Section: 8.133 UP Function Selection Indication Flags
Content: The UP Function Selection Indication Flags information element shall be coded as depicted in Figure 8.133-1. Figure 8.133-1: UP Function Selection Indication Flags For each message, the applicable flags of the UP Function Selection Indication Flags IE shall be clearly specified in the individual message clause. The remaining flags of the UP Function Selection Indication Flags IE not so indicated shall be discarded by the receiver. The receiver shall consider the value of the applicable flags as "0", if the UP Function Selection Indication Flags IE is applicable for the message but not included in the message by the sender. The following bits within Octet 5 shall indicate: - Bit 8 to 2 – Spare, for future use and set to zero. - Bit 1 – DCNR (Dual connectivity with NR): If this bit is set to 1, it indicates to the SGW-C and PGW-C that it is desired to select a specific SGW-U and PGW-U for UEs supporting dual connectivity with NR and not restricted from using NR by user subscription. UE signals its support for dual connectivity with NR to the MME and S4-SGSN with the DCNR of the UE network capability IE in 3GPP TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ]  [23]. Subscription restriction to use NR as secondary RAT is specified in "NR as Secondary RAT Not Allowed" bit within Access Restriction Data in 3GPP TS 29.272[ Evolved Packet System (EPS); Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocol ]  [70].