With the TELNET software in TCP/IP Services, you can log in to a remote internet system. This is called establishing a TELNET session. Your terminal appears to be attached directly to the remote system.

You can establish a TELNET session with a host that uses IBM 3270 model terminals (TN3270).

Note that you can also use RLOGIN to log in to remote internet hosts. However, RLOGIN does not have the ability to manage a 3270 session. To determine the best remote login service for your needs, see Section 1.1.2. For more information about RLOGIN, see Chapter 3.

The following table lists the TELNET/TN3270 network terminal services and the sections that explain how to use them.

Capability	Section
Use either DCL or UNIX command syntax.	4.1
Establish a network terminal session with any other host that uses TCP/IP as a transport.	4.3
Log all terminal output to a file.	4.5
Toggle between the remote host and the local TELNET prompt.	4.7
Suspend TELNET/TN3270 to spawn a subprocess at the DCL prompt.	4.8
Establish multiple TELNET sessions.	4.9
Toggle between open sessions.	4.9.1
Customize the way TELNET interprets control characters, sends and receives transmissions, and displays processing on your terminal.	4.6.2 4.10
Send commands to the remote host that affect processing of commands you have entered.	4.11
Run IBM 3270 model terminal emulation (TN3270).	4.12
Record a TN3270 screen's contents.	4.12.5

To use the network terminal services, you need the following:

• A user account on the remote host also running TELNET
• A user account on the OpenVMS system that runs TCP/IP Services

To use TELNET, enter the commands summarized in Table 4-1. (For complete command descriptions, see Section 4.13.)

Table 4-1 TELNET/TN3270 Commands Summary

DCL Style	UNIX Style	Description
Starting (at the DCL Prompt)
TELNET	telnet	Invokes TELNET.
TELNET remote_host	telnet remote_host	Invokes TELNET and establishes a connection to a remote host.
TN3270	N/A	Invokes TELNET and TN3270.
TN3270 remote_host	N/A	Invokes TELNET, runs TN3270, and establishes a connection to a remote host.
Getting In and Out of Sessions
CONNECT	open	Establishes a connection between the local host and a remote host.
CREATE_SESSION	N/A	Establishes a pseudodevice and connects it to a remote listener port.
DELETE_SESSION	N/A	Deletes a pseudodevice created by the CREATE_SESSION command.
DISCONNECT	close	Terminates your current session.
Ctrl/]	Ctrl/]	Takes you from the remote host back to the TELNET prompt.
EXIT	quit	Closes open connections and exits from TELNET.
HELP	help ?	Invokes online help.
RESUME	[Return]	Resumes an open connection.
SPAWN	z	Suspends your TELNET session and takes you to the DCL prompt.
Customizing the TELNET Environment
DISABLE AUTOFLUSH	toggle autoflush	Disables the automatic flushing of output when interrupt characters are sent.
DISABLE AUTOSYNCH	toggle autosynch	Disables the automatic sending of interrupt characters in urgent mode.
DISABLE BINARY	toggle binary	Disables transmission in binary mode.
DISABLE CRLF	toggle crlf	Disables the sending of carriage returns as Return LF.
DISABLE CRMOD	toggle crmod	Disables the mapping of received carriage returns.
DISABLE DEBUG	toggle netdata	Disables the display of data flow information in hexadecimal.
DISABLE LOCAL_CHARS	toggle localchars	Disables the interpretation of certain control characters by your local TELNET client and passes them to the remote TELNET server.
DISABLE OPTIONS_VIEW	toggle options	Disables the display of option negotiations between the client and server.
ENABLE AUTOFLUSH	toggle autoflush	Enables the automatic flushing of output when interrupt characters are sent.
ENABLE AUTOSYNCH	toggle autosynch	Enables the automatic sending of interrupt characters in urgent mode.
ENABLE BINARY	toggle binary	Enables transmission in binary mode.
ENABLE CRLF	toggle crlf	Enables the sending of carriage returns as Return LF.
ENABLE CRMOD	toggle crmod	Enables the mapping of received carriage returns.
ENABLE DEBUG	toggle netdata	Enables the display of data flow information in hexadecimal.
ENABLE LOCAL_CHARS	toggle localchars	Enables the interpretation of certain control characters by your local TELNET client and prohibits them from being passed to the remote TELNET server.
ENABLE OPTIONS_VIEW	toggle options	Enables the display of option negotiations between the client and server.
SHOW DEVICE		Displays the current devices.
SHOW PARAMETERS	display	Displays the current parameter settings.
SHOW SESSION		Displays the current sessions.
SHOW STATUS	status	Displays the current status.
SET ECHO	set echo	Sets the echo character to the specified character.
SET ERASE	set erase	Sets the erase character to the specified character.
SET ESCAPE	set escape	Sets the escape character to the specified character.
SET FLUSHOUTPUT	set flushoutput	Sets the flush output character to the specified character.
SET INTERRUPT	set interrupt	Sets the interrupt character to the specified character.
SET KILL	set kill	Sets the kill character to the specified character.
SET MODE	mode	Sets the transmission mode to character or line.
SET QUIT	set quit	Sets the quit character (an alternate interrupt character) to the specified character.
SET TERMINAL		Sets the terminal type to the specified model.
Sending Commands to the Remote Host
SEND AO	send ao	Sends the Abort Output command.
SEND AYT	send ayt	Sends the Are You There command, testing the path to the remote application and eliciting connection status information from the remote host.
SEND BRK	send brk	Sends the Break command.
SEND EC	send ec	Sends the Erase Character command.
SEND EL	send el	Sends the Erase Line command.
SEND GA	send ga	Sends the Go Ahead command.
SEND IP	send ip	Sends the Interrupt character.
SEND NOP	send nop	Sends the No Operation command to test whether data can be sent to the remote host, eliciting an error if the connection is not open.
SEND SYNCH	send synch	Sends the Synchronize character.

4.1 Typing TELNET/TN3270 Commands

Use the following rules when you enter a TELNET command line.

4.1.1 DCL and UNIX Command Formats

With the TELNET command and most of the commands entered at the TELNET prompt, you can use either DCL or UNIX syntax. For example, the following two commands produce the same results:

$ TELNET TELNET> SHOW PARAMETERS

$ TELNET TELNET> DISPLAY

4.1.2 Quotation Marks

Do not include quotation marks on the command line, as shown in the following examples:

• The TELNET command line:

  $ TELNET CENTRAL

• The TN3270 command line:

  $ TN3270 CENTRAL

• Commands at the TELNET prompt:

  TELNET> CONNECT CENTRAL

The following example connects to UNIX host migain and sets a terminal type with the /TERMINAL_TYPE qualifier. No quotation marks are needed to pass a terminal type to migain in lowercase, as demonstrated with the remote host's printenv command.

$ TELNET MIGAIN /TERMINAL_TYPE=vt300 %TELNET-I-Trying, Trying ...11.90.208.56 %TELNET-I-SESSION, Session 01, host migain, port 23 -TELNET-I-Escape, Escape character is '^]' Hello from UNIX host migain login: root Password:... . . . migain# printenv TERM=vt300 HOME=/ SHELL=/bin/csh USER=root PATH=/bin:/usr/bin:/usr/ucb:/etc:/usr/etc:. LOGNAME=root PWD=/ migain#

4.2 Obtaining Online Help

You can obtain online help for the TELNET and TN3270 services by entering any of the following commands at the DCL prompt:

$ HELP TELNET $ HELP TN3270 $ HELP TCPIP_SERVICES TELNET

You can also enter the HELP command at the TELNET prompt:

TELNET> HELP

4.3 Starting TELNET and TN3270

You can start a TELNET or TN3270 session with a remote host (also called establishing a connection and opening a connection) in one of the following ways:

• At the DCL prompt, enter either the TELNET or the TN3270 command and specify a remote host.
• At the DCL prompt, enter either the TELNET or the TN3270 command with no parameters. At the TELNET or TN3270 prompt that appears, enter the CONNECT or open command, and specify a remote host.
• Invoke and use TELNET or TN3270 from a command procedure (see Section 4.6.1).

The following example shows three ways to establish a connection interactively:

$ TELNET CENTRAL /TERMINAL_TYPE=IBM-3278-2 $ TELNET TELNET> CONNECT CENTRAL 23 VT200 $ TN3270 CENTRAL /TERMINAL_TYPE=IBM-3278-3

You can invoke TELNET or TN3270 and, without connecting to a remote host first, enter certain commands that customize the sessions and display parameters or status, as shown in the following example:

$ TELNET TELNET> SHOW STATUS %TELNET-E-NOSESSION, No active session Escape character: '^]' TELNET>SET DEVICE TERMINAL=VT300 TELNET> OPEN GALAXY %TELNET-I-TRYING, Trying ... 1.20.208.10 %TELNET-I-SESSION, Session 01, host galaxy, port 23 -TELNET-I-ESCAPE, Escape character is ^] Compaq Tru64 UNIX (galaxy.udb.com) (ttyp5) login:

4.4 Exiting TELNET and TN3270

You can end a TELNET or TN3270 session (close the connection) in one of the following ways:

• At the remote host's system prompt, log out.
• At the remote host's system prompt, return to the TELNET or TN3270 prompt and disconnect the session, as follows:
  1. At the remote host's system prompt, press the TELNET/TN3270 escape character (Ctrl/] is the default).
  2. At the TELNET or TN3270 prompt, enter either the DISCONNECT or the close command.

The following example shows two ways to close connections:

% logout %TELNET-S-REMCLOSED, Remote connection closed -TELNET-I-SESSION, Session 01, host galaxy, port 23 TELNET> TELNET> EXIT $ % [Ctrl/]] (characters not echoed) TELNET> DISCONNECT galaxy.udp.com> TELNET> DISCONNECT %TELNET-S-LCLCLOSED, Local connection closed -TELNET-I-SESSION, Session 01, host galaxy, port 23 TELNET>

4.5 Keeping a Log of Your TELNET Session

To keep a log of your TELNET session, use the /LOG_FILE qualifier. (You cannot use this qualifier with a TN3270 session.)

The following example establishes a TELNET connection to node central , sets the terminal type to VT200, and logs all session output to the file CENT.LOG in your current directory.

$ TELNET/LOG_FILE=CENT.LOG/TERMINAL_TYPE=VT200 CENTRAL

4.6 Command Procedures

With DCL command files, you can start TELNET and TN3270 sessions (see Section 4.6.1) and customize the TELNET/TN3270 environment (see Section 4.6.2).

4.6.1 Starting TELNET/TN3270

You can create a command procedure containing the DCL commands DEFINE and TELNET (or TN3270) commands.

The following shows an example of a TELNET command procedure:

$! My TELNET startup command file, START_TELNET.COM. $! $! This command procedure establishes a TELNET session $! with UNIX host central. $! $ DEFINE /USER_MODE SYS$INPUT TT: $ TELNET CENTRAL

4.6.2 Initialization Command Files

You can create initialization command files to customize your TELNET/TN3270 sessions with SET, ENABLE, and DISABLE commands. These command files:

• Are optional. They eliminate the need to enter individual TELNET commands.
• Have the following requirements:
  • Location: Your login directory
  • Name: TELNETINIT.INI
  • Format: one command per line
• Run automatically when you invoke TELNET or TN3270.
• Let you specify the logical name, TELNETINIT, to point to an initialization file.

The following example shows a TELNET initialization command procedure:

! This file, TELNETINIT.INI, sets my TELNET parameters ! the way I like them. ! DISABLE AUTOFLUSH ENABLE BINARY ENABLE DEBUG SET DEVICE /TERMINAL=VT300 SET ESCAPE "^p"

4.7 Toggling Between the Remote Host and Local TELNET/TN3270

During a session with a remote host, you can toggle between the local TELNET or TN3270 process and the connected host. For example, at the TELNET prompt, you might want to display status, modify a TELNET parameter, or spawn a DCL subprocess.

• To return to the local TELNET or TN3270 prompt (TELNET command mode), enter the TELNET escape sequence (the default is Ctrl/]) at the remote host's prompt (TELNET input mode).
• To resume your session with the remote host, enter one of the following at the TELNET (or TN3270) prompt.

  TELNET> [Return]

  
  or

  TELNET> RESUME

  
  or

  TELNET> RESUME n

  
  where n is the number of the session to which you want to return.

• To change the default escape sequence, enter the following at the TELNET (or TN3270) prompt:

  TELNET> SET ESCAPE "^escape_character"

The following example toggles between remote UNIX host biway and the local OpenVMS system.

biway> [Ctrl/]] (characters not echoed) TELNET> SHOW STATUS Session 1 Active Host biway Port 23 Operating Mode: Character-at-a-time Escape character: '^]' Options: Echo - Remote Terminal Type - Local Terminal Type - VT300 Suppress Go Ahead - Local Suppress Go Ahead - Remote Terminal Dataoveruns: 0 Suspended Network I/Os: 0 . . . TELNET> [Return] biway>

In the next example, user BENTLEY, working at OpenVMS node EAGLE, uses TELNET to do the following:

1. Establish a connection to UNIX host fern .
2. Return to the local TELNET prompt.
3. Display status.
4. Establish a connection to host gannet .
5. Return to the TELNET prompt.
6. Display status.
7. Connect to sands . But sands closes the connection because BENTLEY incorrectly enters the password three times.
8. Try to resume the session with gannet . However, RESUME without specifying a session number fails:
   • With multiple sessions, RESUME's default is the "active" session, the one with the most recently opened connection.
   • The host to which BENTLEY connected most recently is sands . However, because BENTLEY incorrectly typed the password during login, sands closed the TELNET connection and displayed the following:

     No current session.

   • Because no connection is active (or current), BENTLEY must specify a session number on the RESUME command line.

$ TELNET FERN . . . fern> [Ctrl/]] (characters not echoed) TELNET> SHOW STATUS Session 1 Active Host FERN . . . TELNET> CONNECT GANNET . . . gannet> [Ctrl/]] (characters not echoed) TELNET> SHOW STATUS Session 2 Active Host GANNET Operating Mode: Character-at-a-time Escape character: '^]' . . . Session 1 Waiting Host FERN TELNET> CONNECT SANDS %TELNET-I-Trying, Trying...11.18.222.95 %TELNET-I-SESSION, Session 03, host sands, port 23 -TELNET-I-Escape, Escape character is '^]'. . . . Username: BENTLEY Password: User authorization failure Username: BENTLEY Password: User authorization failure Username: BENTLEY Password: User authorization failure Remote connection closed TELNET> RESUME No current session TELNET> SHOW STATUS Session 1 Waiting Host FERN Session 2 Waiting Host GANNET . . . TELNET> RESUME 2 gannet> [Ctrl/]] (characters not echoed) TELNET> SHOW STATUS Session 2 Active Host GANNET Operating Mode: Character-at-a-time Escape character: '^]' . . . Session 1 Waiting Host FERN TELNET>