0                                       1
  0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 |PFX|FRE|FWD|APM|DIG|        RSV        |CID|EXT|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+