The Home Subscriber Server (HSS) is a network element residing in the Control Plane that acts as a central repository of all subscriber-specific authorizations and service profiles and preferences for an IMS network. The HSS integrates several functions, some of which exist already in the functions of the Home Location Register of mobile networks:
- Subscriber Profile Database
- Subscriber Service Permissions
- Subscriber Preference Settings
- Mobile Authentication Server
- Home Location Register (HLR) for mobile roaming
- Subscriber Presence Function
- Subscriber Location Function
Once a network is large enough to require two or more HSS, the Subscriber Location Function (SLF) is a network element used by the CSCF’s to determine which HSS to interface for a given end-device.
The HSS data includes the Public and Private identities of subscribers, credentials used for authentication, data defining which services and media types are allowed for each subscriber, and call control logic in the form of Initial Filter Criteria (IFC)’s used to instruct the S-CSCF in terms of Session Initiation Protocol (SIP) message routing. IFC act as triggers in terms of instructing the S-CSCF what to do for session control.
Other functions within the HSS include support for mobility management, provisioning, application services, and intelligent network services.
Interfaces to/from the HSS support communications to the GMSC, MSC/VLR, gsmSCF, SGSN, GGSN, SIP AS, OSA-SCS, IM-SSF, and CSCF’s.
For more information, see: