From senator-bedfellow.mit.edu!bloom-beacon.mit.edu!panix!news.mathworks.com!udel!gatech!swrinde!news.uh.edu!news.sccsi.com!nuchat!yob!bill.garfield Tue Dec 13 11:35:07 EST 1994 In article: James Savage writes: > I've just started messing with a pair of v.34 modems (Motorola v.3400's > in this case). I have yet to get a connection at 28.8K. I seem to get 24k > or 26.4k connections. In the REAL world, what can I expect to see? Do I Expecting 28,800 bps? Your results -will- vary. If you find that you're unable to achieve full speed 28,800 bps connections or your new 28.8k modem sometimes behaves erratically, the reason is most likely a phone line impairment. Either insufficient bandwidth, poor signal to noise ratio, or an imbalance in the phone lines... either yours, the phone lines of the system you are calling, or in the lines and telephone switching equipment anywhere along the way. Here are the minimums: 28,800 bps V.FC/V.34 requires 3200 Hz bandwidth, from 320 - 3520 Hz. 26,400 bps V.FC/V.34 requires 3000 Hz bandwidth, from 375 - 3375 Hz. 24,000 bps V.FC/V.34 requires 2800 Hz bandwidth, from 467 - 3267 Hz. I should qualify the above by stating that V.34 can shift the whole baseband down a bit further to compensate for a poor top end but I'm sure everyone gets the idea. By contrast... a 14.4k bps (V.32bis) link requires a usable bandwidth of only 2400 Hz, from 600 - 3000 Hz. Alas, while most U.S. domestic phone lines can easily support the requirements of 14400/V.32 bis, many fall short of being able to provide the technical operating parameters necessary for V.FC and V.34 to function at _FULL_ speed. This, in a nutshell, is what you (and several others) are experiencing. Compared to V.32 & V.32 bis, 28,800 bps requires 33% more bandwidth, 26,400 bps requires 25% more bandwidth and 24,000 bps needs 17% more bandwidth. This additional bandwidth _MUST_ be there from end to end, all the way from one modem to the other. Either you have it or you don't, and your modem is as much as telling you by its performance. As the domestic telephone companies race to install fiber optic cables and new digital switching machines, the bandwidth situation should gradually improve. Until then there ARE several things you can -try- for improving your high speed modeming: Go throughout the house and disconnect -ALL- telephonic devices attached to the phone line. This includes extension phones, answering machines, fax machines, caller-id boxes, line-in-use indicators, cordless phone base units, demon dialers, and voltage spike protectors or line filters like those commonly found in PC Desktop master-switch power directors and power line conditioning units. If you find that any of this helps, then start plugging things back in one by one until the culprit is identified. It could even be a combination of things. At the office you'll likely find that your 28.8k modem will perform better when provisioned with an outside line, one which _doesn't_ go through the pbx or a multi-line key system. If your telephone wiring is a rat's nest and/or you've strung some extension lines yourself and not used genuine telephone-type wiring, consider having a professional replace your haywired additions. Your telephone wiring should also be well _AWAY_ from the A/C power wiring in walls & ceilings. At the office, avoid the use of "category" wire. All the category 3 and category 5 wiring I've seen is 100-ohm impedance for use with high speed (digital) data. If your commo group has put in all new category 5 wire and uses it for both digital data and analog voice grade telephone work, they've done you a terrible disservice. Analog phone service is not meant to be on cat-5 wire. Your new modem is looking for a VOICE circuit with an impedance of 600-ohms. If your phone service arrives via a subscriber loop concentrator or remote terminal or other pair gain device such as the ubiquituous SLC-96 then all bets are off and you'll probably have to settle for 24,000 and below on most calls with 26,400 being a rare treat, indeed. I've never heard of anyone regularly achieving 28,800 through a slick. I suppose now that I've made that statement there'll be 100 respondents who will naturally claim otherwise. :-) :-) Of course it should go without saying that your mileage will vary. Opinions are my own. I represent no one other than myself in this forum. Bill Garfield Beta site for Multi-Tech & USRobotics modems * OLX 3.0 * New Pentium warning label: INTEL INSIDE ---- +------------------------------------------------------------------------+ |Ye Olde Bailey BBS Zyxel 713-520-1569(V.32bis) Hayes 713-520-9566 (V.FC)| | Houston,Texas yob.com Home of alt.cosuard | +------------------------------------------------------------------------+