5G/NR - Network Architecture - 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 >





UDM Functionality


Based on 23.501-6.2.7, the functionality of UDM is descrbed as follows.

  • Generation of 3GPP AKA Authentication Credentials.
  • User Identification Handling (e.g. storage and management of SUPI for each subscriber in the 5G system).
  • Support of de-concealment of privacy-protected subscription identifier (SUCI).
  • Access authorization based on subscription data (e.g. roaming restrictions).
  • UE's Serving NF Registration Management (e.g. storing serving AMF for UE, storing serving SMF for UE's PDU Session).
  • Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions.
  • MT-SMS delivery support.
  • Lawful Intercept Functionality (especially in outbound roaming case where UDM is the only point of contact for LI).
  • Subscription management.
  • SMS management.
  • 5G-VN group management handling.
  • Support of external parameter provisioning (Expected UE Behaviour parameters or Network Configuration parameters).


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




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