What does HSS do?
Today, let’s dive into the role of the HSS – the Home Subscriber Server – in an LTE network. Since we’ve previously talked about elements like the MME and SGW, it’s a good time to understand how HSS fits into the big picture and how it interacts with these nodes to manage your access and mobility.
In LTE, the HSS is a critical core network component responsible for managing all subscriber-related information. If I break it down for you, it’s like the brain that stores who you are, what services you can use, and how the network should treat your device when you’re moving or requesting services.
Main Functions of HSS
Let me explain the major tasks the HSS performs, so you can clearly understand why it’s so important:
- Subscriber Profile Management: HSS stores your subscription information like voice, data plans, and service restrictions. It ensures that the network applies the right rules based on what you’re allowed to use.
- Authentication and Authorization: Every time your device connects, HSS helps verify your identity using parameters like IMSI and security keys. It ensures that only legitimate users can access the network.
- Mobility Management: HSS tracks your last known location by working with the MME. So when you switch between cells or travel to another city, the network knows how to route traffic to you.
- Session Handling: When you’re accessing the internet or making a call, the HSS provides the necessary session information to other nodes like the PCRF and PGW to apply correct QoS policies.
- Interworking with IMS: If you’re using VoLTE services, the HSS works closely with the IMS (IP Multimedia Subsystem) and stores SIP-related information for call handling and features like call forwarding.
HSS Role in LTE Architecture
To give you a clearer view, here’s a table that shows how HSS interacts with other components in the LTE core network:
| Network Element | Interaction with HSS |
|---|---|
| MME (Mobility Management Entity) | Queries HSS for authentication vectors, subscriber profile, and location updates. |
| PCRF (Policy and Charging Rules Function) | Uses HSS data to apply QoS policies based on user subscription. |
| IMS (IP Multimedia Subsystem) | Accesses HSS to retrieve SIP credentials and service data for voice services. |
As you see, HSS isn’t just a passive database. It actively responds to network elements to ensure a seamless experience for you as a user. Whether you’re starting a data session, moving from one area to another, or making a call over VoLTE, HSS is always in the background helping the network make real-time decisions about how to treat your session.
Now that you know what HSS does, it’s also useful to look into how it supports features like roaming or how it fits into 5G where it’s replaced by the UDM. But before we jump there, you might also want to revisit how MME uses the authentication vectors from HSS during the attach procedure, which we covered earlier.