Difference between character_maximum_length and character_octet_length
As described in the MSDN documentation CHARACTER_OCTET_LENGTH is the length in bytes, and CHARACTER_MAXIMUM_LENGTH is the length in characters. 

For parameters of type char or varchar they will be the same, but for parameters of type nchar or nvarchar they will be different, with OCTET-LENGTH being twice (usually if not always) the CHARACTER_LENGTH.