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When a 5G user (UE) browses the Internet and downloads web content, the UP (user) side adds IP headers to the data and then hands it over to the UPF for processing, as described below;   I. UPF Processing   After adding the IP header, the user packets will be routed through the IP network to the UPF, which provides an entry point to the 5G core network. the IP network relies on its lower layers to transmit packets between routers; and the Ethernet operable Layer 2 agreement transmits IP packets between routers; The UPF is specifically responsible for mapping TCP/IP packets to specific QoS flows belonging to specific PDU sessions by using packet inspection to extract various header fields, which the UPF compares to a set of SDF (Service Data Flow) templates to identify the appropriate PDU sessions and QoS flows. For example, a unique combination of {source IP address 'X'; destination IP address 'Y'; source port number 'J'; destination port number 'K '} in unique combinations to map packets to specific PDU sessions and QoS flows; in addition, the UPF receives a set of SDF templates from the SMF (Session Management Function) during PDU session setup.   II.Data Forwarding   After identifying the appropriate PDU session and QoS flow, the UPF forwards the data to the gNode B using a GTP-U tunnel (the 5G core network architecture may link multiple UPFs - the first UPF must use a GTP-U tunnel to forward the data to another UPF, which then forwards it to the gNode B). Setting up a GTP-U tunnel for each PDU session implies that the TEID (tunnel endpoint identifier) within the GTP-U header identifies the PDU session but not the QoS flow. The “PDU Session Container” is added to the GTP-U header to provide information to identify the QoS flow. Figure 215 shows the structure of the GTP-U header containing the “PDU Session Container” as specified in 3GPP TS 29.281, and the content of the “PDU Session Container” as specified in 3GPP TS 38.415. III.PDU Session Container   As shown in Figure 216 below, when the value of “PDU Type” is “0”, it means that the PDU is a downlink packet instead of an uplink packet. the PPP (Paging Policy Presence) field indicates whether or not the header contains PPI (Paging Policy Indicator). (Paging Policy Indicator). the UPF may provide PPI to gNode B to provide paging priority that may be triggered by the arrival of a downlink packet - i.e. when the UE is in the RRC Inactive state. the RQI (Reflected QoS Indicator) specifies whether or not Reflected QoS should be applied to this QoS stream.     IV.GTP-U Tunneling   Using the UDP/IP protocol stack, UDP and IP headers are usually added before forwarding packets over the transport network.UDP provides simple connectionless data transfer.The structure of the UDP header is shown in Figure 217 below, where the source and destination ports identify the higher-level application. The higher-level application in this scenario is GTP-U whose registered port number is 2152.   V.GTP-U Headers   Adding IP headers for routing across GTP-U tunnels means that packets now have two IP headers. These are commonly referred to as the internal and external IP headers. Figure 218 shows these two headers; the UPF can use the DSCP field in the external IP header to prioritize packets, and the header associated with the GTP-U tunnel is removed at the far end of the tunnel, that is, at gNode B or, if the core network architecture is using chained UPF, at another UPF.

I. Network and Agreement Stack In SA (Independent Networking) 5G (NR) wireless network is usually divided into CU (Centralized Unit) and DU (Distributed Unit), where: DU (Distributed Unit) hosts the RLC, MAC, and PHY (Physical) layers, and CU (Centralised Unit) hosts the SDAP and PDCP layers; the user side of the network. The protocol stack is shown in the figure below:   II. the user data transfer to the end user (UE) to browse the Internet and download Web page content, for example, Internet browsers in the application layer using HTTP (Hypertext Transfer) protocol; assuming that the end user (UE) to host the Web page to be downloaded to the server to send the HTTP GET command, the application server will continue to use the TCP / IP (Transmission Control Protocol / Internet Protocol) packets to begin downloading the web content to the end user; the following header additions are required;   2.1 TCP Header Addition As shown in Figure 213, the TCP layer header is added with a standard header size of 20 bytes, but the size may be larger when optional header fields are included.The TCP header specifies the source and destination ports to identify higher-level applications. By default HTTP uses port number 80. the header also includes a sequence number to allow for reordering and packet loss detection at the receiver. The acknowledgement number provides a mechanism for acknowledging the packet, while the data offset defines the size of the header. The window size specifies the number of bytes the sender is willing to receive. Checksums allow for error bit detection in the header and payload. Emergency pointers can be used to indicate that certain data needs to be processed with high priority   2.2 IP Layer Header Addition Assuming IPv4 is used, the standard size of the header added at the IP layer, as shown in Figure 214, is 20 bytes (but the size may be larger when the optional header field is included).The IP header specifies the source IP address and the destination IP address, and the router uses the destination IP address to forward the packet in the appropriate direction. The version header field has a value of 4 when using IPv4, where the HDR (header) length field specifies the size of the header and the total length field specifies the size of the packet; DSCP (Differential Service Code Point) can be used to prioritize packets, and ECN (Explicit Congestion Notification) can be used to indicate network congestion. The agreement field specifies the type of content within the packet payload; TCP uses protocol number 6 for identification.  

Whenever a terminal (UE) is ready to make a call or transmit data in a mobile communication system, it needs to connect with the core network first, which is due to the fact that the system temporarily removes the connection between the UR and the core network after the first time it is powered on or in an idle state for a period of time; the connection and management of the access connection between the terminal (UE) and the core network (5GC) in 5G (NR) is handled by the AMF unit, whose connection management (CM) is used to establish and release the control plane signaling connection between the UE and the AMF.   I. CM State Describes the signaling connection management (CM) state between the terminal (UE) and the AMF, which is mainly used for transmitting NAS signaling messages; for this purpose 3GPP defines two connection management states for the UE and the AMF respectively: CM-Idle (Connection Management in Idle state) CM-Connected (Connected state connection management)   CM-Idle and CM-Connected states are maintained by UE and AMF through NAS layer;   II.CM Characteristics Depending on the connection between the UE and the AMF. where: CM-Idle state the mobile equipment (UE) has not entered the signaling transmission state (RRC-Idle) with the core node (AMF). when the UE is in CM-Idle state it can move between different cells through mobile control according to the cell reselection principle. CM-Connected state the UE establishes a signaling connection (RRC-Connected and RRC-Inactive) with the AMF. the UE and the AMF can establish a connection based on the N1 (logical) interface will enter the CM-Connected state for the following intra interactions: RRC signaling between the UE and the gNB N2-AP signaling between the gNB and the AMF.   III.CM state transition The connected state of UE and AMF can be initiated by UE or AMF respectively, as shown in the following figure:   3.1 UE Initiated State Transition Once the RRC connection is established the UE state will enter CM-Connected; within the AMF once the established N2 context is received the UE state will enter CM-Connected; this can be performed by a registration request and a service request; where: When the UE is powered on for the first time, it selects the best gNB according to the cell selection process and sends a registration request to initiate the RRC connection setup signaling to the gNB and sends the N2 signaling to the AMF. The registration request triggers the transition from CM-Idle to CM-Connected. When the UE is in CM-Idle state and must send uplink data, the UE triggers a Service Request NAS message to the AMF and changes the CM-Idle to CM-Connected.   3.2 Network initiated state transition When there is downlink data to be transmitted to the CM-Idle UE, the network MUST use paging to initiate the state transition process. Paging triggers the UE to establish an RRC connection and send a Request NAS message to the AMF. The request triggers the N2 signaling connection to move the UE to CM-Connected.   When the signaling connection is released or the signaling connection fails, the UE can move from CM-Connected to CM-Idle.

  Ⅰ、ANTENNA PORTS Antenna ports as defined in the 4G (LTE) standard do not (necessarily) correspond to physical antennas, but are logical entities distinguished by their reference signal sequence. Multiple antenna port signals may be transmitted on a single transmitter antenna (e.g., C-RS port 0 and UE-RS port 5); similarly a single antenna port may be distributed over multiple transmitter antennas (e.g., UE-RS port 5).   Ⅱ、PDSCH transmission in 4G (LTE) As an example of antenna ports used for PDSCH distribution, they may have the most variations. Initially the demodulator only supports transmission on pairs of antenna ports 0, (0 and 1), (0, 1, 2), or (0, 1, 2, 3); these ports are considered as C-RS antenna ports, each of which has a different arrangement of C-RS resource elements. Various configurations using these C-RS antenna ports are thus defined, including 2- or 4-port Tx diversity and 2-, 3- or 4-port spatial multiplexing.   Ⅲ、Beam Assignment The single layer PDSCH assignment that can be transmitted on port 5 after the introduction of beam assignment support. Since then LTE demodulators have been enhanced to support LTE Release9 This release adds transmission Mode8 - two-layer beam fouling (i.e. beamforming + spatial multiplexing) - where PDSCH is transmitted on antenna ports 7 and 8 (please note that single-layer beamforming in Rel9 can use either port 7 or port 8 in addition to port 5). The new transmission mode in the standard Rel10 - TM9 adds up to 8 layers of transmission using ports 7-14 (LTE-Advanced demodulators support TM9).   Ⅳ、Since ports 0-3 are indicated by the presence of C-RS, ports 5 and 7-14 are indicated by UE-specific reference signals (UE-RS); the following table summarizes the various PDSCH mappings that can be used with the corresponding reference signals and antenna ports.     V、 MIMO and Tx Diversity In a MIMO or Tx Diversity configuration each C-RS antenna port must transmit on a separate physical antenna creating spatial diversity between paths. On the other hand single layer beamforming is achieved by sending the same signal to each antenna but changing the phase of each antenna signal with respect to the other antennas. Since each antenna sends the same UE-RS sequence, the received UE-RS sequence can be compared with a reference sequence and the weights applied to the antennas to accomplish beamforming can be calculated.   VI、MULTILAYER BEAMFORMING The complexity of beamforming is increased by transmitting as many UE-RS columns as the number of layers to allow demodulation of the PDSCH data for each layer. The UE-RS sequence at each antenna port is orthogonal to the other sequences, both in the time/frequency domain and in the code domain. This can be thought of as independent beamforming for each layer. n Layer beamforming is an extension of two-layer beamforming that supports up to eight data layers being able to beamform each layer separately. For reference, the following table lists the different LTE downlink reference signals and the antenna ports used.     VII.Transmit-Receive Paths For single-layer, single-antenna LTE signals (using C-RS only) there is only one antenna port signal that can be received wirelessly, but in general the reception of LTE signals will contain a combination of multiple transmit antennas, each of which may be transmitting a combination of multiple antenna ports.LTE standards do not specify any particular transmit antenna setting, but since the C-RS antenna ports are are used for most control channels and PDSCHs, the LTE demodulator uses cell-specific RS antenna ports rather than transmit antennas when indicating the transmit path between the transmitter and receiver. The C-RS antenna port is typically indicated in the user interface and documentation using the helper C-RSn, where n is the antenna port number. Correspondingly, the receive channel is denoted by Rxm, where m is the measurement channel number -1. Together, these two endpoints form the transmit-receive path from the transmitter to the receiver. The transmit-receive path is denoted by C-RSn/Rxm, so that C-RS2/Rx1 on the MIMO Information Sheet shows the metrics calculated based on the C-RS antenna port 2 signal received on measurement channel 2.

Base station power in mobile communications is a key factor in determining wireless cell coverage and communication quality; in the 5G (NR) system base station (gNB) total power, cell power and reference signal power in addition to the BBU (baseband unit) output, but also with the antenna (Port) number and the cell bandwidth (BW) related to the calculation are as follows;   I. Reference Signal Power This is the power value measured and reported by the terminal (UE) and the total transmit power of the cell can be calculated by the following formula first for each channel power;   In the above equation: Maximum Transmit Power: Transmit power per single channel (in dBm); Reference Signal Power (Reference Signal Power): single channel per RE power (in dBm units). RBcell (cell bandwidth): the total number of RBs in the cell (each RB has 12 REs).   Calculation example Assuming that the maximum output power of the BTS system configuration is 40dBm (10W per channel), the results for different subcarrier intervals are as follows.   1. at subcarrier interval 15KHz 270RBs (cell bandwidth 50MHz): Reference signal power = 40-10 x log10(270x12) = 40-35.10 Reference signal power = 4.9dBm   2. at subcarrier spacing of 30 KHz 273 RBs (cell bandwidth 100MHz): Reference signal power = 40-10 x log10(273 x12) = 40 - 35.15 Reference signal power = 4.85 dBm   3. At subcarrier spacing of 60KHz 130RBs (cell bandwidth 100MHz) Reference signal power = 40-10 x log10(130x12) = 40 - 31.93 Reference signal power = 8.07dBm     II.the total transmit power of 5G (NR) base station The calculation needs to take into account the maximum transmit power and the number of Tx antennas, which can be calculated by the following formula:   Antennas and cells with the same maximum power are 40 dBm, which can be calculated for different antenna configurations total Tx (transmit) power, which:8, 16, 64 and 128 antenna system when respectively as follows: 8Tx antenna total transmit power = 40 + 10xlog10(8) = 40 + 9.03 = 49.03 dBm Total transmit power of 16Tx antenna = 40+10xlog10(16) = 40+12.04 = 52.04 dBm 64Tx antenna total transmit power = 40+10 x log10(64) = 40+18.06 = 58.06 dBm 128Tx antenna total transmit power = 40+10x log10(128) = 40+21.07=61.07dBm   ----- Total transmit power is the top-of-air power, including the antenna gain (directional gain in dBi) used to calculate the equivalent omnidirectional radiated power (EIRP).  

The radio access network (RAN) in a mobile communication system must be connected to the core network through an interface and then interoperate with public communications and the Internet. After that, the mobile terminal (UE) can realize data and voice communication; this interface is N3 in 5G.   I. N3 interface It is the interface between NG RAN (radio access network) and 5GC (core network) in 5G (NR) system; the main function is to realize the exchange of user data and signaling messages between core network and radio access network. Fig. 1.N3 interface location in 5G system     II.N3 uses mainly include the following; Data transmission:The N3 carries user-plane and control-plane traffic, where the user plane is responsible for transmitting user data, such as Internet traffic, voice calls, and multimedia content, between the user equipment and the 5G core network. Control signaling:In addition to user data, the N3 interface handles control signaling messages. These messages are critical for establishing, managing and releasing connections between user equipment (UE) and 5G core network functions. Interface Protocols:The N3 interface relies on a variety of protocols to communicate and ensure that the core network and RAN elements correctly transmit and interpret data and signaling messages.Common protocols used on the N3 interface include IP (Internet Protocol), SCTP (Stream Control Transmission Protocol), and other protocols specific to the 5G network architecture. Dynamic Connectivity:The N3 interface allows for dynamic and flexible connection management, a key feature of 5G networks. It supports seamless switching, Quality of Service (QoS) tuning, and efficient resource allocation to provide a superior user experience. Slicing Support:Network slicing is a fundamental concept in 5G that supports the creation of multiple virtual networks within a single physical infrastructure.The N3 interface plays a critical role in supporting network slicing by ensuring that traffic for each slice is properly routed and managed within the NG RAN. Scalability:The N3 interface is designed to handle large volumes of data traffic and signaling messages, making it suitable for a variety of 5G use cases, including: eMBB (enhanced mobile broadband), URLLC (ultra-reliable low-latency communication), and mMTC (massive machine type communication). The N3 interface is a key component of the 5G (NR) system architecture, enabling high-performance communications between the 5G core network and the radio access network, and it is critical to take advantage of the benefits of 5G technology to bring it to the user (UE) and its applications.    

Whenever a terminal (UE) is ready to make a call or transmit data in a mobile communication system, it needs to connect with the core network first, which is due to the fact that the system temporarily removes the connection between the UR and the core network after the first time it is powered on or in an idle state for a period of time; the connection and management of the access connection between the terminal (UE) and the core network (5GC) in 5G (NR) is handled by the AMF unit, whose connection management (CM) is used to establish and release the control plane signaling connection between the UE and the AMF.     I. CM State Describes the signaling connection management (Connection Management) state between the terminal (UE) and the AMF, which is mainly used for transmitting NAS signaling messages; for this reason 3GPP defines two connection management states for the UE and the AMF respectively: CM-Idle (Connection Management in Idle state) CM-Connected (Connected state connection management)   CM-Idle and CM-Connected states are maintained by the UE and AMF through the NAS layer;   II.CM CHARACTERISTICS Depending on the connection between the UE and the AMF. among others: CM-Idle state the mobile equipment (UE) has not entered the signaling transmission state (RRC-Idle) with the core node (AMF). when the UE is in CM-Idle state it can move between different cells when it moves by mobile control according to the cell reselection principle. CM-Connected state the UE establishes a signaling connection with the AMF (RRC-Connected and RRC-Inactive). the UE and the AMF can establish a connection based on the N1 (logical) interface will enter the CM-Connected state to perform the following intra interactions: RRC signaling between the UE and the gNB N2-AP signaling between the gNB and the AMF III. CM State Transition The connection state between the UE and the AMF can be initiated by the UE or the AMF respectively as shown in the following figure: 3.1 UE Initiated State Transition Once the RRC connection is established the UE state will enter CM-Connected; within the AMF once the established N2 context is received the UE state will enter CM-Connected; this can be performed by a registration request and a service request; where: When the UE is powered on for the first time, it selects the best gNB according to the cell selection process and sends a registration request to initiate the RRC connection setup signaling to the gNB and sends the N2 signaling to the AMF. The registration request triggers the transition from CM-Idle to CM-Connected. When the UE is in CM-Idle state and must send uplink data, the UE triggers a Service Request NAS message to the AMF and changes the CM-Idle to CM-Connected.   3.2 Network initiated state transition When there is downlink data to be transmitted to the CM-Idle UE, the network MUST use paging to initiate the state transition process. Paging triggers the UE to establish an RRC connection and send a Request NAS message to the AMF. The request triggers the N2 signaling connection to move the UE to CM-Connected.   When the signaling connection is released or the signaling connection fails, the UE can move from CM-Connected to CM-Idle.

SMO (Service Management and Orchestration) defined by Open RAN Alliance is a wireless resource automation platform for mobile communications.SMO framework specification is defined by Open RAN Alliance as a component of OSS system to support a variety of deployment options to meet the needs of end-users; SMO can be deployed in a distributed system, but also deployed in the telecom cloud services and other places.   I. Platform Architecture The SMO platform is shown in the following figure (1) The architecture includes consists of O-CU (Open Central Unit), O-DU (Open Distributed Unit) and Near RT-RIC (Near Real Time Radio Intelligent Controller), which are defined as cloud-native virtualization functions running on cloud infrastructure, also known as O-Cloud.   Ⅱ. SMO features are responsible for overseeing network functions and O-Cloud lifecycle management.SMOs include Non-Real-Time Radio Intelligent Controllers or Non-RT-RICs.The architecture defines a variety of SMO interfaces, O1, O2, and A1, that allow SMOs to manage multi-vendor Open RAN networks.ORAN is standardizing on extensions to the O1, A1, and R1 interfaces to enable a competitive ecosystem and accelerate new features to market. ORAN is standardizing extensions to the O1, A1 and R1 interfaces to enable a competitive ecosystem and accelerate time-to-market for new features. Supports licensing, access control and AI/ML lifecycle management and legacy northbound interfaces; Support for existing OSS features such as service orchestration, inventory, topology and policy control; The R1 interface allows rApp portability and lifecycle management. By supporting third-party Equipment Management System (EMS) specific proprietary southbound interfaces, SMO will be able to automate existing, purpose-built multi-vendor RAN as well as Open RAN networks. Ⅲ​. SMO interfaces mainly include: R1 interface:R1 interface for multi-vendor rApp, designed to support multi-vendor rApp portability and provide value-added services for rApp developers and solution providers; the interface enables Open APIs to be integrated into SMO; as a service it includes: service registration and discovery services, authentication and authorization services, AI/ML workflow services, and A1, O1 and O2 related services. A1 Interface: The interface is used for policy guidance; SMO provides fine-grained policy guidance, such as allowing user devices to change frequencies, as well as providing other data enrichment capabilities to RAN functions through the A1 interface. O1 Interface:SMO supports the O1 interface for managing OAM (Operations and Maintenance) for multi-vendor Open RAN functions, including fault, configuration, accounting, performance and security management, software management, and file management functions. O2 Interface:The O2 interface in SMO is used to support cloud infrastructure management and deployment operations for Open RAN functions in the O-Cloud infrastructure hosting network.The O2 interface supports the orchestration of O-Cloud infrastructure resource management (e.g., inventory, monitoring, provisioning, software management, and lifecycle management) and the deployment of Open RAN network functions to provide logical services for managing the lifecycle of deployments using cloud resources. M-Plane:SMO supports the organization of Cloud infrastructure resource management (e.g., inventory, monitoring, configuration, software management and M-Plane: SMO supports the Open FrontHaul M-plane based on NETCONF/YANG as an alternative to the O1 interface to support multi-vendor O-RU integration. the Open FrontHaul M-plane supports management functions including boot installation, software management, configuration management, performance management, fault management, and file management.   IV.RAN Optimization The SMO framework can be used for RAN optimization with the help of Non-RT RICs and rApps. non-RT RICs enable non-real-time intelligent RAN optimization by providing policy-based guidance using data analytics and AI/ML models. non-RT RICs can take advantage of SMO solutions, such as data collection and configuration services for O-RAN nodes. Additionally, rApps that are modular applications can leverage the functionality exposed by the non-RT RIC and SMO frameworks through the R1 interface to perform multi-vendor RAN optimization and assurance.

Ⅰ、MIMO (Multiple Input Multiple Output) technology enhances wireless communication by using multiple antennas at the transmitter and receiver. It improves data throughput, extends coverage, improves reliability, resists interference, improves spectral efficiency, supports multi-user communications and saves energy, making it a key technology in modern wireless networks such as Wi-Fi and 4G/5G.   Ⅱ、MIMO Advantages MIMO (Multiple Input Multiple Output) is a technology used in communication systems (especially wireless and radio communications) that involves multiple antennas on the transmitter and receiver.The advantages of MIMO system are as follows: Data throughput enhancement:One of the main advantages of MIMO is its ability to increase data throughput. It is by using multiple antennas at both ends (transmitter and receiver), a MIMO system can send and receive multiple data streams simultaneously. This results in higher data rates, which is especially important in high-demand scenarios such as streaming HD video or online gaming. Extended Coverage:MIMO can improve the coverage of a wireless communication system. By using multiple antennas, the system allows signals to be transmitted in different directions or paths, reducing the likelihood of signal fading or interference. This is especially beneficial in environments with obstacles or interference. Increased Reliability:MIMO systems are more reliable because they can mitigate the effects of fading and interference by using spatial diversity, where if one path or antenna is jammed or faded, the other can still transmit data; this redundancy increases the reliability of the communication link. Greater Resistance to Interference:MIMO systems are inherently more resistant to interference from other wireless devices and the environment. The use of multiple antennas allows the use of advanced signal processing techniques such as spatial filtering, which can filter out interference and noise. Increased Spectral Efficiency:MIMO systems can achieve greater spectral efficiency, meaning they can transmit more data using the same amount of available spectrum. This is critical when available spectrum is limited. Multi-User Support:MIMO can support multiple users simultaneously through the use of spatial multiplexing. Each user can be assigned a unique spatial stream, allowing multiple users to access the network without significant interference. Increased Energy Efficiency:MIMO systems can be more energy efficient than traditional single antenna systems. By optimizing the use of multiple antennas, MIMO can transmit the same amount of data with lower power consumption. Compatibility with Existing Facilities:MIMO technology can often be integrated into existing communications infrastructure, making it a practical option for upgrading wireless networks without a complete overhaul.   MIMO (Multiple Input Multiple Output) technology offers a variety of advantages, including increased data throughput, improved coverage and reliability, immunity to interference, enhanced spectral efficiency, support for multiple users, and improved energy efficiency. These advantages make MIMO a fundamental technology for modern wireless communication systems, including Wi-Fi, 4G and 5G networks.

After accessing the 5GC via non3GPP WALN, the terminal (UE) starts PDU session establishment after completing registration, authentication and authorization, during which user data, uplink and downlink traffic and QoS are defined as follows;   I. User plane After completing the PDU session establishment and establishing the user plane IPsec sub-SA between the UE and the N3IWF, the UE can use the established IPsec sub-SA and the associated GTPU tunnels between the N3IWF and the UPF to send upstream and downstream traffic with various QoS flows for the session over the untrusted WLAN network.   II.When the UE has to transmit a UL PDU, it shall determine the QFI associated with the PDU using the QoS rules of the corresponding PDU session and encapsulate the PDU in a GRE packet, with the QFI value located in the header of the GRE packet.The UE shall forward the GRE packet to the N3IWF via the IPsec sub-SA associated with the QFI by encapsulated into an IPsec packet in tunnel mode, with the source address being the UE IP address and the destination address being the UP IP address associated with the sub-SA.   When the N3IWF receives a UL PDU, it shall decapsulate the IPsec header and the GRE header and determine the GTPU tunnel ID corresponding to the PDU session.The N3IWF shall encapsulate the UL PDU in a GTPU packet and place the QFI value in the header of the GTPY packet and forward the GTPU packet to the UPF via the N3. III.Downstream Traffic When the N3IWF receives a DL PDU from the UPF via the N3, the N3IWF shall decapsulate the GTPU header and use the QFI and the PDU session identifier in the GTPU header to determine the IPsec Child SA to be used to send the DL PDU to the UE via the NWu.   The N3IWF shall encapsulate the DL PDU within a GRE packet and place the QFI value in the header of the GRE packet.The N3IWF may also include a Reflected QoS Indicator (RQI) in the GRE header, which shall be used by the UE to enable Reflected QoS.The N3IWF shall forward the GRE packet, along with the DL PDU, through the IPsec Child SA associated with the QFI to the UE by encapsulating the GRE packet into an IP packet in tunnel mode, where the source address is the UP IP address associated with the sub-SA and the destination address is the address of the UE.   IV.QoS For UEs accessing the 5GCN over untrusted WLANs, the N3IWF supports QoS differentiation and mapping of QoS flows to non 3GPP access resources.The QoS flows are controlled by the SMF and can be pre-configured or established through the PDU session establishment or modification process requested by the UE.The N3IWF shall determine the user plane to be established based on the local policy, configuration, and QoS profile received from the network. profile to determine the number of user plane IPsec sub-SAs to be established and the QoS profile associated with each sub-SA. The N3IWF shall then initiate an IPsec SA creation process to the UE to establish the sub-SAs associated with the QoS flows of the PDU session.The QoS functions of the UE, the N3IWF, and the UPF are specified in figure (1) below.   Figure 1.QoS for ungranted WLAN access to 5GCNs   Non-granted non 3GPP access essentially corresponds to a WLAN interworking with 5GCN, which is served over N3IWF. However, unlike earlier architectures in which the WLAN pass-through network elements (PDG/ePDG) were part of the 3GPP core network, the N3IWF acts as an access network similar to the 3GPP access. This allows common procedures for registration, authentication and session handling in both 3GPP Access and non 3GPP Access. Paging, mobile registration, and periodic registration are not supported in non-granted WLANs. Multiple PDU sessions can be established on both 3GPP access and non-granted WLANs, and PDU sessions can be switched between them. It is also possible to establish multiple access PDU sessions on 3GPP Access and Ungranted WLANs that support ATSSS.