TELECOM Digest Tue, 16 Nov 93 11:45:00 CST Volume 13 : Issue 764 Inside This Issue: Moderator: Patrick A. Townson Re: No ISDN Despite Big Talk (Fred R. Goldstein) Re: No ISDN Despite Big Talk (Carl Oppedahl) Re: No ISDN Despite Big Talk (Marco S. Hyman) Re: No ISDN Despite Big Talk (R. Kevin Oberman) Re: No ISDN Despite Big Talk (Dick Rawson) Re: TDMA vs. CDMA = Betamax vs. VHS? (Samir Soliman) Re: TDMA vs. CDMA = Betamax vs. VHS? (David Boettger) Re: TDMA vs. CDMA = Betamax vs. VHS? (James R. Ebright) Re: TDMA vs. CDMA = Betamax vs. VHS? (Tom Crawford, Qualcomm via Alex Cena) Re: TDMA vs. CDMA = Betamax vs. VHS? (David Hough) ---------------------------------------------------------------------- From: goldstein@carafe.dnet.dec.com (Fred R. Goldstein) Subject: Re: No ISDN Despite Big Talk Date: 15 NOV 93 17:48:14 Organization: Digital Equipment Corp., Littleton MA USA In article , jebright@magnus.acs.ohio- state.edu (James R Ebright) writes: > Huh? ISDN was originally a way to get 56KB service ... but modems on > regular analog lines can almost do this today. ISDN vs market forces. > ISDN 0, Market 1. > Buy a V.fast modem for $499 and get most of the benefit without > the aggrevation of Waiting For Godot ... At the risk of seeming boring, let me restate the laws of physics. Modems are designed for analog lines, which in turn are implemented in most cases using digital techniques. So you take a 62ish (64 kbps minus signaling) kbps channel, convert it to analog for the modem, and convert data to analog in the modem. With these two conversions on a GOOD line, you can get 28.8 kbps with a V.fast modem. That's the bleeding edge, and approaches the "Shannon limit" for typical lines (though some phone lines are better). ISDN just takes the 64 kbps channel, which _might_ lose 8 kbps for signaling, and passes it right to the end user without the D:A:D conversion. So it's roughly twice as fast as any modem can ever be. IF you can get ISDN, then it'll blow the doors off of any modem. And yes, you can compress data over ISDN. Take a BRI with two B channels, run serious compression over low-entropy data, and get a megabit/sec over a local phone line! Of course, that's only if you believe in 8:1 compressibility, which applies to very little data in any case. Fred R. Goldstein goldstein@carafe.tay2.dec.com k1io or goldstein@delni.enet.dec.com voice:+1 508 952 3274 Standard Disclaimer: Opinions are mine alone; sharing requires permission. ------------------------------ From: oppedahl@panix.com (Carl Oppedahl) Subject: Re: No ISDN Despite Big Talk Date: 15 Nov 1993 19:36:06 -0500 Organization: PANIX Public Access Internet and Unix, NYC In jebright@magnus.acs.ohio-state.edu (James R Ebright) writes: > In article john.eichler@grapevine. > lrk.ar.us (John Eichler) writes: >> oppedahl@panix.com (Carl Oppedahl) wrote: >>> I should think that New York Telephone, which fills the front pages of >>> every telephone directory with glowing talk of up-to-date digital >>> technology, would be embarassed at its apparent failure to deploy ISDN >>> beyond a handful of Manhattan exchanges. >> It's almost a 'catch-22' proposition. The phone companies are slow to >> implement ISDN because there is little demand for it and the demand is >> waiting for the service to become available. > Huh? ISDN was originally a way to get 56KB service ... but modems on > regular analog lines can almost do this today. ISDN vs market forces. > ISDN 0, Market 1. No, that's not right. even a V.fast modem only reaches what, 28 kbps. Some people say "oh, but with data compression the rate can be much higher". But that same data compression can be employed on a 56KBPS line (or, if the carriers get it worked out, 64KBPS) to maintain a two-to-one advantage. Besides which, the fundamentally asynchronous nature of V.32++ modems is ever-so-slightly less efficient in the time domain than a synchronous link. Finally, let's not forget that for some applications the call setup time really matters. ISDN call setups can be less than a second, I'm told, while a local V.32bis/V.42bis setup can take 22 seconds or more, and a long-distance one can be 50 seconds or more. If you want to have a real-time pseudo-continuous link between, say, two LANs, where the link is setup when needed and then turned off, the call setup time of a modem might be prohibitive. And for some people, the D channel of ISDN is likely to be handy. Burglar alarm monitoring, credit card validations ... lots of other things too. For still others, the B channel data delivery on voice calls would be handy. (ANI, CNID, etc.) >> This is just another example of the difficult time we will have >> installing a nationwide 'information highway'. > It will be if TPC (the phone company) is in charge of installation ;) >> I guess the only way to move the telephone companies is for tens of >> thousands of us little guys to keep asking them for ISDN until they >> wake up and realize that they are losing big bucks in not providing >> this vital service. > Buy a V.fast modem for $499 and get most of the benefit without > the aggrevation of Waiting For Godot ... Of course for many applications you are right. But for some applications, ISDN would offer advantages. Carl Oppedahl AA2KW (patent lawyer) 1992 Commerce Street #309 Yorktown Heights, NY 10598-4412 voice 212-777-1330 ------------------------------ From: marc@dumbcat.sf.ca.us (Marco S Hyman) Subject: Re: No ISDN Despite Big Talk Organization: Codewrights/Ascend Communications Date: Mon, 15 Nov 1993 18:31:10 GMT In article jebright@magnus.acs.ohio- state.edu (James R Ebright) writes: > Huh? ISDN was originally a way to get 56KB service ... but modems on > regular analog lines can almost do this today. Arrgggghhh! How come this apples to oranges comparison comes up again and again? Your analog modem today does 14.4 kbit/s and uses compression to get to 57.6. This is fine IFF YOUR DATA CAN BE COMRESSED 4:1. If you're sending pre-compressed data you get 14.4. If your 14.4 kbit/s phone line does 57.6 then my 56 kbit/s digital service can do 224 kbit/s and isdn lines can do 256 kbit/s. Of course this leaves out the other difference -- your modem probably has an async serial interface and the digital service probably has a sync serial interface. marc marc@dumbcat.sf.ca.us or marc@ascend.com ------------------------------ From: oberman@ptavv.llnl.gov Subject: Re: No ISDN Despite Big Talk Date: Mon, 15 Nov 93 18:41:06 GMT Organization: Lawrence Livermore National Laboratory In article jebright@magnus.acs.ohio- state.edu (James R Ebright) writes: > Buy a V.fast modem for $499 and get most of the benefit without > the aggrevation of Waiting For Godot ... V.Fast modems are pretty impressive, but ISDN they ain't! I don't understand how people can keep saying that V.fast is "just about as fast as ISDN". I belive that V.fast is 28 Kbps. That's a LOT less than a single 64 Kbps ISDN B channel and not even in the ballpark of the 128 Kbps available on the two B channels in a BRI. While some modem purveyors are claiming much faster speeds, these are the result of data compression which works just as well over ISDN as over a modem. If you stick to apple-apples comparisons it's still 128 Kbps vs. 28 Kbps and that's a big difference by any measure. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: koberman@llnl.gov (510) 422-6955 ------------------------------ From: drawson@Tymnet.COM (Dick Rawson) Subject: Re: No ISDN Despite Big Talk Date: 15 Nov 1993 17:19:50 GMT Organization: BT North America, San Jose CA. > Buy a V.fast modem for $499 and get most of the benefit without > the aggrevation of Waiting For Godot ... "Most of the benefit"? Well, half the speed! On a clear day, you can see, say, 24 to 28 k bits/sec from a "V.fast" modem. That's at most half the 56 to 64 k bits/sec of a single ISDN B-channel, and the ISDN Basic Rate Interface has two B-channels. (And your LEC would like to charge you for both of them.) You can run a compression algorithm over either bit stream, so it is not appropriate to compare a "compressed V.fast" with "uncompressed B-channel" connection. Dick Rawson drawson@tymnet.com ------------------------------ Date: Mon, 15 Nov 93 13:49:53 -0800 From: Samir Soliman Subject: Re: TDMA vs. CDMA = Betamax vs. VHS? In article , Ed Casas wrote: > I think these "technical advantages" are mostly a result of Qualcomm > marketing. For example, I looked at Qualcomm's claims for capacity > improvement and found that their claims were made on the basis of > grossly unfair comparisons. For example, the Qualcomm system assumed: > more-directional base station antennas, turning off the transmitter > during silent periods to reduce interference, the use of low-rate > high-gain codes, the use of low-rate speech coding, etc. > A fair comparison would have been between a second-generation TDMA > system (which could make use of many of the above techniques) and a > CDMA system. I think you would then see the capacity advantage for > CDMA eliminated. You should understand that a CDMA receiver starts > off with a major handicap -- its correlator cannot separate signals > anywhere near as well as a TDMA receiver's IF filter. You have to use > a lot of tricks to overcome that initial disadvantage. > To me (at least) the technical superiority of CDMA is far from proven. All the features you have mentioned (except for the more-directional base station antennas) are true features of the existing CDMA system. A system that has been extensively tested by Qualcomm and other interested customers. Some customers did the testing on their own and others in cooperation with Qualcomm. I don't know what did you mean by "more-directional base station antennas". If you mean more sectorized sites, let me tell you that although sectorization improves the trunking efficiency in CDMA, nevertheless we don't count its effect in calculating the relative capacity of CDMA (we usually compare the CDMA capacity to AMPS capacity, therefore if the AMPS uses sectorized cells we calculate capacity based on sectorized sites too). The parameters that really gets factored into the capacity equations are the voice activity factor, processing gain and the frequency reuse efficiency. Talking about fairness, you need to compare what TDMA can offer now vs. what CDMA can offer now. Otherwise you are giving fairness a bad name. Samir S. Soliman Staff Engineer/Manager Qualcomm Incorporated email: ssoliman@qualcomm.com ------------------------------ Date: Mon, 15 Nov 1993 14:18:00 +0000 From: David Boettger Subject: Re: TDMA vs. CDMA = Betamax vs. VHS? In article was written: > In article , wrote: >> I personally suspect this is a bit of a religious debate, > I think these "technical advantages" are mostly a result of Qualcomm > marketing. For example, I looked at Qualcomm's claims for capacity > improvement and found that their claims were made on the basis of > grossly unfair comparisons. For example, the Qualcomm system assumed: > more-directional base station antennas, turning off the transmitter > during silent periods to reduce interference, the use of low-rate > high-gain codes, the use of low-rate speech coding, etc. Have you read IS-95 (CDMA spec) or IS-54B (TDMA) spec? You cite discontinuous transmission, high-gain channel coding, and low-rate source coding as reasons why the comparison is "grossly unfair". First, they are not assumptions; they are part of the CDMA spec. Second, IS-54B _also_ specifies high-gain channel coding and low-rate source coding. I don't see the gross unfairness. As far as "more directional base station antennas" goes, I've not heard anything of that. > CDMA eliminated. You should understand that a CDMA receiver starts > off with a major handicap -- its correlator cannot separate signals > anywhere near as well as a TDMA receiver's IF filter. You have to use > a lot of tricks to overcome that initial disadvantage. What do you mean "separating signals"? If your're talking about multipath, IS-95 specifies a five-fingered RAKE receiver, designed for just that. If you're talking about co-channel interference, the reason CDMA works is that, if one chooses codes properly, many users can share one frequency resource. CDMA's correlators, by definition, MUST do a superlative job of signal separation. > To me (at least) the technical superiority of CDMA is far from proven. I certainly won't take issue with that. David Boettger boettger@bnr.ca I don't speak for my employer. ------------------------------ From: jebright@magnus.acs.ohio-state.edu (James R Ebright) Subject: Re: TDMA vs. CDMA = Betamax vs. VHS? Date: 16 Nov 1993 03:43:27 GMT Organization: The Ohio State University In article edc@ee.ubc.ca (Ed Casas) writes: > A fair comparison would have been between a second-generation TDMA > system (which could make use of many of the above techniques) and a > CDMA system. I think you would then see the capacity advantage for > CDMA eliminated. You should understand that a CDMA receiver starts > off with a major handicap -- its correlator cannot separate signals > anywhere near as well as a TDMA receiver's IF filter. You have to use > a lot of tricks to overcome that initial disadvantage. > To me (at least) the technical superiority of CDMA is far from proven. TDMA is certainly in wider use than CDMA ... but that's not saying much :) The phone folks I spoke to were experimenting with CDMA but if they had to put something on the air today, most used TDMA and hoped for the abovementioned improvements. BTW, did the Qualcomm suit against the other CDMA vendor ever get settled? Single vendor technologies are not usually welcomed in the telcom industry ;) Jim Ebright e-mail: jre+@osu.edu ------------------------------ Date: Tue, 16 Nov 93 10:55:49 EST From: Alex Cena Re: TDMA vs. CDMA = Betamax vs. VHS? Attached are comments from Tom Crawford at Qualcomm after I forwarded him a copy of the TDMA vs CDMA debate on the Digest. ----------------- Alex, I am sure you knew the TDMA vs. CDMA comments would get under my skin and I would have to respond. How do I send this response to Ed Casas, or to the network? My comments are in caps: In article , wrote: >> I personally suspect this is a bit of a religious debate, >> exactly like Betamax vs. VHS, and while technical arguments >> pro and con can be made, whoever has the best marketing is >> going to win. (wink wink) CARRIERS ARE GOING TO INVEST HUNDREDS OF MILLIONS OF DOLLARS, IF NOT MORE, IN DIGITAL TECHNOLOGY. I SUSPECT THEY WILL LOOK BEYOND THE "BEST MARKETING" PITCH TO THE UNDERLYING CAPABILITIES OF THE TECHNOLOGIES. > It's certainly the case that the debate will be settled > politically, but it turns out that CDMA has major technical > advantages: ... I think these "technical advantages" are mostly a result of Qualcomm marketing. For example, I looked at Qualcomm's claims for capacity improvement and found that their claims were made on the basis of grossly unfair comparisons. For example, the Qualcomm system assumed: more-directional base station antennas, turning off the transmitter during silent periods to reduce interference, the use of low-rate high-gain codes, the use of low-rate speech coding, etc. "GROSSLY UNFAIR COMPARISONS" ARE HARDLY AN ACCURATE WAY TO DESCRIBE CLEAR ADVANTAGES. QUALCOMM'S CAPACITY IS 10X TO 20X AMPS CAPACITY USING A 3 SECTOR CELL, HARDLY "MORE-DIRECTIONAL BASE STATION ANTENNAS". CDMA CAN READILY UTILIZE HIGHER DEGREES OF SECTORIZATION TO ATTAIN EVEN HIGHER CAPACITY SHOULD THAT BE NEEDED. UTLIIZATION OF HIGHER DEGREES OF SECTORIZATION IS ACHIEVED MUCH MUCH MORE EASILY WITH CDMA THAN IN A TDMA SYSTEM WHERE FREQUENCY PLANNING ISSUES BECOME INCREASINGLY COMPLEX AS SECTORIZATION INCREASES. WITH RESPECT TO "TURNING OFF THE TRANSMITTER DURING SILENT PERIODS TO REDUCE INTERFERENCE", WHAT DO YOU THINK TDMA DOES? IT ONLY TRANSMITS 1/3 OF THE TIME. WHY? INTERFERENCE. THIS DOES NOT SOUND LIKE AN "UNFAIR COMPARISON" TO ME. "the use of low-rate speech coding" IS AN OFTEN MISUNDERSTOOD ADVANTAGE OF CDMA. IS-95 USES A VARIABLE RATE VOCODER. WHEN THE CALLER IS SPEAKING, THE CONVERSATION IS ENCODED AT 8 KBPS. DURING A PAUSE THE RATE GOES DOWN TO 4, OR 2, OR 1 KBPS. THIS VOCODER AVERAGES ABOUT 4 KBPS. JUST BECAUSE TDMA USES AN 8 KBPS VOCODER ALL THE TIME IS THIS AN UNFAIR COMPARISON? NOT AT ALL. BY USING A VARIABLE RATE VOCODER, AND THROUGH THE COMMON USE OF THE CDMA CHANNEL BY ALL CALLERS SIMULTANEOUSLY, CDMA IS ABLE TO USE THE VOICE ACTIVITY FACTOR AND ESSENTIALLY IMPLEMENT DIGITAL SPEECH INTERPOLATION. THIS IS SOMETHING TDMA IS EVOLVING TO WITH ETDMA. HOWEVER, NOTE A VERY BIG DIFFERENCE: ETDMA WILL HAVE TO UTILIZE A HALF RATE VOCODER (4 KBPS) TO OBTAIN THE ADDITIONAL CAPACITY. THIS MEANS HALF RATE ALL THE TIME, NOT JUST ON AVERAGE. WE DO NOT FEEL THAT VOCODER TECHNOLOGY CAN CURRENTLY PROVIDE QUALITY COMMUNICATIONS LINK USING A HALF RATE VOCODER. IF WE ARE WRONG AND A GOOD HALF RATE VOCODER IS AVAILABLE, QUALCOMM CAN ALSO USE IT IN A VARIABLE RATE IMPLEMENTATION (AGAIN THROTTLING DOWN DURING PAUSES) TO ACHIEVE AN ADDITIONAL FACTOR OF 2 IN CAPACITY GAIN, IE NOW 20X TO 40X AMPS. ALSO, ETDMA'S USE OF DIGITAL SPEECH INTERPOLATION WILL REQUIRE RAPID CHANNEL ALLOCATION, ESSENTIALLY MINI-HANDOFFS DURING EACH PAUSE. THIS IS DIFFICULT TO ACHIEVE WITHOUT SOME CLIPPING OF SPEECH. QUALCOMM'S COMMUNICATION CHANNEL IS ALWAYS UP, HENCE NO DYNAMIC ALLOCATION OF CHANNELS IS NECESSARY. THESE BENEFITS ARE INHERENT TO CDMA. A fair comparison would have been between a second-generation TDMA system (which could make use of many of the above techniques) and a CDMA system. I think you would then see the capacity advantage for CDMA eliminated. FROM MY DISCUSSION ABOVE YOU SHOULD NOW REALIZE THIS STATEMENT IS FALSE. ETDMA WILL UTILIZE A HALF RATE VOCODER (INCREASING TDMA CAPACITY FROM 3X TO 6X, AND DIGITAL SPEECH INTERPOLATION, INCREASING THE CAPACITY FROM 6X TO ABOUT 12X OR 15X, ASSUMING EVERYTHING WORKS WELL). CDMA, WITH A HALF RATE VOCODER WILL THEN BE AT 20X TO 40X (EVEN WITHOUT BETTER USE OF SECTORIZATION). You should understand that a CDMA receiver starts off with a major handicap -- its correlator cannot separate signals anywhere near as well as a TDMA receiver's IF filter. THE CDMA SIGNAL IS ACTUALLY BELOW THERMAL NOISE LEVEL, AND IS "SEPARATED" FROM THE OTHER SIGNALS THROUGH THE PROCESSING GAIN, A FEAT ANY TDMA RECEIVER IF FILTER WOULD BE UNABLE TO DO. THE WHOLE POINT OF CDMA IS THAT YOU DO NOT HAVE TO SEPARATE THE SIGNALS OVER THE CHANNEL BY FREQUENCY OR TIME. DIFFERENT CODES PERMIT YOU TO PICK OUT YOUR CONVERSATION. You have to use a lot of tricks to overcome that initial disadvantage. To me (at least) the technical superiority of CDMA is far from proven. "TRICKS" IMPLY DECEPTION. CDMA'S TECHNICAL PERFORMANCE AND BENEFITS HAVE BEEN WELL TESTED AND PROVEN AGAIN AND AGAIN IN NUMEROUS TRIALS. THESE TRIALS HAVE TAKEN PLACE IN: NEW YORK CITY, NEW YORK; CHICAGO,ILLINOIS; TAMPA, FLORIDA; WASHINGTON, D.C.; DALLAS, TEXAS; SAN DIEGO, CALIFORNIA; SEOUL, KOREA; MUNSTER, GERMANY; GENEVA, SWITZERLAND; AND SYDNEY, AUSTRALIA. CARRIERS HAVE PUBLISHED REPORTS ON TRIALS IN SEVERAL OF THESE CITIES. IN ADDITION, CDMA HAS BEEN THROUGHALLY EXAMINED AND PROBED BY THE TIA IN PREPARATION FOR IS-95 STANDARDIZATION. THE RESULTS OF CDMA TESTING, CLEARLY DEMONSTRATING THE BENEFITS, ADVANTAGES AND PERFORMANCE CAPABILITIES ARE READILY AVAILABLE TO PARTIES WHO ARE TRUELY INTERESTED IN EXAMINING THEM. THOMAS R. CRAWFORD DIRECTOR OF MARKETING, DIGITAL CELLULAR AND WIRELESS TECHNOLOGY QUALCOMM tcrawford@qualcomm.com Tom Crawford (X 4820) ------------------------------ From: dave@llondel.demon.co.uk (David Hough) Subject: Re: TDMA vs. CDMA = Betamax vs. VHS? Reply-To: dave@llondel.demon.co.uk Date: Tue, 16 Nov 1993 07:16:22 GMT TDMA has one big disadvangate in the modern world ... it can cause all sorts of interference to nearby electronics. In the UK, the first GSM phones have arrived, and one of their characteristics is to cause a buzz at a few hundred hertz in sensitive electronics nearby. Most susceptible appears to be hearing aids, especially if the phone user also wears one! As any radio amateur worth his salt will know, 100% amplitude modulation of a signal with what amounts to a square wave is bound to cause problems. Still, look at it the other way: now we have something else to blame when the TV picture breaks up into a mass of interference :-) Dave G4WRW @ GB7WRW.#41.GBR.EU AX25 dave@llondel.demon.co.uk Internet g4wrw@g4wrw.ampr.org Amprnet ------------------------------ End of TELECOM Digest V13 #764 ****************************** ****************************************************************************** Downloaded From P-80 International Information Systems 304-744-2253