What is the Difference Between Similar But Different Things, Terms, and Objects

What is the Difference between Pstn, Centrex, Key System, Pbx and Voip

Telephones are the necessary part of any business, but in case of large organizations with more than 30-40 employees working at different workstations, a proper business telephone system become mandatory. Today, business telephone systems are available in cute range and Pstn, Centrex, Key System, Pbx and Voip are the examples of such various types of telephone systems. Let’s see the difference between them.


PSTN or Public Switched Telephone Network is a telephone system that was once analog-based, but today fully equipped with latest digital technologies like FDDI and ISDN. It is an international telephone network that makes possible to inter-connect telephones anywhere in the world thanks to switching centers.


Centrex is a type of telephone exchange. In this type of telephone system, the central office of a telephone company keeps and runs all the equipments and softwares of Centrex at its own and provides the services of Centrex to various customers.

Key System

Key system is the old solution of business telephone system. It consists of simply a server telephone that is equipped with wide range of buttons and respected lights to indicate the busy lines in a key system network and also to call directly to the central office of Telephone Company by simply pressing a single button.


PBX or Private Branch Exchange is a type of telephone network that provides facility to PBX users to make telephone calls by sharing PBX lines and avoiding expense of separate lines. In this way, we can connect equipments and individual user lines in a company to connect with trunk lines of Telephone Company by means of a smaller unit called PBX.


Voip or Voice over Internet Protocol is the way of using standard internet connection for free phone calls. This super-fine technology enables the users to make long distance calls just free of cost by converting analog audio calls into digital data by means of using internet.

Pstn, Centrex vs Key System vs Pbx vs Voip

The difference between PSTN and VOIP is that PSTN use latest digital technologies to inter-connect telephone lines in a business network in contrast to VOIP that converts voice into digital data by using internet protocol and providing facility of making free long distance calls. Key system is the oldest among all other business telephone systems and feasible for small companies having less than 50 employees. Moreover, Key System is an expensive solution as compared to PBX that is cheaper one due to requirement of less numbers of external wires. Similarly, PBX is suitable for larger companies that own PBX systems in contrast to Centrex that is just like PBX but with little advanced variation in which the central telephone unit is operated by Telephone Company itself.

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