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Voice Over WiFi Surveys

Voice over IP is Internet telephony. It is also known as VoIP and Voice over Internet Protocol. The Internet Protocol is the system that organizes addressing and routing for the Internet. Wi-Fi is a trademark for Wireless networks. The two technologies both deal with sound waves. VoIP converts sound to data and back again, and Wi-Fi converts data to waves and back again.

VoIP Codec

The engine of a VoIP system is a "codec." This is a protocol that specifies the conversion of sound into blocks of data. The size of data blocks varies with the codec, but it is defined by a sample interval and a sample size. A sample is a "grab" of sound recorded by the microphone of the VoIP system. A higher sample size creates more bits to represent each second of sound. The higher the bit rate, the more data is generated per second. A codec with a high bit rate generates high quality sound but requires a faster Internet connection so it can transport a larger amount of data.

VoIP Transport

VoIP sound quality can be affected by delayed or lost packets. Higher quality size uses smaller blocks to transport data. This does not mean that a Codec that produces smaller blocks produces higher quality sound. A transport protocol breaks up the lager codec blocks into smaller blocks and gives each a sequence number. This information is then packaged into a data packet by the User Data Protocol and the Internet Protocol, with addressing details showing both the source and destination application and computer for the packet. The Session Initiation Protocol, or SIP emulates the session management functions of a normal telephone such as dialling, ringing, busy signals, picking up, hanging up, etc.

Wi-Fi Modulation

Wireless networks transmit binary data as radio waves. The frequency of a wave tells how many waves occupy a second. A higher frequency has more, thinner waves. Frequency is measured in Hertz, which expresses cycles -- waves -- per second. Wi-Fi systems use 2.4 Gigahertz and 5 Gigahertz. A Gigahertz is a thousand million Hertz. For a comparison, speech travelling down a telephone uses between 300 Hertz and 3,300 Hertz, so the frequency of Wi-Fi networks is very high in comparison. The wireless network adapter creates a square wave from the data. It transmits a standard wave at the transmission frequency. This is called a carrier wave. The adapter merges the data wave with the carrier wave by a process called modulation, and then transmits the resulting wave.

Wi-Fi Demodulation

A Wi-Fi signal beams out in all directions and gets attracted to any metal it hits. The copper wire inside a receiving antenna gets hit by the wave, which travels down the wire to the receiving network adapter. This subtracts the carrier wave to get the data wave. The data wave is transformed into a binary number and passed to the receiving computer.

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