Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!usc!ucsd!ucbvax!agate!telecom-request From: dave@westmark.westmark.com (Dave Levenson) Newsgroups: comp.dcom.telecom Subject: Calling Party ID on Two Party Lines Message-ID: Date: 1 Apr 91 04:42:04 GMT Sender: Telecom@eecs.nwu.edu Organization: Westmark, Inc., Warren, NJ, USA Lines: 34 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 261, Message 5 of 10 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 6857