Permanent signal

left off-hookpermanent loop
Permanent Signal (PS) in US telephony jargon, or Permanent Loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time.wikipedia
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On- and Off-hook

off-hookon-hookon hook
Permanent Signal (PS) in US telephony jargon, or Permanent Loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time.
When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a permanent loop or permanent signal.

Off-hook tone

high toneHowler/off-hook warningoff-hook
This is indicated in modern switches by the silent termination after the off-hook tone times out and the telephone exchange computer puts the telephone line on its High & Wet list or Wetlist. In older switches, however, a Permanent Signal Holding Trunk (PSHT) would play either a howler tone or a 480/500 Hz high tone (which would subsequently bleed into adjacent lines via crosstalk). Howler tone is a tone of increasing intensity that is intended to alert telephone users to the fact that the receiver has been left off the hook without being connected in a call.
See permanent signal.

Timeout (computing)

timeouttimeoutstime-out
This is indicated in modern switches by the silent termination after the off-hook tone times out and the telephone exchange computer puts the telephone line on its High & Wet list or Wetlist.
Permanent signal

Telephony

digital telephonytelephonedigital
Permanent Signal (PS) in US telephony jargon, or Permanent Loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time.

Plain old telephone service

POTSLocal Telephone Servicetelephone
Permanent Signal (PS) in US telephony jargon, or Permanent Loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time.

Telephone exchange

exchangescentral officeexchange
This is indicated in modern switches by the silent termination after the off-hook tone times out and the telephone exchange computer puts the telephone line on its High & Wet list or Wetlist.

Telephone line

phone linelinetelephone lines
This is indicated in modern switches by the silent termination after the off-hook tone times out and the telephone exchange computer puts the telephone line on its High & Wet list or Wetlist.

Crosstalk

cross-talkcross talkleakage
In older switches, however, a Permanent Signal Holding Trunk (PSHT) would play either a howler tone or a 480/500 Hz high tone (which would subsequently bleed into adjacent lines via crosstalk).

Telephone call

callphone callphone calls
Howler tone is a tone of increasing intensity that is intended to alert telephone users to the fact that the receiver has been left off the hook without being connected in a call.

Trunking

trunktrunk linetrunks
Permanent signal can also describe the state of a trunk that is seized but has not been dialed upon, if it remains in a busy condition (sometimes alerting with reorder).

Reorder tone

reordercircuit busynumber unavailable tone
Permanent signal can also describe the state of a trunk that is seized but has not been dialed upon, if it remains in a busy condition (sometimes alerting with reorder).

Junctor

junctor circuitdistrict junctor
In most mid-20th-century switching equipment, a permanent signal would tie up a junctor circuit, diminishing the ability of the switch to handle outgoing calls.

Crossbar switch

crossbarcross-bar switchmatrix switch
When flooded cables or other conditions made this a real problem, switch staff would open the cable, or paper the off-normal contacts of the crossbar switch, or block the line relay from operating.

Stored program control

stored program control exchangecomputer controlcomputerized
Stored program control exchanges finally solved the problem, by setting a bit mask in the scanning program and running a low priority periodic checking program against the wetlist.

Dial tone

dial-tonedialling tonestutter dial tone
If no digits are forthcoming, the permanent signal procedure is invoked, often eliciting a special information tone and an intercept message, followed by the off-hook tone, requiring the caller to hang up and redial.

TXE

TXE1
In the event of a cable breakdown or similar event which may result in permanent loops on subscribers lines, after a predetermined time the register would be forcibly released and the subscriber put into a parked condition.

Intercept message

recorded announcementrecordingerror messages
If a phone receiver is left off-hook, sometimes this message is played:

Telephone hook

switchhookhandset cradlehook switch
Permanent signal