What! Me worry about quality! What would you do when you want to go for a holiday? Pack your luggage of course! So you start throwing in your toiletries, your clothing and many other personnel stuff. Before you know it, you realize that you have packed too much stuff into your luggage. Well, it’s either you repack your stuff or start trying to squeeze as much as you can into your luggage. The same thing can be said for transmission of voice via IP. To receive a VoIP call with the quality of the voice comparable to that of a typical telephone call, you would need a data transmission speed of 64kb/s. Now, there is no way of dedicating such a large bandwidth on a data network for voice. Therefore, there has to be some form of compression taking place which would squeeze the voice data into a considerable size prior sending it over a packet switching network. Other than the bandwidth issue, there is a time delay issue as well. Time is needed to compress voice data, transmit and then decompress it, process and finally making it audible to the receiving party. All this streaming would result in a delay of a few hundred milliseconds. In other words, both callers may not be able to speak at the same time.
Delay will also result in jitter as well. That is to say, when a voice data packet does not arrive in time at the end of a gateway while a voice streaming is taking place, the packet will be dropped and will not be recovered. This will cause the receiver to hear jittering of speech from the caller. With the realization of VoIP, voice and data will be carried over a single network. In such a multi service environment, data traffic can be highly unpredictable and because each business organization tends to load their network to the maximum, packet loss is inevitable .
The scenario above has caused much headache for the research folks. On one hand, they have a technology that brings great promises but on the other hand, it poses many barriers against having wide acceptance of the new technology. And since then, the world has seen a huge advancement in Internet telephony technology. Voice specification (H.323) has been endorsed by the International Telecommunication Union (ITU), many companies have developed Internet telephony software , VoIP vendors have been busy researching and coming out with voice gateways, Internet phones, and other IP telephony hardware If we can take a step back and look at the Internet as a whole, it is actually one huge best effort transport mechanism. Ok, so what does that got to do with VoIP? Not only does it has everything to do with VoIP, it walks the talk. To better explain how voice is being transferred over the Internet, let us draw upon a scenario.
Let’s just say that you were shifting office from one location to another, you would have to pack all office equipment into boxes and transport them to the new office location. Now, let’s just say that you ended up with ten boxes of office equipments and you have loaded them up to 10 different vehicles. And each vehicle takes a different route to the new location. All this while, your colleague who are waiting at the new location, would unpack the boxes when they arrive and set up the new office.
The same notion can be said for transmitting data over the Internet. According to the Internet protocol, information which has to be sent from one location to another, is broken down into smaller parts called packets . Each packet will travel along its own route to reach the destination, where it will be re-assembled into the original information at its destination. Now, just replace the word “information” with “voice” and you would have the idea of how voice is being transmitted over the Internet or voice over IP (VoIP). In a nutshell, VoIP or Internet telephony, if you will, is an Internet protocol technology that uses packet switch network, instead of the tradition circuit switch network (PSTN), to transmit telephone calls.
The ways of VoIP As there are many ways to skin a cat, there are many ways where VoIP services can be implemented. One of them would be from a computer to a telephone. Since PSTN is involved in this exchange, a gateway is needed to interface with both the packet switch network and the circuit switch network. Next, calls can be made between two computers without the need of a circuit switch gateway and they are usually software driven. Examples of software are ICQ 2000b and Microsoft NetMeeting. Other than providing a VoIP service, many of these software also enable some other services like video conferencing and application sharing. Calls can also be made from a telephone to another using the Internet. However, this would require several VoIP equipments and the initial investment will be considerably huge in the league of six figures. But in the long run, there will be a significant savings on long distance or overseas calls. There are already service providers offering a kind of stored value calling card which allow users to make overseas calls via VoIP at half the IDD rates.
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