Party line (telephony)
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In twentieth-century telephone systems, a party line (also multiparty line or shared service line) was an arrangement in which two or more customers were connected directly to the same local loop. Prior to World War II in the United States, party lines were the primary way residential subscribers acquired local telephone service. British users similarly benefited from the party line discount. Farmers in rural Australia used party lines, where a single line travelled miles from the nearest town out to one property then the next.
Originally, in order to distinguish one line subscriber from another, operators developed different ringing cadences for the subscribers, so that if the call was for the first subscriber to the line, the ring would follow one pattern such as two short rings, if the call was for the second subscriber, the ring would sound another way, such as a short ring followed by a long one, and so on. Since all parties utilized the same line, it was possible for subscribers to listen in on other subscribers' calls. Frequently ringing phones were an annoyance, so selective ringing methods were introduced in the mid-twentieth century.
Especially effective on two-party lines was the distinction between tip party and ring party. Each telephone bell, rather than being connected across tip and ring as usual, was connected from one wire to local ground. Thus only the selected station in a two party line would ring. For multiparty lines all the "tip parties" or all the "ring parties" would ring, in this semi-selective scheme. This system was also used in the United Kingdom where X and Y subscribers on an A&B wire system would be rung on B wire and earth for the X subscriber and on the A wire to earth in the case of the Y subscriber. The momentary earth condition to initiate a call by first getting dial tone would have a similar convention. This arrangement was therefore susceptible when lines were reversed or parts of the 'bridge tap' were reversed; otherwise the system did work satisfactorily in the absence of a complete pair per line or subscriber. Frequently, only sets that are owned and installed by the connecting telephone company are permitted on the party line; the phone's bell had to be configured and grounded by a technician for the appropriate ringing signal. An off-the-shelf telephone may ring for both lines if plugged into the party line.
Later, independent systems applied multiple ringing frequencies for fully selective ringing. (The Bell System eschewed frequency selective ringing.) The ringers in party-line phones were tuned to distinguish several different ringing signals so that only the desired party's phone would actually ring. In this arrangement the only inconvenience of a party line was occasionally finding the line in use (by hearing talking) when one picked up the phone to make a call. If one of the parties used the phone heavily, then the inconvenience for the others was more than occasional, as depicted in the 1959 comedy film Pillow Talk.
Even for lines with selective ringing, calls to another party on the same party line, known as "reverting calls", required special equipment and procedures. One such piece of equipment allowed a user to hear the conversation on the line without interrupting the conversation.
Characteristics of party lines
- In rural areas in the early twentieth century, additional subscribers and telephones were frequently connected to the single loop available, with numbers reaching into the several dozen, leading to extreme congestion.
- With party line service, it was usually necessary to complete a long distance call through the operator to identify and correctly bill the calling party.
- A two-party line split between tip party and ring party could be created in such as way as to allow the central office to determine which party placed an outbound toll call by detecting that one of the ringers was disconnected when that subscriber went off-hook. This system would fail if any provision was made to allow the subscriber to turn off the bells (do not disturb) for privacy or unplug the telephone; it also presumed that each subscriber only had one telephone connected to the line.
- When the party line was already in use, if any of the other subscribers to that line picked up the phone, they could hear and participate in the conversation. Eavesdropping opportunities abounded, as shown in the 1959 film Pillow Talk.
- The completely non-private party lines were a cultural fixture of rural areas for many decades, and were frequently used as a source of entertainment and gossip, as well as a means of quickly alerting entire neighborhoods in case of emergencies such as fires, as written in The Thorn Birds by Colleen McCullough. Mischievous teens soon discovered that calling their own number and hanging up would make all phones on the network ring whereas all the residents on the system, sometimes a half a dozen or more, would all answer the phone at the same time.
- Party lines were typically operated using mechanical switching systems which recognised certain codes (such as "dial 4101 and hang up" to ring a phone on the same line) which no longer work on modern electronic switching systems or digital switchgear.
- In the local-battery system of the early cranked magneto phones, the phone's own battery powered its transmitter as well as the receiver of the called phone. If too many phones were off-hook and listening, the additional receivers would load down the transmitter's battery with a voltage so low that no phone could receive an intelligible signal.
- Party lines remain primarily in rural areas where local loops are long and private loops uneconomical when spread sparsely over a large area. Privacy is limited and congestion often occurs. In isolated communities, party lines have been used without any direct connection to the outside world.
- Party lines are not suitable for Internet access. If one customer is using dial up, it will jam the line for all other customers of the same party line. Bridge taps make party lines unsuitable for DSL. Telcos typically do not allow client-owned equipment to be directly connected to party lines, posing an additional obstacle to their use for data.
- Many areas have laws requiring a person engaged in a call on a party line to end the call immediately if another party needs the line for an emergency. These laws additionally provide penalties for falsifying an emergency situation to the parties in an existing telephone call, in order to gain access to a party line.
- Party lines were widely used in Australia where sparsely populated remote properties are spread across large distances. These were operated by the Government Post Master General department.
- One of the last manual telephone exchanges which still used party lines in Australia was closed down in 1986 at the township of Collarenebri, New South Wales. In that town, most town residents had a telephone number of only three digits, and to make a call outside the exchange area it was necessary to call the exchange to place a call. For rural residents, many were on a single telephone line identified by a number and a property name, for example one party line was called Gundabluie 1 line. Each party on that single line was identified by a letter, and so to call that party, the exchange would be called and the number asked for would be Gundabluie 1 S for example. The exchange rang a distinct ring down the Gundabluie 1 line, signalling the party's corresponding letter in morse code. This distinctive ring would alert all parties on the line who the call was for. Three short rings signified the call was for the party with the S letter and so on.
Use on railways
Party line usage was at one time common on railways, where numerous telephones were connected to a single pair of wires. Usually a long ring of many turns of the handle would alert the exchange that a connection was required to another destination. The problem of selective calling was also solved by a mechanical device which could selectively ring one or a group of stations.
Party lines still in existence
One example of a community linked by party line is in Big Santa Anita Canyon high in the mountains above Los Angeles, near Sierra Madre, California, where 81 cabins, a group camp and a pack station all communicate by magneto-type crank phones. One ring is for the pack station, two rings for the camp and three rings means all cabins pick up.
-  NSW State Parliament speech "Subscriber Trunk Dialling Call Zones", 3 May 2000
- International Correspondence Schools "Electricity and Magnetism; Principles of Telephony; Subscribers' Station ..." (1916), page 20. Retrieved May 27, 2008
- Amazon Patents Reverting call
- Adam's Pack Station (Internet Archive 2007/01/08)