AMF

manages UE registration
initiates authenttication
mobility management
{mobility management , registration} , responsible for supporting the device to move between different radio cells , also responsible for establishing signaling encrypted connection to the device so the device can register itself and can get authenticated and ready to acess the internet

AUSF (authentication server function)

AMF invokes the authentication
- passes UE identity to AUSF
AUSF retrieves authentication vector from UDM and passes it to AMF(authentication vector generated by UDM based on the secret key which is there with the UDM , this authentication vector passed to AMF)
AMF challenges UE with a random number(random number in authentication vector)
(UE generates a authentication response after recieving authentication number) AUSF checks if authentication response is valid
{security} supports AMF with authentication related function during different procedures

establishes and manages PDU session
interacts with PCF for policy decisions about Qos(PCF decides under given network condtions wheather PDU session can be established or what Qos this PDU session needs)
UPF selection (can be more than one so have to select one while moving)
IP address allocation
before the device transmits the data the network needs to establish a new session , give the device an IP address and release the sesssion when device has finished its activity . AMF forwardsall session related messages to SMF

point of contact with data network
- data routing
anchor point for NG-RAN mobility
Qos enforcement on PDU flow(PCF decides Qos => decision taken by SMF => enforcement done by UPF)
data traffic forwarding {mobility anchor , policy enforcement . lawful interception} , provides interface to intent to make sure the devices does not exceed the amount of data that the user have in their subsciption

access authorization
- holds security keys
tracking AMF of UE
subscriber information
- data network Qos profile
- access restrictions
- mobility permissions
- roaming restrictions
user subscription data is stored in user data repository (UDR) , UDM is the frontend for the user subscription data , the AMF dosnt contain user sub data , UMF supports AMF for registration of devices

dynamic policy descisions
- based upon network conditions
  - congestion
  - subscriber geo-location
eg UE in bad channel conditions wants to make a video call
- throttle its data
- refuse the call
mgmt of service areas
- list of allowed and not allowed TA's(target areas)
can interact with AMF and SMF
decides how a flow is charged
session mgmt policies , non-session policies , charging devices depending on usage of device

AF is an external server
- communicates with core network to request a new packet flow
eg AF can be an IMS(IP MULTIMEDIA SUBSYSTEM , used to generate voice calls over IP) node
- requesting voice call