swatt (08/08/82)
From decvax!genradbolton!rob Sat Aug 7 00:49:35 1982 Date: Fri Aug 6 07:27:41 1982 To: decvax!ittvax!swatt Subject: DF03 We are going to buy an auto-dialing modem. Can you tell me if all uucp and cu software work with the DF03? Do you have any feelings of these versus the 3451PA? Thanks. Rob Wood (decvax!genradbolton!rob) [Note to Rob: I'm copying USENET on this becuase it's a fair amount of work just to write down my answer and I feel others should get some benefit/chance to throw stones ... ] First, about UUCP and "cu": we got DF03-modified sources for the UUCP module that does the dialing from decvax. We also got from them a MUCH better cu-like program called "tip", originally written by Sam Leffler at sytek, and worked on some more by Bill Shannon at decvax (The "at"'s here are historical; Sam is now at UCB and Bill is now with Sun Microsystems). So yes, you can get UUCP and a cu equivalent to work with DF03's. If you can't get "tip" from decvax anymore, you can get it from us. We don't have a 3451PA so I can only compare the two from the specs: 1) The 3451P has no positive dialtone detection. It does have a 5-second pause, which should prove adequate for most uses. The DF03 has what it calls "access pause", which claims to be positive dialtone detection. We've never used this feature but expect to shortly. 2) The 3451P has only a fixed 24 second timeout from the time the last digit is dialed to when the modem detects carrier. The specs are a little vague on this as the Vadic triple modem protocol detection itself can take 10-15 seconds, but I suspect the timer is "held" on any carrier signal so the timeout effectively means time to remote pick-up. The DF03 has switch-selectable 27 or 52 second timeout. Neither one (alas) will vary the timeout based on number of digits dialed. I think the 52 second timeout should be adequate even for calls to foreign exchanges, but the 24 second one is likely to cause trouble. 3) The 3451P claims to do autobaud detection, setting the modem to the correct speed for the terminal. Changing speeds on the DF03 is tricky; you have to change a front panel switch setting. However this only changes the speed for the modem; the dialer speed can only be changed by disassembling the unit and changing an AMP switch. It is possible to change modem speeds under software control, but this requires toggling the rs232 secondary transmit signal, which not all multiplexers support and not all UNIX systems support. Tip has code to do this for df03's if the system supports it. 4) The 3451P's autodialer is clearly intented to be run by a person sitting at a terminal and insists on being "friendly". Controling these kinds of dialers from a program is messy at best. The "tip" code I've seen to handle Bizcomp and Ventel is enough to make me think at least twice before buying one. The DF03 is quite simple to handle; there are only 6 commands to the dialer, and only three responses back; all are single characters. 5) The 3451P claims to put the modem in "transparent mode" once the connection is established, so there is no worry about disconnecting because of any sequence of binary characters. The DF03 works the same way; the dialer removes itself from the circuit once connection is established. The only way to disconnect is either have the modem sense carrier loss, or drop DTR from the host. To this end, you will probably have to modify the kernel sources dz.c and dh.c to force DTR low on last close; it's a trivial fix and is required anyway if you want to use any kind of local area network or port contender. UUCP requires an 8-bit binary data path; cu and tip could make do without. What follows are my thoughts and experiences with the DF03, which you might find useful as a guide. The DF03 is a pulse-only dialer. You cannot select tone dialing even with a strap setting. I would NEVER buy a pulse-only autodialer again. The reason is that dial pulses are not passed by the local exchange once a connection is established. They can't be: their only interpretation would be "disconnect". This means you can't dial out to a number which is itself a PABX and then pass more dial instructions. If you want to put your dialer on your PABX (good reasons to: saves trunk lines), either your autodialer must do tone dialing, or your PABX has to accept pulse commands. Further, your PABX has to pass the pulses on to the outside trunk line. I just found all this out recently and we've lucked out in that our PABX will accept pulse commands and will allow dial pulses to pass onto the outside line. However, once a connection is made, no dial pulses get through the local exchange. Tone dialing is what they call "in-band" signalling, which means the signalling occupies the same frequency band as voice, so you can always pass dial commands over ANY connected circuit. The only "out-band" signal left is disconnect (there was a lot of criticism of this design choice when the so-called "black boxes" were all the rage, but looked at from this viewpoint, it makes good sense). The classiest autodialer I've seen so far is the Vadic 811/821 (821 is the 811 with MACS, or "Multiple Automatic Call Select"). This will do either pulse or tone dialing and figures out which one to use by itself. It does this by tossing the first digit out as a tone and if the dialtone changes, it assumes the exchange understands tone dialing and continues. If the dialtone remains the same, it assumes the exchange can only understand pulse dialing and redials the first digit and the rest of the number as pulse commands. It resets its notion of which type of dialing to use for each new number dialed, and each time it pauses to detect a dialtone. Thus you can dial out on a pulse-only exchange into a PABX and pass tone dialing commands to the PABX. Unfortunately, the 811 only makes sense for rack-mounted Vadic modems, where the MACS feature lets you distribute the cost of the autodialer out among several modems. Since the dialer is a separate rs232 port from the modem, handling different speeds is relatively simple. You just keep the dialer on a single speed and change the modem port speeds to whatever is appropriate. You have to specify in the dial command to the MACS dialer which modem type to select to originate the calls however. Summary: If I had it to do all over again, I would get rack mounted Vadic modems with their 821 dialer. Hacking UUCP would take a little time (actually, tpdcvax has already done this), but well worth it. With the new 2400 baud modems coming out, this begins to look even more attractive. Don't let the initial high cost scare you: there are too many things you can use autodialers for, once you've got them and using them is convenient enough. We have two DF03's, and could easily keep two more busy. As an example, there are several dialup database and research services that offer a lot of value for modest cost. We have people here using them from modems connected directly to terminals simply because we don't have enough autodialers to support it. They therefore have to go to a lot of trouble to get hardcopy printout when they could have "tip" maintain a session log for them. - Alan S. Watt (decvax!ittvax!swatt)