Question

What is AMF/UPF functionality in 5G?

Answer 1

AMF stands for Access and Mobility Management Function. Following are the functions of 5G NR AMF node. 
• Termination of RAN CP interface (N2) 
• Termination of NAS (N1), NAS ciphering and integrity protection.
• Registration management.
• Connection management.
• Reachability management.
• Mobility Management.
• Lawful intercept (for AMF events and interface to LI System).
• Provide transport for SM messages between UE and SMF.
• Transparent proxy for routing SM messages.
• Access Authentication and Access Authorization
• Provide transport for SMS messages between UE and SMSF.
• Security Anchor Functionality (SEAF). It interacts with the AUSF and the UE, receives the intermediate key that was established as a result of the UE authentication process. In the case of USIM based authentication, the AMF retrieves the security material from the AUSF.
• Security Context Management (SCM). The SCM receives a key from the SEAF that it uses to derive access-network specific keys.
• Location Services management for regulatory services.
• Provide transport for Location Services messages between UE and LMF as well as between RAN and LMF.
• EPS Bearer ID allocation for interworking with EPS.
• UE mobility event notification.

In addition to the above mentioned functions, AMF also support functionalities for non 3GPP access networks.

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UPF stands for User plane function. Following are the functions of 5G NR UPF node. 
• Anchor point for Intra-/Inter-RAT mobility (when applicable).
• External PDU Session point of interconnect to Data Network.
• Packet routing & forwarding
• Packet inspection 
• User Plane part of policy rule enforcement, e.g. Gating, Redirection, Traffic steering. 
• Lawful intercept (UP collection).
• Traffic usage reporting.
• QoS handling for user plane, e.g. UL/DL rate enforcement, Reflective QoS marking in DL.
• Uplink Traffic verification (SDF to QoS Flow mapping).
• Transport level packet marking in the uplink and downlink.
• Downlink packet buffering and downlink data notification triggering.
• Sending and forwarding of one or more "end marker" to the source NG-RAN node.

Answer 2

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With the functionality of the 4G Mobility Management Entity (MME) now decomposed, the 5G Core Access and Mobility Management Function (AMF) receives all connection and session related information from the User Equipment (UE) (N1/N2) but is responsible only for handling connection and mobility management tasks.