How does VoIP work?

* When you speak at the handset or a mike or a microphone, your voice generates electrical signals inside the gadget. These are analog signals i.e. the voltage level can take up any value within a range.

* The analog signal is converted to a digital signal using an algorithm implemented by the device you are using. It can be a stand-alone VoIP phone or a softphone running on your PC. If you are using an analog phone, you will need a Telephony Adapter (TA) for this purpose. The digitized voice is arranged in packets (i.e. collection of bytes) and sent over the IP network.

* The data is channeled through gateways and servers to the destination. If the called number is on the PSTN, the server opens a connection to the PSTN and routes your call there.

* While going to the PSTN or at the end device of a VoIP connection, the voice is again brought back to its analog form so that it is perceptible to a human ear.

Introduction to VoIP

What is VoIP?

VoIP is the short form of Voice over Internet Protocol. It is also called IP Telephony, Internet telephony or Digital Phone. It utilizes the IP network (Internet or intranets) for telephone conversations. The service it provides is similar as that of normal landline phones but generally offers a cheaper solution. It has some added advantages and as any other service, it faces some challenges too.

How is this useful? VoIP can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free VoIP software that is available to make Internet phone calls, you're bypassing the phone company (and its charges) entirely.

Public switched data network

A public switched data network (PSDN) is a publicly-available packet-switched network, distinct from the PSTN.

Originally this term referred only to Packet Switch Stream (PSS), an X.25-based packet-switched network, mostly used to provide leased-line connections between local area networks and the Internet using permanent virtual circuits (PVCs). Today, the term may refer not only to Frame Relay and Asynchronous Transfer Mode (ATM), both providing PVCs, but also to Internet Protocol (IP), GPRS, and other packet-switching techniques.

PSTN (Public Switched Telephone Network)

Definition: PSTN is the global collection of interconnects originally designed to support circuit-switched voice communication. The PSTN provides the traditional Plain Old Telephone Service (POTS) to residences and many other establishments. Parts of the PSTN are also utilized for DSL, VoIP and other Internet-based network technologies.

Switching in computer networks

A network switch or switching hub is a computer networking device that connects network segments.
The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (Layer 3) and above are often referred to as Layer 3 switches or multilayer switches. The term network switch does not generally encompass unintelligent or passive network devices such as hubs and repeaters.