Public telephone

Concept

Akindofartificialtelephoneexchangethatisusedbythetelephoneofficetoprovidetelephoneuserswithcallpower.Itappearedinthelate19thcentury.ChinastartedtouseitinBeijingin1910.Duetothedevelopmentoftheapplicationofautomatictelephoneexchanges,commonelectricexchangesaremainlyusedformanualconnectionoflong-distancecallsandintra-citytelephoneconnectionincitiesandregionswithasmallnumberofusers.

Classification

Accordingtothepurpose,thecommontelephoneexchangecanbedividedintothelocaltelephonecommonelectricexchange,theusertelephonecommonelectricexchangeandthelong-distancetelephonecommonelectricexchange.Thelocaltelephonecommonswitchismainlyusedforthecallconnectionbetweenusersinthelocalarea.Therearetwotypes:eachuserhasonlyoneplugholeontheswitchmachine,andtheoutgoingandincomingcallsmustbeconnectedthroughthisplughole,whichiscalledasingleInadditiontoadedicatedansweringplugforoutgoingconnectionontheexchangemachine,eachuserhasanumberofmultipleplugsthataremultiplexedwiththeansweringplugforincomingandoutgoingconnections,whicharecalledDuplexcommonpowerswitch.Theusertelephonecommonswitchismainlyusedfortheinternalconnectionofagencies,enterprisesandotherunits.Thelong-distancecommonpowerswitchismainlyusedtoconnectthelong-distancecircuitbetweenthetwoplaces,andthencompletetheconnectiontaskofthelong-distancecallthroughthelocaltelephoneexchangeswitchofthetwoplaces.

Usage

Commontelephoneexchangesusesignallightstoshowvarioususerstatessuchascall,answer,callandcalltermination,andplugholes,plugsandcordsareusedasthecallcircuitTheconnectiondevice,theworkingprogramofthecontrolcircuitwithelectrickeysandasmallnumberofrelays,theoperatorisresponsibleforhandlingtheconnectionanddisconnectionofthecall.Whenthecallingpartypicksupthephonetomakeacall,theusernumberlightontheswitchboardison,andtheattendantinsertstheansweringpluginthecordcircuitintotheansweringplughole,asksforthenumbertobecalled,andthenusesthecallplugintheduplexofthecalleduserPerformabusytestontheplughole.Ifthecalledpartyisbusy,theattendantimmediatelyinformsthecallingpartyandpullsouttheansweringplugfordisconnection;ifthecalledpartyisfree,immediatelyinsertsthecallingplugintothecalledparty'sdoubleplugholeandsendsaringingsignal.Whenthecalleduserhearstheringtoneandresponds,thetwopartiescantalk,andthemonitoringlightofthecallingandcalledusersonthemachinegoesout.Afterthecalliscompleted,thecallingandcalledusershangup,themonitorlightonthemachineturnson,andtheattendantcandisconnect.