what is the maximum size in bytes of IEEE802.15.4 standard that can be transmitted from physical layer of a node and is HEADER of a frame configurable

Hi,

can anyone please tell me the maximum number of bytes (header +data payload) that can be transmitted from a node using ieee 802.15.4. 

Also is the HEADER of a frame configurable .i am asking with respect to fields of HEADER.

Can i avoid some of the fields of HEADER with respect to my application.

thank you