dave@westmark.westmark.com (Dave Levenson) (04/01/91)
John Higdon asks how party identification works on two party lines.
The party whose ringer is connected between Tip and ground, known as
the 'tip party', has the hookswitch wired so that part of the ringer
is connected between tip and ground without the normal DC blocking
capacitor whenever the handset is off-hook. The other party, called
the 'ring party', does not. After collecting enough digits to
identify the called party, the originating register in a five-crossbar
switch performs a tip-to-ground resistance check for about 100 msec.
This is the 'click-plunk' you hear when originating from either party
on such a line. If it finds resistance less than about 2000 Ohms, it
identifies the caller as tip party.
This is why, years after most of us could walk into almost any
appliance store and buy a telephone set equipped with a modular jack
and take it home and plug it in, subscribers on party lines are denied
this right. The fine print in the phone book, and some mouldy old
Bell System Practice, no doubt, requires that only non-modular
telephone sets furnished by the telephone company may be used on
two-party service with ANI.
The telco must wire the correct selective ringing and party
identification option when installing the set.
Any why doesn't the unbalanced line condition result in hum during the
call? Because the ringer's inductance hides the ground-loop-induced
AC hum path!
Dave Levenson Internet: dave@westmark.com
Westmark, Inc. UUCP: {uunet | rutgers | att}!westmark!dave
Warren, NJ, USA AT&T Mail: !westmark!dave
Voice: 908 647 0900 Fax: 908 647 6857wb8foz@mthvax.cs.miami.edu (David Lesher) (04/02/91)
John Higdon asks how party identification works on two party lines. Dave Levenson explains... > This is why, years after most of us could walk into almost any > appliance store and buy a telephone set equipped with a modular jack > and take it home and plug it in, subscribers on party lines are denied > this right. Err, Ma didn't always do this correctly. A technician (who worked on a project of mine at a past agency) bought his party-line 500 set from Ohio Bell. He wanted to install some more sets. You guessed it - he was ring party! We wired the other 500 sets to also provide the ground through the ringer. I never *did* figure out how Ma was so confused that She could provide party line service, charge for party line service, and yet not KNOW it when they offered to sell him the phone! Yet when he called them about it, they pitched him about getting private line service. ;_] By the way, Lou was one of the hold-outs I mentioned. He had been the ONLY party on the pair for several years, and had NO intention of giving in, when I last talked to him.