Software Vault: The Diamond Collection/The Diamond Collection (Software Vault)(Digital Impact).ISO/cdr16/tc15_034.zip/TC15-034.TXT

Text File | 1995-01-22 | 28KB | 632 lines

TELECOM Digest     Tue, 17 Jan 95 10:14:00 CST    Volume 15 : Issue 34

Inside This Issue:                          Editor: Patrick A. Townson

    B8ZS, AMI, Bipolar Line Coding (William Wood)
    India Opens Doors to Foreign Telco's (Nikhil)
    Belgacom and Panaphone Greece (Viviane Engels)
    Antenna For Cellular Phone in Bangkok (Roland Peter Sauermann)
    GSM Information Wanted (Vincent Erwig)
    Question on Call-Back Operators (John Hacking)
    Anyone Have Experience With LDDS/Metromedia? (Chuck Lukaszewski)

TELECOM Digest is an electronic journal devoted mostly but not
exclusively to telecommunications topics. It is circulated anywhere
there is email, in addition to various telecom forums on a variety of
public service systems and networks including Compuserve and America
On Line. It is also gatewayed to Usenet where it appears as the
moderated
newsgroup 'comp.dcom.telecom'.

Subscriptions are available to qualified organizations and individual
readers. Write and tell us how you qualify:

                 * [e-mail] *

The Digest is edited, published and compilation-copyrighted by Patrick
Townson of Skokie, Illinois USA. You can reach us by postal mail, fax
or phone at:
                    9457-D Niles Center Road
                     Skokie, IL USA   60076
                       Phone: [phone]
                        Fax: [phone]
  ** Article submission address only: [e-mail] **

Our archives are located at lcs.mit.edu and are available by using
anonymous ftp. The archives can also be accessed using our email
information service. For a copy of a helpful file explaining how to
use the information service, just ask.

**********************************************************************
***
*   TELECOM Digest is partially funded by a grant from the
*
* International Telecommunication Union (ITU) in Geneva, Switzerland
*
* under the aegis of its Telecom Information Exchange Services (TIES)
*
* project.  Views expressed herein should not be construed as
represent-*
* ing views of the ITU.
*
**********************************************************************
***

Additionally, the Digest is funded by gifts from generous readers such
as yourself who provide funding in amounts deemed appropriate. Your
help
is important and appreciated. A suggested donation of twenty dollars
per
year per reader is considered appropriate. See our address above.

All opinions expressed herein are deemed to be those of the author.
Any
organizations listed are for identification purposes only and messages
should not be considered any official expression by the organization.
----------------------------------------------------------------------

Date: Tue, 17 Jan 1995 06:24:16 -0800
From: [e-mail] (William Wood)
Subject: B8ZS, AMI, Bipolar Line Coding


In telecom 15.29.20, Phillip Schuman asks the question which many
people have asked about the issues of B8ZS, AMI and bipolar line
coding and their relationship to bit robbing for voice. Though I am
not an engineer and have limited understanding of some technical
issues, I offer my experience on the matter for those who wish to
listen. I hasten to add that it is my intent to convey concept level
information in order to build mental constructs which can act as a
framework for understanding technicalities. I have often been accused
of oversimplification in my efforts. I take this as a compliment,
flames notwithstanding, because the majority of people in
telecommunications do not have the technical training necessary for
understanding engineering level material; but were not stupid, and
can understand a coherent explanation if one is offered.

First the simple answer. There is no direct relationship between bit
robbing and line coding. Even so, there are some indirect
relationships
if you skew you vision just a little. In order to understand, a bit of
history is needed.

Bit robbing is a process for transporting single line supervision and
signaling between two individual digital carrier (T type) channel
units.  It developed in a more or less logical fashion from the
necessity for converting battery and ground (DC) type supervision into
something which could go thru a carrier system.

The drop, loop, line, customer, user, access or phone side of a switch
(in Plain Ol Telephone Service POTS) consists of two wires. Battery
(-48v in USA, 50 v elsewhere) is applied to one of the wires by the
switch and ground to the other. When the phone is taken off hook a
loop closure is made (known as loop start signaling) which allows
current flow between the two (tip and ring) wires. This is supervision
to the switch to tell it to put dial tone on the loop pair toward the
telephone. Next, the user signals what number they want by either
rotary dialing or pushing keys on the DTMF (dual tone multifrequency)
pad.

In the case of the rotary dial, current flow (battery to ground) is
interrupted in series intervals which in turn tell the switch where to
connect. This kind of DC (direct current) signaling/supervision works
fine as long as all the lines are physically attached to the same
switch.

Let us say though, that you want to connect to a line that is out of a
switch which is in another city, state or country. The facilities
between switches are shared on an as-needed basis and are know as
trunks. The most significant thing to know at this point is that
battery and ground signaling and supervision cannot now, nor could
they ever, be sent over a carrier system. Carrier systems are used to
connect switches by providing the physical facilities for the trunks.
(The techies will insist that metallic [no carrier] trunks can send
DC. True, but there are so few left in the USA, and the Dxing methods
so numerous, I will not deal with them here.)

Analog carrier systems can transport only audible (voice) tones so a
conversion process is done to change battery and ground signaling into
an audible tone. Each of the individual voice frequency channels in a
carrier system are band limited to 4 KHz. The usable part (for
transporting conversations) of this pancake of capacity is further
limited to around 3 KHz (300 - 3400 Hz).  This range is known as the
VF
Band to transmission folks.

DC signaling/supervision can be converted into a tone that is either
in-the-band or out-of-the-band. As an example, type N1 carrier
channels internally can convert a battery on-off signal into a 3700 Hz
on-off tone signal. This tone is out of voice band signaling because
it's above 3500 Hz. Filters in the channel units block the
signaling tones from the callers. A second option is to use an
external tone generator such as an SF (signal/single frequency) unit.
SF units typically convert DC supervision and signaling into 2600 Hz
(USA) on-off tones. This is an in band (between 300 and 3400
Hz) signal type. Notch filters are supposed to keep this tone from the
callers too. (Sometimes the filters dont kick in quick enough and
you can hear the tone chirp for just an instant as the distant
end hangs up on some long distance calls even today. Not much of the
in-band left because a good whistler can put up bogus calls so the
phone companies have disconnected most of these types of trunks.)

With the advent of digital carrier systems (T carrier in early 60's) a
decision was made to continue to use in-band (SF) signaling but also
support a twist on the out-of-band idea. Because the signal leaving an
individual channel unit was now digital, a single pulse (bit) out of
the
periodic series of eight bits belonging to that channel could be
designated as a signaling/supervision bit. To illustrate; say that an
off-hook, battery or seizure signal was presented to the channel unit
by the phone or switch. This seizure would cause the channel unit's
signaling function to stop applying an idle state mark bit onto the
trunk facility. The receiving channel unit would detect the change
from
marking to spacing for this bit position and in turn apply a seizure
toward its own switch or phone.

The earliest T systems reserved this bit all the time for signaling
(and
sometimes even a second bit position) but this was soon replaced by
the
current system. Because each channel creates an eight bit unit (octet
or
byte), any single bit occurs 8 thousand times a second (the Nyquist
rate
for a 4 Hz channel). The system was originally designed to facilitate
only interoffice dial pulse trunks. (In fact, in my area the telephone
company didn't even originally consider T as a carrier system. It
was an interoffice transport mechanism belonging to a different union
group than that which maintained carrier systems.) The rate for dial
pulses is only 10 to 12 pulses per second, so using a full 8 Kbps of
channel bits is massive overkill.

The current system still uses a single bit out of the eight, but now
it only does it during the sixth appearance of the time slot into
which the channel byte or octet is regularly dumped. The concept is
that there is 64 Kbps signal (8 K Nyquist x 8 bit unit) ostensibly
being created by the channel unit for payload transfer, but
occasionally (every 6th byte or octet from the channel) a single bit
is robbed and designated as a signaling/supervision indicator for a DC
state on the drop side of the channel unit. This still results in
creating a 1.3 Kbps out of (voice) slot signaling sub channel (sliced
into A, B, and sometimes C & D sub-sub channels) which is only
semi-massive overkill. Because dial pulsing is so slow for address
transfer, some trunking over T carrier uses the bit robbing function
for off /on hook supervision only and MF (multi-frequency which is not
the same set of tones as DTMF) for address transfer. In some
applications the bit rob is not used at all.  SF is used for hook
supervision and DTMF for address transfer. Lots of variations here on
the main theme of using a carrier transmission bit on/off as a
representation of a signaling/supervision battery on/off condition.
Hold this thought.

The Bipolar, AMI and B8ZS question relates to the composite, or
multiplexed, signal leaving the digital (channel bank) mux. A standard
DS1 digital stream consists of 24 DS0 time division multiplexed to run
at a combined rate of 1.544 Mbps (24 x 64 Kbps + 8 Kbps framing) plus
or
minus a little . On twisted pair cables this is, even today, a
significant number of bits. The digital square wave which is the DS1
stream is physically constructed of either +3, -3 or zero voltage
pulse
positions. The +3 and -3 volt pulses are known as marks and the zero
voltage pulse or time positions are called spaces, (words straight
out of  19th century telegraph). For a number of technical reasons,
the
transmitter is required to reverse the DC voltage value as each mark
is
transmitted. That's where AMI gets its name. Each Alternation of a
Mark
must be Inverted in voltage value. Example with mark as 1, and space
as
0: 101010111000001 could be transmitted (left to right) as
+3,z,-3,z,+3,z,-3,+3,-3,z,z,z,z,z+3. This signal form came to be known
as bipolar because it has two (bi) poles of voltage, although it is
actually a ternary (three) form because zero volts also counts as a
state.

If you've stayed with me this long, you get the reward here.

The B8ZS is what seems to put the twist in everyone's knickers. Since
the earliest days of T carrier, there has been a ones density and
consecutive zero requirement for the DS1 stream. For our purposes, the
most significant is that there be no more than 15 consecutive spaces
(zero voltage bit times) in the ongoing DS1 stream.  On the face of
it,
this would not seem to be a problem because each channel generates
only
an 8 bit unit for transmission. Even if it sent an all zero octet, no
harm would be done. Remember though the DS1 is a serial, time division
multiplexed stream with one channel octet following another like ducks
in an endless row. If two consecutive channel time positions contained
all zero octets the total zeros in series would be 16, which is
sufficient to cause clocking errors on the system.

There are three solutions to this problem. The first, and original, is
to restrict each individual channel from ever sending an all zero
byte.
This is the solution which has always restricted services like DDS
from
sending 64 Kbps. Each individual DDS channel unit allows only seven of
the eight bits to be used for DDS payload and reserves the 8th bit to
make it a mark in order to insure the channel can't send all zeros.
Because the Nyquist rate in T carrier channels is always 8 k, and the
DDS channel unit gives over only 7 bits to it, the result is 56 Kbps.
It's important to note here that even though the results of
restricting
zeros and bit robbing for signaling/supervision may result in a
channel
payload of less than the full 64 Kbps DS0, the two things are not
related.

The second way to meet pulse density rules is to have the transmitter
actively monitor the DS1 stream as it is applied to the transmission
line. This is the B8ZS solution. In this process when the transmitter
recognizes a series of eight or more zeros (and it doesn't need to
know
if they are all from one channel or a combination of two channels) it
will substitute a different digital bit pattern for that series of
eight. Instead of sending z,z,z,z,z,z,z,z it will send
z,z,z,v,s,z,v,s.
The z is zero volts, the v is a 3 volt pulse in the same polarity as
the
last valid mark signal which is technically a violation of the AMI
rule. The s is a substitution bit for the original zero value at this
time position. At the receiver, this string is converted back to
z,z,z,z,z,z,z,z and given over to the channel receivers. Bipolar 8
Zero
Substitution (binary 8 zero suppression?) permits any individual
channel
to send any combination of 8 bits with no restrictions. This allows
interoffice systems to provide clear channel 64 Kbps service. Once
again, notice that this has no direct relationship to bit robbing for
supervision. It has an indirect (skew your vision a little)
relationship
because a robbed bit could be changed on the line to conform to B8ZS
format, but it will be changed back at the receiver to its correct
form
with the process being transparent between the near and far channel
units. European systems can also do this process but use a different
substitution pattern.

 The third way is called ZBTSI for Zero Byte Time Slot Interchange.
But,
that's a story for another time.


WE Wood    Technotranslater
Techish to English Translation
Techtrans Animatics Group

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

From: Nikhil <[e-mail]>
Subject: India Opens Doors to Foreign Telcos
Organization: National Centre for Software Technology, India
Date: Tue, 17 Jan 1995 06:52:35 GMT


India has opened its doors to foreign telecom companies for providing
the telephone service in the local loop. So far, the Indian Government
held the monopoly for telecom for the last fifty years. This resulted
in a long waiting list of up to ten years for getting a telephone
connection.

For the last three years India has been reforming its economic
policies
to speed up the development. Realizing that good telecommunications
are a necessity in a liberal economy, it has opened it doors to
foreign
telcos and banned government companies from investing in the telecom
sector.

The highlights of the new guidlines anounced yesterday are:

* Foreign telecom companies can bid for providing services
  as joint venture with a local company.

* Companies presently having minimum 0.5 million lines in
  service can qualify to bid.

* Foreign equity participation must be minimum 10% and
  maximum 49%.

* Area divided for bidding into Telecom circles of class
  A,B and C where class A circle is high density city.

* Minimum net worth of the joint venture company should be
  Rs.300 crores (US$ 100 million) for Class A, Rs.200 cr.
  for Class B and Rs.100 crores for Class C areas.

* Assured business for next fifteen years with provision to
  extend for another ten years.

However the long distance and international business still remain a
monopoly of government companies for the next five years.


Nikhil Thakkar
email: INTERNET: [e-mail]
X.400 : G=SYSTEMS S=NOVASOFT A=VSNB C=IN

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

From: [e-mail] (Viviane Engels)
Subject: Belgacom Be-Panaphone Greece
Date: 17 Jan 1995 05:59:36 GMT
Organization: University of Ghent, Belgium


I send this letter to protest for the services of Belgacom Proximus
Cellular Telephone service and that of the Greek Panaphone.  I am an
owner of a Panaphone number and I am visiting Belgium since 10
December 1994.  My telephone is not working in a certain area of
Belgium even the Proximus signal is very stong. This area is
established between the cities: Ghent, Antwerpen, Brugge, Kortrijk. In
none of the above cities the phone is working (except Kortrijk). The
Belgium coast has also a problem.  The networks work normal at the
rest of Belgium (as far as I checked).

After my contact with both companies they just blame each other.
Belgacom thinks the problem is for whole Belgium territory (so its a
Greek problem) and the Greeks say there is a problem in a part of
Belgium without being able to define where (Belgium problem).  My
remark is that all these people except doing their best to solve the
problem there are also deaf (they have a client service department
just to put nice music on the phone when someone is waiting for an
answer).  Finally except that they are losing money and credibility
for their services, they are also against the law since in Greece is
advertised use of Greek cellular phones in whole Belgium territory.
If someone responsible is listening I whould appreciate an answer.

P.S. I know Greek people doing business in Belgium that they were
forced to buy a Belgian-Proximus number also just to work.


[TELECOM Digest Editor's Note: Ah, readers ... does the complaint
above sound familiar. Telco blames long distance carrier, and long
distance carrier blames telco for whatever is wrong. Each convinced
the other must correct the problem. Are there any European readers of
the Digest who can make suggestions to this fellow?    PAT]

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

From: [e-mail] (Roland Peter Sauermann)
Subject: Antenna For Cellular Phone in Bangkok
Date: 17 Jan 1995 11:31:54 GMT
Organization: National Electronics and Computer Technology Center,
Bangkok


I am struggling with pretty poor AMPS 800 service in Bangkok on my
three
Watt Diamond-Tel cellular phone that I have permanently mounted in my
car.  I have noisy calls, call overlapping, and disconnected calls.
The problems are probably not unique to any big city where the cells
are overloaded, and there are lots of tall buildings and interference.

My question is what is the optimum antenna for this environment? I
currently have one of those antennas where the cable side is glued on
one side of the windshield and the antenna proper is on the other
side.
My windshield is also very steep on my truck so the angle between the
base and the antenna is very small.

·

Would I do better with a Magnetic mounted antenna on the roof? What
would
suit me better a 3db or a 5db one?  There seem to be a whole bunch of
options, some cost three times others. One guy told me the material
was
different ... some antennas simply have squiggles in them others have
a
thick section of a ceramic or hard plastic. I know I need to be sure I
get one for the correct phone system (we have five different types
here
from 470mhz, 800, 900 to the new Digital stuff). How do I evaluate
these
different antennas that run between $25-$60 and apparently have
different
properties?

Thanks for any suggestions.


Cheers,

Roland P. Sauermann   [e-mail]   Bangkok, Thailand

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

From: [e-mail] (Vincent Erwig)
Subject: GSM Information Wanted
Date: Tue, 17 Jan 1995 13:32:37
Organization: Eindhoven University of Technology, The Netherlands


Can anybody give me some information on where and how I can find
information about GSM?  I'm interested in the development of the GSM
network, and the specific features that GSM / GSM telephone has, what
new technologies have been used, and the advantages / disadvantages
compared to other cellular phone systems.

I need this information for a study project.

Many thanks in advance.


Vincent Erwig    [e-mail]

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

Date: Tue, 17 Jan 1995 20:55:00 +1000
From: [e-mail]
Subject: Question on Call-Back Operators


There has been a great deal of discussion in the Australian media
lately about Call-Back Operators and I'm interested in how they
operate from a customer's point of view.

 From the little I know, it would appear that there are four possible
ways of Call-Back Operator customers placing calls.  These are:

1.  Customer calls an international freecall number and talks to a
live
    operator who then calls the customer back and presents the
customer
    with dial-tone. The customer then dials the international number
    required.

2.  Automatic version of the above -- customer calls an international
    freecall number, lets it ring three times and then hangs up. Then
some
    sort of black box works out which customer called, calls the
customer
    back and presents the customer with dial-tone. The customer then
dials
    the international number required. The customer can only do this
from
    one telephone number.

3.  Customer calls an international freecall number, enters an account
number
    PIN number and the number that they are calling from.  A black box
then
    validates the customer account details and then calls the customer
back
    on the phone number they entered and presents the customer with
dial-tone.
    The advantage of this method over two is that the customer can get
the
    call back to any phone number.

4.  A "bombardment" system -- the call back operator's black box polls
    the customer's phone line somehow and presents the customer with
dial-tone
    without any call back.

My questions are:

a)  Are there any other methods of operation available? Obviously
method four
    is the most convenient from the customer point of view.

b)  How does the "bombardment" system work (method four)?

c)  Are there significant savings in using call-back operators or is
it
    just a matter of a few cents per minute depending on time of day?

d)  Are there any hidden tricks or traps that customers should be
aware of?

I run a small business and make a significant number of calls to the
USA, UK
and Canada and I'm interested in saving money on my international
traffic.
Any information or advice would be appreciated.


Thanks in anticipation.

John Hacking   Manager
Queensland Training Systems


[TELECOM Digest Editor's Note: Why would method four (polling) be the
most
convenient? I think it would be the least convenient since you never
know
when you are going to want to make a call versus when it the next time
you
are going to be 'polled'. The other thing to watch out for where
callback
systems are concerned are the *huge* number of misdialed calls (and/or
telemarketer calls) to your 'callback number' which result in a call
being
made to you at all hours of the day and night (relative to your time
of
day) resulting in many cases in admin charges levied to your account
for
calls you did not make, to say nothing of the inconvenience of
answering
the phone at three in the morning your time to be greeted with
callback
dialtone you don't want merely because some fool in the USA
accidentally
dialed your callback number and let it ring a couple times before
deciding
he dialed in error. I sold a service called Telepassport for awhile,
and
wrong number/telemarketer calls to the numbers on their switch were an
awful nuisance to their subscribers. They tried everything to reduce
the
instances of wrong numbers, i.e. they set their switch so if *more
than
one ring was received* before the caller disconnected, it was assumed
to
be a wrong number. This meant legitimate subscribers had to be
instructed
to dial their callback number and disconnect *IMMEDIATLY* when they
heard
a 'click' indicating they had connected and the switch was about to
return
an audible ringing signal. The assumption was telemarketers would let
it
ring at least three or four times before disconnecting, as would most
people getting a wrong number. Then instead of using numbers in lower
Manhattan -- apparently an area where incorrect dialing is legion --
they
got blocks of numbers in New Jersey, from an area where it is assumed
telemarketers are less interested due to the demographics of the area.
You know what? Their callback subscribers still get awakened at odd
hours
by unsolicited callbacks due to someone in the USA triggering the
switch
in error (or on purpose, trying to sell something).

There ought to be a flag which tells the CO receiving a call if the
call
is from within or without the USA, and to reject those calls which
originate
in the USA. ("I'm sorry, the number you dialed cannot be reached from
within the USA").  I am pretty certain this can be done since not long
ago
I tried to call a place in Haiti (of all places!) and the response I
got
at the distant end after dialing the number was "the telephone you are
calling does not accept calls from international points ... this is a
Cable & Wireless recording, <switch number ID>".   PAT]

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

From: [e-mail] (chuck lukaszewski)
Subject: Anyone Have Experience With LDDS/Metromedia?
Date: Tue, 17 Jan 1995 14:23:22 GMT
Organization: Minnesota Regional Network


I received some information from LDDS/Metromedia yesterday about their
long distance service. The rates seem entirely too good to be true,
and I'm wondering if anyone here has experience (good or bad) that
they would share.

At the moment, I'm spending a lot of time on the telephone to NYC.
After a pretty exhaustive evaluation of AT&T, Sprint and MCI we found
the lowest we could get was 23.7 cents per minute peak on AT&T.  LDDS
claims to charge 15 cents per minute with a one year commitment
(includes a 90-day out clause). I talked to AT&T and they're pulling
the "we're regulated and can't compete with those numbers" routine.


chuck lukaszewski    [e-mail]   [e-mail]

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

End of TELECOM Digest V15 #34
*****************************