Permanent signal
Encyclopedia
Permanent Signal 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. 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 howler tone or 480 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
.
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
).
In most middle 20th century switching equipment, a permanent signal would tie up a junctor circuit
, diminishing the ability of the switch to handle outgoing calls. 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. These methods had the disadvantage of blocking all outgoing calls from that line until it was manually cleared. Manufacturers also sold devices that monitored the talk wires and held up the cutoff relay or crossbar hold magnet until the condition cleared. Some crossbar line circuit designs had a park condition allowing the line circuit itself to monitor the line.
Stored program control exchange
s finally solved the problem, by setting a bit mask in the scanning program and running a low priority periodic checking program against the wetlist. Depending on software version, a wetlisted line may also be in PLO or lockout state.
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
jargon, or Permanent Loop in British usage, is a condition in which a POTS
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
line is off-hook
Off-hook
In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...
without connection for an extended period of time. This is indicated in modern switches by the silent termination after the off hook tone times out
Timeout (telecommunication)
In telecommunication and related engineering , the term timeout or time-out has several meanings, including...
and the telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
computer puts the telephone line
Telephone line
A telephone line or telephone circuit is a single-user circuit on a telephone communication system...
on its High & Wet list or Wetlist. In older switches, however, a Permanent Signal Holding Trunk (PSHT) would play either howler tone or 480 Hz high tone
High Tone
High Tone is a dub band from Lyon, France. Formed in 1997, the band came with an emergence of the French dub music Scene, with bands like Brain Damage Sound System, Kaly Live Dub, Le Peuple de l'Herbe, Improvisators Dub or Meï Teï Shô...
(which would subsequently bleed into adjacent lines via crosstalk). Howler tone
Off-hook tone
The off-hook tone is a telephony signal used to alert a user that the telephone has been left off-hook for an extended period, effectively disabling the telephone line...
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
Telephone call
A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...
.
Permanent signal can also describe the state of a trunk
Trunking
In modern communications, trunking is a concept by which a communications system can provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually. This is analogous to the structure of a tree with one trunk and many branches. Examples of...
that is seized but has not been dialed upon, if it remains in a busy condition (sometimes alerting with reorder
Reorder tone
The reorder tone, also known as the fast busy tone, is the congestion tone or all trunks busy tone of a public switched telephone network. It varies from country to country; in the USA it is a dual-frequency tone of 480 Hz and 620 Hz at a cadence of 0.25 seconds on, 0.25 off; that is two beeps per...
).
In most middle 20th century switching equipment, a permanent signal would tie up a junctor circuit
Cord circuit
In telecommunication, a cord circuit is a switchboard circuit in which a plug-terminated cord is used to establish connections manually between user lines or between trunks and user lines. A number of cord circuits are furnished as part of the switchboard position equipment. The cords may be...
, diminishing the ability of the switch to handle outgoing calls. 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
Crossbar switch
In electronics, a crossbar switch is a switch connecting multiple inputs to multiple outputs in a matrix manner....
, or block the line relay from operating. These methods had the disadvantage of blocking all outgoing calls from that line until it was manually cleared. Manufacturers also sold devices that monitored the talk wires and held up the cutoff relay or crossbar hold magnet until the condition cleared. Some crossbar line circuit designs had a park condition allowing the line circuit itself to monitor the line.
Stored program control exchange
Stored Program Control exchange
Stored Program Control exchange is the technical name used for telephone exchanges controlled by a computer program stored in the memory of the system. Early exchanges such as Strowger, panel, rotary, and crossbar switches were electromechanical and had no software control...
s finally solved the problem, by setting a bit mask in the scanning program and running a low priority periodic checking program against the wetlist. Depending on software version, a wetlisted line may also be in PLO or lockout state.