19-04-2013, 02:27 PM
VoIP
VoIP.pdf (Size: 562.86 KB / Downloads: 25)
INTRODUCTION
The public telephone network and the equipment that makes it possible are taken
for granted in most parts of the world. Availability of a telephone and access to a
low cost ,high quality worldwide network is considered to be essential in modern
society .Anything that would jeopardize this is usually since more and more
communication is in digital format and transported via packet networks such as
IP,ATM cells etc. Since data traffic is growing much faster than telephone traffic,
there has been considerable interest in transporting voice over data networks.
Support for voice communication using the Internet Protocol (IP), which is
usually just called “voice over IP” or VoIP, has been become especially attractive
given the cost, flat rate pricing of the public internet. In fact, toll quality telephone
over IP has now become one of the key steps leading to the convergence of the
voice, video, and data communication industries. The feasibility carrying voice
and call signaling messages over the Internet has already been demonstrated but
delivering high quality commercial products, establishing public services, and
convincing users to buy in to the vision are just beginning.
HOW VoIP WORKS?
In VoIP, for transmitting voice, it is pocketsize and then transmitted through
packet switching networks. This process is described in following steps.
1. Our voice is converted into analog electrical signal using micro phone
2. These electrical signals are digitized using PCM-Pulse Code Modulation PCM
samples analog signal at a rate of 8000 samples/sec and coded into 64
kb/sec. Each sample there fore represents 125 microseconds of a voice
stream, and is 8 bits, or 1byte long.
3. These digital voice samples are buffered on IP gate way- it converts PCM data
into IP packets using DSP. DSP s(Digital Signal Processors ) are responsible
for converting from analog to digital as well as compression. This has
following steps.
STANDARDS
One important consideration of VoIP software is interoperability. Many Internet
telephony products require all communicating parties to use the same application.
All the vendors begin to support an international can implement this
telecommunications union (ITU-T) standard for multimedia communications
systems known as H.323.It is important standard set of procedures that provide a
specification for voice, data and video communications over packet switched
network (or TCP/IP networks). Using H.323, a device or application from one
vendor can place a call to another.
HOW VOICE GOES OVER IP?
When we talk of sending voice over Internet connections, the first question that
pops up is “how can you do that, when the connections are not even broad enough
to handle regular data?”. Traditionally, voice is a lot of data and if sent as a
regular analog data, it would simply clog the networks and won’t be able to get
through. Instead the voice is sampled, compressed and packetized to send it over
an IP network. This may need much less bandwidth.
THE DEATH OF DISTANCE
Long distance voice telephony is where telcos make most of their money. The
further away our call is to the more we are charged. This means that we think
twice before making that long distance call, and even when we make the call we
keep the conversation short. Traditional economics says that if the cost of the call
were reduced, the more people would make the call, and if properly done, the
voice service provider could end up making more money than before. So telcos
have extended the distance we can call for the same amount.
When we send mail over the internet we do not pay different rates for different
destinations of the mail .we do not pay more for our internet connection when we
are downloading software from an FTP server in Iceland as against when we are
accessing a web page on a sever in Mumbai.
CONCLUSION
With the advances in computer technology, phenomenal growth in Internet use
and declining cost of computer hardware, there has been growing interest in
recent years in developing real time voice communication software for Internet telephony. In spite of the numerous Internet telephony systems available today,
these are still at infancy and far from being substitutes of conventional telephony
systems. While the Internet telephony may have difficulty matching the reliability
of switched voice networks, it is dirt-cheap and is growing rapidly. Moreover with
advances in compression algorithms, standards, network technology and higher
bandwidth in future, these problems will diminish overtime.