For an introduction to channel variables, please see the section "Channel Variables" in Chapter 6, XML Dialplan .
There are various pages in official documentation about channel variables, and the one where we are trying to centralize all info is:
https://freeswitch.org/confluence/display/FREESWITCH/Channel+Variables
Below is a list of some of them, grouped "thematically" for your future reference (for details please search https://freeswitch.org/confluence).
Also, please note that if you need a variable (an information on some aspect of the channel, call, system, user, or a way to tweak a parameter) is almost certain that it exists: if the information or parameter exists, it is probably available as a variable. Search our ...
