of the transmitted data. <br>
Sent only as a reply to ECHO or NO ECHO. <br>
Hide your input 133 The intention is that a server will send <br>
this signal to a user system which is <br>
echoing locally (to the user) when the user <br>
is about to type something secret (e.g. a <br>
password). In this case, the user system <br>
is to suppress local echoing or overprint <br>
the input (or something) until the server <br>
sends a NOECHO signal. In situations where <br>
the user system is not echoing locally, <br>
this signal must not be sent by the server. <br>
INS --- This is the "Interrupt on Send" signal, <br>
defined by the Host-to-Host protocol and <br>
implemented by the Network Control Program <br>
(NCP). See SYNCH. <br>
Postel [Page 4] <br>
RFC 318 Telnet Protocol April 1972 <br>
SYNCH --- This is a condition indicated by the <br>
combination of the DATA MARK and the INS. <br>
User-to-Server: The Server is to examine <br>
the input data stream looking for a DATA <br>
MARK signal; if a DATA MARK is found, the <br>
server must not process further until an <br>
INS is received. If the server receives an <br>
INS, it is required to examine the data <br>
stream at once, taking any appropriate <br>
action on "break type" characters (e.g. <br>
etx, sub, BREAK), up to a DATA MARK signal <br>
and thereupon continue its normal processing. <br>
The passed over characters may be discarded. <br>
Server-to-User: If the user finds a DATA <br>
MARK in the data stream, it must wait for <br>
an INS. If the user receives an INS, it <br>
must examine and discard characters up to <br>
and including a DATA MARK. <br>
DATA TYPES <br>
Telnet normally deals in ASCII characters, but there are provisions <br>
for escaping to other code sets. If one of these escapes is used, it <br>
is undefined (here) whether or not the Telnet signals still have <br>
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