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Posted by FRANKLYN (203.197.143.150) on December 16, 2003 at 03:19:34:
In Reply to: Re: Regarding EPABX posted by Tomi Engdahl on December 16, 2002 at 06:01:35:
: : Sir,
: : want to know the principle and operation of an EPABX.
: PABX (Private Automatic Branch eXchange) is a telephone exchange operated within an organisation, used for switching calls between internal lines and between internal and PSTN lines. A PABX can route calls without manual intervention, based entirely on the number dialed.
: EPABX is a PABX built using electronics.
: EPABX technology can be divided roughly into four parts:
: 1. A trunk interface that connects the system to the telephone service provider (usually T1, E1, ISDN, etc. can be also a set of analogue lines in some old systems)
: 2. A station interface that telephone handsets plug into
: 3. The switching fabric that connects the trunk to the outside line
: 4. A call control database that handles all the normal features such as call forwarding, do-not-disturb functions, and other call control rules
:
: The operation principle how this thign works when someone is calling from line out (goes on-and-on from 1 if everythign is successful):
: 1. Wait until someone picks up the phone
: 2. Send dial to tone to user
: 3. Wait for the user to dial the number
: 4. If number was 0 (or other dial-out code), then connect the user line to a free outside line (if there is any) or try to make a connection to a line indicated by number or send error tones if operation is not possible (no such lines, system if full with existing calls, number not allowed etc.). Making connection controls the switch fabric in EPABX.
: 5. Detect that call has been connected and store the time when call has been made to EPABX information storage. Possibly print information to printer/terminal.
: 5. Wait for the call to end.
: 6. Disconnect the phone line connection (control switch fabric)
: 7. Update the stored information on the EPABX information storage that call has ended. Print information on the call to printer/terminal.
: 8. Send call has ended tone to user.
: 9. Wait that the user puts the phone on-hook
: 10. Go to state 1 to wait for a new call
: In addition to those basic steps errors and special situations needs to be take into account.
: All internal lines wait for somedody to make a connection to this line in the following way:
: 1. Wait that somebody wants to connect to this line
: 2. Ring the phone line (activate ring generator for this line)
: 3. Wait that the user picks up the phone
: 4. Stop the ring generator
: 5. Complete the connection to this line (connect this line physically to switch fabric, signal other parts that connection is made)
: 6. Wait for the phone to go back to on-hook state
: 7. Discomnect the line (disconnect from switch fabric, signal that call has ended to rest of the system)
: 8. Go back to state 1
: There would be one this kind of task running per line in the system which combines those described functions.
: Or there one very clever which can handle multiple lines and multiple calls in it.
: This is just basic quicly written down simplified description how those things work...
: : Can and EPABX be desinged using Microcontroller 89c52.
: Maybe if you don't need very many lines or most fancy features....
: : If yes, kinldy suggest some idea for the same.
: Here are some links to some PBX and telephone information which coudl be useful:
: How a PBX works
: http://www.soho-telecom.com/phone-systems/tutorial/how-a-pbx-works.html
: How IP PBX works
: http://techupdate.zdnet.com/techupdate/stories/main/0,14179,2805999-4,00.html
: Business telephone systems links
: http://www.epanorama.net/links/telephone.html#business
: Telephone circuits links
: http://www.epanorama.net/links/telephone.html#circuits
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