Ground start

Ground start

In telephony, a ground start or GST is a method of signaling from a terminal or subscriber local loop to a telephone exchange, in which method a cable pair is temporarily grounded to request dial tone. Most middle 20th century American payphones used "coin first" ground start lines, with the starting ground passing through the coin itself.

Ground start trunk

Local telephone companies typically provide two types of dial tone switched trunks -- ground start and loop start. PBXs work best on ground start trunks because those trunks can give them an on hook signal allowing for timely clearing. Many will work -- albeit intermittently -- on both types.

Normal single line phones and key systems typically work on loop start lines. A PBX user must be careful to order the correct type of trunk line from the local phone company and correctly install the telephone system at the PBX end -- so that they match. Line equipment in most 20th century CO switches had to be specially rewired to create a ground start DDCO line. Crossbar switch did it by a paper sleeve on the Vertical Off Normal contact, 5ESS switch by translation, and DMS-100 by a slide switch on the line card, all according to what the customer ordered.

Technically, a ground start trunk initiates an outgoing trunk seizure on an idle circuit by applying a momentary connection to ground (maximum local resistance of 550 ohms). In an idle circuit, the CO is giving -48v (nominally) on the Ring and an open on the Tip. When the PBX merely shorts the pair, this does not operate the Line Relay in the CO, hence the line remains idle. In order to start the line, the PBX applies a ground to the shorted pair, which operates the Line Relay, causing the CO to send dial tone. Along with dial tone, the CO puts a ground on the Tip side. The PBX senses the resulting voltage difference across the pair, releases its Ground Start condition, maintains the connection as a simple current loop, and outpulses the telephone number. When conversation is finished and the line is to be cleared, the CO removes the short across the pair, and the PBX accepts this on-hook condition as indicating an idle line.


* [ Glossary of telecommunications terms]

ee also

*Loop Start Trunk
*Foreign exchange office
*Foreign exchange station

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • ground start —    A signaling method given to a central office when one station detects that a circuit is grounded at the other end indicating an off hook condition …   IT glossary of terms, acronyms and abbreviations

  • гальваническая сигнализация ground-start — Сигнализация ground stаrt используется на двухпроводных соединительных линиях между УАТС и стандартными городскими АТС и позволяет избежать конфликтных ситуаций, таких как одновременное появление на одних и тех же соединительных линиях входящих и …   Справочник технического переводчика

  • ground — ground1 noun 1》 the solid surface of the earth.     ↘land of a specified kind: marshy ground.     ↘an area of land or sea with a specified use: fishing grounds.     ↘(grounds) an area of enclosed land surrounding a large building.     ↘Brit. the… …   English new terms dictionary

  • ground — ground1 [ground] n. [ME grund < OE, ground, bottom, akin to Ger grund, ON grunnr: for IE base see GRIND] 1. a) Obs. the lowest part, base, or bottom of anything b) the bottom of a body of water 2. the surface of the earth, specif. the solid… …   English World dictionary

  • Ground support equipment — (GSE) is found at an airport, usually on the ramp, the servicing area by the terminal. This equipment is used to service the aircraft between flights. As its name implies, GSE is there to support the operations of aircraft on the ground. The… …   Wikipedia

  • Ground Control (video game) — Ground Control Developer(s) Massive Entertainment Publisher(s) Sierra On Line …   Wikipedia

  • Start — can refer to multiple topics:* Takeoff, the phase of flight where an aircraft transitions from moving along the ground to flying through the air * Standing start and rolling start, in an auto race * Start signal, in telecommunications * Start… …   Wikipedia

  • ground — I (New American Roget s College Thesaurus) n. earth, terra firma, soil; foundation, basis; cause, reason; viewpoint. See covering. v. base, establish; settle, fix; instruct. adj. pulverized, grated; whittled, sharpened, abraded. See land, support …   English dictionary for students

  • Ground improvements at British football stadia — A large number of English football clubs have ongoing schemes to redevelop existing grounds, or to move to newly constructed stadiums. A trend towards all seater stadiums was initially prescribed by the Taylor Report, and was originally a… …   Wikipedia

  • ground — ground1 W1S1 [graund] n ▬▬▬▬▬▬▬ 1¦(earth)¦ 2¦(area of land)¦ 3¦(reason)¦ 4¦(subject)¦ 5¦(opinion)¦ 6¦(sport)¦ 7 hold/stand your ground 8 get off the ground 9 gain ground 10 lose ground …   Dictionary of contemporary English

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.