Editor's Note: Some questions seem too fundamental to ask, but HP 3000 customers are always grateful when basics get explained by those with real-world experience. That's what happened recently out on the HP 3000 newsgroup, when a manager asked the proper way to configure a modem at any speed for a DTC port. Since the DTC is exclusive to the HP 3000, we figured the answer would be especially useful to those readers who don't yet have their HP 3000s linked to the Internet. Wirt Atmar, founder of AICS and a software provider who stays in close contact with his company's customers through support modems, was kind enough to let us reprint his reply here, off the electronic highways.
By Wirt Atmar
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, 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, the majority of modems nowadays are 100 percent Hayes compatible.
The following configuration information applies only to true Hayes-compatible modems (Hayes, Boca, Supra, Practical Peripherals, Magnum, Zoom, Intel, etc.). 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 about. 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 HP 3000 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 to minimize the negotiation time and try again.
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):
ITU-T V.34 data modulation at 28800 bps
Rockwell V.FC data modulation at 28800 bps
ITU-T V.32bis modulation at 14400 bps
ITU-T V.32 modulation at 9600 and 4800 bps
ITU-T V.22bis modulation at 2400 bps
ITU-T V.22 (Bell 212A) at 1200 bps
ITU-T V.23 at 1200 bps
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: ITU-T V.42 LAPM (link access protocol for modems) error control; MNP Class 2, 3, and 4 error control; ITU-T V.42bis data compression and MNP Class 5 data compression.
The fax protocols supported are 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.
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. We just configured 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 8 are present) connected between the modem and HP 3000 for flow control and proper disconnect. These pin pairs are respectively: send/receive data, data terminal/set ready (DTR/DSR), and request to send/carrier detect (RTS/CD). While other configurations can be made to work, this is the configuration required for the maximum advantageous use of a "modem" port on the HP 3000 (DTC or ATP). If you have your modem port properly configured and have this cable in place, the HP 3000 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.
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.
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 in Configuring a Modem above. This is actually the more important step because it is the modem that entrains the port, not the other way around.
Speed Thrills
There are now three speeds associated with every
modem transmission: (1) the local (digital) speed from your terminal or PC
to your local modem, (2) the negiotated analog speed, modem-to-modem, and
(3) the remote digital speed from the remote modem to the remote HP 3000'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 want to insure that the modem-to-HP 3000 digital speed is as high
as possible so that it does not become a persistent bottleneck.