Sample essay topic, essay writing: Voip - 1237 words
CONTENTS 1. Introduction: What is VoIP? 2. Circuit Switching 3. Packet Switching 4. Packet Switching in VoIP5.
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 SWITCHINGCircuit 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 or not. That's no way to set up an efficient data network. Instead, data networks use a method called packet switching.3. PACKET SWITCHINGWhile circuit switching keeps the connection open and constant, packet switching opens the connection just long enough to send a small chunk of data, called a packet, from one system to another. What happens is this: The sending computer chops data into these small packets, with an address on each one telling the network where to send them.
When the receiving computer gets the packets, it reassembles them into the original data. Packet switching is very efficient. It minimizes the time that a connection is maintained between two systems, which reduces the load on the network. It also frees up the two computers communicating with each other so that they can accept information from other computers as well. 4.
PACKET SWITCHING IN VOIPVoIP technology uses this packet-switching method to provide several advantages over circuit switching. In VoIP, analog voice signal is digitized using PCM. These digital voice samples are then buffered on an IP gateway. This device converts the PCM data stream into a compressed IP packet stream using DSPs (Digital Signal Processors). DSPs are responsible for converting from analog to digital as well as compression. The set of PCM samples are analyzed as a discrete set of binary data.
It checks the speech for all the moments of silence, which are a lot. Even when we speak, there are pauses in between that go unnoticed to the human ear, but are quite discernible to the sampling device. The length and beginning of these pauses is noted, while the remaining 'silence' is removed from the data set. Similarly, redundant data is also removed, making the data set more compact. Finally, an IP header is attached to this compressed data, which is then sent out on the network as discrete data packets. Once the voice packet is sent out, it finds its way to the destination just like any other data packet.
It passes through various routers and switches to reach the destination gateway. Here, it gets decompressed, meaning all the periods of silence and redundant data are reinserted, and is finally decoded to produce an approximation of the original sound. The compression algorithms used in this process can compress the voice signals and can even carry voice over as little as 5.3 kbps bandwidth. Voice (source)- - ADC - - Internet - - DAC - - Voice(dest)Probably one of the most compelling advantages of packet switching is that data networks already understand the technology. By migrating to this technology, telephone networks immediately gain the ability to communicate the way computers do. For telephones to communicate with each other and with other devices, such as computers, over a data network, they need to speak a common language called a protocol.
5. PROTOCOLSThere are two major protocols being used for VoIP. Both protocols define ways for devices to connect to each other using VoIP. Also, they include specifications for audio codecs. A codec, which stands for coder-decoder, converts an audio signal into a compressed digital form for transmission and back into an uncompressed audio signal for replay. The first protocol is H.323, a standard created by the International Telecommunications Union (ITU).H323 protocol is used, for example, by Microsoft Netmeeting to make VoIP calls.
H.323 is a comprehensive and very complex protocol. It provides specifications for real-time, interactive videoconferencing, data sharing and audio applications such as IP telephony. Actually a suite of protocols, H.323 incorporates many individual protocols that have been developed for specific applications. H.323 Protocol SuiteVideo Audio Data TransportH.261H.263 G.711G.722G.723.1G.728G.729 T.122T.124T.125T.126T.127 H.225H.235H.245H.450.1H.450.2 H.450.3RTPX.224.0An alternative to H.323 emerged with the development of Session Initiation Protocol (SIP) under the auspices of the Internet Engineering Task Force (IETF). SIP is a much more streamline...
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