📄 rfc854.4up.ps
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/user_header_right_str (Page 8 of 16) def%%EndPageSetupdo_header5 725 M(RFC 854 May 1983) s5 686 M( the network and the user's local host\) which should be cleared;) s5 673 M( the appropriate way to do this is to transmit the "Synch") s5 660 M( signal \(described below\) to the user system.) s5 634 M( Are You There \(AYT\)) s5 608 M( Many systems provide a function which provides the user with) s5 595 M( some visible \(e.g., printable\) evidence that the system is) s5 582 M( still up and running. This function may be invoked by the user) s5 569 M( when the system is unexpectedly "silent" for a long time,) s5 556 M( because of the unanticipated \(by the user\) length of a) s5 543 M( computation, an unusually heavy system load, etc. AYT is the) s5 530 M( standard representation for invoking this function.) s5 504 M( Erase Character \(EC\)) s5 478 M( Many systems provide a function which deletes the last) s5 465 M( preceding undeleted character or "print position"* from the) s5 452 M( stream of data being supplied by the user. This function is) s5 439 M( typically used to edit keyboard input when typing mistakes are) s5 426 M( made. EC is the standard representation for invoking this) s5 413 M( function.) s5 387 M( *NOTE: A "print position" may contain several characters) s5 374 M( which are the result of overstrikes, or of sequences such as) s5 361 M( <char1> BS <char2>...) s5 335 M( Erase Line \(EL\)) s5 309 M( Many systems provide a function which deletes all the data in) s5 296 M( the current "line" of input. This function is typically used) s5 283 M( to edit keyboard input. EL is the standard representation for) s5 270 M( invoking this function.) s5 244 M( THE TELNET "SYNCH" SIGNAL) s5 218 M( Most time-sharing systems provide mechanisms which allow a) s5 205 M( terminal user to regain control of a "runaway" process; the IP and) s5 192 M( AO functions described above are examples of these mechanisms.) s5 179 M( Such systems, when used locally, have access to all of the signals) s5 166 M( supplied by the user, whether these are normal characters or) s5 153 M( special "out of band" signals such as those supplied by the) s5 140 M( teletype "BREAK" key or the IBM 2741 "ATTN" key. This is not) s5 127 M( necessarily true when terminals are connected to the system) s5 114 M( through the network; the network's flow control mechanisms may) s5 101 M( cause such a signal to be buffered elsewhere, for example in the) s5 88 M( user's host.) s5 36 M(Postel & Reynolds [Page 8]) s_R_RS%%Page: (9-12) 3%%BeginPageSetup_S24 818 translate%Page: (9) 9%BeginPageSetup_S% N-up sub-page 1/40 -392 translate0.490859 dup scale/pagenum 9 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc854.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc854.txt) def% User defined strings:/fmodstr (Fri Oct 05 00:00:00 1990) def/pagenumstr (9) def/user_header_p true def/user_header_left_str (RFC854) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 9 of 16) def%%EndPageSetupdo_header5 725 M(RFC 854 May 1983) s5 686 M( To counter this problem, the TELNET "Synch" mechanism is) s5 673 M( introduced. A Synch signal consists of a TCP Urgent notification,) s5 660 M( coupled with the TELNET command DATA MARK. The Urgent) s5 647 M( notification, which is not subject to the flow control pertaining) s5 634 M( to the TELNET connection, is used to invoke special handling of) s5 621 M( the data stream by the process which receives it. In this mode,) s5 608 M( the data stream is immediately scanned for "interesting" signals) s5 595 M( as defined below, discarding intervening data. The TELNET command) s5 582 M( DATA MARK \(DM\) is the synchronizing mark in the data stream which) s5 569 M( indicates that any special signal has already occurred and the) s5 556 M( recipient can return to normal processing of the data stream.) s5 530 M( The Synch is sent via the TCP send operation with the Urgent) s5 517 M( flag set and the DM as the last \(or only\) data octet.) s5 491 M( When several Synchs are sent in rapid succession, the Urgent) s5 478 M( notifications may be merged. It is not possible to count Urgents) s5 465 M( since the number received will be less than or equal the number) s5 452 M( sent. When in normal mode, a DM is a no operation; when in urgent) s5 439 M( mode, it signals the end of the urgent processing.) s5 413 M( If TCP indicates the end of Urgent data before the DM is found,) s5 400 M( TELNET should continue the special handling of the data stream) s5 387 M( until the DM is found.) s5 361 M( If TCP indicates more Urgent data after the DM is found, it can) s5 348 M( only be because of a subsequent Synch. TELNET should continue) s5 335 M( the special handling of the data stream until another DM is) s5 322 M( found.) s5 296 M( "Interesting" signals are defined to be: the TELNET standard) s5 283 M( representations of IP, AO, and AYT \(but not EC or EL\); the local) s5 270 M( analogs of these standard representations \(if any\); all other) s5 257 M( TELNET commands; other site-defined signals which can be acted on) s5 244 M( without delaying the scan of the data stream.) s5 218 M( Since one effect of the SYNCH mechanism is the discarding of) s5 205 M( essentially all characters \(except TELNET commands\) between the) s5 192 M( sender of the Synch and its recipient, this mechanism is specified) s5 179 M( as the standard way to clear the data path when that is desired.) s5 166 M( For example, if a user at a terminal causes an AO to be) s5 153 M( transmitted, the server which receives the AO \(if it provides that) s5 140 M( function at all\) should return a Synch to the user.) s5 114 M( Finally, just as the TCP Urgent notification is needed at the) s5 101 M( TELNET level as an out-of-band signal, so other protocols which) s5 88 M( make use of TELNET may require a TELNET command which can be) s5 75 M( viewed as an out-of-band signal at a different level.) s5 36 M(Postel & Reynolds [Page 9]) s_R%Page: (10) 10%BeginPageSetup_S% N-up sub-page 2/4278 -392 translate0.490859 dup scale/pagenum 10 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc854.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc854.txt) def% User defined strings:/fmodstr (Fri Oct 05 00:00:00 1990) def/pagenumstr (10) def/user_header_p true def/user_header_left_str (RFC854) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 10 of 16) def%%EndPageSetupdo_header5 725 M(RFC 854 May 1983) s5 686 M( By convention the sequence [IP, Synch] is to be used as such a) s5 673 M( signal. For example, suppose that some other protocol, which uses) s5 660 M( TELNET, defines the character string STOP analogously to the) s5 647 M( TELNET command AO. Imagine that a user of this protocol wishes a) s5 634 M( server to process the STOP string, but the connection is blocked) s5 621 M( because the server is processing other commands. The user should) s5 608 M( instruct his system to:) s5 582 M( 1. Send the TELNET IP character;) s5 556 M( 2. Send the TELNET SYNC sequence, that is:) s5 530 M( Send the Data Mark \(DM\) as the only character) s5 517 M( in a TCP urgent mode send operation.) s5 491 M( 3. Send the character string STOP; and) s5 465 M( 4. Send the other protocol's analog of the TELNET DM, if any.) s5 439 M( The user \(or process acting on his behalf\) must transmit the) s5 426 M( TELNET SYNCH sequence of step 2 above to ensure that the TELNET IP) s5 413 M( gets through to the server's TELNET interpreter.) s5 387 M( The Urgent should wake up the TELNET process; the IP should) s5 374 M( wake up the next higher level process.) s5 348 M( THE NVT PRINTER AND KEYBOARD) s5 322 M( The NVT printer has an unspecified carriage width and page length) s5 309 M( and can produce representations of all 95 USASCII graphics \(codes) s5 296 M( 32 through 126\). Of the 33 USASCII control codes \(0 through 31) s5 283 M( and 127\), and the 128 uncovered codes \(128 through 255\), the) s5 270 M( following have specified meaning to the NVT printer:) s5 244 M( NAME CODE MEANING) s5 218 M( NULL \(NUL\) 0 No Operation) s5 205 M( Line Feed \(LF\) 10 Moves the printer to the) s5 192 M( next print line, keeping the) s5 179 M( same horizontal position.) s5 166 M( Carriage Return \(CR\) 13 Moves the printer to the left) s5 153 M( margin of the current line.) s5 36 M(Postel & Reynolds [Page 10]) s_R%Page: (11) 11%BeginPageSetup_S% N-up sub-page 3/40 -794 translate0.490859 dup scale/pagenum 11 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc854.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc854.txt) def% User defined strings:/fmodstr (Fri Oct 05 00:00:00 1990) def/pagenumstr (11) def/user_header_p true def/user_header_left_str (RFC854) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 11 of 16) def%%EndPageSetupdo_header5 725 M(RFC 854 May 1983) s5 686 M( In addition, the following codes shall have defined, but not) s5 673 M( required, effects on the NVT printer. Neither end of a TELNET) s5 660 M( connection may assume that the other party will take, or will) s5 647 M( have taken, any particular action upon receipt or transmission) s5 634 M( of these:) s5 608 M( BELL \(BEL\) 7 Produces an audible or) s5 595 M( visible signal \(which does) s5 582 M( NOT move the print head\).) s5 569 M( Back Space \(BS\) 8 Moves the print head one) s5 556 M( character position towards) s5 543 M( the left margin.) s5 530 M( Horizontal Tab \(HT\) 9 Moves the printer to the) s5 517 M( next horizontal tab stop.) s5 504 M( It remains unspecified how) s5 491 M( either party determines or) s5 478 M( establishes where such tab) s5 465 M( stops are located.) s5 452 M( Vertical Tab \(VT\) 11 Moves the printer to the) s5 439 M( next vertical tab stop. It) s5 426 M( remains unspecified how) s5 413 M( either party determines or) s5 400 M( establishes where such tab) s5 387 M( stops are located.) s5 374 M( Form Feed \(FF\) 12 Moves the printer to the top) s5 361 M( of the next page, keeping) s5 348 M( the same horizontal position.) s5 322 M( All remaining codes do not cause the NVT printer to take any) s5 309 M( action.) s5 283 M( The sequence "CR LF", as defined, will cause the NVT to be) s5 270 M( positioned at the left margin of the next print line \(as would,) s5 257 M( for example, the sequence "LF CR"\). However, many systems and) s5 244 M( terminals do not treat CR and LF independently, and will have to) s5 231 M( go to some effort to simulate their effect. \(For example, some) s5 218 M( terminals do not have a CR independent of the LF, but on such) s5 205 M( terminals it may be possible to simulate a CR by backspacing.\)) s5 192 M( Therefore, the sequence "CR LF" must be treated as a single "new) s5 179 M( line" character and used whenever their combined action is) s5 166 M( intended; the sequence "CR NUL" must be used where a carriage) s5 153 M( return alone is actually desired; and the CR character must be) s5 140 M( avoided in other contexts. This rule gives assurance to systems) s5 127 M( which must decide whether to perform a "new line" function or a) s5 114 M( multiple-backspace that the TELNET stream contains a character) s5 101 M( following a CR that will allow a rational decision.) s5 75 M⌨️ 快捷键说明
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