UE_STATE_MANAGEMENT_IN_5G.md

UE state management

• 5G system needs to be able to keep track of each UEs
  • availability
  • reachability
• keeps track of 3 states of UE
  1. RRC radio resource control (between UE and gNB)
  2. CM connection management (between UE and AMF) also called non access stratum connection(NAS)
  3. RM registration management (between UE and AMF)

1. RRC (radio resouce control) state

• status of RRC connection between UE and gNB
• RRC-idle : No RRC connection
  • UE monitors broadcast info(that it is recieving from the gNB)
  • cell selection/reselection
• RRC connection required for
  • registration
  • voice call etc
• RRC connected
  • UE location known to cell level

• RRC-inactive : intermediate state introduced in 5G(saves battery power)
  • RRC connection context (parameters) stored in UE and gNB
  • RRC connection can be ativated with minimum signalling
  • decrease in signalling
  • suitable for massive IOT

UE mobility in RRC_inactive state: RAN areas

• RAN area are very like TAs nut relevant to the RAN
• size of RAN area
  • min --> one cell of a TA
  • mac --> all the cells of a TA
• RAN areas do not overlap
• each RAN area is identified using RAN area ID

UE mobility in RRC_inactive state: RAN-based notification areas(RNAs)

• one or more RAN areas of same TA can be grouped as RNA(RAN-based notification areas)
• the 5G RAN can assign a RNA to a UE
• in RRC_INACTIVE state,
  • the RAN knows the RNA in which mobile is in
  • RAN notifies the network if it moves to another RNA
  • to contact UE , RAN pages all the cells in a RNA
• reduced signaling : RNA updates instead of cell updates
• in case of RRC_INACTIVE case the UE only notifies RAN about cell change if that cell belongs to a diff RNA this reduces load and save battery life of UE

2. CM (connection management) state

• whether an active NAS connection exists between UE and AMF or not
• also called N1 signalling link
• CM-idle : no N1 connection between UE and AMF (AMF knows ue registration area)
• CM-connected used for (AMf knows UEs current gNB)
  • registration
  • data transfer
  • registration update

registraion area = UE TA list

3. RM (registration management) state

• RM state is used to indicate the status of registration of the Ue with 5G network
• RM-deregisterd
  • swithed off or deregistered
• RM-registered
  • registered with %GC
  • served by an AMF
  • assigned a 5G-GUTI
  • registration update
    • UE enter another RA

combined state diagram