Unified Data Management (UDM): Replacing HSS (Home Subscriber Server) in 5G

Hello Folks, welcome back to Learnizo Global. This article will focus on Unified data management (UDM) which is a core 5G network function.

UDM manages network user data in a single, centralized element.

UDM is similar to the 4G network’s Home Subscriber Server (HSS) but is cloud-native and designed for 5G specifically.

It can be paired with the User Data Repository (UDR) which stores the user data such as customer profile information, customer authentication information, and encryption keys for the information. UDM resides on the control plane and utilizes microservices to communicate between the user plane and the control plane.

The storage space of all the UDM’s information could reside in a hyperconverged infrastructure (HCI). 5G and HCI work together because 5G needs the virtualization HCI applies to the compute, networking, and storage resources so the network can be entirely virtualized.

Stateful and Stateless Versions of UDM

A stateful UDM keeps data on hand locally, while a stateless version stores data externally in the UDR. A stateful architecture shares data among microservices that orchestrate communication between the network planes. Some organizations prefer to have stateful microservices because of the record they keep. The downside is that if a problem arises, then all microservices sharing information must be taken off the network at once.

A stateless architecture keeps subscriber data separate from the functions it supports. This way, database access is kept separate from the operation of the network, improving stability and flexibility. The downside is that multiple nodes can’t update the same points of information at once, which can cause lag in the network.

UDM Function

The UDM manages data for access authorization, user registration, and data network profiles. Subscriber data is provided to the Session Management Function (SMF), which allocates IP addresses and manages user sessions on the network.

Depending on the construction of the 5G architecture, both UDM software and the UDR can send and store data. In a stateless network, user information is stored in the UDR, but the UDM function retrieves the data, sends it to other network functions, and generally manages it. The UDM can do this with many UDRs.

The Access and Mobility Function (AMF) receives user information sent through the network. It then forwards the information to the SMF, which uses it to determine what session manager would be best assigned to the user. Consider the SMF as a gateway from the user plane to the control plane of the network.

UDM and HSS

The HSS of 4G networks fills a similar function to the UDR. It stores customer profile data and authentication information along with encryption keys. In a 5G network, the function of the HSS is split into the Authentication Server Function (AUSF), the UDM, and the UDR (when it is a stateless architecture). The AUSF authenticates servers and provides encryption keys. The UDM stores and manages the data. The move from the HSS to a UDM and UDR is one of the many changes coming in the 4G to 5G transition.