5G/NR - Network Architecture - UDM
NR CORE - UDM
UDM stands for Unified Data Management. As the name implies it is a function/service that manges Data. What kind of data it manages ? It is user data (i.e, data of subscribers). In 4G, HSS played this role.. but in 5G, the HSS role split into two different services : UDM and AUSF. AUSF is mainly for Authentication Process and UDM is managing the user data for all other process. As shown in the illustration below, UDM is interfaced with many other services : AUSF, AMF, SMF, SMSF. It means when AUSF, AMF, SMF, SMSF needs subscriber data, it request it to UDM and UDM provide the data to the services that requested.
Followings are the name of each network component.
AMF Access and Mobility Management Function ==> Equivalent to MME in 4G
AUSF Authentication Server Function
DN Data Network
NEF Network Exposure Function
NRF Network Repository Function
NSSF Network Slice Selection Function
PCF Policy Control Function ==> Equivalent to PCRF in 5G
(R)AN (Radio) Access Network
SMF Session Management Function
UDM Unified Data Management ==> Equivalent to HSS in 4G
UPF User Plane Function ==> Equivalent to PGW in 4G
SMSF SMS Function
SEAF SEcurity Anchor Function ==> part of AMF function
ARPF Authentication credential Repository and Processing Function
SIDF Subscription Identifier De-concealing Function
Inter play between UDM and Other Components
Even though the illustrations shown above indicates the interplay beween UDM and other components, I think following diagram shows better with focus on UDM.
< 29.503-Figure 4.1-1: Reference model – UDM >
Based on 23.501-6.2.7, the functionality of UDM is descrbed as follows.
NOTE 1: The interaction between UDM and HSS, when they are deployed as separate network functions, is defined in TS 23.632 and TS 29.563 or it is implementation specific.
NOTE 2: The UDM is located in the HPLMN of the subscribers it serves, and access the information of the UDR located in the same PLMN