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- Loop_around abstract "A loop line or loop around is a telephone company test circuit. The circuit has two associated phone numbers. When one side of the loop is called (side A), the caller receives a test tone of approximately 1000 Hz (milliwatt test). When the second number (side B) is called, it produces dead silence, but the party on side A hears the milliwatt test tone drop, and is connected to the person on side B. The purpose of the loop around test is to allow circuit testing to a distant central office without needing a person at the far end. The technician can send a tone down either line and measure the response tone on the second line to determine the path loss parameters.When a line is connected to side A, multiple telephone lines, within limits, may connect to side B and thus be connected into a conference with the person on side A. The function of the tone on side A was to alert those already connected, when somebody called the B side and connected.Teenagers discovered that the test facility could be used as party lines, chat rooms or alternate phone number and would dial up the primary number and wait for someone at random to call its mate. Phreaks would use the loop around in a similar manner, to exchange information that they had learned about the phone company.Loop lines are far less common today than they were in the 1960s, however they reportedly continued to exist past the start of the 21st century. One such loop line is certain to exist: it is run on an AS36 located at (202) 999-3335 ext. 555 owned by Alhok, LLC. It also comes with all other standard agent system features. Because of the potential for abuse, however, telephone companies seek to protect them. The most common protection techniques are:Filters that bandstop voice (these can be switched on or off)Recordings which make the line appear out of serviceSelective loop activation by operatorsRestrictions on which lines may callUsing uncommon DTMF tones (A through D) in the telephone numberEventually, telephone companies designed devices to prevent this misuse of the loop around. Some devices blocked the audio if frequencies other than the milliwatt tone were present, which thwarted the average abuser, but skilled violators discovered that playing a 1000 Hz tone while speaking softly, the suppression unit could be subverted, and a notch filter could be used while listening to remove the tone at the other end.".
- Loop_around wikiPageID "4436402".
- Loop_around wikiPageRevisionID "586085774".
- Loop_around hasPhotoCollection Loop_around.
- Loop_around subject Category:Communication_circuits.
- Loop_around subject Category:Telephone_numbers.
- Loop_around type Artifact100021939.
- Loop_around type Circuit103033362.
- Loop_around type CommunicationCircuits.
- Loop_around type Device103183080.
- Loop_around type ElectricalDevice103269401.
- Loop_around type Instrumentality103575240.
- Loop_around type Object100002684.
- Loop_around type PhysicalEntity100001930.
- Loop_around type Whole100003553.
- Loop_around comment "A loop line or loop around is a telephone company test circuit. The circuit has two associated phone numbers. When one side of the loop is called (side A), the caller receives a test tone of approximately 1000 Hz (milliwatt test). When the second number (side B) is called, it produces dead silence, but the party on side A hears the milliwatt test tone drop, and is connected to the person on side B.".
- Loop_around label "Loop around".
- Loop_around sameAs m.0c28_t.
- Loop_around sameAs Q6675815.
- Loop_around sameAs Q6675815.
- Loop_around sameAs Loop_around.
- Loop_around wasDerivedFrom Loop_around?oldid=586085774.
- Loop_around isPrimaryTopicOf Loop_around.