Section: 9.1.1 NAS message format
Content: Within the protocols defined in the present document, every 5GS NAS message is a standard L3 message as defined in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [11]. This means that the message consists of the following parts: 1) if the message is a plain 5GS NAS message: a) extended protocol discriminator; b) security header type associated with a half spare octet or PDU session identity; c) procedure transaction identity; d) message type; e) other information elements, as required. 2) if the message is a security protected 5GS NAS message: a) extended protocol discriminator; b) security header type associated with a half spare octet; c) message authentication code; d) sequence number; e) plain 5GS NAS message, as defined in item 1 The organization of a plain 5GS NAS message is illustrated in the example shown in figure 9.1.1.1. Figure 9.1.1.1: General message organization example for a plain 5GS NAS message The PDU session identity and the procedure transaction identity are only used in messages with extended protocol discriminator 5GS session management. Octet 2a with the procedure transaction identity shall only be included in these messages. The organization of a security protected 5GS NAS message is illustrated in the example shown in figure 9.1.1.2. Figure 9.1.1.2: General message organization example for a security protected 5GS NAS message Unless specified otherwise in the message descriptions of clause 8 and annex D, a particular information element shall not be present more than once in a given message.