+----------------+
             | Outer Content  |
             |   Type (OCT)   |
             |                |
             |   OCT == 20   -+--> ChangeCipherSpec (DTLS <1.3)
             |   OCT == 21   -+--> Alert (Plaintext)
             |   OCT == 22   -+--> DTLSHandshake (Plaintext)
             |   OCT == 23   -+--> Application Data (DTLS <1.3)
             |   OCT == 24   -+--> Heartbeat (DTLS <1.3)
packet  -->  |   OCT == 25   -+--> DTLSCiphertext with CID (DTLS 1.2)
             |   OCT == 26   -+--> ACK (DTLS 1.3, Plaintext)
             |                |
             |                |   /+----------------+\
             | 31 < OCT < 64 -+--> |DTLSCiphertext  |
             |                |    |(header bits    |
             |      else      |    | start with 001)|
             |       |        |   /+-------+--------+\
             +-------+--------+            |
                     |                     |
                     v          Decryption |
               +---------+          +------+
               |  Reject |          |
               +---------+          v
                            +----------------+
                            | Decrypted      |
                            | Content Type   |
                            | (DCT)          |
                            |                |
                            |     DCT == 21 -+--> Alert
                            |     DCT == 22 -+--> DTLSHandshake
                            |     DCT == 23 -+--> Application Data
                            |     DCT == 24 -+--> Heartbeat
                            |     DCT == 26 -+--> ACK
                            |     else ------+--> Error
                            +----------------+