I'm an old Telecom guy, -just waiting for take it easy-life style.
1. Generally there are only 2 types; digital and analog. Analog has gone obsolete and if they are still in use they're no longer practical with maintenance too demanding. Most systems are digital where the differences are focused on line and drop interfaces and system support features. Grab hold of a Nortel Succession switch flyer and review its features to get ideas.
PABX concept has taken sea change with latest technological development. But the concept still remain the same.
The main telecommunication providers have their main telephone exchanges single or multiple depending on the area of city or number of subscribers. They provide centralised communication with connectivity through copper cables or optical fibre cable with dedicated individual cable line for each subscriber number.
Large industrial units , Hospitals or offices cannot provide individual telephone number from the main telecommunication provider for all their officers and staff as there number being very large.But proper communication facility is essential. In such cases they install PABX ( Private Automatic Branch Exchanges) for their internal connectivity with internal dedicated numbers. The subscribers can contact between each other without going through external service providers.For those extensions which needs external connectivity can be connected through junction lines to the PABX .They can be programmed to receive or receive and initiate outgoing calls to the main exchange through the junction lines. ( Example 10+50 / 20+100 / 50+500/ 100+1000 etc. ) the first number indicate junction lines and the second the extensions.
Some service providers give a cluster of their exchange as PABX for large customers with out charging call charges for their internal communication.This is possible if the provider has a optical fibre cable network which can be extended to the subscriber's ( factory, hospital, offices software development centers etc.) vicinity.
Now there are small PABX available that can be operated by a receptionist or security guard . This looks like multifunction telephone instrument with one or more junction line and many extensions connected to it.
Intercom is also similar to EPABX but do not have the provision for external connectivity . They can be installed in similar way as any telephone system
pabx
Re: pabx
