N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 6 - Internet, Intranet, Extranet, e-Commerce and Web Services                                      Slide 51 of 70 _________________                                                                                  __________

                                               What is VOIP?

                                            Voice Over the PSTN

                                            A Digital Voice Channel - 64 K bps

                                            Compression Technology

                                            IP Telephony

_________________                                                                                  __________

The  reliable Public Switches Telephone Network (PSTN), analog in nature, has delivered voice with superb speech quality. The PSTN used 4 K Hz bandwidth for each voice communications. Now Plain Old Telephone Services (POTS) are giving way to modernization, service integration, and convergence of two technologies: voice and data. Next-generation communications networks transmit information in a packet format. Voice-Over-IP (VOIP) is the transmission of telephone calls over the Internet network.

Voice Over PSTN - Analog, 4 K Hz bandwidth

A Digital Voice Channel - 4 K Hz analog channel = 64 K bps, same speech quality as an analog channel.

Compression Technology - Normal voice communication has too many silent periods. The communications channel is not used during the silent periods. Compression technology removes the silent periods, and compresses data from 64 K bps to 8 K bps for voice communications in each direction. Many Compression technology protocols have evolved. The two major protocols are H.323 from the ITU and Session Initiation Protocol (SIP), developed under the auspices of the Internet Engineering Task Force (IETF).

IP Telephony - The communications industry has developed many protocols that can deliver voice over the Internet or a LAN by using the Internet Protocol with the hope of matching the quality of the PSTN.