VoIP and Voice over WLANs
Overview of voice over IP (VoIP)

Over the past decade, the telecommunications industry has witnessed rapid changes in the way people and organizations communicate. Many of these changes come from the explosive growth of the Internet and from applications based on the IP. The Internet has become a popular means of communication, and the total amount of packet-based network traffic has quickly surpassed traditional voice, or circuit-switched, network traffic.

Voice traffic and services is expected to become one of the next major application areas to take full advantage of IP. This expectation is based on the impact of VoIP technologies, which are sometimes referred to as IP telephony. Figure illustrates some of the ways that VoIP can be used.

VoIP offers many benefits, which include the following:

  • Cost savings – By moving voice traffic to IP networks, companies can reduce or eliminate the toll charges associated with transporting calls over the Public Switched Telephone Network (PSTN). Service providers and end users can also conserve bandwidth by investing in additional capacity only when it is needed. This is made possible by the distributed nature of VoIP and by reduced operations costs as companies combine voice and data traffic onto one network.
  • Open standards – By adopting open standards, multi-vendor interoperability is ensured. Both businesses and service providers can purchase equipment from multiple vendors and eliminate their dependency on proprietary solutions.
  • Integrated voice and data networks – When voice becomes another IP application, companies can build truly integrated networks for voice and data. These integrated networks provide the same quality and reliability as the PSTN, while enabling companies to quickly and flexibly take advantage of new opportunities within the changing world of communications.

In 1995, the first commercial VoIP products began to emerge in the market. These products were targeted at companies that wanted to reduce their telecommunications expenses by moving voice traffic to packet networks. Early adopters of VoIP networks built toll-bypass solutions to take advantage of the favorable regulatory treatment of IP traffic. Without any established standards, most early implementations were based on proprietary technology.

As these packet telephony networks grew and interconnection dependencies emerged, it became clear that the industry needed standard VoIP protocols. There are four different standardized signaling and call-control protocols used for VoIP:

  • H.323
  • Media Gateway Control Protocol (MGCP)
  • Session Initiation Protocol (SIP)
  • H.248/Megaco

Other protocols that work with these signaling and control protocols include Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), and Resource Reservation Protocol (RSVP).

Each of these protocols will be discussed in the following sections.


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