Voip Paper

CONTENTS

1. Introduction: What is VoIP?

2. Circuit Switching

3. Packet Switching

4. Packet Switching in VoIP

5. Protocols

6. Setting up VoIP

7. Calling

8. Why was Internet telephony illegal?

9. VoIP limitations and solutions

10. VoIP- The Future

1. Introduction: What is VoIP?

VoIP stands for 'V'oice 'o'ver 'I'nternet 'P'rotocol, popularly known as IP telephony. As the term says VoIP tries to let go voice (mainly human) through IP packets and, in definitive through Internet. Thus Voice-over IP (VoIP), is the transmission of telephone calls over a data network like one of the many networks that make up the Internet. While you probably have heard of VoIP, what you may not know is that many traditional telephone companies are already using it in the connections between their regional offices.

Let us learn about VoIP and the technology that makes it possible. We'll talk about VoIP's major protocols, about the various services provided and the low-cost, often free software that allows you to take advantage of them.

But first, let's discuss the fundamental problem with existing telephone networks -- namely, their reliance on circuit switching.

2. CIRCUIT SWITCHING

Circuit switching is a very basic concept that has been used by telephone networks for over 100 years. What happens is that when a call is made between two parties, the connection is maintained for the entire duration of the call. Because you are connecting two points in both directions, the connection is called a circuit. This is the foundation of the Public Switched Telephone Network (PSTN).

Here's how a typical telephone call works:

1. You pick up the receiver and listen for a dial tone. This lets you know that you have a connection to the local office of your telephone carrier.

2. You dial the number of the party you wish to talk to.

3. The call is routed through the switch at your local carrier to the party you are calling.

4. A connection is made between your telephone and the other party's line, opening the circuit.

5. You talk for a period of time and then hang up the receiver.

6. When you hang up, the circuit is closed, freeing your line.

Let's say that you talk for 10 minutes. During this time, the circuit is continuously open between the two phones. Telephone conversations over the traditional PSTN are transmitted at a fixed rate of about 64 kilobits per second (Kbps), in each direction, for a total transmission rate of 128 Kbps. Since there are 8 kilobits (Kb) in a kilobyte (KB), this translates to a transmission of 16 KB each second the circuit is open, and 960 KB every minute it's open. So in a 10-minute conversation, the total transmission is 9600 KB, which is roughly equal to 9.4 megabytes (MB).

If you look at a typical phone conversation, much of this transmitted data is wasted. While you are talking, the other party is listening, which means that only half of the connection is in use at any given time. Based on that, we can surmise that we could cut the file in half, down to about 4.7 MB. Plus, a significant amount of the time in most conversations is dead air -- for seconds at a time, neither party is talking. If we could remove these silent intervals, the file would be even smaller.

Data networks do not use circuit switching. Your Internet connection would be a lot slower if it maintained a constant connection to the Web page you were looking at. Instead of simply sending and retrieving data as you need it, the two computers involved in the connection would pass data back and forth the whole time, whether the data was useful