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The Public Warning System (PWS) is a communications system operated by government agencies or related organizations for providing public warning information in emergency situations. In 5G (NR) networks, PWS messages are broadcast via 5G (NR) base stations connected to the 5G Core (5GC). The base stations are responsible for scheduling and broadcasting warning messages and using paging to notify user equipment (UE) of the broadcasted warning messages, thereby ensuring rapid dissemination and wide coverage of emergency information. 3GPP defines PWS Restart Indication and PWS Failure Indication in TS 8.413 as follows:   1. The PWS Restart Indication procedure notifies the AMF to reload PWS information for some or all cells of the NG-RAN node from the CBC, if necessary. The Restart Indication procedure uses non-UE-associated signaling; successful operation is shown in Figure 8.9.3.2-1, where:   The NG-RAN node initiates this procedure by sending a PWS Restart Indication message to the AMF. Upon receipt of the PWS Restart Indication message, the AMF shall proceed as defined in TS 23.527. If an emergency area ID is available, the NG-RAN node should also include it in the list of emergency area IDs used for the Restart IE.   2. PWS anomalies primarily occur when PWS notification operations fail (or become invalid) in individual cells within the wireless network. 3GPP defines PWS Failure Indication in TS 38.413 as follows.   The PWS Failure Indication procedure is intended to notify the AMF that an ongoing PWS operation in one or more cells of the NG-RAN node has failed. The procedure is shown in Figure 8.9.4.2-1 below. The PWS Failure Procedure utilizes non-UE-associated signaling. The NG-RAN node initiates this procedure by sending a PWS Failure Indication message to the AMF. Upon receipt of the PWS Failure Indication message, the AMF should proceed as defined in TS 23.041.

1. Mini-Slot Scheduling Mini-Slot transmission in the downlink path mainly involves PDSCH (Physical Downlink Shared Channel) that carries user data. By scheduling Mini-Slot, the system can quickly transmit data to reduce latency.   2. Scheduling Principle Mini-Slot can be scheduled at any time in a time slot, that is, once the gNB (5G base station) is ready, it will use 2, 4 or 7 OFDM symbols to send data immediately (depending on the data size and required latency). The terminal (UE) side will pay close attention to the specific search area to find the Mini-Slot allocation and decode the data as needed.       In the figure above: the PDSCH on the left is presented in the form of 2 OFDM symbol Mini-Slot in time slot #n. The PDSCH on the right is presented in the form of 4 OFDM symbol Mini-Slot in time slot #1; this highlights how 5G (NR) can adapt to time-sensitive traffic through flexible scheduling.   3. Parameter Sets and Mini-Slot Transmission Mini-Slot operation is closely related to the 5G (NR) parameter set, which defines the subcarrier spacing (SCS) and mini-slot duration. A larger subcarrier spacing reduces the mini-slot duration, further reducing latency. The relationship between these two parameters is as follows:   As shown in the figure above, the capacity of all subcarrier spacings in the frame, subframe, and slot structures of different parameter sets, measured in bits per Hz, is the same. As the parameter set increases, the subcarrier spacing increases, but the number of symbols per unit time also increases. The figure above only illustrates the cases of 15kHz and 30kHz subcarrier spacing, where the number of subcarriers is halved, but the number of slots per symbol per unit time doubles.   The relationship between a typical mini-slot and its duration (2 OFDM symbols) is as follows: μ = 0/15kHz/1ms to 0.14ms μ = 1/30kHz/0.5ms to 0.07ms μ = 2/60kHz/0.25ms to 0.035ms μ = 3/120kHz/0.125ms to 0.018ms   The above equations illustrate how a larger subcarrier spacing (SCS) and shorter slots work together with mini-slot transmission to help achieve the ultra-low latency goals of 5G (NR).

  1. The 5G (NR) time slot structure is flexible and dynamic, where each time slot contains 14 OFDM symbols that can be allocated to uplink (UL), downlink (DL), or a combination of the two; in addition, the UL/DL allocation within the time slot can be changed dynamically, and a Mini-Slot shorter than a full time slot can be used to further enhance the flexibility of low-latency applications. The specific length of the time slot depends on the subcarrier spacing (parameter set). The larger the spacing, the shorter the time slot.   2. Mini-Slot 5G (NR) needs to achieve Urllc (ultra-low latency and high reliability), which is crucial for applications such as autonomous vehicles, industrial automation, and mission-critical IoT. To meet this function, the system introduces Mini-Slot transmission technology; unlike traditional full-slot scheduling, Mini-Slot can transmit data immediately without waiting for the next time slot boundary.   3. Slot and Mini-Slot: In 5G (NR), the figure below shows how the PDSCH (Physical Downlink Shared Channel) utilizes symbols 2 and 4 in various time slot structures. This flexibility and efficiency are the new design features that 5G (NR) brings to downlink communications.   4. Mini-Slot Transmission: Mini-slots use fewer OFDM symbols and have a shorter TTI (Transmission Time Interval). While a time slot typically contains 14 OFDM symbols, a mini-slot can consist of 2, 4, or 7 OFDM symbols. This allows for immediate data transmission, eliminating latency. As shown in Figure 1, a Mini-Slot can transmit 2, 4, or 7 OFDM symbols within a single Time Slot. Traditional scheduling starts at the Time Slot boundary, resulting in higher latency. However, starting at any time (depending on the time slot timing) allows for very low latency (immediate transmission). Practical use cases include eMBB, mMTC, and URLLC (low-latency, highly flexible applications). Figure 1 shows a Mini-Slot of 2 and 4 OFDM symbols, which can be scheduled at different times. Each Mini-Slot is located within the time slot structure labeled Time Slot #n and Time Slot #1. This also demonstrates how 5G supports asynchronous and independent downlink transmission scheduling.   5. Mini-Slot Features: Reduced Latency: Data can be sent immediately without waiting for a time slot boundary. Efficient Scheduling: Ideal for time-sensitive traffic such as URLLC (Ultra-Reliable Low Latency Communication). Flexibility: Dynamic and mixed parameter sets can be accommodated within the same cell. Enhanced Coexistence: Allows for simultaneous management of eMBB and URLLC traffic.

  1. In 5G, alert messages typically refer to system health notifications and network-hazardous operations. They can also refer to legitimate emergency alerts, such as those sent via the 5G network's WEA (Wireless Emergency Alert) system to notify public safety of natural disasters and other events.   2. Message transmission typically uses a "write-replace" approach to initiate or override the broadcast of alert messages. Alert message transmission utilizes non-terminal-associated signaling. The successful operation process is shown in Figure 8.9.1.2-1 below, where:   The AMF initiates this process by sending a "Write-Replace Alert Request" message to the NG-RAN node. Upon receiving a Write-Replace Warning Request message, the NG-RAN node shall prioritize allocating its resources to processing warning messages, where:   ​If, in an area, the broadcast of a warning message is ongoing and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message with a Message Identifier IE and/or Sequence Number IE that are different from those in the warning message being broadcast, and if the Concurrent Warning Message Indicator IE is not present, the NG-RAN node shall replace the warning message being broadcast with the newly received warning message for that area. If an NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message with a warning message identified by the Message Identifier IE and Sequence Number IE, and if no previous warning message has been broadcast in any of the warning areas indicated in the Warning Area List IE, the NG-RAN node shall broadcast the received warning message for those areas. If one or more warning messages are being broadcast in an area and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message containing a different Message Identifier IE and/or Sequence Number IE than in any of the currently broadcast warning messages, and a Concurrent Warning Message Indicator IE is present, the NG-RAN node shall arrange for the received warning message to be broadcast in that area. If the Concurrent Warning Message Indicator IE is present and a value of "0" is received in the "Requested Number of Broadcasts" IE, the NG-RAN node SHOULD broadcast the received warning message indefinitely until a request to stop broadcasting is received, unless the Repetition Period IE is set to "0". If one or more warning messages are already being broadcast in an area and the NG-RAN node receives a WRITE-REPLACE WARNING REQUEST message containing the Message Identifier IE and Sequence Number IE corresponding to a warning message already being broadcast in that area, the NG-RAN node SHOULD NOT initiate a new broadcast or replace an existing one, but SHOULD still reply by sending a WRITE-REPLACE WARNING RESPONSE message containing the Broadcast Completed Area List IE set based on the ongoing broadcast. If the WRITE-REPLACE WARNING REQUEST message does not include the Warning Area List IE, the NG-RAN node shall broadcast the indicated message in all cells within the NG-RAN node. If the WRITE-REPLACE WARNING REQUEST message includes the Warning Type IE, the NG-RAN node shall broadcast the primary notification regardless of the settings of the Repetition Period IE and the Requested Number of Broadcasts IE, and process the primary notification according to TS 36.331 and TS 38.331. If the WRITE-REPLACE WARNING REQUEST message includes both the Data Coding Scheme IE and the Warning Message Content IE, the NG-RAN node shall schedule the broadcast of the warning message based on the values ​​of the Repetition Period IE and the Requested Number of Broadcasts IE, and process the warning message according to TS 36.331 and TS 38.331. If the Warning Area Coordinates IE is included in the WRITE-REPLACE WARNING REQUEST message, the NG-RAN node shall include this information with the warning message broadcast according to TS 36.331 and TS 38.331. 3. NG-RAN Processing The NG-RAN node acknowledges the WRITE-REPLACE WARNING REQUEST message by sending a WRITE-REPLACE WARNING RESPONSE message to the AMF. If the WRITE-REPLACE WARNING RESPONSE message does not contain the Broadcast Completion Area List IE, the AMF shall assume that the broadcast was unsuccessful in all cells within the NG-RAN node.

  1. The purpose of the RAN Downlink Configuration Transfer procedure is to transfer RAN configuration information from the AMF to the NG-RAN node; the configuration transfer procedure is shown in Figure 8.8.2.2-1 below and uses non-UE-associated signaling.     2. The Downlink RAN ​​Configuration Transfer procedure is initiated by the AMF sending a "Downlink RAN ​​Configuration Transfer" message to the NG-RAN. Here, the following steps are used:   If the NG-RAN node receives a SON Information IE containing a SON Information Request IE in a SON Configuration Transfer IE or an EN-DC SON Configuration Transfer IE, it may transfer the requested information back to the NG-RAN node indicated in the Source RAN Node ID IE of the SON Configuration Transfer IE, or to the eNB indicated in the Source eNB-ID IE of the EN-DC SON Configuration Transfer IE, by initiating the Uplink RAN ​​Configuration Transfer procedure. If the NG-RAN node receives an Xn TNL Configuration Information IE containing an Xn Extended Transport Layer Address IE in the SON Configuration Transfer IE, it may use it as part of its ACL function configuration operation (if such ACL function is deployed). If the NG-RAN node receives a SON Information IE containing a SON Information Reply IE (including the Xn TNL Configuration Information IE as a reply to a previous request) in the SON Configuration Transport IE, it can use it to initiate Xn TNL establishment. If the IP-Sec Transport Layer Address IE is present and the GTP Transport Layer Address IE in the Xn Extended Transport Layer Address IE is not empty, GTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in the IP-Sec Transport Layer Address IE. If the IP-Sec Transport Layer Address IE is not present, GTP traffic will terminate at the endpoint specified by the address list in the Xn GTP Transport Layer Address IE in the Xn Extended Transport Layer Address IE. If the Xn GTP Transport Layer Address IE is empty and the IP-Sec Transport Layer Address IE is present, SCTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in the IP-Sec Transport Layer Address IE in the Xn Extended Transport Layer Address IE. If the Xn SCTP Transport Layer Address IE is present and the IP-Sec Transport Layer Address IE is also present, the associated SCTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in this IP-Sec Transport Layer Address IE, within the Xn Extended Transport Layer Address IE. If an NG-RAN node receives a SON Information IE containing a SON Information Report IE, it may use it as specified in TS 38.300. If an NG-RAN node receives an Inter-System SON Information IE containing an Inter-System SON Information Report IE, it may use it as specified in TS 38.300. If an NG-RAN node receives an Inter-System SON Information IE containing an Inter-System SON Information Request IE or an Inter-System SON Information Reply IE, it may use it as specified in TS 38.300. If the "Reporting System IE" in the Inter-System SON Information Request IE is set to "No Report", the "Downlink RAN ​​Configuration Transfer" message shall be ignored. If the NG-RAN node is configured to use one IPsec tunnel for all NG and Xn traffic (IPsec hub-and-spoke topology), traffic to the peer NG-RAN node SHOULD be routed through this IPsec tunnel and the IP-Sec Transport Layer Address IE SHOULD be ignored.

  1. RAN Configuration Transfer in 5G is a NGAP procedure used to transfer RAN configuration information, such as Self-Organizing Network (SON) information, between NG-RAN nodes (e.g., gNBs) and access and AMFs (mobility management functions). This non-UE-associated signaling allows the AMF to relay configuration information to other RAN nodes or manage configuration data by accepting and forwarding information without interpretation, thereby supporting functions such as transferring SON configuration data between different RAN nodes.   2. Configuration Transfer Purpose: There are two types of configuration transfers delivered via NGAP: RAN Configuration Data Transfer: This transfers RAN configuration information from an NG-RAN node to the AMF. SON Information Relay: The AMF can transparently transfer Self-Organizing Network (SON) configuration information to other target RAN nodes, thereby facilitating network automation.   3. Uplink RAN ​​Configuration Transfer Initiation: The purpose of this procedure is to transfer RAN configuration information from the NG-RAN node to the AMF. The AMF does not interpret the transferred RAN configuration information. The transfer procedure is shown in Figure 8.8.1.2-1 below. The transfer procedure uses non-UE-associated signaling. The relevant information is as follows:   The NG-RAN node initiates the Uplink RAN ​​Configuration Transfer procedure by sending an UPLINK RAN CONFIGURATION TRANSFER message to the AMF.   If the AMF receives a SON Configuration Transfer IE, it shall transparently transfer the SON Configuration Transfer IE to the NG-RAN node indicated in the Target RAN Node ID IE contained in the SON Configuration Transfer IE. If the NR CGI IE is contained in the Target RAN Node ID IE, the AMF shall (if supported) ignore the Global RAN Node ID IE in the Target RAN Node ID IE and use it to identify the target gNB, as described in TS 38.300. If the AMF receives an EN-DC SON Configuration Transfer IE, it shall transparently transfer the EN-DC SON Configuration Transfer IE to the MME serving the eNB indicated in the Target eNB-ID IE contained in the EN-DC SON Configuration Transfer IE. If the AMF receives an Inter-System SON Configuration Transfer IE, it shall transparently transfer the Inter-System SON Configuration Transfer IE to the MME serving the eNB indicated in the Target eNB-ID IE contained in the Inter-System SON Configuration Transfer IE.

  In mobile communication networks, "system overload" occurs when excessive service traffic or too many devices simultaneously attempt to connect overwhelm network resources, leading to congestion, slow speeds, or connection failures. System protection mechanisms are activated to address these overloads. Specific strategies include network operators releasing more licensed spectrum, allocating resources through network slicing, implementing throttling within core network functional units, and enabling mechanisms such as backoff timers and overload messages to effectively control and manage the volume of users.   1. Overload Activation: In a 5G (NR) network, the Access and Mobility Management Function (AMF) sends an "Overload Activation" message to other relevant network elements (such as gNBs) based on its processing capacity (configuration) thresholds, indicating an overload condition. This triggers congestion control measures (such as rejecting connection requests from some user equipment (UEs)) to protect the network from failure. Overload Activation involves the AMF sending an NGAP Overload Activation message to the NG-RAN (Radio Access Network) node, requesting it to limit certain types of traffic and redirect or reject requests to maintain network stability during periods of high demand.   1.1 Overload Control Involves   Congestion Detection: The AMF or other network elements, such as the User Plane Function (UPF), monitor network load and identify when predefined congestion thresholds are exceeded. Overload Control Message: Upon detecting an overload, the AMF sends an NGAP Overload Control message to the connected NG-RAN node. Congestion Control Actions: Upon receiving the message, the NG-RAN node initiates control actions to manage the overload. These actions include: Rejecting Certain Connections: The NG-RAN may reject connection requests from user equipment (UE) for non-emergency or high-priority services. Limiting Uplink Signaling: The NG-RAN can limit the transmission of uplink NAS (Non-Access Stratum) signaling to the AMF, further reducing the load on the network core. Traffic Limiting: The network may limit or reduce the amount of traffic it handles to prevent system failure.   1.2 Overload Control has three objectives: Maintaining Network Stability: The primary goal is to prevent complete network failure during periods of extreme traffic or unexpected load spikes. Ensuring Service Continuity: By managing load, the network can continue to provide essential services even if less critical services are temporarily limited. Protecting Resources: Overload control protects resources such as UDM bandwidth and other critical network functions from being overwhelmed by excessive control plane signaling.   2.the Overload Stop procedure signals the NG-RAN node to which the AMF is connected that the overload situation has ended and that normal operations should resume. The Overload Stop procedure uses non-UE-associated signaling. A successful Overload Stop operation is shown in Figure 8.7.8.2-1 below, where:   An NG-RAN node that receives the "OVERLOAD STOP" message should assume that the overload situation for the receiving AMF has ended and should resume normal operations for traffic applicable to the AMF.

  1. System Overload: In 5G networks, "overload" refers to excessive traffic or too many devices attempting to connect simultaneously, overwhelming network resources and leading to congestion, slow speeds, or connection failures. Strategies for addressing this overload include releasing more licensed spectrum, allocating resources through network slicing and core network functions, and implementing mechanisms such as throttling, exit timers, and overload messages to effectively control and manage traffic.   2. The overload initiation process notifies the NG-RAN node to reduce the signaling load directed to the associated AMF. This initiation process uses non-UE-associated signaling. As shown in Figure 8.7.7.2-1 below, the initiation process includes:     An NG-RAN node receiving an overload initiation message should assume that the receiving AMF is in an overloaded state. If the Overload Start message contains the Overload Action IE and the AMF Overload Response IE, the NG-RAN node shall use it to identify the relevant signaling traffic. This information is used when the Overload Action IE is set to: “Reject RRC connection establishment for non-emergency mobile originated data transfers” (i.e., reject traffic corresponding to the RRC causes “mo-data”, “mo-SMS”, “mo-VideoCall”, and “mo-VoiceCall” in TS 38.331 or “mo-data” and “mo-VoiceCall” in TS 36.331), or “Reject RRC connection establishment for signaling” (i.e., reject traffic corresponding to the RRC causes “mo-data”, “mo-SMS”, “mo-signalling”, “mo-VideoCall”, and “mo-VoiceCall” in TS 38.331 or “mo-data”, “mo-signalling”, and “mo-VoiceCall” in TS 36.331), or “Allow RRC connection establishment only for emergency sessions and mobile terminated services” (i.e., allow only traffic corresponding to TS 38.331 or the RRC causes "emergency" and "mt-Access" in TS 36.331), or "RRC connection establishment is only allowed for high-priority sessions and mobile terminated services" (i.e., only traffic corresponding to the RRC causes "highPriorityAccess," "mps-Priority Access," "mcs-PriorityAccess," and "mt-Access" in TS 38.331 or "highPriorityAccess," "mo-ExceptionData," and "mt-Access" in TS 36.331 is allowed). 3. Overload Handling: The NG-RAN handles the situation as follows: If the OVERLOAD START message contains the AMF Traffic Load Reduction Indication IE, the signaling traffic is reduced by the indicated percentage; otherwise, only signaling traffic not indicated as rejected is sent to the AMF. If the Overload Start NSSAI List IE is included in the OVERLOAD START message, the NG-RAN node shall: If the Slice Traffic Load Reduction Indication IE is present, reduce the UE's signaling traffic by the indicated percentage, provided that the IE is present and the requested NSSAI contains only the S-NSSAI contained in the Overload Start NSSAI List IE and the signaling traffic reduction indicated by the Overload Action IE in the Slice Overload Response IE; otherwise, ensure that only signaling traffic from the UE (if the requested NSSAI matches, only signaling traffic from the UE's requested NSSAI containing S-NSSAIs other than the S-NSSAI contained in the Overload Start NSSAI List IE) or signaling traffic not reduced as indicated by the Overload Action IE in the Slice Overload Response IE) is sent to the AMF. If overload control is in progress and the NG-RAN node receives another OVERLOAD START message, the NG-RAN node shall replace the previously received message content with the new content.

  1. AMF (The Access and Mobility Management Function ) is a critical control plane element in 5G, responsible for managing user equipment (UE) access, mobility, and security within the 5G system. It handles initial UE registration and authentication, and manages handovers between network cells and access networks. The AMF collaborates with other network functions (such as the SMF) to establish and maintain data sessions for users.   2. The AMF's responsibilities are divided into the following areas: UE Registration and Authentication: The AMF authenticates the UE, verifies its identity and subscription credentials, and grants it access to 5G services. Mobility Management: Responsible for handling the complex process of moving a UE from one cell to another or between different radio access networks (NG-RANs). Context Management: Maintains the UE context, which includes information about the UE's current location, session state, and security. Interaction with Other Network Elements SMF (Session Management Function): The AMF collaborates with the SMF to establish, modify, and manage user data sessions. UDM (Unified Data Management): It communicates with the UDM to retrieve and manage user subscription information.      AUSF (Authentication Server Function): The AMF selects the appropriate AUSF to authenticate the UE's identity during registration. NSSF (Network Slice Selection Function): The AMF uses the NSSF to discover and select the appropriate network slice and functions based on the UE's location and requirements. Network Function Management: The AMF uses a service-based interface and the Network Repository Function (NRF) to discover and select other network functions. 3. The AMF Status Indication procedure is designed to support AMF management functions. This procedure uses non-UE-associated signaling and successful operation is shown in Figure 8.7.6.2-1 below, where:   The AMF initiates this procedure by sending an "AMF Status Indication" message to the NG-RAN node. Upon receipt of the AMF Status Indication message, the NG-RAN node shall assume that the indicated GUAMI is unavailable and perform AMF reselection as defined in TS 23.501. If supported, the NG-RAN node shall take appropriate action as specified in TS 23.501 based on the existence of the timer method for the GUAMI removal IE. If the Backup AMF Name IE is included in the AMF Status Indication message, the NG-RAN node shall (if supported) perform AMF reselection according to the AMF indicated by the Backup AMF Name IE as specified in TS 23.501. If the Extended Backup AMF Name IE is included in the AMF Status Indication message, the NG-RAN node shall (if supported) perform AMF reselection according to the AMF indicated by the Extended Backup AMF Name IE as specified in TS 23.501.

  1. System Abnormalities: Deviations from the design may occur during the normal operation of the 5G network. These include performance issues such as network security threats, signal interference, insufficient coverage, and potential failures in network software and hardware. These abnormalities can manifest as service interruptions, system crashes, slow network speeds, or dropped calls. They are typically identified by analyzing network data anomaly detection systems and can be categorized into the core network and radio network.     2. 5GC Abnormalities: If the NG RESET message includes the UE-associated Logical NG Connection List IE, but neither the AMF UE NGAP ID IE nor the RAN UE NGAP ID IE is present in the UE-associated Logical NG Connection Item IE, the AMF shall ignore the UE-associated Logical NG Connection Item IE. The AMF may return an empty UE-associated Logical NG Connection Item IE in the UE-associated Logical NG Connection List IE in the NG RESET ACKNOWLEDGE message.     3. NG-RAN Anomalies: If the NG RESET message contains the UE-Associated Logical NG Connection List IE, but neither the AMF UE NGAP ID IE nor the RAN UE NGAP ID IE is present in the UE-Associated Logical NG Connection Item IE, the NG-RAN node shall ignore the UE-Associated Logical NG Connection Item IE. The NG-RAN node may return an empty UE-Associated Logical NG Connection Item IE in the UE-Associated Logical NG Connection List IE in the NG RESET ACKNOWLEDGE message.     4. NG RESET message crossover typically occurs in the following two scenarios:   If an NG reset procedure is in progress in an NG-RAN node and the NG-RAN node receives an NG RESET message from a peer entity on the same NG interface that is associated with one or more UE associations that were previously requested to be reset (as explicitly or implicitly indicated in the received NG RESET message), the NG-RAN node shall respond with an NG RESET ACKNOWLEDGE message as specified in clause 8.7.4.2.1.   If an NG reset procedure is in progress in the AMF and the AMF receives an NG RESET message from a peer entity on the same NG interface that is related to one or more UE associations that were previously requested to be reset (indicated explicitly or implicitly in the received NG RESET message), the AMF shall respond with an NG RESET ACKNOWLEDGE message as specified in clause 8.7.4.2.