ckcbwr.txt

C-Kermit源码。是使用串口/Modem和网络通讯的程序

cannot be included in a C string, since it is the C string terminator.

If you really want to output a backslash followed by a B, an L, or an N (as is
needed to configure certain modems, etc), use "output \\B".

In C-Kermit 6.1 or later, you can disarm and re-arm the special OUTPUT-command
escapes (\B, \L, and \N) with SET OUTPUT SPECIAL-ESCAPES { OFF, ON }.


(3) MULTIPLE SESSIONS

C-Kermit does not support multiple sessions.  When you SET LINE (or SET PORT,
same thing) to a new device, or SET HOST to a new host, the previous SET LINE
device or network host connection is closed, resulting in hangup of the modem
or termination of the network connection.  In windowing environments like
HP-VUE, NeXTSTEP, OS/2, etc, you can run separate copies of Kermit in different
windows to achieve multiple sessions.

To achieve multiple sessions through a single serial port (e.g. when dialing
up), you can install SLIP or PPP on your computer and then use C-Kermit's
TCP/IP support over the SLIP or PPP connection, assuming you also have
TCP/IP networking installed on your computer.

On UNIX systems that support the "term" program, you can establish a
connection to another UNIX system with C-Kermit and then achieve multiple
sessions using "term" client programs like trsh (see ckubwr.txt and the term
documentation for details).


(4) NETWORK COMMUNICATION

The most frequently asked question in many newsgroups is "Why does it take
such a loooong time to make a telnet connection to (or from) my (e.g.) Linux
PC?" (this applies to C-Kermit or to regular Telnet).  This question has
two answers, one of them specific to C-Kermit 7.0:

 1. Most telnet servers nowadays perform reverse DNS lookups on the client
    (for security and/or logging reasons).  If the Telnet client cannot be
    found by the local DNS server, the DNS request goes out to the Internet at
    large, and this can take quite some time.  The solution to this problem is
    to make sure that both client and host are registered in DNS.

 2. C-Kermit 7.0 strictly enforces Telnet protocol rules.  One such rule is
    that all negotiations must be responded to.  If C-Kermit sends a
    negotiation and the host does not respond, C-Kermit will wait a long time
    for the reply (in case the network is congested or the host is slow), but
    eventually will time out.  To eliminate the waits (and therefore risk
    possible protocol mismatches -- or worse --  between Telnet client and
    server), tell C-Kermit to SET TELNET WAIT OFF (or include the /NOWAIT
    switch with the TELNET command).

C-Kermit itself performs reverse DNS lookups unless you tell it not to.  This
is to allow C-Kermit to let you know which host it is actually connected to
in case you have made a connection to a "host pool" (multihomed host).  You
can disable C-Kermit's reverse DNS lookup with SET TCP REVERSE-DNS-LOOKUP OFF.

In multiuser operating systems such as UNIX and VMS, TCP/IP RLOGIN connections
are available only to privileged users, since "login" is a privileged socket.
And assuming you are allowed to use it in the first place, it is likely to
behave differently depending on what type of host you are rlogging in to, due
to technical reasons having to do with conflicting interpretations of RFC793
(Out-Of-Band Data) and Rlogin (RFC1122)...  "Specifically, the TCP urgent
pointer in BSD points to the byte after the urgent data byte, and an
RFC-compliant TCP urgent pointer points to the urgent data byte. As a result,
if an application sends urgent data from a BSD-compatible implementation to an
RFC-1122 compatible implementation then the receiver will read the wrong
urgent data byte (it will read the byte located after the correct byte in the
data stream as the urgent data byte)."  Rlogin requires the use of OOB data
while Telnet does not.  Therefore, it is possible for Telnet to work between
all systems while BSD and System V TCP/IP implementation are almost always a
bad mix.

On a TCP/IP TELNET connection, you should normally have PARITY set to NONE and
(except in VMS C-Kermit) FLOW-CONTROL also set to NONE.  If file transfer does
not work with these settings (for example, because the remote TELNET server
only gives a 7-bit data path), use SET PARITY SPACE.  Do not use SET PARITY
MARK, EVEN, or ODD on a TELNET connection -- it interferes with TELNET
protocol.

If echoing does not work right after connecting to a network host or after
dialing through a TCP/IP modem server, it probably means that the TELNET
server on the far end of the connection is executing the TELNET protocol
incorrectly.  After initially connecting and discovering incorrect echoing
(characters are echoed twice, or not at all), escape back, give the
appropriate SET DUPLEX command (FULL or HALF), and then CONNECT again.
For a consistently misbehaving connection, you can automate this process in
a macro or TAKE file.

TELNET sessions are treated just like serial communications sessions as far as
"terminal bytesize" and "command bytesize" are concerned.  If you need to view
and/or enter 8-bit characters during a TELNET session, you must tell C-Kermit
to SET TERMINAL BYTESIZE 8, SET COMMAND BYTESIZE 8, and SET PARITY NONE.

If you SET TERMINAL DEBUG ON or SET DEBUG SESSION (same thing), TELNET
protocol negotiations will be displayed on your screen.  But most of the
interesting negotiations happen at the time the SET HOST or TELNET command
is given, before CONNECT mode is entered, so you won't see them on your
screen.  However, you can still capture them in the debug log ("log debug").

C-Kermit version 6.0 has a new set of SET TCP commands, to control TCP-level
parameters, such as "keepalive" protocol (that allows C-Kermit to detect
more quickly and reliably when a connection is broken).  Use SHOW NET to see
their values and SET TCP to change them.


(5) THE SERVICES DIRECTORY

Is explained fully in "Using C-Kermit", 2nd Edition, Chapter 7.


(6) MODEMS AND DIALING

Warning: Some phone companies are eliminating the busy signal.  Instead,
they issue a voice message such as "press 1 to automatically redial until
the number answers, or...".  Obviously this is a disaster for modem calls.
If your service has this feature, there's nothing Kermit can do about it.
Your modem will respond with NO CARRIER rather than BUSY, and Kermit will
declare the call a failure, rather than trying to redial the same number.

The list of modem types supported by C-Kermit is obtained by typing:

  set modem type ?

at the C-Kermit> prompt.  Note that the ITU-T (V.25bis) modem type is
supported only in asynchronous mode, not synchronous (HDLC) mode -- there is
no support in C-Kermit for synchronous communication (except for SET NET X.25,
which is only available on certain platforms).

If a built-in modem type doesn't work for you, and the modem is a modern
high-speed (data compressing, error correcting) modem that uses the Hayes AT
command set, try:

  SET MODEM TYPE GENERIC-HIGH-SPEED

Modems can be used by C-Kermit only when they are visible as or through a
regular serial port device.  Note that certain modems can not be used in this
normal way on many kinds of computers: Winmodems, RPI modems, Controllerless
modems, the IBM Mwave, etc; all of these require special drivers that perform
some, most, or all of the modem's functions in software.  Such drivers are
generally NOT available in UNIX or other non-Windows (or non-OS/2, in the case
of the Mwave) platforms.

An important change in C-Kermit 6.0 is that when you give a SET MODEM TYPE
command to tell Kermit what kind of modem you have, Kermit also sets a number
of other modem-related parameters automatically from its internal modem
database.  Thus, the order in which you give modem-related commands is
significant, whereas in prior releases they could be given in any order.

In particular, MODEM SPEED-MATCHING is set according to whether the modem
is known to be capable of speed buffering.  SET MODEM TYPE HAYES-2400
automatically turns SPEED-MATCHING ON, because when the Hayes 2400 reports
a particular speed in its CONNECT message, that means its interface speed
has changed to that speed, and C-Kermit's must change accordingly if it is
to continue communicating.  This might cause some confusion if you use
"set modem type hayes" for dialing a more advanced type of modem.

The new default for flow control is "auto", meaning "do the right thing".
So (for example) if your version of C-Kermit supports SET FLOW RTS/CTS and
your modem also supports RTS/CTS, then Kermit will automatically set its
flow control to RTS/CTS *and* set modem's flow control to RTS/CTS too before
attempting to use the modem.

For this reason, don't assume that "set modem type hayes" should be used for
any modem that uses the Hayes AT command set.  "set modem type hayes" really
does mean Hayes 1200 or 2400, which in turn means no hardware flow control,
and no speed buffering.  This choice will rarely work with a modern high-speed
modem.


(7) DIALING HINTS AND TIPS

If you want to dial a number that starts with #, you'll need to quote the
"#" character (as \# or \{35}), since it is also a comment introducer:

  C-Kermit>dial #98765421-1-212-5551212   ; Looks like a comment
  ?You must specify a number to dial
  C-Kermit>dial \#98765421-1-212-5551212  ; Works OK

When using a dialing directory, remember what happens if a name is not found:

  C-Kermit>dial xyzcorp
  Lookup: "xyzcorp" - not found - dialing as given

This normally does no harm, but some modems might behave strangely when given
dial strings that contain certain letters.  For example, a certain German
modem treats any dial string that contains the letter "s" as a command to
fetch a number from its internal list, and replies OK to the ATD command,
which is normally not a valid response except for partial dialing.  To avoid
this situation, use:

  lookup xyzcorp
  if success dial

Remember: In many C-Kermit implementations (depending on the underlying
operating system -- mostly Windows, OS/2, and System-V-based UNIX versions,
and in C-Kermit 6.1, also VMS), you can't CONNECT to a modem and type the
modem's dialing command (like "ATDT7654321") manually, unless you first tell
C-Kermit to:

  SET CARRIER-WATCH OFF

This is because (in these implementations), the CONNECT command requires the
modem's Carrier Detect (CD) signal to be on, but the CD signal doesn't come on
until after dialing is complete.  This requirement is what allows C-Kermit to
pop back to its prompt automatically when the connection is hung up.  See the
description of SET CARRIER-WATCH in "Using C-Kermit".

Similarly, if your dialed connection drops when CARRIER-WATCH is set to AUTO
or ON, you can't CONNECT back to the (now disconnected) screen to see what
might have happened unless you first SET CARRIER-WATCH OFF.

Don't SET FLOW RTS/CTS if your modem is turned off, or if it is not presenting
the CTS signal.  Otherwise, the serial device driver might get stuck waiting
for this signal to appear.

The HANGUP command has no effect when C-Kermit is in remote mode.  This is
on purpose.  If C-Kermit could hang up its own controlling terminal, this
would (a) most likely leave behind zombie processes, and (b) pose a security
risk.

If you have a high-speed, error-correcting, data-compressing, speed-buffering
modem, you should fix the modem's interface speed as high as possible,
preferably (at least) four times higher than its maximum connection
(modulation) speed to allow compression to work at full advantage.  In this
type of setup, you must also have an effective means of flow control enabled
between C-Kermit and the modem, preferably hardware (RTS/CTS) flow control.
On platforms that do not support hardware flow control, it is usually possible
to select software flow control (Xon/Xoff), and C-Kermit will do its best to
set the modem for local Xon/Xoff flow control too (but then, of course,
Ctrl-S and Ctrl-Q characters can not be transmitted on the connection).

C-Kermit knows about a large number of modems, depending on how it was built
(type "set modem type ?" and "show features" for further info).  This
knowledge is imbedded in the SET MODEM and DIAL commands.  If you are having
trouble dialing your modem, SET DIAL DISPLAY ON to watch the dialing
interactions between C-Kermit and your modem.  Consult Chapters 3-4 of "Using
C-Kermit" (2nd Ed) for modem-dialing troubleshooting instructions.

If it takes your call longer to be completed than the timeout interval that
C-Kermit calculates, you can use the SET DIAL TIMEOUT command to override
C-Kermit's value.  But beware: the modem has its own timeout for completing
the call.  If it is a Hayes-like modem, C-Kermit adjusts the modem's value
too by setting register S7.  But the maximum value for S7 might be smaller
than the time you need!  In that case, C-Kermit sets S7 to 0, 255, or other
(modem-specific) value to signify "no timeout".

WARNING: Certain modems might have a maximum dial timeout shorter than what
Kermit expects it to be.  If Kermit attempts to set register S7 to a value
higher than your modem's maximum, the modem will say "ERROR" and you will get
a "Failure to initialize modem" error.  In that case, use SET DIAL TIMEOUT to
override C-Kermit's calculation of the timeout value with the highest value
that is legal for your modem, e.g. 60.

If you DIAL a modem, disconnect, then SET HOST or TELNET, and then HANGUP,
Kermit sends the modem's hangup command, such as "+++ATHO".  There is no good
way to avoid this, because this case can't reliably be distinguished from the
case in which the user does SET HOST <terminal-server>, SET MODEM TYPE <name>,
DIAL.  In both cases we have a valid modem type selected and we have a network
connection.  If you want to DIAL and then later make a regular network
connection, you will have to SET MODEM TYPE NONE or SET MODEM HANGUP RS232 to
avoid this phenomenon.

The SET MODEM KERMIT-SPOOF command works only for Telebit and US Robotics
modem types; it is OFF by default.  You may wish to experiment with large
packets (1K or greater) and various window sizes with spoofing disabled in the
modem.  In most situations the transfer rates achieved by Kermit with sliding
windows and long packets are better than with protocol spoofing turned on.
Also, attribute (A) packets are not passed by Telebit modems with spoofing
enabled so if they are desired spoofing must be turned off.

Some modems have a feature called adaptive dialing.  When they are told to
dial a number using Tone dialing, they check to make sure that dialtone has
gone away after dialing the first digit.  If it has not, the modem assumes the
phone line does not accept Tone dialing and so switches to Pulse.  When
dialing out from a PBX, there is almost always a secondary dialtone.
Typically you take the phone off-hook, get the PBX dialtone, dial "9" to get
an outside line, and then get the phone company's dialtone.  In a situation
like this, you need to tell the modem to expect the secondary dialtone.  On
Hayes and compatible modems, this is done by putting a "W" in the dial string
at the appropriate place.  For example, to dial 9 for an outside line, and
then 7654321, use ATDT9W7654321.  In Kermit 95, this is accomplished with:

  SET PBX-OUTSIDE-PREFIX 9W

(replace "9" with whatever your PBX's outside-line prefix is).

DEC modems...  Reportedly, these don't work right when connected to a DEC
terminal server -- result codes are never reported (on the other hand, this
might be a modem configuration problem).  Dialing "by hand", "blind" still
works.  Also, reportedly "For people who do have DEC modems directly connected
to DEC computers the DF03, DF100-series, and DF200-series modem dialers should
work.  The only thing that is not straightforward is that the DF124-CA,
DF124-CM modems must use the DF200-series since they speak Digital Modem
Command Language (DMCL) and AT commands.  The Digital Scholar Plus is a DF242
so it uses the DF200-series."

If C-Kermit's dialing methods are insufficient for your purposes, you can
write a C-Kermit script program to do the dialing.

(7.1) DIALING AND FLOW CONTROL