gandrews@netcom.COM (Greg Andrews) (05/24/91)
In article <X31D33w164w@pain.UUCP> adamr@pain.UUCP (Adam Ravid) writes: > >The Telebit had a few added features: security, built-in protocols, >louder carrier for attempting to prevent fallback in v42bis, and about >^^^^^^^^^^^^^^ > >The teasing feature: louder carrier, I reasoned would probably be useful >^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >in a v32 connection, but when v32bis is released, because of the growing >back to the maximum speed after a fallback due to line noise is added, the >prevention of fallback will not be as important. > "Louder carrier" is not a feature Telebit advertises in the T1600. Matter of fact, I have no idea what that term could mean. The FCC regulates the output power a modem may (legally) transmit to the phone line, and last time I looked the level was still -9dBm. The user has the ability to boost the output level (resistor change) in order to operate over leased lines, but it's illegal to do that for the public switched network in the U.S. and Telebit doesn't advertise that ability for dialup use. Sounds like a spec sheet was misinterpreted, or somebody's writing their own spec sheets for the T1600... > ism!wilbur!techsys!pain!adamr -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
steve@pro-hindugods.cts.com (Steve Fenwick) (05/26/91)
In-Reply-To: message from gandrews@netcom.COM What _is the advantage of a louder carrier? Steve ------- CoSysop: pro-hindugods
gandrews@netcom.COM (Greg Andrews) (05/27/91)
In article <1991May26.044327.5598@clark.edu> steve@pro-hindugods.cts.com (Steve Fenwick) writes: >In-Reply-To: message from gandrews@netcom.COM > >What _is the advantage of a louder carrier? > If you read my article, you would have seen me state that there is no such thing for dialup lines. There's no advantage in something that doesn't exist. Over leased lines, the advantage of boosting the output level is the same as when you shout on a noisy phone call. Your louder talking helps the other person hear your voice over the noise. If the phone line makes the modem signals too faint, they will be lost in noise when they get to the other end of the line. Boosting the output can help get the modem signals louder than the noise so the other modem can hear them properly. >Steve -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
floyd@ims.alaska.edu (Floyd Davidson) (05/28/91)
In article <1991May26.231210.14794@netcom.COM> gandrews@netcom.COM (Greg Andrews) writes: >In article <1991May26.044327.5598@clark.edu> steve@pro-hindugods.cts.com (Steve Fenwick) writes: >>What _is the advantage of a louder carrier? > ...there is no such thing for dialup lines. ... > >Over leased lines, the advantage of boosting the output level is the same >as when you shout on a noisy phone call. Your louder talking helps the >other person hear your voice over the noise. If the phone line makes the >modem signals too faint, they will be lost in noise when they get to the >other end of the line. Boosting the output can help get the modem signals >louder than the noise so the other modem can hear them properly. The output level on dial-up modems is almost always fixed at about -10 Dbm (within a couple db). That is because the normal line loss for a dial-up line is estimated at about 3 dB, and the desired level for a modem is -13 dBm at the central office switch (at a point where a test tone would be 0.0 dBm). Since most dial-up modems have a very good dynamic range, there is no practical effect if the level is plus or minus 3-4 dB from the -13 dB design figure (as could happen if you live very close or very far from the telco). Leased line modems can usually be adjusted for just about any output level from -21 to +5 dBm, but the level that is actually used is carved in stone by the circuit engineer who specifies the various equipment that is on the circuit at different places. The level out of the modem depends on what equipment the customer has and what kind of an interface the phone company has. But the result is always the same: At any point along the circuit where a full level 1 KHz tone would be 0.0 dBm, the modem level is going to be -13 dBm. The actual levels vary, of course, but the 13 dB difference is set (there are some very few exceptions). If the modem output is less than the design level, the signal to noise ratio is worse, and the result is as Greg described. If the modem output is too much, it can cause distortion as it passes through equipment at the telco (analog to digital converters, analog or digital carrier systems, etc.). Almost everything the telco puts in a circuit is designed to either clip or compress anything that is too "loud". The resulting distortion will severely interfere with the data transmitted. And any testboard technician who measures a modem tone that is more than 3 dB "hot" is going to plug the circuit off until the level is corrected. Thus a "louder" modem, even a leased line modem, really doesn't exist. One modem may have a couple dB or so higher level than another, but that small a difference doesn't affect the data. Floyd -- Floyd L. Davidson | Alascom, Inc. pays me, |UA Fairbanks Institute of Marine floyd@ims.alaska.edu| but not for opinions. |Science suffers me as a guest.
root@zswamp.uucp (Geoffrey Welsh) (05/28/91)
In a letter to All, Steve Fenwick (steve@pro-hindugods.cts.com ) wrote:
>What _is the advantage of a louder carrier?
If we assume that the noise level on a line is fairly constant (or, at
least, determined as soon as you complete your dialling), a louder carrier
gives you a higher signal/noise ratio and therefore, theoretically, a cleaner
data link.
There is also merit to the argument that a higher peak-peak amplitude
results in more precise reproduction of the carrier over pulse-coded
modulation ("PCM", read: digitized) trunk lines used for long distance and
even some local hops.
Of course, this becomes invalid if the volume is so high that it causes
distortion.
Manufacturers set their levels as high as they can without significantly
increasing the number of connections that will fail because of volume-induced
distortion.
--
Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171)
root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root
602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553
"He who claims to know everything can't possibly know much" -melstowell@pyrnova.pyramid.com (Lon Stowell) (05/29/91)
In article <1991May26.044327.5598@clark.edu> steve@pro-hindugods.cts.com (Steve Fenwick) writes: >In-Reply-To: message from gandrews@netcom.COM > >What _is the advantage of a louder carrier? On a PSTN line it will improve your social life...gets you all sorts of letters, phone calls etc. (This is true for the Permissive type of line which is engineered for a -9dBm xmit level...) There are other switched lines, such as RJ45 programmed data jacks which use a programming resistor to set your xmit level. The xmit energy of modems is limited in the PUBLIC switched network to avoid crosstalk and interference with OTHER voice and data users. The levels were established in antiquity...and may be excessively conservative for modern lines and gear. It is illegal to xmit at higher than the limits set by the governments and the telco's.....but the limit is measured in a somewhat strange manner. Exceeding the limit is possible, but if you are caught, and the violation is willful, the penalties are pretty severe. If this is done willfully by a manufacturer, they could lose their FCC or other PTT certification...a pretty nasty penalty. Possibly the "louder" carrier is just a predistortion of the xmit spectrum to compensate for roll-off in the network...or it even could be a higher energy signal suitable for leased lines OR totally private switched networks. I would find it hard to believe a manufacturer would be stupid enough to advertise a feature which actually would violate the mandated limits...
adamr@pain.UUCP (Adam Ravid) (06/01/91)
steve@pro-hindugods.cts.com (Steve Fenwick) writes: > In-Reply-To: message from gandrews@netcom.COM > > What _is the advantage of a louder carrier? > According to the Telebit Rep, it means that over a long distance line, where the volume of the carrier might drop (or even local for some areas), this is a preventive measure. The other modem will 'hear' the carrier and not fallback.... Further questions on this subject should be refered to someone with Telebit. -- ism!wilbur!techsys!pain!adamr Public Access Information Network (818/776-1447) ++ Waffle BBS v1.64 ++
gandrews@netcom.COM (Greg Andrews) (06/04/91)
In article <4LFu33w164w@pain.UUCP> adamr@pain.UUCP (Adam Ravid) writes: >steve@pro-hindugods.cts.com (Steve Fenwick) writes: > >> In-Reply-To: message from gandrews@netcom.COM >> >> What _is the advantage of a louder carrier? >> > >According to the Telebit Rep, it means that over a long distance line, >where the volume of the carrier might drop (or even local for some areas), >this is a preventive measure. The other modem will 'hear' the carrier and >not fallback.... > >Further questions on this subject should be refered to someone with Telebit. > Hi. I'm a Telebit support tech, and the term "Loud Carrier" is completely meaningless to me. As I explained in my original posting on this topic, the modem's output is limited to a certain level over dial-up lines. This sounds to me like someone is making up specs on their own. If you heard this from someone at Telebit (not just a salesperson at a distributor), then please e-mail me who it was. I'd rather not have Telebit folks quoting bogus specifications to modem users... > ism!wilbur!techsys!pain!adamr -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'