About "canreinvite" option

what is “canreinvite” option in asterisk

is it mandatory ?
i set it as no

i am newbie in asterisk so please give the best answer i am in confused

“canreinvite” is the obsolete name for “directmedia”. It is not mandatory, although I am not sure of the default. For all the options see sip.conf.sample, however it basically says whether Asterisk will try to get party A to send its audio directly to party B and v.v. This can only happen if Asterisk doesn’t need to look at the audio (or dialled digits) stream itself. If it can be used, it wiill greatly reduce the processing load on the machine running Asterisk.