struct {
        ContentType type;
        ProtocolVersion legacy_record_version;
        uint16 epoch = 0
        uint48 sequence_number;
        uint16 length;
        opaque fragment[DTLSPlaintext.length];
    } DTLSPlaintext;

    struct {
         opaque content[DTLSPlaintext.length];
         ContentType type;
         uint8 zeros[length_of_padding];
    } DTLSInnerPlaintext;

    struct {
        opaque unified_hdr[variable];
        opaque encrypted_record[length];
    } DTLSCiphertext;

    0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |0|0|1|C|S|L|E E|
    +-+-+-+-+-+-+-+-+
    | Connection ID |   Legend:
    | (if any,      |
    /  length as    /   C   - Connection ID (CID) present
    |  negotiated)  |   S   - Sequence number length
    +-+-+-+-+-+-+-+-+   L   - Length present
    |  8 or 16 bit  |   E   - Epoch
    |Sequence Number|
    +-+-+-+-+-+-+-+-+
    | 16 bit Length |
    | (if present)  |
    +-+-+-+-+-+-+-+-+

    struct {
        uint64 epoch;
        uint64 sequence_number;
    } RecordNumber;