ADTS header format

Hi All,
   I am new to AAC. While reading the MPEG4 AAC ADTS header 
bitstream, the header gives the aac frame length as 0x0820 bytes in 
decoder, but the maximum allowed input buffer length is only 0x0600 
bytes? 
  Sometimes the header is giving the aac frame length as 0x1800 bytes 
or 0xc000 bits? Even If I am having a maximum frame size of 1024 
words, then the value should be less than or equal to 0x0800 bytes or 
0x4000 bits. How it is giving 0xc000 bits?
 Is my ADTS header is wrong? But I can able to decode the bitstream 
using the decoder...!

Thanks and Regards,
Jothi