NAS， non-access-stratum
NAS 消息格式
在本文档中定义的协议内，每个 5GS NAS 消息都是 3GPP TS 24.007 [11] 中定义的标准 L3 消息。 这意味着消息包含以下部分：
如果该消息是普通的 5GS NAS 消息：
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.
Figure 9.1.1.1: General message organization example for a plain 5GS NAS message
如果该消息是受安全保护的5GS NAS消息：、
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
Figure 9.1.1.2: General message organization example for a security protected 5GS NAS message