# What is an HSS (Home Subscriber Server)?

> The HSS (Home Subscriber Server) is the central subscriber database of a 4G LTE / IMS core network — the Diameter-based successor to the 2G/3G HLR. It stores subscriber identities, authentication keys, and service profiles, and answers S6a/S6d signaling from the MME during attach and SMS delivery. On 5G standalone its role passes to the UDM. See /answers/what-is-hlr, /answers/diameter-s6a-explained, and /products/hlr-lookup.

- Canonical URL: https://www.broadnet.me/answers/what-is-hss
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [What is IMS (IP Multimedia Subsystem)?](https://www.broadnet.me/answers/what-is-ims)
- [What is an HLR (Home Location Register)?](https://www.broadnet.me/answers/what-is-hlr)
- [Diameter S6a — the 4G equivalent of MAP](https://www.broadnet.me/answers/diameter-s6a-explained)
- [What is a VLR (Visitor Location Register)?](https://www.broadnet.me/answers/what-is-vlr)
- [How does HLR lookup and MNP number intelligence work?](https://www.broadnet.me/answers/hlr-mnp-number-intelligence)
- [HLR Lookup](https://www.broadnet.me/products/hlr-lookup)
- [Signaling & CDR Intelligence](https://www.broadnet.me/platforms/signaling-cdr)