This holds the filename, with a mandatory '.o' extension, of a compiled CAS signaling variant file that must already exist on the media gateway's local hard disk, typically placed there by FTP transfer before this object is set. CAS variant files encode country/protocol-specific signaling behavior that is not built into firmware, so this object is how an admin points the gateway at a custom or updated variant without a software upgrade, but the file transfer step has to happen first or the set fails. An admin adding support for a new R2 country variant might FTP a file named 'r2_brazil.o' to the gateway and then set this object to that filename to activate it.