uccess 0000 0011 Failure 0000 0100 Identifier Identity 0000 0001 Length Notification 0000 0010 Legacy NAK 0000 0011 EAP-Method Expanded NAK 1111 1110 The Code field corresponds to a Authentication methods EAP-Method data Request or Response message Figure 6.4. EAP message structure The EAP is composed of a four-byte header and possibly an EAP-Method message. 110 Wi-Fi Integration to the 4G Mobile Network Code: this field, coded on one byte, identifies the type of EAP message: - Request: this message enables the authentication server to communicate with the supplicant, for example, to transmit to it an EAP-Method message; the supplicant can also transmit this message to the authentication server to request its identity during mutual authentication; - Response: this message is sent in reply to the previous message; it can correspond, for example, to the supplicant's authentication data contained in an EAP-Method message; - Success: this message is used by the authentication server to inform the supplicant that it has been successfully authenticated; - Failure: this message is used by the authentication server to inform the supplicant that authentication has failed. Identifier: this field, coded on one byte, enables correlation of the messages exchanged between the supplicant and the authentication server or the authenticator. Length: this field, coded on two bytes, indicates the size of the EAP message. This value is identical to the value of the Packet Body Length field in the EAPOL protocol header. When the EAP message is a request or a reply, the header encapsulates an EAP-Method message that contains the Type field, coded on one byte, identifying the type of data in the EAP-Method message. The first three values in the Type field are reserved for specific messages (Identity, Notification and NAK). The other values pertain to identification methods such as EAP-message digest 5 (MD5) (Type = 4), EAP-TLS (Transport Layer Security) (Type = 13) or EAP-TTLS (Tunneled TLS) (Type = 21). 6.1.2.1. EAP-Method Identity mes