The 1.5G wireless access network architecture
mainly includes a 5G access network and a 5G core network, where NG-RAN stands for 5G access network and 5GC stands for 5G core network.
What does the 5G core network mainly include? Let me talk about the key AMF / SMF / UPF
AMF : the full name of Access and Mobility Management Function, access and mobility management functions, terminal access rights and handover, etc. It is responsible for it.
Some or all AMF functions can be supported in a single instance of AMF:
-Terminate the RAN CP interface (N2).
-Terminate NAS (N1), NAS encryption and integrity protection.
-Registration management.
-Connection management.
-Accessibility management.
-Liquidity management.
-Legal interception (applicable to the interface of AMF events and LI systems).
-Provide transmission for SM messages between UE and SMF.
-Transparent proxy for routing SM messages.
-Access authentication. -Access authorization.
-Provide SMS message transmission between UE and SMSF.
-Security anchor function (SEAF).
-Positioning service management of supervision services.
-Provides transmission of location service messages between UE and LMF and between RAN and LMF.
-EPS bearer ID allocation for interworking with EPS.
-UE mobile event notification.
In addition to the above-mentioned functions of AMF, AMF can also include the following functions to support non-3GPP access networks :
-Support N2 interface and N3IWF. On this interface, some information defined by 3GPP access (eg, 3GPP cell identity) and procedures (eg, related to handover) may not be applied, and non-3GPP access specific information that is not applicable to 3GPP access may be applied.
-Support NAS signaling via UE on N3IWF. Some procedures supported by NAS signaling on 3GPP access may not be suitable for untrusted non-3GPP (eg paging) access.
-Supports authentication of UEs connected via N3IWF.
-Manage the mobility, authentication and individual security context status of UEs connected via non-3GPP access or connected via 3GPP and non-3GPP simultaneously.
-Supports coordinated RM management context, which is valid for 3GPP and non-3GPP access.
-Supports dedicated CM management context for UEs for connection through non-3GPP access.
SMF : Full name Session Management Function, session management function, providing service continuity, uninterrupted user experience of services, including changes in IP addresses and / or anchor points.
A single instance of SMF can support some or all of the SMF functions:
-Session management, such as session establishment, modification, and release, including tunnel maintenance between UPF and AN nodes.
-UE IP address allocation and management (including optional authorization).
-DHCPv4 (server and client) and DHCPv6 (server and client) functions.
-IPv6 Neighbor Solicitation Proxying for ARP proxy and / or Ethernet PDU. SMF responds to ARP and / or IPv6 neighbor request requests by providing a MAC address corresponding to the IP address sent in the request.
-Select and control UP functions, including controlling UPF proxy ARP or IPv6 neighbor discovery, or forwarding all ARP / IPv6 neighbor request traffic to SMF for Ethernet PDU sessions.
-Configure UPF flow control to route traffic to the correct destination.
-Terminate the interface to the policy control function.
-Legal interception (used for SM events and LI system interface).
-Charge data collection and support billing interface.
-Control and coordinate the collection of UPF's charging data.
-Terminate the SM part of the SM message.
-Downstream data notification.
-The initiator of AN specific SM information is sent to AN through AMF via N2.
-Determine the SSC mode of the session.
-Roaming function:
-Process local implementation to apply QoS SLA (VPLMN).
-Billing data collection and billing interface (VPLMN).
-Legal interception (the interface of VPLMN and LI systems in SM events).
-Support interaction with external DN to transmit signaling of PDU session authorization / authentication through external DN.
UPF : Full name User Plane Function, user plane management function, the area where PDU sessions associated with UPF can be served by (R) AN node through (R) N3 interface between AN and UPF, without adding a new UPF or Remove / Re-Assign UPF.
Some or all of the UPF functions can be supported in a single instance of UPF:
-An anchor point for intra-RAT / inter-RAT mobility (when applicable).
-A conversation point where the external PDU is interconnected with the data network.
-Packet routing and forwarding (for example, support for uplink classifiers to route traffic to instances of the data network, support for branch points to support multi-homed PDU sessions).
-Packet inspection (for example, application inspection based on service data flow templates and optional PFD received from SMF).
-The implementation of some user plane policy rules, such as gating, redirection, and traffic steering).
-Legal interception (UP collection).
-Flow usage report.
-User plane QoS processing, such as UL / DL rate implementation, reflected QoS marking in DL.
-Uplink traffic verification (SDF to QoS traffic mapping).
-Transmission level packet marking in the uplink and downlink.
-Downstream data packet buffering and downstream data notification trigger.
-Send and forward one or more "end tags" to the source NG-RAN node.
-IPv6 Neighbor Solicitation Proxying for ARP proxy and / or Ethernet PDU. UPF responds to ARP and / or IPv6 neighbor request requests by providing a MAC address corresponding to the IP address sent in the request.
