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From: varney@ihlpf.att.com (Al L Varney)
Newsgroups: comp.dcom.telecom
Subject: Re: Reference Book Wanted on Telephones
Message-ID: <9620@accuvax.nwu.edu>
Date: 11 Jul 90 15:54:54 GMT
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X-Telecom-Digest: Volume 10, Issue 475, Message 9 of 9


In article <9506@accuvax.nwu.edu> sgtech!adnan@ico.isc.com (Adnan
Yaqub) writes:

>Could some kind body please point me to a suitable reference which
>describes the signaling between the main office and my home phone.  I
>would like to know such things as how much power is provided, what the
>ring signal is like, how the click for call waiting is done, etc.

There is no true reference for this, since the answer depends on where
you look at the subscriber loop; central office or customer end.
There are no requirements I know of that mandate requirements on
central office output viewed at the subscriber end of the loop.
Essentially, central offices have "requirements" (with lots of
exceptions) for inputs and outputs at the central office end of the
loop, designed to work with various customer equipment over various
loop distances/conditions.  The primary "voluntary" requirement
document for the central office switch today is the Bellcore LSSGR
series, particularly,

  TR-TSY-000506, Signaling,
          (this might answer your "signaling" question)
  TR-TSY-000510, System Interfaces
          (here's the power and electrical stuff)
  TR-TSY-000515, Electromagnetic and Electrical Environment
          (lightning protection, EMI, etc. on the loop)
  TR-TSY-000522, Features Common to Residence and Business Customers III
          (Call Waiting is in here, & other Custom Calling stuff)

Also of interest is an older publication,
  PUB 61100 Analog Voiceband Interface between the Bell System Local Exchange
            Lines and Terminal Equipment  -- I believe this replaced with
  TA-NPL-000912, Compatibility Information for Telephone Exchange Service
  (order reference RFC 89-0007)

There are a series of Technical Advisories (TA) that don't cost money,
but Bellcore says they are distributed to "members of the
telecommunications industry."  The TRs above will cost about $200;
they take plastic on (201) 699-5800.  Ask about TAs, usually you have
to write.

Note that the output of a switch is not necessarily connected to your
telephone, so don't make any assumptions about your end of the loop.
There are Pair-gain, analog carrier, digital carrier, loop multiplex
and range extension equipment that could sit between your switch and
your telephone.  They each have their own set of requirements for the
telephone side of the subscriber "loop".  Even if you knew the
information today, it could change tomorrow, and no notice would be
given.  So long as the "standard" telephone works, the loop can
change.

So, let's say you found out all this stuff for YOUR TELEPHONE line and
wanted to use the information in building an interface to the
telephone system.  Unfortunately, many manufacturers did this in the
past, and were dismayed (or their customers were) to find that
telephone lines are not the same everywhere, or even the same from day
to day.  The requirements on YOUR end of the loop are specified in the
FCC part of the published Federal Regulations (47 CFR) Section 68.
Any reasonable library should have a copy.  This will give you power,
ringing, timing and signaling requirements your equipment must meet.
There are all kinds of requirements, including such things as (para.
68.318(c)1 -- "...Automatic dialing to a particular number must cease
after fifteen successive attempts."  Want to guess how many
modems/terminal emulators violate this?  Also check out EIA Standard
RS-470, Telephone Instruments with Loop Signaling for Voiceband
Applications.

In summary, there is no detailed single reference, any library has
general references (except for the Call Waiting signal) under the
Telephony heading, and Section 68 details your equipment's allowed
behavior for legal access.  I don't believe the FCC has requirements
for the switch interface, but the LSSGR documents the interface that
most switches meet, and a lot of PUC rulings and court cases over many
years probably define the telephone company's real legal interface to
a particular customer.

The opinions above are my own, the facts speak for themselves.


Al Varney, AT&T Network Systems, Lisle, IL