Defining the Conversation on the Dial-up Link
The dial-out machine and its remote peer communicate across the PPP link by negotiating
and exchanging various instructions. When configuring a dial-out machine, you need to determine what instructions
are required by the local and remote modems. Then you create a file that
is called a chat script that contains these instructions. This section discusses information about configuring
modems and creating chat scripts.
Contents of the Chat Script
Each remote peer that the dial-out machine needs to connect to probably requires its
own chat script.
Note - Chat scripts are typically used only on dial-up links. Leased-line links do not use
chat scripts unless the link includes an asynchronous interface that requires startup configuration.
The contents of the chat script are determined by the requirements of your modem
model or ISDN TA, and the remote peer. These contents appear as a set
of expect-send strings. The dial-out machine and its remote peers exchange the
strings as part of the communications initiation process.
An expect string contains characters that the dial-out host machine expects to receive from the
remote peer to initiate conversation. A send string contains characters that the dial-out machine sends
to the remote peer after receiving the expect string.
Information in the chat script usually includes the following:
Modem commands, often referred to as AT commands, which enable the modem to transmit data over the telephone
Phone number of the target peer
This phone number might be the number that is required by your ISP, or a dial-in server at a corporate site, or an individual machine.
Time-out value, if required
Login sequence that is expected from the remote peer
Login sequence that is sent by the dial-out machine
Chat Script Examples
This section contains chat scripts that you can use as a reference for creating
your own chat scripts. The modem manufacturer's guide and information from your ISP and
other target hosts contain chat requirements for the modem and your target peers. In
addition, numerous PPP web sites have sample chat scripts.
Basic Modem Chat Script
The following is a basic chat script that you can use as a
template for creating your own chat scripts.
ABORT BUSY
ABORT 'NO CARRIER'
REPORT CONNECT
TIMEOUT 10
"" AT&F1M0&M5S2=255
SAY "Calling myserver\n"
TIMEOUT 60
OK "ATDT1-123-555-1212"
ogin: pppuser
ssword: \q\U
% pppd
The next table describes the contents of the chat script.
Script Contents |
Explanation |
|---|
ABORT BUSY |
Abort transmission if
the modem receives this message from the opposite peer. |
ABORT 'NO CARRIER' |
Abort transmission if the modem reports ABORT 'NO CARRIER'
when dialing. The cause for this message is usually a dialing or modem negotiation failure. |
REPORT CONNECT |
Gather
the CONNECT string from the modem. Print the string. |
TIMEOUT 10 |
Set initial timeout to 10
seconds. The modem's response should be immediate. |
"" AT&F1M0&M5S2=255 |
M0 – Turn off the speaker during connect. &M5
– Make the modem require error control. S2=255 – Disable the TIES “+++” break sequence. |
SAY "Calling myserver\n" |
Display
the message Calling myserver on the local machine. |
TIMEOUT 60 |
Reset the timeout to 60 seconds to
allow more time for link negotiation. |
OK "ATDT1-123-555-1212" |
Call the remote peer by using the phone
number 123-555-1212. |
ogin: pppuser |
Log in to the peer by using UNIX-style login. Supply the user name
pppuser. |
ssword: \q\U |
\q – Do not log if debugging with the -v option. \U – Insert in
this location the contents of the string that follows -U, which is specified on
the command line. Usually, the string contains the password. |
% pppd |
Wait for the %
shell prompt, and run the pppd command. |
/etc/ppp/myisp-chat.tmpl Chat Script Template
Solaris PPP 4.0 includes the /etc/ppp/myisp-chat.tmpl, which you can modify for use at
your site. /etc/ppp/myisp-chat.tmpl is similar to the basic modem chat script except that the template
does not include a login sequence.
ABORT BUSY
ABORT 'NO CARRIER'
REPORT CONNECT
TIMEOUT 10
"" "AT&F1"
OK "AT&C1&D2"
SAY "Calling myisp\n"
TIMEOUT 60
OK "ATDT1-123-555-1212"
CONNECT \c
Script Contents |
Explanation |
|---|
ABORT BUSY |
Abort transmission if the modem receives this message
from the opposite peer. |
ABORT 'NO CARRIER |
Abort transmission if the modem reports ABORT 'NO CARRIER' when dialing. The cause for
this message is usually a dialing or modem negotiation failure. |
REPORT CONNECT |
Gather the CONNECT string from the
modem. Print the string. |
TIMEOUT 10 |
Set initial timeout to 10 seconds. The modem's response should
be immediate. |
"" "AT&F1" |
Reset the modem to factory defaults. |
OK "AT&C1&D2" |
Reset the modem so that, for &C1,
DCD from the modem follows carrier. If the remote side hangs up the phone
for some reason, then the DCD drops. For &D2, DTR high-to-low transition causes
the modem to go “on-hook” or hang up. |
SAY "Calling myisp\n" |
Display the message “Calling myisp” on
the local machine. |
TIMEOUT 60 |
Reset the timeout to 60 seconds to allow more time for
link negotiation. |
OK "ATDT1-123-555-1212" |
Call the remote peer by using the phone number 123-555-1212. |
CONNECT \c |
Wait for the
CONNECT message from the opposite peer's modem. |
Modem Chat Script for Calling an ISP
Use the next chat script as a template for calling an ISP from a
dial-out machine with a U.S. Robotics Courier modem.
ABORT BUSY
ABORT 'NO CARRIER'
REPORT CONNECT
TIMEOUT 10
"" AT&F1M0&M5S2=255
SAY "Calling myisp\n"
TIMEOUT 60
OK "ATDT1-123-555-1212"
CONNECT \c
\r \d\c
SAY "Connected; running PPP\n"
The following table describes the contents of the chat script.
Script Contents |
Explanation |
|---|
ABORT BUSY |
Abort transmission if
the modem receives this message from the opposite peer. |
ABORT 'NO CARRIER' |
Abort transmission if the modem receives this
message from the opposite peer. |
REPORT CONNECT |
Gather the CONNECT string from the modem. Print the
string. |
TIMEOUT 10 |
Set initial timeout to 10 seconds. The modem's response should be immediate. |
"" AT&F1M0M0M0M0&M5S2=255 |
M0 – Turn
off the speaker during connect. &M5 – Make the modem require error control. S2=255
– Disable the TIES “+++” break sequence. |
SAY "Calling myisp\n" |
Display the message Calling myisp on the local machine. |
TIMEOUT 60 |
Reset
the timeout to 60 seconds to allow more time for link negotiation. |
OK "ATDT1-123-555-1212" |
Call the
remote peer by using the phone number 123-555-1212. |
CONNECT \c |
Wait for the CONNECT message from the
opposite peer's modem. |
\r \d\c |
Wait until the end of the CONNECT message. |
SAY “Connected; running PPP\n” |
Display
the informative message Connected; running PPP on the local machine. |
Basic Chat Script Enhanced for a UNIX-Style Login
The next chat script is a basic script that is enhanced for calling a
remote Solaris peer or other UNIX-type peer. This chat script is used in
How to Create the Instructions for Calling a Peer.
SAY "Calling the peer\n"
TIMEOUT 10
ABORT BUSY
ABORT 'NO CARRIER'
ABORT ERROR
REPORT CONNECT
"" AT&F1&M5S2=255
TIMEOUT 60
OK ATDT1-123-555-1234
CONNECT \c
SAY "Connected; logging in.\n"
TIMEOUT 5
ogin:--ogin: pppuser
TIMEOUT 20
ABORT 'ogin incorrect'
ssword: \qmypassword
"% " \c
SAY "Logged in. Starting PPP on peer system.\n"
ABORT 'not found'
"" "exec pppd"
~ \cThe following table explains the parameters of the chat script.
Script Contents |
Explanation |
|---|
TIMEOUT 10 |
Set initial timeout
to 10 seconds. The modem's response should be immediate. |
ABORT BUSY |
Abort transmission if the modem receives
this message from the opposite peer. |
ABORT 'NO CARRIER' |
Abort transmission if the modem receives this message from
the opposite peer. |
ABORT ERROR |
Abort transmission if the modem receives this message from the opposite peer. |
REPORT CONNECT |
Gather the
CONNECT string from the modem. Print the string. |
"" AT&F1&M5S2=255 |
&M5 – Make the modem require error
control. S2=255 – Disable the TIES “+++” break sequence. |
TIMEOUT 60 |
Reset the timeout to 60 seconds to
allow more time for link negotiation. |
OK ATDT1-123-555-1234 |
Call the remote peer by using the phone
number 123-555-1212. |
CONNECT \c |
Wait for the CONNECT message from the opposite peer's modem. |
SAY "Connected; logging in.\n" |
Display the informative
message Connected; logging in to give the user status. |
TIMEOUT 5 |
Change the timeout to enable quick display of
the login prompt. |
ogin:--ogin: pppuser |
Wait for the login prompt. If the prompt is not received,
send a RETURN and wait. Then, send the user name pppuser to the peer. The
sequence that follows is referred to by most ISPs as the PAP login.
However, the PAP login is not related in any way to PAP authentication. |
TIMEOUT 20 |
Change
the timeout to 20 seconds to allow for slow password verification. |
ssword: \qmysecrethere |
Wait for the
password prompt from the peer. When the prompt is received, send the password \qmysecrethere.
The \q prevents the password from being written to the system log files. |
"% " \c |
Wait for
a shell prompt from the peer. The chat script uses the C shell. Change
this value if the user prefers to log in with a different shell. |
SAY "Logged in. Starting PPP on peer system.\n" |
Display the
informative message Logged in. Starting PPP on peer system to give the user status. |
ABORT 'not found' |
Abort the transmission if the shell encounters
errors. |
"" "exec pppd" |
Start pppd on the peer. |
~ \c |
Wait for PPP to start on the peer. |
Starting PPP right after the CONNECT \c is often called a PAP login by ISPs, though
the PAP login is actually not part of PAP authentication.
The phrase ogin:--ogin: pppuser instructs the modem to send the user name pppuser in response
to the login prompt from the dial-in server. pppuser is a special PPP
user account name that was created for remote user1 on the dial-in server. For
instructions about creating PPP user accounts on a dial-in server, refer to How to Configure Users of the Dial-in Server.
Chat Script for External ISDN TA
The following chat script is for calling from a dial-out machine with a ZyXEL
omni.net. ISDN TA.
SAY "Calling the peer\n"
TIMEOUT 10
ABORT BUSY
ABORT 'NO CARRIER'
ABORT ERROR
REPORT CONNECT
"" AT&FB40S83.7=1&K44&J3X7S61.3=1S0=0S2=255
OK ATDI18882638234
CONNECT \c
\r \d\c
SAY "Connected; running PPP\n"The following table explains the parameters of the chat script.
Script Contents |
Explanation |
|---|
SAY "Calling the peer" |
Display this message
on the screen of the dial-out machine. |
TIMEOUT 10 |
Set the initial timeout to 10 seconds. |
ABORT BUSY |
Abort transmission
if the modem receives this message from the opposite peer. |
ABORT 'NO CARRIER' |
Abort transmission if the modem receives
this message from the opposite peer. |
ABORT ERROR |
Abort transmission if the modem receives this message from
the opposite peer. |
REPORT CONNECT |
Gather the CONNECT string from the modem. Print the string. |
"" AT&FB40S83.7=1&K44&J3X7S61.3=1S0=0S2=255 |
The letters
in this line have the following meaning:
&F – Use factory default B40 – Do asynchronous PPP conversion S83.7=1 – Use data over speech bearer &K44 – Enable CCP compression &J3 – Enable MP X7 – Report DCE side rates S61.3=1 – Use packet fragmentation S0=0 – No auto answer S2=255 – Disable TIES escape
|
OK ATDI18882638234 |
Make an ISDN call. For multilink, the second
call is placed to the same telephone number, which is normally what is required
by most ISPs. If the remote peer requires a different second phone number, append
“+nnnn.”. nnnn represents the second phone number. |
CONNECT \c |
Wait for the CONNECT message from the
opposite peer's modem. |
\r \d\c |
Wait until the end of the CONNECT message. |
SAY "Connected; running PPP\n" |
Display this message on
the screen of the dial-out machine. |
Refer to the chat(1M) man page for descriptions of options and other detailed information
about the chat script. For an explanation of expect-send strings, refer to Chat-Script Field in /etc/uucp/Systems File.
For More Chat Script Examples
A number of web sites offer sample chat scripts and assistance in creating the
chat scripts. For example, see http://ppp.samba.org/ppp/index.html.
Invoking the Chat Script
You call chat scripts by using the connect option. You can use connect "chat ..." in
any PPP configuration file or on the command line.
Chat scripts are not executable, but the program that is invoked by connect
must be executable. You might use the chat utility as the program to be
invoked by connect. In this instance, if you store the chat script in
an external file through the -f option, then your chat script file is not executable.
The chat program that is described in chat(1m) executes the actual chat script. The
pppd daemon invokes the chat program whenever pppd encounters the connect "chat ..." option.
Note - You can use any external program, such as Perl or Tcl, to create
advanced chat scripts. Solaris PPP 4.0 provides the chat utility as a convenience.
How to Invoke a Chat Script (Task)
- Create the chat script as an ASCII file.
- Invoke the chat script in any PPP configuration file by using the following syntax:
connect 'chat -f /etc/ppp/chatfile'
The -f flag indicates that a file name is to follow. /etc/ppp/chatfile represents the
name of the chat file.
- Give read permission for the external chat file to the user who runs
the pppd command.
Caution - The chat program always runs with the user's privileges, even if the connect 'chat ...' option is
invoked from a privileged source. Thus, a separate chat file that is read with
the -f option must be readable by the invoking user. This privilege can be
a security problem if the chat script contains passwords or other sensitive information.
Example 22-1 Inline Chat Script
You can place the entire chat script conversation on a single line, similar to
the following:
connect 'chat "" "AT&F1" OK ATDT5551212 CONNECT "\c"'
The complete chat script follows the chat keyword. The script terminates with "\c"'.
You use this form in any PPP configuration file or on the command line
as an argument to pppd.
More Information
Chat Script in an External File
If the chat script that is needed for a particular peer is long
or complicated, consider creating the script as a separate file. External chat files are easy
to maintain and to document. You can add comments to the chat file by
preceding the comments with the hash (#) sign.
The procedure How to Create the Instructions for Calling a Peer shows the use of a chat script that is contained
in an external file.
Creating a Chat File That Is Executable
You can create a chat file that is an executable script to be run
automatically when the dial-up link is initiated. Thus, you can run additional commands during
link initiation, such as stty for parity settings, besides the commands that are contained in
a traditional chat script.
This executable chat script logs in to an old-style UNIX system that requires 7
bits with even parity. The system then changes to 8 bits with no
parity when running PPP.
#!/bin/sh
chat "" "AT&F1" OK "ATDT555-1212" CONNECT "\c"
stty evenp
chat ogin: pppuser ssword: "\q\U" % "exec pppd"
stty -evenp
How to Create an Executable Chat Program
- Use your text editor to create an executable chat program, such as the previous example.
- Make the chat program executable.
# chmod +x /etc/ppp/chatprogram
- Invoke the chat program.
connect /etc/ppp/chatprogram
Chat programs do not have to be located within the /etc/ppp file system. You
can store chat programs in any location.