Difference between POTS and VoIP

[mikesyl]

Working with a application that works with .WAV files. Samples are taken many times per second. I was trying to get an understanding on what VoIP does with the transmitted packet during compression and decompression that would alter the waveform when a comparison is done with a standard wired POTS line.

[Will.Spencer]

Ahh... you are wanting to talk about compression.

Each VoIP connection uses a CODEC to convert the analog voice signal to a digital signal for transmission over the IP network. The same CODEC, on the other end of the communication, converts the digital signal back into an analog signal.

These CODEC's are designed to provide the highest levels of compression possible while still maintaining a reasonable level of audio quality.

Voice communications does not require much audio quality. VoIP communications typically do not give you anything like CD-quality audio.

VoIP CODEC's encode voice in as little as 4.8 Kbps (CLEP), or as much as 64 Kbps (PCM). VoIP CODEC's do this by being lossy.

A lossy compression mechanism is one where some data is lost -- permanently -- during compressions.

With VoIP CODEC's, the lost data is typically sound outside of the normal range of human hearing.

Newer VoIP CODEC's also remove the silent moments from a conversation. When there is silence, they transmit nothing. This tends to save considerable bandwidth.

[mikesyl]

Thanks for the response. I can now see why the changes in the patterns can be significant.