Technology Behind POTS
Let's take a closer view into how a POTS network actually works. Back in the days of early telephony, establishing a connection between two parties that needed to connect required stretching wires between them. Yes, much like a tin can telephone, albeit over longer distances.Obviously, this meant the longer the distance, the steeper the costs. With the emergence of POTS lines, this cost was knocked down some.
One-way PSTN managed to achieve this was by placing switches at centralized points in the network. These switches acted as communication nodes between any two points in the network. To connect one phone to another, a telephone call is routed through one or more switches operating on a local, regional, national, or international level.
But voice as we speak it cannot transmit through the POTS line. The sound waves from a caller's voice need to be converted into electrical signals in order to flow through the network. This falls on the telephone handset on both the caller's and receiver's ends. The copper line is susceptible to interference, and the signal is also prone to get weak where long distances are involved. For this reason, amplification may be called for along the way.
The early copper network only transmitted analog signals, which require a dedicated circuit since they travel in a continuous stream. This can be both a blessing and a curse. On the upside, a dedicated circuit is as reliable as circuit technologies come. But it is handicapped by the fact that the line has to be reserved for one call and one call only. This type of switching is what is known as circuit switching.
Back in the old days, circuit switching was the reason you needed an operator's assistance when making calls. In those days, operators would sit by one giant wooden switchboard, plugging copper wires into a common patch panel. In the case of connections that required two exchanges, two operators would go about simultaneously plugging the caller's and receiver's wires into the same inter-exchange wire. This wire was known as a "trunk". Long-distance calls were unbearably costly because calling long distance was akin to renting the use of a very long piece of copper wire each time you wanted to make a call.
As technology advanced, so too did circuit switching. The first stab at automated switching came in 1891 following the invention of the Strowger switch. It was also known as a step-by-step (SWS) switch due to its operational features. Later, it pressed into service after the invention of the rotary dial. It changed once, and then twice, finding favor among the masses. Eventually, it was phased out by the crossbar switch. Despite their reliability, crossbars were faulted for being complicated, bulky, and costly.
You can only imagine how challenging it must have been to provide excellent customer service under those conditions back then.
Enter The Transistor
Thankfully, a disruption came in the form of one of the best things to happen to the world since man bashed two stones together to ignite a fire: the invention of the transistor. The transistor heralded the electronic exchange era, which slowly paved the way for the digital network. Current phone lines have been upgraded to carry digital signals in the form of "packets." Packet-based technology does not dominate the transmission channel by demanding a continuously open and dedicated circuit, unlike its analog counterpart. Rather, it uses the underlying network to transmit voice (and data) messages independently through the switches.
A copper line is a bi-directional 64Kbps service capable of carrying human voice both ways at the same time (i.e. full duplex). However, it has a limited frequency band of 300 to 3400 Hz, meaning it cannot transmit digital signals which are in the form of "0s" and "1s". For this to happen, a critical hardware component needs to be added to the PSTN.
Enter The Modem
This is a device that was designed to exploit the digital nature of the public switched telephone network without overhauling your entire phone system. This should come as good news for small business owners who are not planning to upgrade their analog communications systems any time soon, especially considering the wealth of options available on the market.
1. DSL (Digital Subscriber Line) technology makes it possible to transmit data over your copper-wire telephone system. A transceiver connected to your personal computer uses the local telephone network to connect to an ISP's network.
The network in turn routes data to the World Wide Web.
This type of service is most popular among small business setups. Why? Because it provides just enough bandwidth for a sizable number of users to access the Internet.
2. ISDN (Integrated Services Digital Network), ISDN is another technology that allows digital transmission over a regular telephone line. ISDN makes it possible to transmit both voice and data over a single copper line. To establish a network connection, users have to dial in. The fees are determined by the duration of the transmission.
ISDN promises faster call setup and higher quality calls compared to the classic telephone system. Businesses also prefer it because it comes with the option of integrating with other phone systems (PABX). This allows them to take advantage of a host of other features. For example, using a 100-number range, queues, groups, on-hold music, etc. It is ideal for larger businesses or those looking to expand in the near future.