PBX

Short for private branch exchange, a private telephone network used within an enterprise. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX.

Most medium-sized and larger companies use a PBX because it's much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it's easier to call someone within a PBX because the number you need to dial is typically just 3 or 4 digits.

A new variation on the PBX theme is the centrex, which is a PBX with all switching occurring at a local telephone office instead of at the company's premises.

A PBX (private branch exchange) is a telephone system within an enterprise that switches calls between enterprise users on local lines while allowing all users to share a certain number of external phone lines. The main purpose of a PBX is to save the cost of requiring a line for each user to the telephone company's central office.



The PBX is owned and operated by the enterprise rather than the telephone company (which may be a supplier or service provider, however). Private branch exchanges used analogtechnology originally. Today, PBXs use digital technology (digital signals are converted to analog for outside calls on the local loop using plain old telephone service (POTS ).

A PBX includes:

In some situations, alternatives to a PBX include centrex service (in which a pool of lines are rented at the phone company's central office), key telephone systems, and, for very small enterprises, primary rate Integrated Services Digital Network (ISDN).
 * Telephone trunk (multiple phone) lines that terminate at the PBX
 * A computer with memory that manages the switching of the calls within the PBX and in and out of it
 * The network of lines within the PBX
 * A console or switchboard for a human operator (optional)

(http://searchunifiedcommunications.techtarget.com/definition/private-branch-exchange)

there’s three types of PBX architecture like: IP Architecture: Hybrid IP Architecture: Legacy Time Division Multiplier (TDM) architecture: http://rantsonsoftware.com/ip-pbx-architecture/
 * IP
 * Hybrid IP
 * Legacy Time Division Multiplier (TDM)
 * 1) it does all the switching
 * 2) there is no transcoding between TDM bus and IP bus
 * 3) it is scalable
 * 4) doesnt require additional hardwares to do digital signal processing to convert media
 * 5) cisco call managers and Asterisk are examples
 * 1) must convert its media between TDM and IP
 * 2) requires more resources to do the transcoding
 * 3) has limitations on how many ip phones can be used
 * 4) Avaya Communication Manager, Avaya IP office, are examples
 * 1) it is TDM only solution so no converting between IP and TDM bus
 * 2) Avaya Definity, Avaya Partner are examples