1). Introduction:
This document explains about VoIP systems. Recent happenings like Internet diffusion at low cost, new integration of dedicated voice compression processors have changed common user requirements allowing VoIP standards to diffuse. This how to tries to define some basic lines of VoIP architecture.
What is VoIP?
VoIP stands for ' Vâ„¢oice Ëœoâ„¢ver ËœIâ„¢nternet ËœPâ„¢rotocol. As the term says VoIP tries to let go voice (mainly human) through IP packets and, in definitive through Internet. VoIP can use accelerating hardware to achieve this purpose and can also be used in a PC environment.
How does it work?
Many years ago we discovered that sending a signal to a remote destination could have be done also in a digital fashion: before sending it we have to digitalize it with an ADC (analog to digital converter), transmit it, and at the end transform it again in analog format with DAC (digital to analog converter) to use it.
VoIP works like that, digitalizing voice in data packets, sending them and reconverting them in voice at destination.
Digital format can be better controlled. We can compress it, route it, convert it to a new better format, and so on; also we saw that digital signal is more noise tolerant than the analog one (see GSM vs. TACS).
TCP/IP networks are made of IP packets containing a header (to control communication) and a payload to transport data: VoIP use it to go across the network and come to destination.
Voice (source) - -ADC - -Internet - - DAC- - Voice (dest.)
2). Background:
The past:
For the past 100 years people have relied on the PSTN for voice communication. The two parties using the line. No other information can travel over the line, although there is often during a call between two locations, the line is dedicated to plenty of bandwidth available.
Later, as data communications emerged, companies paid for separate data lines so their computers could share information, while voice and fax communications were still handled by the PSTN.
More than 30 years ago Internet didnâ„¢t exist. Interactive communications were only made by telephone at PSTN line cost.
Data exchange was expansive (for a long distance) and no one had been thinking to video interactions (there was only television that is not interactive, as known).
The present:
Today we can see a real revolution in communication world: everybody begins to use PCs and Internet for job and free time to communicate each other, to exchange data (like images, sounds, documents) and, sometimes, to talk each other using applications like Net meeting or Internet Phone. Particularly starts to diffusing a common idea that could be the future and that can allow real-time vocal communication: VoIP.
Today, with the rapid adoption of IP, we now have a far-reaching, low-cost transport mechanism that can support both voice and data. A VOIP solution integrates seamlessly into the data network and operates alongside existing PBXs, or other phone equipment, to simply extend voice capabilities to remote locations. The voice traffic essentially "rides for free" on top of the data network using the IP infrastructure and hardware already in place.
The future:
We cannot know what is the future, but we can try to image it with many computers, Internet almost everywhere at high speed and people talking (audio and video) in a real time fashion. We only need to know what will be the means to do this: UMTS, VoIP (with video extension) or other? Anyway we can notice that Internet has grown very much in the last years, it is free (at least as international means) and could be the right communication media for future.
3). Requirement:
Hardware Requirement:
To create a little VoIP system you need the following hardware:
1. PC 386 or more
2. Sound card, full duplex capable
3. A network card or connection to internet or other kind of interface to allow communication between 2 PCs
Software requirement:
We can choose what O.S. To use:
1. Win9x
2. Linux
4). VOIPâ„¢s implementation:
The IP Gateway: The gateway was the first "stand alone" form of IP technology; a separate piece of hardware that is placed onto an Intranet above a phone endpoint. Once in place, it converts an existing network of traditional analog phones into a network of Voice over IP phones, while continuing to allow the phones to place calls through the PSTN.
When a call is placed, standard voice transmission from the phone is compressed and transferred in a gateway-to-gateway format.
Traditional Analog Phone Connection
VoIP Gateway System
The IP Phone:
The IP phone implements the same technology, packet zing voice data and transmitting it over data signaling lines; but it combines this technology with the features of an office phone network in one platform.
The primary advantage to the phone is having IP capability without having to add any hardware to the communication chain. It appears in an office environment as a standard desktop phone, but delivers the functionality and savings of IP technology.
Traditional Office Communication System
VoIP Gateway System
5). Classification of connection: The VoIP connection can be classified by the type of devices performing an Internet call. Please note that the term PC can be applied to any device capable of transmitting voice over data network. It does not necessarily have all the features of a standard computer. It could just look like a traditional telephone with the basic elements of a computer to execute an Internet call. We have the following generic classifications.
PC to PC:
Figure 1 PC-to-PC Scenario
For users who already have an Internet access and an audio-capable PC. This scenario can take advantage of integration with other Internet services such as World Wide Web, instant messaging, e-mail, etc.
PC to telephone or telephone to PC:
Figure 2 PC to Phone or Phone to PC Scenario
In this scenario, PC-callers may reach also the PSTN users. A gateway converting the Internet call into a PSTN call has to be used. Traditional telephone users also can make a call to a PC going through the gateway that connects the IP network with PSTN.
