Codec configuration is very versatile in FreeSWITCH. In IP telephony, there are several differing scenarios for negotiating and choosing codecs. To meet the varying demands, FreeSWITCH has several configurable modes of operation as well as real-time variables that can influence how codec negotiation takes place. Typically the goal should be to reduce transcoding or resampling as much as possible. Transcoding is the case where two sides of the call have different codecs and audio flowing in either direction has to be completely decoded and re-encoded to the opposite channel's format. Resampling is similar but it is required when each side of the call is running at a different sample rate and the audio has to be "resampled" to the correct rate. One or both of these can be necessary depending on where you direct your calls to and how you have your codec configuration set.