Hacker Chronicles 2 (Alt)/The_Hacker_Chronicles_Volume_II-CD2.iso/td/td13_764.txt

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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: [e-mail] (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 <[e-mail]>, [e-mail]-
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   [e-mail]
k1io             or [e-mail]   voice:[phone]
Standard Disclaimer:  Opinions are mine alone; sharing requires permission.

------------------------------

From: [e-mail] (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 <[e-mail]> [e-mail]
(James R Ebright) writes:

> In article <[e-mail]> john.eichler@grapevine.
> lrk.ar.us (John Eichler) writes:

>> [e-mail] (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: [e-mail] (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 <[e-mail]> [e-mail]-
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     [e-mail] or [e-mail]

------------------------------

From: [e-mail]
Subject: Re: No ISDN Despite Big Talk
Date: Mon, 15 Nov 93 18:41:06 GMT
Organization: Lawrence Livermore National Laboratory


In article <[e-mail]> [e-mail]-
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: [e-mail] [phone]

------------------------------

From: [e-mail] (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 [e-mail]

------------------------------

Date: Mon, 15 Nov 93 13:49:53 -0800
From: Samir Soliman <[e-mail]>
Subject: Re: TDMA vs. CDMA = Betamax vs. VHS?


In article <[e-mail]>, Ed Casas <[e-mail]>
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: [e-mail]

------------------------------

Date: Mon, 15 Nov 1993 14:18:00 +0000
From: David Boettger <[e-mail]>
Subject: Re: TDMA vs. CDMA = Betamax vs. VHS?


In article <[e-mail]> was written:

> In article <[e-mail]>, <[e-mail]> 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    [e-mail]
I don't speak for my employer.

------------------------------

From: [e-mail] (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 <[e-mail]> [e-mail] (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: [e-mail]

------------------------------

Date: Tue, 16 Nov 93 10:55:49 EST
From: Alex Cena <[e-mail]>
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 <[e-mail]>, <[e-mail]> 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
[e-mail]
Tom Crawford
(X 4820)

------------------------------

From: [e-mail] (David Hough)
Subject: Re: TDMA vs. CDMA = Betamax vs. VHS?
Reply-To: [e-mail]
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
[e-mail]  Internet
[e-mail]      Amprnet

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End of TELECOM Digest V13 #764
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