What is PSTN?

PSTN Definition - Public Switched Telephone Network

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PSTN is the abbreviated term used for landline telephone system. Another term commonly used for it is POTS, which stands for Plain Old Telephone System, a non-geek way of naming the landline that is now old and quite plain and flat when compared to new competitors on the market. 

This network was created mainly for analog voice communication over cables that covered countries and continents. It is an improvement over the basic telephone system discovered by Alexander Graham Bell. It brought to the system better management and hauled it to the level of being an industry, and a very lucrative and revolutionary one at that. 

The PSTN and Other Communication Systems

PSTN is now very often expressed and referred to, especially in the media, in contrast with other emerging communication technologies. Mobile telephony emerged as the first alternative to PSTN when it comes to voice communication. Cellular communication (2G) allowed people to communicate on the go while the PSTN allowed people to make and receive calls only within the reach of the wires, that is at home or in the office.

Nevertheless, the PSTN has still been able to keep its place in modern telephony as it remained the so far unchallenged leader in call quality, with a Mean Opinion Score (MOS) of 4 to 5, 5 being the ceiling value. It has also kept its place at home and in businesses for several reasons. Until the recent past, many people (including people who are not digital natives or digital immigrants) had still not adopted mobile telephony and could therefore only be reached through their plain old landline phone number. Also, the PSTN is the main carrier for Internet connectivity in most parts of the world. Subsequently, being able to use alternative means of communication like VoIP  and other OTT technologies often required the PSTN line for there to be Internet connectivity, through an ADSL line for instance. 

Speaking of VoIP, which is the very topic of this site, it has been a more serious competitor to PSTN operators than any other technology by allowing people to communicate locally and worldwide for free or cheaper. Think of Skype, WhatsApp and all the other VoIP services and apps, which are even banned in some countries as a means to protect the local and often government-owned telcos. 

How The PSTN Works 

In the early days of telephony, establishing a voice communication line between two parties required stretching wires between them. This meant higher cost for longer distances. The PSTN came to level the cost despite the distance. As the name suggests, it consists of switches at centralized points on the networks. These switches act as nodes for communication between any point and any other on the network. This way, one person can talk to another on the other side of the country-wide network, by being on the end of a circuit that consists of a number of switches between them.

This circuit is dedicated to the two corresponding parties throughout the length of the call, hence the rate you pay for each minute of call. This type of switching is called circuit-switching. IP networks like the Internet brought around packet switching, which used the same underlying network but without reserving any portion of the line. The voice (and data) messages were split into small parcels called packets which were disseminated through the switches independent of each other and reassembled on the other end. This made voice communication free on the Internet through VoIP.