In the 3GPP terminology the database that stores subscription-related data has been called a User Data Repository, UDR, for quite some time now. The very same acronym – UDR – also appears in the 5G environment: as a database for the 5G-specific information about the subscriptions. The “UDR” acronym, though, in the 5G environment stands for “Unified Data Repository”, not “User Data Repository” as was the case previously. What would having a quick look at the (possibly new) characteristics of the 5G UDR reveal?

Data in the 5G UDR

The 5G Unified Data Repository stores data grouped into distinct collections of subscription-related information:

  • Subscription Data;
  • Policy Data;
  • Structured Data for Exposure;
  • Application Data.


These four different collections of parameters are made available to various 5G Network Functions: the Subscription Data is made available via the Unified Data Management (UDM) front-end to a number of NFs that control the UE’s activities within the network: AMF, SMF, AUSF, … The Policy Data is made available (directly, via the N36 interface) to the PCF – meaning that the UDR effectively replaces the earlier functionality of the Subscriber Profile Repository (SPR). Application Data is placed into the UDR by the external AFs, via the Network Exposure Function (NEF), in order to be made available to whichever 5G NFs need – and are authorized to request – subscriber-related information.

Deployment of the 5G UDRs

Defining distinct groups of parameters also enables for distributed UDR deployments, with the different functionalities defined along the lines of the parameter collections. The 23.501 3GPP standard comments as follows: “There can be multiple UDRs deployed in the network, each of which can accommodate different data sets or subsets, (e.g. subscription data, subscription policy data, data for exposure, application data) and/or serve different sets of NFs. Deployments where a UDR serves a single NF and stores its data, and, thus, can be integrated with this NF, can be possible.”

The standards also, for security reasons, explicitly suggest a solution where a UDR can store data for a particular set of UEs. As a UDR is, through a NEF, exposed to external influence separate UDRs for different customers allow for isolation of the database resources between environments of different companies.

Also, regarding the deployments of the UDRs, the 3GPP standards point out the following options:

  • “UDR accessed by the NEF belongs to the same PLMN where the NEF is located;
  • UDR accessed by the UDM belongs to the same PLMN where the UDM is located if UDM supports a Split Architecture;
  • UDR accessed by the PCF belongs to the same PLMN where the PCF is located.”

5G UDR usage in roaming scenarios

Another interesting feature in the 5G UDR is the fact that in the roaming scenarios the visited UDR can store the roamers’ parameters locally. Both the Policy Data and Data for Exposure of roaming UEs can be stored in the UDR in the visited network and made locally available to the relevant NFs – making it therefore similar in functionality to the 2G/3G VLR.

If you are interested in the various 5G Core Network functions, have a look at our 5G Core Network Architecture course.

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