Mike Farrell writes:
>For once and all somebody please describe the proper way to
>configure a modem (AT compatible) and (any speed) connected
>to a DTC port. This includes port configuration and modem
>configuration. It appears there are quite a number of us out there
>with modem connection problems.
>Humbly!
Well, given that constraint -- and with all the humility I can muster, please
allow me to say the following:
1. Hayes Compatible Modems
It is important to understand that not all modems that use the "AT" command
are Hayes-compatible. Some modem manufacturers, such as USRobotics, MultiTech
and Racal, do their best to be non-Hayes compatible -- and then hide that
fact using advertising phrases such as "uses the popular AT command set".
These companies may start their commands with "AT", but they have their own
command sets and their own encoding mechanisms -- and their own agendas. You
have to read their advertising carefully to decide whether or not the modem
you will be purchasing is truly Hayes-compatible or not. Luckily, most modems
nowadays are 100% Hayes compatible.
The following configuration information applies only to true Hayes-compatible
modems (Hayes, Boca, Supra, Practical Peripherals, Magnum, Zoom, Intel,
etc.). However, it is also important to understand that there are two
28.8Kbaud modem standards, V.FC and V.34. The two transmission standards are
incompatible and will not talk to each other. V.FC was invented by Rockwell
and was first to market. V.34 was slower to arrive, but it has been certified
as the standard by the ITU and is now the common standard. If you purchase a
28.8Kbaud modem in preference to 14.4K (and you should), you will want to
make sure that the modem is minimally V.34, and better yet, both V.34 and
V.FC compatible.
We have now bought and configured Hayes-compatible modems for approx. 200 of
our North American customers. We've used a variety of brands (Boca, Hayes,
Magnum, and Supra primarily). I have been equally satisified with all of
them. Do not let price be a consideration. In the last five years, modems
have gotten cheap, reliable (and unfortunately, a little complicated).
The new, "cheap" Hayes modems are basically compatible with every modem ever
manufactured. The only pain that you may experience is that you will not
achieve maximum speed, data compression, or error correction with an older or
non-standard modem. But some common speed between the two modems is bound to
exist and allow you to make a connection. If an odd modem dials in, or you
dial into an odd modem, the first thing the modems do is negotiate a common
maximum speed with a common modulation protocol (e.g., the V.34 28.8K modems
will not be compatible with the V.FC 28.8K modems at 28,800 bps). The
originating modem tries each speed and protocol by walking down the list
until it can find a common speed. It then tries to negotiate a common
error-correcting protocol and data-compression protocol, if it can find one.
The only adverse effect we've ever encountered with these cheap, high-speed
modems is that when a remote user has a slow, odd (often the HP-support)
modem on the other end, the HP3000 will occasionally time out the connection
attempt before the two modems have a chance to lock. When that happens, we
must manually reprogram the modem on our end to begin negotiation farther
down on the evolutionary ladder in order to minimize the negotiation time and
try again.
2. More Than You Wanted To Know
All of the newer Hayes-compatible modems support the following speed
protocols (which is about everything with the potential exception of both
V.34 and V.FC simultaneously):
o V.34 data modulation at 28800 bps.
o V.FC data modulation at 28800 bps.
o ITU-T V.32bis modulation at 14400 bps.
o ITU-T V.32 modulation at 9600 and 4800 bps.
o ITU-T V.22bis modulation at 2400 bps.
o ITU-T V.22 (Bell 212A) at 1200 bps.
o ITU-T V.23 at 1200 bps
o ITU-T V.21 (Bell 103) at 300 bps.
Also supported (but not officially documented) are 26400, 24000, 21600,
19200, 16800, 12000, and 7200 bps speeds in the 28.8K modems and 12000 and
7200 bps in the 14.4K modems.
The compression and error-correction protocols that the newer Hayes modems
support are:
o ITU-T V.42 LAPM (link access protocol for modems) error control
o MNP Class 2, 3, and 4 error control
o ITU-T V.42bis data compression
o MNP Class 5 data compression
The fax protocols supported are:
o ITU-T V.17, V.29, V.27ter(bo) and V.21 Channel 2 for Group 3 (Class 1
and 2) fax operation.
[*ITU stands for the International Telecommunication Union (based in Geneva),
and MNP stands for Micom Network Protocol.]
As to the compression algorithms employeed, the MNP Class 5 protocol (which
is in effect only when a MNP Class 2-4 connection has been made) can
maximally obtain only a 2:1 compression. The V.42bis compression algorithm
(which requires an LAPM connection) is said to regularly obtain its
theoretical maximum of 4:1, resulting in effective data transmission rates
exceeding 100,000 bps. The LAPM protocol is clearly the default protocol in
the "Hayes" modems, but you can manually change that, as you can almost
everything else about the modems, if you wish.
3. Configuring a Modem
To configure a modem, the process is quite simple. Disconnect a
DB25-connected terminal from the back of your DTC and plug it in to the back
of the modem. The DTC port and the modem are wired exactly the same way.
Set your terminal speed to 19.2Kbaud. This is important. The modem listens
and auto adapts its speed to the last "AT" command it hears from you. By
doing this, you're going to train the modem to speak at 19.2Kbaud -- and when
you later plug the modem into the DTC, it will auto-train the DTC port to
19.2Kbaud also.
Now type the following commands, each followed by a carriage return. (As any
number of people may point out, you can string all of these commands
together, but I have found that it has been easier and safer to type each
command individually.) As you progress down the set, the modem will become
progressively quieter until the end, when you will be typing the commands in
with no echo and no reply.
AT&F Set active profile to factory defaults
ATS37=0 Connect at last AT speed
ATS0=1 Answer on first ring
AT&Y0 Upon reset, load settings from profile 0
AT&K3 Enable RTS/CTS flow control (see below)
AT&D2 When an on-to-off DTR transition occurs, hang up and reset
(see below)
AT&C0 Assume presence of carrier detect signal
ATV0 Turn Off Verbose mode
ATQ1 Turn On Quiet mode
ATE0 Turn Off Command Echo
AT&W0 Save settings in profile 0
Now, once done, type ATZ1 to recall the settings in profile 1 so that you can
see what you are doing again and type AT&V to see the modem profiles. What we
just did was configure the modem to have two distinct profiles, 0 and 1.
Profiles 0 and 1 were both set at the factory to be dial-out modem profiles.
We just changed profile 0 to be an auto-answer profile. Profile 0 is also
desiginated by the manufacturers to be the cold-load profile so that if the
power should fail to the modem, it will automatically come back up in the
auto-answer mode.
Note: The AT&K3 setting above presumes that you have a proper modem cable
(pins 2, 3, 7, 6, 20, 4, and 5 are present) connected between the modem and
HP3000 for flow control and proper disconnect. These pin pairs are
respectively: send/receive data, data terminal/set ready (DTR/DSR), and
clear/ready to send (CTS/RTS). While other configurations can be made to
work, this is the configuration required for maximally advantageous use of a
"modem" port on the HP3000 (DTC or ATP). If you have your modem port properly
configured and have this cable in place, the HP3000 will properly hang the
modem up (if AT&D2 or AT&D3 is set) at the instance of a ":BYE" or, likewise,
terminate the current session if the modem drops carrier.
4. The Right Cable
Once the modem has been configured, connect the modem to the DTC port with a
"null modem" cable (one that crosses over the pins mentioned above). This is
essential because both the modem and the DTC port are wired in the same
manner.
5. Configuring the DTC
Use NMMGR to configure your DTC port as you normally would. HP supplies a
modem configuration profile that is very close to what you want. It's called
TR10M96 (which stands for: terminal, term type 10, modem, 9.6Kbaud). After
going to the DTS and Profiles screens, bring up and modify the profile to
19.2Kbaud -- and then save it under a new name (TR10M192 would be
appropriate).
Associate this profile with your desired modem port(s), and then save and
validate your new configuration files. Once done, shut your machine down and
perform a START NORECOVERY to reload your DTC(s).
Note: The new versions of NMMGR now list 38,400 bps as an allowed speed.
Unfortunately, the hardware we have on hand do not seem to support this speed
-- but yours may (I truly don't know). If it does, then you will want to set
the configuration profile to 38.4K above rather than the 19.2K listed.
Similarly, you will want to set your terminal speed to 38.4K rather than
19.2K, as recommended above. This is actually the more important step because
it is the modem that entrains the port, not the other way around.
6. Speed Thrills
There are now three speeds associated with every modem transmission: (i) the
local (digital) speed from your terminal or PC to your local modem, (ii) the
negiotated analog speed, modem-to-modem, and (iii) the remote digital speed
from the remote modem to the remote HP3000's DTC port. If the modems on both
ends are programmed NOT to be slaved to the analog channel speed (and they
should not be -- and aren't in the configuration above), then all three
speeds can now be different in the new modems. The slowest of the three
speeds will determine your throughput -- thus you especially want to insure
that the remote modem-to-HP3000 digital speed is as high as possible so that
it does not become a persistent bottleneck.
Wirt Atmar
P.S. But perhaps the most important question of all though is, Mike, are you
any relation to the Mike Farrell who played B.J. on M*A*S*H?
|
