What is Plain Old Telephone Service or POTS?

July 19, 2011

Plain Old Telephone Service or POTS is the name given to the telephone system and service used during the late 19th century. It is a predecessor to more advanced telephony technologies like Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) that are used today. In this article, we will have brief look at the Plain Old Telephone Service, its general working including advantages and disadvantages of this service.

Plain Old Telephone Service (POTS)


What is a Plain Old Telephone Service? To answer this question, look at the diagram above. This is the representation of  a Plain Old Telephone Service (POTS) for a single subscriber. The links used between  the Telephone User and Telephone Exchange as well as links between two Telephone Exchanges are analogue. Both voice and signalling communication take place in analogue form in Plain Old Telephone Service (POTS). Thus the Plain Old Telephone Service (POTS) is defined as the telephone system in which all the communication takes place in analogue form.

Now, if there are more then one Telephone User than we need more lines. If one Telephone User is using one line, then second Telephone User cannot use Telephone service until that line gets free. If there is another line available then Telephone User will use that to avail the service. In short, if we have ten user and they all want to use the service at the same time, then we will need ten lines between two Telephone Exchange to accommodate them, otherwise they will have to wait until the available lines get free.

Moreover, due to the analogue usage of communication in Plain Old Telephone Service (POTS), Quality of Service (QoS) is poor. This is because regenerated Analogue Signal is difficult. Amplifiers are used to regenerate analogue signals but they cannot regenerate the signal back to 100%.

Although the equipment used in Plain Old Telephone Service is simple and easy to design but the QoS and support for number of subscriber in POTS makes it a poor choice for today’s system. Thats why we moved to Public Swtiched Networks (PSTN ) and Integrated Services Digital Network (ISDN).