riedl@cs.purdue.EDU (John T Riedl) (02/09/89)
I'm considering buying a 2400 baud modem from Practical Peripherals.
Any recommendations (positive or negative)? I'd especially
appreciate a pointer to a comprehensive review of 2400 baud
modems, including the Practical Peripheral product.
Thanks!
John Riedl
{ucbvax,decvax,hplabs}!purdue!riedl -or- riedl@cs.purdue.edu
--
John Riedl
{ucbvax,decvax,hplabs}!purdue!riedl -or- riedl@cs.purdue.edumelby@s.cs.uiuc.edu (02/10/89)
I have a Practical Peripherals PM2400SA modem. It has a few minor quirks (the redial and auto-answer features don't work correctly), but it is good for running a BBS that doesn't depend on auto-answer (such as WWIV). The service over at Practical Peripherals is also quite good - when the modem transformer blew, they sent me a free replacement transformer.
sz@cci632.UUCP (Stephen Zehl) (02/10/89)
In article <5996@medusa.cs.purdue.edu> riedl@cs.purdue.EDU (John T Riedl) writes: > >I'm considering buying a 2400 baud modem from Practical Peripherals. >Any recommendations (positive or negative)? I'd especially >-- >John Riedl >{ucbvax,decvax,hplabs}!purdue!riedl -or- riedl@cs.purdue.edu I was recently in the market for some low cost 2400 baud modems and thought about the PP 2400. I ended up purchasing Everex Evercom 2400 modems because for about $20.00 more you get MNP level 3 error correction where as the PP has no built in error correction. Seemed like a better idea to me and they work great. Just thought you'd like to know. Steve. CCCC CCCC IIII Stephen Zehl UUCP: sz@cci632.UUCP CC CC II Computer Consoles. Inc. Csnet: cci632!sz@cs.rochester.EDU CC CC II Rochester, New York. Usenet: rutgers!rochester!cci632!sz CCCC CCCC IIII DISCLAIMER: I speak for myself, not for my employer.
rwp@cup.portal.com (Roger William Preisendefer) (02/11/89)
I have owned a Practical Periferals PM2400SA since April 1988. It provides very clean data over crummy lines. I use it 4 hours per day (average). It has burned twice, and been sent back to the factory (worked well for about 4 months each time, then died). It was repaired and returned free of charge in about 2 weeks. It claims to have a five year warranty, but the technician/engineer who repaired it told me that the president of the company instructed that anything that comes in with Practical Periferals on it, regardless of when it was purchased or how it was damaged, was to be repaired free of charge. A company that stands behind electronic equipment is a rarity these days! Roger Preisendefer
berger@clio.las.uiuc.edu (02/26/89)
That's a real compliment for the company's service policy. But
I don't see why you're so satisfied with a modem that breaks
every 4 months, even if they repair it for free every time.
I have dozens of NEC modems in the field; we get a 5 year
warranty. But I've never had to have any of the modems
repaired. Some of them see very heavy use.
Mike Berger
Department of Statistics
University of Illinois
berger@clio.las.uiuc.edu
{convex | pur-ee}!uiucuxc!clio!bergerphil@calvin.EE.CORNELL.EDU (Phil Erickson) (05/01/89)
I will soon be in the market for a 2400 baud modem, and was curious if
anyone out on the net had a suggestion as to a reasonably priced Hayes
compatible which supports MNP error-checking protocol (in hardware, nat-
urally). I'm especially interested in modems folks have found RELIABLE
over slight to moderately screwed-up telephone lines - here in Ithaca,
I think the central office is trying to get back at all those unregistered
modems lurking about :-)
Suggestions are gratefully appreciated - it's a modem-shopping jungle
out there!
-----------------
Phil Erickson Space Plasma Physics 5143 Upson Hall
Cornell University Ithaca, NY 14853
ARPA: phil@calvin.ee.cornell.edu
or phil%calvin.ee.cornell.edu@cunyvm.cuny.edu
UUCP: {rochester,cmcl2}!cornell!calvin!philBOBC@cup.portal.com (ROBERT JOHN CHRISTIANSEN) (05/07/89)
I've been using an ATI2400etc for 9 months now, and it has been terrific. It is an internal modem, HAYES AT compatible with MNP level 5 support. I paid $149, but have seen them for less recently. There are some other 2400 modems being offered out there at ridicuously low prices ($99) claiming MNP5 support. What you get is a regular old 2400 bps modem with a terminal emulator software package supporting MNP...much inferior to being in the modem's own firmware.
kaufman@polya.Stanford.EDU (Marc T. Kaufman) (05/08/89)
It's easier to do a followup than an original post, but the request is similar. I currently have a US Robotics Courier 2400 baud modem, but have moved into the boonies, and now I am seeing more line noise and hits that cause the modem to drop back into 1200 baud for a while. What I want, is the best 2400 baud signal processing I can find. I am even willing to buy a 9600 baud V.32 modem or a Telebit, on the grounds that the signal processors in them will (may?) provide the extra margin at 2400. [as it turns out, I can use the higher speed on some links, but 2400 is the mainstay for interactive stuff]. What say you all? Marc Kaufman (kaufman@polya.stanford.edu)
wtm@neoucom.UUCP (Bill Mayhew) (05/09/89)
Not all modems are created equal in terms of noise rejection.
There are noticable differences in the quality of filters that are
used to recover the received carrier. The second harmonic overtone
of the transmitted carrier can be problematic where there is a
line impedance mismatch that cuases the originate carrier to be
reflected back into the receiver of the originating modem.
There are three factors that affect performance. First is the
quality of the digital or analog filter that is used to reject the
overtones of the originate carrier. Second is the use (if any) of
an adaptive equalizer to assure flat frequency response over the
passband of the received carrier. Unfortuantely, advertising
literature hardly ever states performance figures or design of the
filtration and/or equalization used in the receiver. I don't think
I've ever seen second harmonic rejection specified. The third
performance parameter is echo cancellation; this shouldn't matter
on a v.22.bis modem as decent filtration in the receiver should be
enough, as the xmit and receive carriers use different fequency
bands.
The line between work and my house is very problematic. Here are
some modems that I have found that work well. Your results may
vary. In all cases, the modem at the other end was a Trailblazer;
I used a variety of modems on my end. The line is so bad that a
Hayes Samrtmodem 1200 will not even connect on the line.
Here are the best:
1. IBM PS/2 internal 1200 baud modem. This modem does not have
MNP correction, but essentially completely corrects for line
impairments (apparently by using adaptive equaliztion). The
unit is made by Racal-vadic for IBM. I have not been very
impressed with other Racal-vadic stand-alone modems.
2. US Robots Courier HST. Not tested in HST mode, as I didn't
have two of them. MNP mode works well. Corrects almost all
line problems even without MNP mode engaged. Tested both 1200
and 2400 baud. Trailblazer would only support up to MNP level
3 on with the HST, due to limitations of the trailblazer.
3. Trailblazer Plus. Noise free in all modes. Good response in
MNP mode. As both ends employed trailblazers, the results with
PEP were very impressive. Interactive turnaround in PEP mode
with short packets is good (both ends using 4.0 firmware).
uucp transfer stats average 1200 char/sec for ~100K files in
PEP mode. I still prefer to use 2400 baud for interactive
editing in vi. I use PEP mode to read news.
4. AT&T 2224 CEO. Resonably decent performance with PEP enabled.
Has annoying ~1.5S delay as modem switches from short to long
packets after ~32 characters are received at maximum baud rate.
Will occasionally refuse to connect at 2400 baud over poor
circuit.
After trying out a bunch of modems, I decided on the Trailblazer as
it is the most flexible and seems to have the best noise rejection
at 1200 and 2400 baud even without the MNP mode engaged. I use the
trailbalzer a lot for uucp transfers, and have cut my connect time
from about an hour to about 5 minutes a day.
If you are looking for v.32 compatibility, the new trailblazer 2500
or the UDS v.32 modem that includes v.22.bis are likely to be good
performers. I tested the older UDS v.32-only modem and found it to
be the best performer, though it was by far not the most expensive
v.32 modem. I have not tested the trailblazer 2500.
Bill
wtm@impulse.UUCPwls@csd4.milw.wisc.edu (Bill Stapleton) (05/10/89)
ROBERT JOHN CHRISTIANSEN writes: >I've been using an ATI2400etc for 9 months now, and it has been terrific. >It is an internal modem, HAYES AT compatible with MNP level 5 support. ... I had heard there would be an external version of the 2400etc. Does anyone know any more about it? Incidentally, the next issue of BYTE magazine will have a guide to inexpensive 2400 bps MNP5 modems. But, but, I want a modem *now*! :-) -- Bill Stapleton wls@csd4.milw.wisc.edu uwvax!uwmcsd1!wls
dplatt@coherent.com (Dave Platt) (05/10/89)
In article <1620@neoucom.UUCP> wtm@neoucom.UUCP (Bill Mayhew) writes: > > Not all modems are created equal in terms of noise rejection. > There are noticable differences in the quality of filters that are > used to recover the received carrier. The second harmonic overtone > of the transmitted carrier can be problematic where there is a > line impedance mismatch that cuases the originate carrier to be > reflected back into the receiver of the originating modem. > > There are three factors that affect performance. First is the > quality of the digital or analog filter that is used to reject the > overtones of the originate carrier. Second is the use (if any) of > an adaptive equalizer to assure flat frequency response over the > passband of the received carrier. Unfortuantely, advertising > literature hardly ever states performance figures or design of the > filtration and/or equalization used in the receiver. I don't think > I've ever seen second harmonic rejection specified. The third > performance parameter is echo cancellation; this shouldn't matter > on a v.22.bis modem as decent filtration in the receiver should be > enough, as the xmit and receive carriers use different fequency > bands. I can't speak to the specifics of modems' filtering technologies, but I can certainly attest that there can be a BIG difference between the noise susceptibilities of different V.22bis modems in the same price range. When our company was getting started, we looked at several brands of V.22bis modems. Our first batch was from Bytecom; these modems support MNP up through level 4 (upgradable to 5, I believe) and were listed as being fully Hayes-compatible. We were severely disappointed. Aside from some dubious human-engineering features (no volume control for the speaker; no transmit-data or receive-data LEDs!) and some firmware bugs in the dialer/connect logic, we found that these modems were quite vulnerable to line noise. At 1200 baud (212 protocol), they were substantially more noise-prone than my 5-year-old Racal-Vadic modem board (which does _not_ have adaptive equalization). At 2400 baud, they were almost unusable on marginal lines, even with MNP enabled... MNP would retry the transmission but would be unable to correct for repeated line glitches. We sent these modems back to the vendor, and replaced them with U.S. Robotics Courier 2400e modems (MNP level 3). These seem to be much cleaner... I've called cross-country with them (AT&T lines) without MNP, and have noticed only a couple of line-hits. My research at the time indicated that the Bytecom modems were OEM implementations based on the CTS modem chip-set. Word on the various nets suggested that this chipset is more sensitive to line-noise than other V.22bis implementations. Most people who owned modems based on this chipset reported having problems with noise. I don't know what it is about the CTS chipset that makes it so prone to noise (or, conversely, what it is about other implementations that make them more noise-immune). Based on results, though, I decided to stay far away from CTS-based modems in the future. I guess the only workable rule for choosing a modem is "Try it in your application; if it doesn't work out well, return it!". The Bytecom modems looked good on paper... but they just didn't work out well for us. -- Dave Platt FIDONET: Dave Platt on 1:204/444 VOICE: (415) 493-8805 UUCP: ...!{ames,sun,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303
chaney@ms.uky.edu (Daniel Chaney) (05/24/89)
In article <18032@cup.portal.com> BOBC@cup.portal.com (ROBERT JOHN CHRISTIANSEN) writes: >paid $149, but have seen them for less recently. There are some other 2400 >modems being offered out there at ridicuously low prices ($99) claiming MNP5 >support. What you get is a regular old 2400 bps modem with a terminal emulator >software package supporting MNP...much inferior to being in the modem's own >firmware. I, too, caught this scam about 10 minutes before I ordered it. In fact, the software is not even invisible (ie, you couldn't run something in front of their software) This strikes me as rude and very misleading. The salesperpeople that I talked to was very evasive but finally admitted that yes, this program would make any 2400 baud modem act like MNP-equipped In fact, file transfer capabilities were never mentioned in our talk. If they don't have that, why have MNP? -- Daniel Chaney Mail guy, archiver or Accidental Student..you decide. {uunet and the like}!ukma!chaney chaney@ms.uky.edu chaney@ukma.BITNET "No! nonono....This is Unix, you take out all the vowels!" - The Uhmmer