What Is the HSS (Home Subscriber Server)?

The HSS is the central database of the LTE core network (EPC), responsible for storing and managing subscriber information, authentication data, and service permissions. It holds details such as the IMSI, phone number (MSISDN), subscriber status (active or inactive), subscription plan, and service options (for example, whether VoLTE is enabled).

However, the HSS does more than just store data. When other core network elements (such as the MME or IMS) send authentication requests, the HSS, through its AuC (Authentication Center) module, generates authentication vectors based on the secret key (Ki) stored in the USIM. These vectors enable the AKA (Authentication and Key Agreement) procedure, which verifies that the device is a legitimate subscriber. In this sense, the HSS is not a passive storage system but an intelligent database that provides the data required for authentication.

The HSS also plays a critical role when subscribers roam onto other operators’ networks. When a visited network asks, “Is this subscriber valid?”, the HSS responds by verifying the subscriber’s validity and supplying the necessary information. This ensures that users can continue to access communication services seamlessly while roaming abroad.

In short, the HSS can be described as the core network’s large-scale subscriber database that not only identifies who the user is but also defines what services they are allowed to use, making it a vital system for both authentication and service control.