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  The purpose of the handover path request process is to establish the relevant signaling connection between the terminal (UE) and the 5GC and, if applicable, request the downlink termination point of the NG-U transport bearer to be switched to a new termination point. For the handover of UE-related services in the PC5 interface in Sildlink, 3GPP defines it in TS38.413 as follows;   I. PC5 QoS Processing The path request in handover of the PC5 interface in Sildlink is defined as follows;   If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message contains the PC5 QoS parameter IE, the NG-RAN node shall (if supported) use it as defined in TS 23.287. If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message contains the A2X PC5 QoS parameter IE, the NG-RAN node shall (if supported) use it as defined in TS 23.256. If the Path Switch Request Acknowledge message includes the Alternate QoS Parameter Set List IE, the NG-RAN node shall (if supported) use it as specified in TS 23.502. II. Path Request in CE-mode-B and User Plane CIoT Handover is defined as follows:   If the Path Switch Request Acknowledge message includes the CE-mode-B Restriction IE, the Enhanced Coverage Restriction IE is not set to "restricted", and the Enhanced Coverage Restriction information stored in the UE context is not set to "restricted", the NG-RAN node shall (if supported) store this information in the UE context and use it as defined in TS 23.501. If the Path Switch Request Acknowledge message includes the UE User Plane CIoT Support Indicator IE, the NG-RAN node shall (if supported) store this information in the UE context and assume that the UE supports User Plane CIoT 5GS Optimization as specified in TS 23.501. If the Path Switch Request Acknowledge message includes the UE Radio Capability ID IE, the NG-RAN node shall (if supported) use it as specified in TS 23.501 and TS 23.502. III. PDU Session Expected UE Activity and Path Request in MDT Handover are defined as follows: For each PDU Session, if the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "PDU Session Expected UE Activity Behavior" IE, the NG-RAN node shall (if supported) process this information as specified in TS 23.501. If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "Management-Based MDT PLMN List" IE, the NG-RAN node shall store it in the UE context and, if supported, use this list to allow subsequent selection of the UE for management-based MDT as defined in TS 32.422. If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "Management-based MDT PLMN Modification List" IE, the NG-RAN node (if supported) shall use this list to overwrite any previously stored management-based MDT PLMN list information in the UE context and use the received information to allow subsequent selection of the UE for management-based MDT as defined in TS 32.422. If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the Time Synchronisation Assistance Information IE, the NG-RAN node (if supported) shall store this information in the UE context and use it as defined in TS 23.501. IV. Path Request in 5G ProSe Handover is defined as follows: If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the 5G ProSe Authorized IE, the NG-RAN node (if supported) shall update its ProSe authorization information for the UE accordingly. If the 5G ProSe Authorization Information (5G ProSe Authorized IE) contains one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take steps to ensure that the UE no longer has access to the associated 5G ProSe services. If the 5G ProSe PC5 QoS Parameters IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node (if supported) should use it as defined in TS 23.304. If the Aerial UE Subscription Information IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node (if supported) should store this information or overwrite any previously stored information in the UE context and use it as defined in TS 38.300. If the 5G ProSe UE PC5 Aggregate Maximum Bit Rate IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node shall (if supported) perform the following actions: Replace the previously provided 5G ProSe UE PC5 Aggregate Maximum Bit Rate (if available in the UE context) with the received value; Use the received value for sidelink communications for the associated UE in the network scheduling mode for the 5G ProSe service.

  1. Network slicing divides a network into independent use cases, each tailored to provide specialized services. In the traditional 4G (LTE) era, APN (Access Point Names) were the first form of network slicing in mobile networks, allowing operators to partition their networks based on service requirements.   2. 5G network slices, defined by 3GPP, feature independent network instances with independent control and user plane processing. These slices require support from the 5G Core Network (5GC), which is only used in 5G with Standalone Architecture (SA).   3. Network Elements and Identifiers: Slicing deployments in 5G include network functions such as the user equipment (UE), next-generation radio access network (NG-RAN), control plane functions (e.g., AMF, PCF, SMF), and user plane functions (e.g., UPF). Each network slice is identified by an S-NSSAI (Slice Service Type), which includes a Slice Service Type (SST) to indicate the service to which the network slice applies. Network operators can use standardized SST values ​​such as: 1 for enhanced mobile broadband, 2 for ultra-reliable low-latency communications, 3 for massive IoT, 4 for vehicle-to-everything (V2X), 5 for high-performance machine-type communications. They can also use locally defined, non-standardized SST values.   4. Terminal Network Slicing Support: For SA (standalone) 5G terminals (UEs) configured with the USRP (UE Routing Policy), they can select S-NSSAI for network slicing (services) based on the desired application (depending on the application's quality of service requirements). For example, Samsung's first Galaxy S24 Ultra equipped with the URSP enables slice selection and service execution within the 5G system.   5. System Network Slicing Support: ADC (Detection and Control) is enabled (a function within the 5G core network elements PCF (Policy Control Function) and SMF (Session Management Function)). ADC is used to identify applications or traffic on the network side, apply policies such as quality of service, billing, or redirection, and implement real-time traffic classification and prioritization.   6. Network Slicing Commercial Deployment Examples: Singapore Telecommunications (Singtel) has launched Singtel 5G+, an advanced "network slicing" innovation that delivers a new standard of connectivity and a prioritized experience through three key features: Singtel 5G+: The only network using the 700MHz spectrum band, delivering optimal nationwide coverage, even indoors. Singtel 5G+ Ehanced: Wider coverage and faster speeds, with consistently up to 2x speeds. Singtel 5G+ Priority: Prioritized network channels with 4x faster speeds, always prioritizing services and detecting emerging

3GPP defines the following in TS 38.413 regarding enhanced coverage restriction, extended connection time, V2X service authorization, and handover path request processing for sidelink aggregation terminals in the 5G system:   I. Enhanced Coverage Restriction and Extended Connection Time   If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message includes the Enhanced Coverage Restriction IE, the NG-RAN node SHOULD (if supported) store this information in the UE context and use it as defined in TS 23.501.   If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message includes the Extended Connected Time IE, the NG-RAN node SHOULD (if supported) use it as defined in TS 23.501.   If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message includes a UE Differentiation Information IE, the NG-RAN node (if supported) should store this information in the UE context for further use in accordance with TS 23.501.   II. NR V2X Service Authorization   If the PATH SWITCH REQUEST ACKNOWLEDGE message includes an NR V2X Service Authorization IE, the NG-RAN node (if supported) should update its NR V2X service authorization information for the UE accordingly.   If the NR V2X Service Authorization IE includes one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take steps to ensure that the UE no longer has access to the associated services.   If the PATH SWITCH REQUEST ACKNOWLEDGE message includes an LTE V2X Service Authorization IE, the NG-RAN node (if supported) should update its LTE V2X service authorization information for the UE accordingly.If the LTE V2X Service Authorization IE contains one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take measures to ensure that the UE no longer has access to the associated services.   If the NR A2X Service Authorization IE contains one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take measures to ensure that the UE no longer has access to the associated services.   If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message contains an LTE A2X Service Authorization IE, the NG-RAN node (if supported) should update its LTE A2X Service Authorization information for the UE accordingly.   If the LTE A2X Service Authorization IE contains one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take measures to ensure that the UE no longer has access to the associated services.   III. Sidelink and Aggregation Processing   If the PATH SWITCH REQUEST ACKNOWLEDGE message contains the NR UE Sidelink Aggregate Maximum Bit Rate IE, the NG-RAN node (if supported) shall perform the following operations: Replace the previously provided UE Sidelink Aggregate Maximum Bit Rate (if available in the UE context) with the received value; Use the received value for sidelink communications with the associated UE in NR V2X serving network scheduling mode.   If the PATH SWITCH REQUEST ACKNOWLEDGE message contains the LTE UE Sidelink Aggregate Maximum Bit Rate IE, the NG-RAN node (if supported) shall perform the following operations: Replace the previously provided UE Sidelink Aggregate Maximum Bit Rate (if available in the UE context) with the received value; Use the received value for sidelink communications with the associated UE in LTE V2X serving network scheduling mode. If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the NR A2X UE PC5 aggregate maximum bit rate IE, the NG-RAN node (if supported) shall perform the following operations: Replace the previously provided NR A2X UE PC5 aggregate maximum bit rate (if available in the UE context) with the received value; In network-scheduled mode, use the received value for NR A2X service sidelink communications for the associated UE. If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the LTE A2X UE PC5 aggregate maximum bit rate IE, the NG-RAN node (if supported) shall perform the following operations: Replace the previously provided LTE A2X UE PC5 aggregate maximum bit rate (if available in the UE context) with the received value; In network-scheduled mode, use the received value for LTE A2X service sidelink communications for the associated UE.

  In a 5G system, a handover path request is a request by a terminal (UE) to establish a UE-related signaling connection with the 5GC and, if applicable, request that the NG-U transport bearer downlink termination point be switched to a new termination point. As 5G supports an increasing number of service types, the content of path requests during handovers will become increasingly complex. 3GPP defines this in TS 38.413 as follows.   I. Packet Delay Budget   If the CN Packet Delay Budget Downlink IE is included in the Path Switch Request Acknowledge Transport IE of the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message, the NG-RAN node SHOULD (if supported) replace the previously provided CN Packet Delay Budget Downlink (if any) and use it as specified in TS 23.502.   If the CN Packet Delay Budget Uplink IE is included in the Path Switch Request Ack Transport IE of the Path Switch Request Ack No WLEDGE message, the NG-RAN node shall (if supported) replace the previously provided CN Packet Delay Budget Uplink (if any) and use it as specified in TS 23.502.   II. Burst Data Handling   If the Burst Arrival Time Downlink IE is included in the Path Switch Request Ack Transport IE of the Path Switch Request Ack message, the NG-RAN node shall (if supported) replace the previously provided value (if any) and use it as specified in TS 23.502.   III. RRC Inactive and Core Network Assistance Information Handling   If the Core Network Assistance Information of the RRC INACTIVE IE is included in the Path Switch Request Confirmation message, the NG-RAN node (if supported) shall store this information in the UE context and use it for RRC_INACTIVE state decisions and the UE's RNA configuration and RAN paging (if any), as described in TS 38.300.   If the Core Network Assistance Information of the RRC INACTIVE IE includes the MICO All PLMN IE, the NG-RAN node (if supported) shall treat the UE's registration area as the complete PLMN and ignore the TAI list of the RRC Inactive IE.   If the Core Network Assistance Information of the RRC INACTIVE IE includes the Paging Cause Indication of the Voice Service IE, the NG-RAN node (if supported) shall store and use it as specified in TS 38.300.   If the Core Network Assistance Information of the RRC INACTIVE IE includes the PEIPS Assistance Information IE, the NG-RAN node (if supported) shall store it and use it for paging subgroups of UEs in the RRC_INACTIVE state, as described in TS 38.300.   If the CN MT Communication Handling IE is included in the Core Network Assistance Information (RRC INACTIVE IE), the NG-RAN node shall (if supported) store this IE and may subsequently request the CN to perform MT communication handling, as described in TS 23.502, depending on the implementation.   If the CN Assisted RAN Parameter Adjustment IE is included in the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message, the NG-RAN node may use this IE as described in TS 23.501.   If the RRC INACTIVE Transition Report Request IE is included in the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message, the NG-RAN node shall (if supported) store this information in the UE context.   V. EPS and SRVCC Processing   If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the Redirection for Voice EPS Fallback IE, the NG-RAN node shall (if supported) store this IE and use it in subsequent voice EPS fallback decisions as specified in TS 23.502.   If the PATH SWITCH REQUEST ACKNOWLEDGE message contains the SRVCC Operation Possible IE information, the NG-RAN node shall (if supported) store the received SRVCC Operation Possible IE content in the UE context and use it as defined in TS 23.216.

In 5G, a path request is a signaling message sent by the target base station to the core network during handover to redirect the path of the terminal (data) session. TS 38.413 defines the following:   I. PDU Session Setup Failures   If any PDU session setup fails, the list of failed sessions shall be included within the “Path Switch Request Setup Failure Transport IE” in the PATH SWITCH REQUEST message. The AMF shall process this information as specified in TS 23.502.   2. User Security and Path Information   For each PDU session, if its "additional redundant DL QoS flow information IE for each TNL" is included in the PATH SWITCH REQUEST Transfer IE of the Path Switch Request message, Then the SMF can use each included UP transport layer information as the downlink termination point for the associated QoS flows contained in this PDU session, and these QoS flows are split into different tunnels for redundant transmission. For each PDU session, if the Path Switch Request Transfer IE of its "Path Switch Request" message contains "Redundant DL NG-U TNL information Reuse IE", then the SMF should (if supported) treat the included DL transport layer address as the DL transport layer address for redundant transfer. As described in TS 23.501. For each PDU session, if the Path Switch Request Transfer IE of its "Path Switch Request" message contains the "Global RAN Node ID of the auxiliary NG-RAN node" IE, the SMF should (if supported) handle this information as stipulated in TS 23.501. For each PDU session contained in the PATH SWITCH REQUEST message, if the "Path Switch Request Transmission IE" contains the "Current QoS Parameter Set Index IE", the SMF should treat it as the currently implemented QoS parameter set among the alternative QoS parameters of the involved QoS flow. The NG-RAN node should (if supported) report the processing indicator IE based on the PDU set in the "PATH SWITCH REQUEST Transmission IE" in the Path Switch Request message. If the "PATH SWITCH REQUEST Transfer IE" in the Path Switch Request message contains a processing indicator IE based on the PDU set, the SMF should (if supported) handle this information as stipulated in TS 23.501. If the "PATH SWITCH REQUEST Transport IE" in the Path Switch Request message contains the MBS support indicator IE, then the SMF should (if supported) handle this information as stipulated in TS 23.247. If supported, the NG-RAN node should report the PATH SWITCH REQUEST transmission of the ECN tag in IE or congestion information report status IE in the Path Switch Request message. If the ECN tag or congestion information reporting status IE is included in the PATH SWITCH REQUEST Transport IE of the Path switch Request message, the SMF should (if supported) use it to infer whether the ECN tag at NG-RAN, the ECN tag at UPF, or congestion information reporting is active. As described in TS 23.501.   3. Upstream Data Processing   If the PATH SWITCH REQUEST ACKNOWLEDGE Transfer IE of the Path Switch Request Acknowledge message contains UL NG-U UP TNL Information IE Then the NG-RAN node should store this information and use it as the uplink termination point for the user plane data of this PDU session. If the PATH SWITCH REQUEST ACKNOWLEDGE Transfer IE of the Path Switch Request Acknowledge message contains additional NG-U UP TNL Information IE, Then the NG-RAN node should store this Information and use the UL NG-U UP TNL Information IE contained therein as the uplink termination point for the user plane data of this PDU session (split into different tunnels). If the PATH SWITCH REQUEST ACKNOWLEDGE transmission IE of the path switch request acknowledge message contains redundant UL NG-U UP TNL information IE, the NG-RAN node should (if supported) store this information. And use it as the uplink termination point of the user plane data for the redundant transmission of this PDU session, as described in TS 23.501. If the PATH SWITCH REQUEST ACKNOWLEDGE transmission IE of the path switch Request acknowledge message contains additional redundant NG-U UP TNL information IE, the NG-RAN node should (if supported) store this information. And use the included UL NG-U UP TNL information IE as the uplink termination point for the user plane data split in different tunnels of this PDU session

Similar to the previous generation 4G (LTE) systems, the Path Switch Request is a signaling message sent by the target base station to the core network during handover to redirect the (user) data path of the terminal's (packet data) session. This message initiates a process where the session management unit instructs the user plane to change the downlink data endpoint from the old site (source) to the new site, ensuring uninterrupted data flow to the user's new location.   I. Path Switch Request In 5G, the path request process establishes a terminal (UE)-related signaling connection with the 5GC and, where applicable, requests switching the downlink terminal point of the NG-U transport bearer to a new terminal point. This process utilizes UE-related signaling.   II. Path Request Process As illustrated in Figure 8.4.4.2-1 below, the “PATH SWITCH REQUEST” is initiated by the target NG-RAN node to the AMF. Its specific definition is as follows: The NG-RAN node initiates the process by sending a Path Switch Request (PATH SWITCH REQUEST) message to the AMF. Upon receiving the PATH SWITCH REQUEST message, the AMF shall transparently transfer the Path Switch Request Transfer IE to the SMF associated with each PDU session indicated in the PDU Session ID IE. Upon receiving the PATH SWITCH REQUEST message, the AMF shall deactivate the activated MT communication processing as described in TS 23.502.   III. Path Request Message Processing If the PATH SWITCH REQUEST message contains an RRC Resume Cause IE, the AMF shall (if supported) use it in accordance with the user plane CIoT 5GS optimization provisions for NG-RAN nodes acting as ng-eNBs specified in TS 23.502. If the PATH SWITCH REQUEST message contains a RedCap Indicator IE or eRedCap Indicator IE, the AMF shall (if supported) treat the UE as a RedCap UE or eRedCap UE previously served by an E-UTRA cell, respectively, and use this IE according to TS 23.501. After all necessary updates (including uplink path switching) are successfully completed in the 5GC, the AMF shall send a Path Switch Request Acknowledge message to the NG-RAN node for at least one PDU session resource included in the Path Switch Request. The process then terminates.   IV. PDU Session Handling For an IAB-MT or mobile IAB-MT where the PDU session ID IE in the PATH SWITCH REQUEST message indicates an unassigned PDU session identifier (as defined in TS 24.007), the AMF shall (if supported) consider the IAB-MT or mobile IAB-MT to lack a PDU session and proceed as specified in TS 23.501. Subsequently, the NG-RAN node shall (if supported) ignore the PDU Session Resource Switched List IE in the Path Switch Request Acknowledge message. For each PDU session where the Path Switch Request Transfer IE within the Path Switch Request message contains an Additional DL QoS Flow per TNL Information IE, The SMF can use each included uplink transport layer information as the downlink termination point for the associated QoS flows split across different tunnels for this PDU session.

As a key device for realizing small-scale network transmission, routers have become an indispensable electronic product around the world. Simply put, it is a connection medium, responsible for "connecting various small local area networks together. With the increasing maturity and popularity of 4G/5G technology, many terminal devices have appeared on the market, especially 4G/5GCPE, because of its excellent performance and flexibility. What is CPE CPE is actually a network terminal device that receives mobile signals and forwards them as wireless Wi-Fi signals. It can support a large number of mobile terminals surfing the Internet at the same time. 4G CPE It is indeed inconvenient to open broadband at home when you live for a short period of time or the broadband cost is not cost-effective. But now with wireless router °4G CPE, everything has become simpler. There is no need to extend the broadband, just plug in the SIM card and turn on the power, and you can easily achieve a high-speed Internet experience from 4G to Wi-Fi. This plug-and-play feature greatly simplifies the network deployment process, allowing renters, small home users, and mobile office users to easily enjoy convenient network services. If you have requirements for the performance of wireless routers and want to be more cost-effective, you can also try our LTE Cat12 equipment such as R80a. The theoretical peak rate is 600Mbps (DL)/150Mbps (UL), which can meet customer requirements for high rate levels. . Qualcomm SDX12 has better power consumption and speed characteristics, bringing users a faster and better mobile communication experience. It also supports both 2.4GHz and 5GHz frequency bands, and can support up to 32 users to connect at the same time, which is very suitable for network environments shared by many people. 5G CPE With the full popularity of 5G, the requirements for home and enterprise networks are getting higher and higher. Our 5G high-performance products are favored and sought after by more and more customers because of their excellent performance. For home users, it can provide high-speed and stable network connections to ensure extremely fast and smooth playback of high-definition videos. In addition, it also tailors high-performance network solutions for small and medium-sized enterprises, equipped with multiple full Gigabit network ports to meet the needs of multi-device access and wired connections, ensuring the stability of the enterprise's internal network, and is suitable for high-definition video conferencing, data transmission and cloud office and other applications. For temporary network needs, such as exhibitions, short-term rentals, outdoor activities, and emergency communications, its plug-and-play characteristics and high-performance performance make it an ideal choice, allowing customers to quickly build an efficient and stable network environment anytime, anywhere.

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.