在24.301 5.5.1.2.2 Attach procedure initiation 中，说明如果UE支持和NR的双连接，那么UE要将ATTACH REQUEST中的DCNR bit 置位。
If the UE supports dual connectivity with New Radio (NR), then the UE shall set the DCNR bit to "dual connectivity with NR supported" in the UE network capability IE of the ATTACH REQUEST message and shall include the UE additional security capability IE in the ATTACH REQUEST message.
24.301 5.5.1.2.4 Attach accepted by the network中，如果网络决定限制UE建立和NR的双链接，则在ATTACH ACCEPT中将RestrictDCNR bit置位。
If the UE indicates support for dual connectivity with NR in the ATTACH REQUEST message, and the MME decides to restrict the use of dual connectivity with NR for the UE, then the MME shall set the RestrictDCNR bit to "Use of dual connectivity with NR is restricted" in the EPS network feature support IE of the ATTACH ACCEPT message.