wn in Figure 6.3. Version Messages EAP Type = 0x00 Packet Type EAPOL-Start Type = 0x01 Packet Body Length EAPOL-Logoff Type = 0x02 EAPOL-Key Type = 0x03 Packet Body EAPOL-Encapsulated-ASF-Alert Type = 0x04 EAPOL-MKA Type = 0x05 EAPOL-Announcement (Generic) Type = 0x06 EAPOL-Announcement (Specific) Type = 0x07 EAPOL-Announcement-Req Type = 0x08 Figure 6.3. Structure of EAPOL message The EAP is made up of a four-byte header and a packet body. Version: this field, coded on one byte, identifies the version of the protocol and has the value of 03 in hexadecimal for the latest standardized version. Packet Type: this field, coded one byte, identifies the type of data encapsulated by the EAPOL header. The EAPOL header can encapsulate an EAPOL message or an EAP message. Packet Body Length: this field, coded on two bytes, indicates the size of the data encapsulated by the EAPOL header. 6.1.1.1. EAPOL-Start message The EAPOL-Start message was transmitted without a message body in version 2 of the protocol. In version 3, the EAPOL-Start message can be transmitted with or without a message body. This message, transmitted by the supplicant, is used to initialize the 802. 1x mechanism. 108 Wi-Fi Integration to the 4G Mobile Network If the least significant bit of the first byte of the message body is set at ONE, the receiver of the EAPOL-Start message must make an announcement. The other bits of the first byte are set at ZERO. The other bytes of the message body, if present, have a type, length, value (TLV) structure, which gives information about network access conditions. 6.1.1.2. EAPOL-Logoff message The EAPOL-Logoff message is transmitted without a message body. This message, transmitted by the supplicant, is used to terminate the 802.1x mechanism. At the end of this message, the supplicant is no longer authenticated and its access to the LAN is blocked. 6.1.1.3. EAPOL-Key message The EAPOL-Key message is transmitted by the supplicant or by the authenticator. It is used for the establishment of authentication and encryption