Home subscriber server (HSS)
The LTE (4G) subscriber database; in the 5G core the UDM and UDR take this role, and the HSS remains for EPC and IMS interworking.
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The home subscriber server (HSS) is the subscriber database of an LTE network. It holds the subscription profile, the authentication data and the address of the node currently serving the device. In the 5G core the UDM and UDR take this role; the HSS remains for EPC and IMS interworking.
Why it matters
The HSS is the authority the core consults before a device attaches or a session starts. If the record is wrong, the radio can be perfect and the device still fails to connect. It replaces the HLR and the authentication center of 2G and 3G, and keeps their role.
The database in the path
- Application
- SMSC
- HLR / HSS
- MSC / MME
- Handset
Text description
The same role appears in every generation: a home copy of the subscription that a serving node queries. The HSS adds authentication data and LTE location to the HLR functions.
What to check
Ask who owns the HSS record and how a profile change propagates to it. In roaming, the visited network queries the home HSS through the home network's signaling, so a delay there looks like a radio problem. The HLR term covers the 2G and 3G predecessor.