IP telephony is technology which allows usage of Internet or any other
IP-based network as mean of realtime international and interurban phone calls
and fax transmission.
Organization or Service Provider has to have gates in cities from/to
which telephone calls are planned in order to perform interurban/international
telecommunication using IP-telephony technology.
The cost of such communication is much less than cost of traditional
telecommunication. This difference is mostly notable for international calls.
IP-telephony is based on 2 main operations: transformation of bidirectional
analog voice into digital form by coding/decoding device (codec) and
placing into packets for transmission over IP-network.
IP telephony uses special system for packets with voice information
In traditional telephone lines direct end-to-end electric circuit during
conversation is created thus providing fixed throughput for data. While
IP-network represent system which switches and routes packets and does not
provide fixed path between endpoints. All information sent over IP
(voice, text, pictures, etc.) is split to data packets, containing source and
destination addresses and sequence number. IP nodes (routers) send
these packets until they arrive at destanation.
After packets arrive at destination, sequence numbers are used to
rebuild initial data. Delay between separate packet isn't important in
applications where packet arrival order and interval isn't significant,
The IP-telephony is one of areas of data transmission where signal
transfer dynamics is important and is provided with modern methods of
coding and transfer of the information. For ensuring of stable
telecommunication on IP-networks special protocols of data transmission,
for example, H.323 and SIP are designed.