Network As Discrete Data Packets example essay topic

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. VoIP stands for 'V'once 'o'very 'I' 'P', 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 or not. That's no way to set up an efficient data network. Instead, data networks use a method called packet switching. 3.

PACKET SWITCHING While 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 VOIP VoIP 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 kips bandwidth. Voice (source) - - ADC - -Internet - -DAC - - Voice (debt) 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. PROTOCOLS There 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 codes. A code, 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). H 323 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 Suite Video Audio Data Transport. SIP is a much more streamlined protocol, developed specifically for IP telephony. SIP is smaller and more efficient than H. 323.6.

SETTING UP VOIP There are different ways in which you can implement VoIP, all of which depend on the size of your network infrastructure, and the kind of application you'd like to use it for. Before implementation, you have to ensure that there's sufficient bandwidth on your network to handle the voice traffic. If not, you " ll have to upgrade infrastructure to support the voice traffic. A basic setup between two locations will consist of an IP gateway on either location. The gateway can be designed inside a PBX or a standalone device such as a router. On one side of this gateway will be the PSTN (Public Switched Telephone Network) or a company's IP WAN, while the other side would have the company's internal network.

PSTN connectivity could be through wireless, ISDN, or analog telephone lines. The IP WAN link could be leased line, frame relay, ATM, etc. The gateway is essentially a device that translates protocols from the network onto the PSTN network. So, the one you choose will depend on the type of connectivity you " re using, and the protocols you " ll use, which in this case will be H. 323.

You can't, however, interface the gateway to a PBX that's connected to the PSTN yet, not because of technology issues, but because the law doesn't permit it; you can use it only to connect your internal network with your WAN. The gateway also has to interface with a router on your company's internal network, which will split the voice and data and assign priorities. On the internal network, you need terminals that are capable of voice communication. These could be PCs with headphones and a microphone.

Terminals support two-way communication over IP. They encode audio signals for transmission, decode them for reception, and also perform some control functions. A terminal uses certain protocols for communication. These include the H. 245, which negotiates channel usage and capability. It also uses Q. 931 for signaling and control; and RTP / RTCP (Real-time Protocol / Real-time Transport Control Protocol) for sequencing the audio packets.

These packets are sent via UDP (User Datagram Protocol). And finally, there's the RAS protocol, which sends Registration / Admission/Status signals to the gatekeeper. All control protocols are sent using TCP. 7. CALLING There are four ways that you might talk to someone using VoIP.

If you " ve got a computer or a telephone, you can use at least one of these methods without buying any new equipment: o Computer-to-computer - This is certainly the easiest way to use VoIP. You don't even have to pay for long-distance calls. There are several companies offering free or very low-cost software that you can use for this type of VoIP. All you need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like you would get through a cable or DSL modem. Except for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance. A good example of this software is MSN Explorer. o Computer-to-telephone - This method allows you to call anyone (who has a phone) from your computer.

Like computer-to-computer calling, it requires a software client. The software is typically free, but the calls may have a small per-minute charge. For example, Net 2 Phone offers free calls to anywhere in the United States for the first five minutes. If the call is over five minutes, a rate of 3.9 cents per minute kicks in. Net 2 Phone's international rates vary widely, ranging from 3.9 cents to $7.52 per minute, depending on where you call. o Telephone-to-computer - A few companies are providing special numbers or calling cards that allow a standard telephone user to initiate a call to a computer user. The caveat is that the computer user must have the vendor's software installed and running on his or her computer.

The good news is that the cost of the call is normally much cheaper than a traditional long-distance call. o Telephone-to-telephone - Through the use of gateways, you can connect directly with any other standard telephone in the world. To use the discounted services offered by several companies, you must call in to one of their gateways. Then, you enter the number you wish to call, and they connect you through their IP-based network. The downside is that you have to call a special number first. The upside is that the rates are typically much lower than standard long distance. 8.

If one were to get philosophical, there are two types of illegalities: those of the moral kind and those of the economic kind. While murder and stealing fall in the first category, Internet telephony clearly does not. So, it could be an economic offence at best. Offence against whom? Is the country losing anything because you use Internet telephony?

Is some other country benefiting at our cost if you switch over to Internet telephony? Clearly not. The only loser is VSNL / BSNL whose revenues would be affected, as the bulk of their revenue still comes from voice traffic, and they seem to be in no hurry to attempt a switch over to a different way of life. No wonder then that Internet telephony (and VoIP) was treated as illegal.

9. VOIP LIMITATIONS & SOLUTIONS The process explained may seem rosy, but that's not the case, as there are various problems associated with VoIP. What if the voice packets get delayed in reaching the destination? This is fairly common in packet-switched networks.

If a router is free, it sends the packets quickly. And if it's under heavy load of traffic, the voice packets will get delayed, leading to latency. The route taken by a packet can also cause delay. If it takes a short path, it will reach quickly. And if it reaches the destination after multiple hops, the delay would be longer. Another problem with VoIP is packet errors.

If a voice packet encounters a bad router, it might get corrupt or get lost altogether. If it's the former, the packet that reaches its destination is of no value. If it gets lost, then the router may ask for it to be retransmitted, in which case the packet would get delayed. All these delays are classified as (de) packet ization, access, and network delays.

There are many ways to solve these issues. One method is to differentiate between the various services-in other words, traffic prioritization. Routers can be configured to give preference to certain type of packets over others. So, voice packets can be given higher priority over normal data packets. Another method is weighted fair queuing. Here, a minimum amount of bandwidth is allocated to certain traffic, in this case, voice.

This can be done using the Resource Reservation Protocol (RSVP). It's a common feature in most high-end routers these days. Controlling and conditioning network traffic can also reduce delays. You could prevent certain type of traffic from passing through a router altogether and so on. VoIP is an emerging area, developments will keep happening at a fast pace. 10.

VOIP- THE FUTURE The most significant advantage of VoIP over the traditional system is: it is cheaper. Although it will take some time to happen, you can be sure that, eventually, all of the circuit-switched networks will be replaced with packet-switching technology. IP telephony just makes sense, in terms of both economics and infrastructure requirements. More and more businesses are installing VoIP systems, and the technology will continue to grow in popularity as it makes its way into our homes..