5G: What is the difference between paging and notification procedure ?

Answer 1

In 5G system, an UE can have 3GPP and non-3GPP connections simultaneously. When an UE moves to MM-IDLE state for a connection (3GPP/non-3GPP) while it stays in MM-CONNECTED for another connection(3GPP/non-3GPP), network uses the notification procedure to notify UE through the connected network(3GPP/non-3GPP) to re-activate the PDUs session belonging to other idle connection(3GPP/non-3GPP).
The important point here is re-activation of PDUs happen through 3GPP access. For example, if an UE is in MM-IDLE state for non-3GPP connection, network notifies UE to reactivate the PDU sessions belonging to non-3GPP through 3GPP access.

Paging procedure comes into picture when UE is IDLE state for both type of connection and there is no other way to reach the UE.

Comments

"The important point here is re-activation of PDUs happen through 3GPP access. " is only partially true, right?
To quote from 24.501,
5.6.3
 Notification procedure
5.6.3.1
 General
The notification procedure is used by the network:
a)to request the UE, by sending the NOTIFICATION message over 3GPP access, to re-establish the user-plane
resources of PDU session(s) associated with non-3GPP access over 3GPP access or to deliver 5GSM downlink
signalling messages associated with non-3GPP access over 3GPP access when the UE is in 5GMM-IDLE mode
over non-3GPP access and in 5GMM-CONNECTED mode over 3GPP access; or
b)to request the UE, by sending the NOTIFICATION message over non-3GPP access, to re-establish user-plane
resources of the PDU session(s) or to deliver downlink signalling associated with 3GPP access over 3GPP access
when the UE is in 5GMM-CONNECTED mode over non-3GPP access and in 5GMM-IDLE mode over 3GPP
access when the UE is not in MICO mode.