PSTN always be known as a ‘telephone line’.This is the most commonly used method by all users that only have the need to use one line for one conversation at a time using only one phone number.As a dedicated service, a PSTN line cannot be used for any other purpose while a call is being made. A PSTN phone number is equivalent to one phone line.The following will show you what does PSTN mean .

PSTN Gateways Introduction

Public switched telephone network (PSTN) gateways are third-party hardware components that translate signaling and media between the Enterprise Voice infrastructure and the PSTN, either directly or through connection to SIP trunks.

In either topology, the gateway terminates the PSTN. The gateway is isolated in its own subnet and is connected to the enterprise network through the Mediation Server.

An enterprise with multiple sites would typically deploy one or more gateways at each site. Branch sites can connect to the PSTN either through a gateway, or through a Survivable Branch Appliance, which combines gateway and servers in a single box. If branch sites use a gateway, both a Registrar and Mediation Server are required on site, unless the WAN link is resilient. One or more Mediation Servers, which are collocated on Front End Servers, can route calls for the one or more gateways at each site. We recommend that the Registrar, Mediation Server, and gateway required on site are deployed as a Survivable Branch Appliance.

Determining the number, size, and location of PSTN gateways is perhaps the most important and expensive decision you must make when planning your Enterprise Voice infrastructure.

Here are the main questions to consider. Keep in mind that the answers to these questions are all interdependent

How many PSTN gateways are needed? The answer depends on the number of users, the anticipated number of simultaneous calls (traffic load), and the number of sites (each site needs one).

What size should the gateways be? The answer depends on the number of users at the site and on the traffic load.

Where should the gateways be located? The answer depends in part on the topology and in part on the geographic distribution of your organization.

You should also consider your gateway topology options (for details, see Gateway Topologies later in this topic).

How Do PSTN Phone Lines Work?

Think of a Public Switched Telephone Network (PSTN) as a combination of telephone networks used worldwide, including telephone lines, fiber optic cables, switching centers, cellular networks, as well as satellites and cable systems. These help telephones communicate with each other.

Put simply, when you dial a phone number your call moves through the network to reach its destination – and two phones get connected. To fully understand how a POTS actually works, consider what happens when you dial a number from your own phone.

Step #1 - Your telephone set converts sound waves into electrical signals. These signals are then transmitted to a terminal via a cable.

Step #2 - The terminal collects the electrical signals and transmits these to the central office (CO).

Step #3 - The central office routes the calls in the form of electrical signals through fiber optic cable. The fiber optic conduit then carries these signals in the form of light pulses to their final destination.

Step #4 - Your call is routed to a tandem office (a regional hub responsible for transmitting calls to distant central offices) or a central office (for local calls).

Step #5 - When your call reaches the right office, the signal is converted back to an electrical signal and is then routed to a terminal.

Step #6 - The terminal routes the call to the appropriate telephone number. Upon receiving the call, the telephone set converts the electrical signals back to sound waves.

This may sound complicated, but the thing to remember is that it takes a few seconds for your call to reach its destination. This process is facilitated by using fiber optic cables and a global network of switching centers.