5G Standards are Becoming Mature with Smooth Development of R16 and R17

In June 2019, 3GPP TSG#84 plenary was held in Newport Beach, USA. 3GPP Rel-16 Stage 2 was frozen on schedule. Stage 3 is expected to be frozen in March 2020. 3GPP Rel-15 is the first version for standalone deployment that can be used for commercial use. It is mainly applied for eMBB scenarios. 3GPP Rel-16 has been enhanced in several aspects, including continuous evolution of the system architecture, enhancement of supporting vertical industry application scenarios, enhancement of supporting multi-access, and enhancement of supporting network data analytics services. Rel-16 is the second version for standalone deployment and can be applied for various application scenarios such as eMBB, URLLC and eMTC.

Timeline

Continuous evolution of 5GC system architecture 

• In the aspect of system architecture, I-SMF is added to solve how to ensure service continuity when the user moves out of the current SMF service area. Call flows such as I-SMF insertion, modification and deletion procedures are specified, and how I-SMF establishes the offload path of the user plane is also specified. This feature is important for domestic operators in China to ensure service continuity when users move across provinces. In this feature, the UPF is enhanced to support IP address allocation.
• The 5G system supports the SRVCC when UE moves from 5G to 3G, which solves how to ensure the continuity of voice service when the user moves out of 5G coverage range.
• The service-based architecture evolves further. The SCP function is introduced to support the indirect communication mode and delegate the target NF/NFS discovery and selection function. The concepts of NF Set and NFS Set are introduced to better support the stateless NF/NFS concept. The user context can also be directly transferred between two sets with the same NF/NFS type.
• The radio capability of the terminal is saved on the network side. Each time the terminal accesses the network, it only needs to carry the related UE radio capability ID. The network obtains the radio capability of the terminal according to the capability ID, thus improving the transmission efficiency of air interfaces.
• The new network function GMLC and the associated service based interfaces are specified to support commercial location services. The related call flows are basically aligned with the location flow supported by EPC with some extra enhancements such as UE location information exposure.
• Other enhancements include IAB node authorization, allowing IMS to invoke the service-based interfaces of 5GC, defining the service-based interfaces between UDM and HSS, enhancement of background data transmission, and other small enhancements, such as DNN replacement, and reporting the cell information of the secondary base stations in the DC scenario.

Support of 5GC for the vertical industry

• To support highly reliable communication, 5GC adopts the dual-PDU session mechanism, and reliability processing is guaranteed by protocols in the application layer such as TSN. The QoS monitoring mechanism is defined, so that applications can percept the communication quality at the 5GC layer. Direct tunnels between ULCLs are specified to ensure the service continuity of MEC services
• The 5GC is enhanced to support NB IoT and eMTC access, so that the CIoT function supported by 5GC is basically aligned with EPC.  
• To meet vertical industry requirements, 5GC is further enhanced in the following three aspects: support of the non public network (NPN) and access control mechanism, and interworking between the NPN and the operator's public network, support of 3 types of group communication mechanisms of 5G-LAN, and enhancement of 5GC as a time sensitive network (TSN) bridge, to support deterministic communication services.
• A new V2X architecture based on 5GC is defined to support V2X communication through Uu or PC5. The PC5 interface supports three modes: unicast, broadcast and multicast. The PC5 QoS supports QoS control based on QoS flow. For V2X communication through the Uu interface the network can send multiple QoS profiles to the base station, and the base station selects an appropriate QoS profile for control according to the actual radio condition.

Enhancement of 5GC with respect to multi-access

• 5GC supports access of trusted non-3GPP networks via TNGF. 5GC supports wireline network access, including BBF access and CableLAB access. 3GPP is working closely with BBF, a standard organization, to reach agreements on key technologies such as network architecture, QoS model, IP address allocation, user ID and IPTV service. The unified 5GC core network standard is gradually matured.

Enhancement of 5GC with respect to data analysis 

• The NWDAF is enhanced to collect the data from the network function, OAM and application layer, and perform data analysis to generate information requested by consumers. Internal and external network consumers can invoke the services provided by NWDAF to obtain such information. Some network functions are also enhanced to support particular user data collection from the NWDAF.

Continuous increase of ZTE for Its Investment in 5G Standardization

ZTE actively participates in 5G technical research and standard activities, and makes contributions to ensure the timely completion of Rel-16 Stage 2. In Rel-16, ZTE led two topics: eNS and ATSSS.

• Network slicing is one of the key technologies of 5GC. ZTE led technical discussions on network slicing in Rel-15, and initiated the network slicing enhancement topic in Rel-16. The enhancement of network slicing has two standardized parts: One is to add the slice-specific authentication in the registration procedure. Second is that, during the 4G-to-5G handover, the handover and registration procedures are enhanced to select a correct network slice instance in 5G.
• Rel-15 5GC has already supported 3GPP access and non-3GPP access. In Rel-16 wireline access is also supported. When the UE is connecting to 5GC via multiple accesses simultaneously, how to steer, switch and split the data traffic between different accesses on demand is a key problem to be solved. ZTE initiates the ATSSS topic in Rel-16. As a result, the concept of MA-PDU Session is adopted and related call flows are specified. New ATSSS rules and MAR rules are defined to guide the UE and UPF respectively to select the correct access type for data traffic. The user plane protocol PMF is defined to measure the performance of the access system.

At the same time, ZTE is taking the lead in the stage 3 standardization of these two topics, which is expected to be completed in March 2020.

In addition, 3GPP has initiated the Rel-17 study, discussed and approved nearly 30 Rel-17 study items. 3GPP SA planned to discuss the priority in September and December plenaries, and officially determined the time plan and contents of Rel-17 in December 2019. It is expected that system architecture will be further evolved in Rel-17, and Rel-17 will continue to study new functions, such as MBMS support, edge computing service and enhanced proximity communication, to meet the new requirements for 5G deployment. ZTE will continue to increase investment in 5G standardization and promote the commercialization of 5G.