What is the difference between the .wav and .gsm file format

I am learning asterisk.In this I have worked with voicemail application.

When I was trying to play the voicemail,I have seen the files in the followi开发者_如何学Pythonng format.

   .wav
   .WAV
   .gsm

There is info on Asterisk wiki:

gsm: raw gsm encoding, good for VoIP 
wav: MS wav format, 16 bit linear 
WAV: MS wav format, gsm encoded (wav49)

You can read about those file formats on Wikipedia: Audio_file_format Remember that .wav files can be created with various codecs.

On Asterisk wiki there is article about sound files with information about converting .wav to .gsm and tools that can be used with those files.