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.
VoIP can be defined as the ability make telephone calls and to send facsimiles or
IP based data networks with suitable quality of service (QoS) and much superior
cost / benefit. Equipments producers see VoIP as a new opportunity to innovate
compete. The challenge for them is turning this vision in to reality by quickly
developing new VoIP enabled equipments. For Internet service providers the
possibility of introducing usage based pricing and increasing their traffic volumes
is very attractive. Users are seeking new types of integrated voice / data
application as well as cost benefits.
Success fully delivering voice over packet networks precedence a tremendous
opportunity; however, implementing the products is not as straight forward a
task as it may first appear.
2. INTERGRATION OF IP & PSTN
Using VoIP we can communicate from PC to any other device – PC, phone, internet
phone, PDA, etc.
1.PC-PC: we can community from one PC to another PC using VoIP i.e. voice mail
or voice chat. For this PC with headphone, a microphone and sound card are
2.PC- Phone: Allows PC user to establish a call with conventional phone. This
facility enables us to make long distance a call with rate cheaper than
conventional telephone call.
3.Phone – Internet Phone: Extension of PC to phone architecture. The IP phone
connects to the Internet through a cable or DSL modem using an RJ-45 Ethernet
3. PSTN vs. INTERNET.
To understand Internet telephony or VoIP, it is necessary to be familiar with the
fundamental principles behind the Internet and how it compares to PSTN.
Although the Internet shares some characteristics of the PSTN, it also has
Computer to computer data communication was far cheaper than voice
communication through Internet. One of the main reasons for these is the basic
difference in the technologies used for voice and data communication. Voice
networks use circuit switching while data network use packet switching. What
this means is that for a voice conversation to happen, one complete and
continuous circuit has to be held open between the two parties during the full
duration of conversation, while for a data transmission such a continuous connect
is unnecessary. In data transmission, the data is split into independent packets
that can take alternate rules to the intended destination, where they are
reassembled. In voice communication, circuit switching is used because it is able
to handle data in real time. Packet switching, on the other hand, can lead to
delays, which can lead to considerable degradation in the quality of the
So the networks when their separate ways till the Real time Transport Protocol
(RTP) was developed. RTP provides support for streaming audio and video over
computer networks. Unlike what its name seems to suggest, RTP does not ensure
real time delivery of data. Instead it provides mechanisms for times stamping the
packets and methods for synchronizing data streams with time properties. Thus
it became technically possible to send voice over the net.
Download Report:Click Here