What is PBX

What is PBX?

PBX means private branch exchange.  Fist need to understand what is exchange.  In Telecom network a switching systems is located in a premise. The premise is exchange or telephone exchange.  Your PSTN phone line connect to the switching system. This is public branch exchange as anyone with phone connection can connect to the switching center and owned by a mobile network operator. A PBX is the exchange located in a personal property and owned by a company or an individual. It uses the same technologies as public exchange uses. A PBX connects to switching center using a trunk. The TDM trunk can allow multiple calls simultaneously.

Using a private branch exchange enables multiple phones to access same trunk by different phones inside premises. Each phone is allocated an extension number which is local to the company. There is a common public phone line to connect PSTN. Same truck can be used by many phone users.

What are PBX Functions?

In an office PBX connects phones internally as like regular phones. This enables free calls among the people sitting inside an office.  An office may be at single location or at multiple.  With VoIp , multiple offices connects over SIP trunking to make free calls.

Provides the queuing of the incoming calls. This is very important for a call center, to not disconnects the call if all agents are busy.

It plays the voice message to the caller and can collect inputs as DTMF digits. So that the caller can reach to the correct person in a call center.

A call can be transfer to another extension , without losing and incoming call.

Provides statistics, which helps in getting customer base for more revenue and boosting the sale of the product or service.

Provides option to share a phone line among multiple callers.

Intelligent call handling.

Call recording.

What is Analog PBX?

Traditional phone lines those connects to the public switching centers  are analog phone lines.  At a single time only data or coice can work on on phone connection.  You might used a dial-up connection for the internet. During internet browsing , if some one calls on landline number, he gets the busy tone.  As the technology advances, the digital or ISDN phones lines were introduce. ISDN is capable of carrying voice and data at the same time and the internet speed can be much more faster than analog lines.   A physical spliter is used for phone and internet router devices. Analog or digital lines connects to a phone system using E1/T1 TDM cards. Each E1 slot has 31 channels. Few can be used for signaling and remaining for actual voice.

A system using analog or digital line is an analog or digital PBX.  There is a dedicated phone line from PBX to the telecom network switching center.  When location of changes , network operator needs to update the configuration and setup a new phone line to the new location. The main issue is the capacity. If concurrent calls increases , there will be requirement for more additional E1/T1 lines.


As telecom growing rapidly and new technologies are emerging.  VoIP or Voice over IP is the new and most popular method of communication.  A VoIP system can have voice and media sessions over IP network. With VoIP an PBX can connect to the public telephone exchange over IP network. Provides a flexible , calling capacity. No need to upgrade any physical wire if concurrent calls capacity needs to increase.  It uses , SIP trunking, which provides required signaling for setup VoIP calls.  It is inexpensive as compared to the analog similar system, as it do not required additional analog or digital cards. . Most of the cost is software only cost.

Hosted PBX:

Now with cloud and data centers , many companies sells software as service. PBX is one of that service and its called Hosted PBX.  This was only possible after VoIP. A company can choose the hosted option, where no need to invest on initial hardware or software. Just buy the required functionality from a service company which have set up PBX in cloud or data centre.

PBX providers:


Here is the list of hosted PBX provider.

How to Setup PBX ?

If you want to set up your system. VoIP is a good choice.  First you can get the SIP trunking connection from a service provider. Install the Asterisk and setup dial plan and extensions.

What is IP enabled PBX ?

Looks this similar to the IP PXB, but there is a difference. The IP enabled PBX have TDM  an IP both capabilities.  It may happen that the internal phones are connected over IP and connection with public switching center is over transitional TDM lines.






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