Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!olivea!oliveb!amdahl!JUTS!duts!kls30 From: kls30@duts.ccc.amdahl.com (Kent L Shephard) Newsgroups: comp.sys.next Subject: Re: The existance of a Software Modem and Fax Machine... Message-ID: <2cqt023R06Lj01@JUTS.ccc.amdahl.com> Date: 22 Mar 91 14:54:05 GMT References: <1991Mar19.214415.27530@oracle.com> Sender: netnews@ccc.amdahl.com Reply-To: kls30@DUTS.ccc.amdahl.com (Kent L. Shephard) Distribution: na Organization: Amdahl Corporation, Sunnyvale CA Lines: 104 In article scott@mcs-server.gac.edu (Scott Hess) writes: >In article <1991Mar19.214415.27530@oracle.com> wayer@oracle.uucp (William Ayer) writes: > At a demonstration of the NeXT machine two years ago, Jobs suggested > that the DSP chip would allow programmers to create a software modem / fax > machine (very little hardware would be needed i.e. a cable). Was this > suggestion wishful thinking, or could such a beast exist? > >Well, this is technically possible. Basically, the internals of a modem >are a DSP chip plus some glue logic [ :-) ]. > >The problem is that in a modem the DSP is dedicated, while on the NeXT >it isn't quite so dedicated. The amount of work needed to be done >outside the DSP is greater on the NeXT than when it's off on that >serial port. The DMA support isn't really there, etc, etc. You could >upgrade your DSP memory (that would fix most of those types of >problems), but in general I think it's a close one as to whether or >not you can run a 9600 baud modem off the DSP. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 9600 baud is not the hardest thing in the world for a 56k DSP. Why now do you think it is possible to have a dedicated modem with a slow DSP and not a fast one? 9600 is "possible". To be realistic a 25Mhz 56k should be able to handle 19200 baud. Remember you can do real time spectral analysis with monster scope. That is a lot harder than determining a bit from a phase modulated signal. (The person I told FSK. I meant PM- phase modulation). > >On the other hand, 2400 should be fully realizable. I've seen schematics >(don't ask me for them - I can't give them out), and I know that people Simple A/D converter and a D/A converter with a phone line interface. you could get away with bits for conversion because the frequency that is modulated is not that high. Remember that phonse have almost no frequency response above 3.5Khz. The DSP can handle sampling rates up at least 88Khz. You can get a telephone interface from Radio Shack. So the hardware is not difficult. >have played with it. One problem is that you need FCC approval to ~~~~~~~~~~~~~ See above. The interface is FCC approved. Your hardware connects to the interface and never to the phone line. The interface used to cost around $10-$15. Now if you want to build your own interface, then you need FCC approval. Why bother, when it's done for you already. >connect this beast to a phone line. With a modem, it's not such a >big deal - after all, there's not alot of memory/disk storage in >a modem, so it's not really a very good computing machine. Meanwhile, >hooking up an interface through the DSP to a NeXT (arguably a fair >computing machine), the possibilities are ripe for infamous 'blue >boxes'. These would be boxes which could be used to rip off the >phone company (free long distance, etc). Not so good. Yes, if you generate the right tones you could rip them off. But you don't need a NeXT for that you can do that with an old eight bit machine. > >Lastly, I think that a DSP modem is sort of silly. Fact: You're >going to be spending >$3500 (after shipping/taxes) on a machine, >and realistically most people will be up over $4000. Fact: The >box to hang between the DSP and the phone line is probably going >to cost $$$ - combined with the appropriate driver software, I'd >be surprised if it were under $150 (very surprised at that). Fact: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Even if it costs $300 that IS cheaper than a comparably price 19200 baud beast. >kermit is free. Stuart is nearly so. (Last) Fact: A Hayes >compatible MNP 5 modem costs under $200 nowdays for a decent one, ~~~~~~~~~~~~~ 2400 baud, 9600 is still a minimum of $400. >lower if you shop. > >I just don't see the need for a DSP modem. It's too much of a >bother, and inflexible to boot. When you can get a cheap modem ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Inflexible how? Once you have the modem hardware built it can function as a FAX with a software change. Or an answering machine. You could even build a detect feature in the software that would distinguish FAX, modem, voice. >and the software to drive it most anywhere, it's silly to try for >another solution which will not be so cheap and will be hardwired >to your machine (you won't need new drivers when NextStep3.0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Maybe, maybe not. A lot of software is broken under the 1.0 - 2.0 upgrade. Your communication program could break the same way anything else could. >comes out if you buy a modem). > >Later, >-- >scott hess scott@gac.edu >Independent NeXT Developer GAC Undergrad > >"Simply press Control-right-Shift while click-dragging the mouse . . ." >"I smoke the nose Lucifer . . . Banana, banana." -- /* -The opinions expressed are my own, not my employers. */ /* For I can only express my own opinions. */ /* */ /* Kent L. Shephard : email - kls30@DUTS.ccc.amdahl.com */