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IP Telephony

Seminar topic for Computer Science department.


The term IP telephony is older than Voice over IP. IP telephony has earlier meant the use of telephones or hybrid equipment and PBXs over IP using gateways to overcome the barriers of various networks. Voice over IP points to a world of carrying voice over IP networks not necessarily needing any separate telephone like equipment nor PBXs. Software phones in PCs are an example of these new implementations. Today the two terms are more or less synonyms or IP telephony is a subset of VoIP.

The characteristics of IP telephony are quite complex, especially compared to streaming video, where large buffers can be used to compensate for the imperfectness of the Internet reagarding real time applications.

How it works:

• In one side gateway connects to the telephone word. It can communicate with any phone in the world.

• On the other side, the gateway connects to the Internet world. It can communicate with any computer in the world.

•The gateway takes the standard telephone signal, digitizes it, compresses it, packetizes it for the Internet using IP protocol and routes it the destination over the Internet.

• The gateway reverses the operation for packets coming in from the network and going out the telephone.

• Both the operations take place at the same time allowing a full duplex conversation.

Call Control Protocol:

• H323 is clearly emerging as the standard call control protocol

• H323 specification define:

  • Packet standards for terminal
  • Equipment and services for multimedia communications over LAN communicating to systems connected to telephony networks such as ISDN

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