The Home Subscriber Server (HSS) is a key element of LTE and IMS core networks; it is a master user database that is stored in one single node. It allows Communications Service Providers (CSPs) to manage customers in real-time and in a cost-effective manner.
A centralized database of subscriber information ensures that signaling is separated from the policy. As a result, it helps CSPs ease their data center load, so they can achieve more efficient performance and greater streamlining of their networks.
HSS allows CSPs to perform specialized functions such as barring of certain services and functions, activation and deactivation of SIM cards, and the creation of a hierarchical segregation of subscribers based on their subscriptions.
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The role of the HSS is to communicate with the network and provide subscriber profile and authentication information. The database stores information about subscribers to help in the authorization, details of devices, as well as the user’s location and service information. The HSS relays this information to the network using Diameter protocol, communicating with the Mobility Management Entity (MME) via the S6a interface. Combined with an Authentication, Authorization, Accounting (AAA) server, the HSS ensures that an LTE network works with legacy or concurrent services.
The HSS also has the capability to communicate with a WiFi infrastructure, which gives operators the ability to generate revenue streams with the creation of WiFi hotspots and WiFi offload. Further, as it supports roaming to non-3GPP networks, CSPs can increase the reach of their networks.
On being queried by the Interrogating-Call Session Control Function (I-CSCF) when a user performs SIP registration, the HSS retrieves the address of the Serving-Call Session Control Function (S-CSCF) and assigns it to a user. The user’s information and profile data are then downloaded and stored by the HSS, from where they can be accessed.