Demystifying Telecom network

The telephone system:

PBX not VOIP and unified communication.

how does telephone call get to you? PSTN public switched telephone network. Central offices every single house having telephone line connected to central network (demarc point to telephone pole).

PSTN network of central offices.north American dialing plan NADP.(routing for telephone system)

NADP used telephone no to route you to central offices.

Trunk Lines: No. of trunk call depend on how many trunk u can connect to central office.

40 people 4 trunk/lines  are enough these many call are going at same time.(incomming or outgoing).

each single trunk/line as single no. (Hunt group for all people calling in if 1 busy got to 2 etc..) if call goes it gives 1 no. if not available forwarded to no.2 if 2 busy to 3 etc… till u use all your Hunt group.

1              410 685 2808

2              410 685 2885

3              410 685 2880

4              410 685 2889

for all line calls going out. programe in PBX allow any no for outgoing only.only certain station or lines are allowed.(out calling groups).

PBX:-> extn : 345 to particular no. also to outside no. call routing(permission, Hunt group,call group,out group).

Voice mail is add on to PBX system. Avaya routing AUDIX. (auto attendent AA message reside on voice mail routing on PBX  so u develop rule #1 –> 309 #2 –> 500, etx 800 is AA etc.)


Just like your inter comm, call boxes in building,telephone system all are connected to PBX.

Transmission option (analog and digital).(using carrier waves it is transmited,interfreance case to reduce quality of it). Digital(1,0) and digital PBX .so analog and digital cannot talk to each other.fax manchine cannot work with digital PBX.mordern PBX have analog port (for fax etc.)and Digital ports. Just like switch.

Subscribers(users of voice mail system)  not always have to attached with stations.voice mail box have auto attendent with have auto reply for each call. PBX(4 incoming line,9 station/trunk line,2 trunk line for voice mail means only 2 auto attendant).voice mail system  No. of ports means that many no can get auto attended. VOIP is not telephone, its real time data communication over data network with simulated telephone.

Telephone System Call Routing:

T-System can send call to you. hunt group, auto attended, extent clinic, voice mail.

PBX- Everything is related to extension. Voice mail,Intercom,Hunt group, call group,voice boxes also have extension. Auto attend are accessed through  extension. Administrative extension nobody will call.

Call Path: What happen to call goes to certain extension.(programmed 1st ring 3 times,2nd call to voice mail). Call 301 to sales manager rings 3 times–> then goes to his Assistant manger  ring 3 times–>no answer-> call group (all phone on group) ring 3 times–>  goes to emergency no.

Call path: 301–> 1st directly voice mail –>(you can do 50 step call path).

OutCalling: outside people calling all request comes to PBX. Out call go through PBX.Out call in PBX forwarding call to extn (504) to PBX route call to mobile phone.(company do not like out calling).Out calling also consumes a trunk for outgoing call.(single call uses 2 trunk one incoming, one out going).

Trunk Group:

-4 trunk lines i.e. phone no.

1              410 685 2808

2              410 685 2885

3              410 685 2880

4              410 685 2889

Trunk group 1 (1,2) extn 800. business 1 –> auto attendant –> person A  (building A)

Trunk group 2(3,4) Extn. 900. bussiness2 –> auto attendant –> person B  (building A)

Auto Attendant AA:

Extension 800 is auto attendant (configuration inside PABX : business hours , business days (e.g. weekdays).Is  this Extn AA or HG, or ? where does voice comes for AA? PBX routes call to Voice Mail

TG AA1  800, 800 is AA

(VM). AA1-> VM 800 –> (press 1 –>300), (press2 –>400),( press 3 –>500),( press 4 –>600). Time out after each 1 minute.

AA –> 800– press 2 for sales –> (2=900)–> 900–> HG (sales)if call come first go to 301 thne 302 etc..configuration  {(#1,301), (#2,301), (#3,301), (#4,301)}.

Waited Hunt Group:(call HG look for which has picked up more call , it will give call to person which has picked least calls).

Call Groups: (every single phone rings at same time. whoever picks the call get else get dialer tone)

Outgoing call.–>

Out TG1 –> Local call.

Dial 1 then only use –>Out TG2 –> Local + Long distance.

15 digit no. and first 4 (1976) then use TG2 –> to call long distance calls.

443-XXX-XXXX– 10 digit no.–> TG1 or  TG2.

11 digit –>and first digit 1 then  Tg2. press (1) –> long distance.

if 11 digit no use TG2–> Long distance ,(9781) – (1)- (443-xxx-xxxx) long distance call.

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