OpenCall Home Subscriber Server (HSS) is the leading database for subscribers’ profiles for IMS / EPS architecture. OpenCall HSS stores a set of functions and services to each subscriber, performs authentication and authorization of users, provides information about the location of the subscriber and stores profiles of user access to network resources.

In this regard OpenCall HSS is similar to location register (HLR). However, HSS operates and supports 3G-network, based on IP protocol. Thus, HSS provides all the functionality of a location register and authentication center, as well as additional functionality specific to 3G networks.

The network can have one or more HSS depending on the number of subscribers, equipment capacity and networking. To support more than one HSS in the network you can use Subscription Locator Function (SLF) to identify the HSS, which stores information for the subscriber. Multi-vendor environment requires individual SLF.

HSS is the primary database for LTE subscribers. Database can be located in general user repository as defined in 3GPP User Data Convergence (UDC).

The product implements Home Subscriber Server function in IMS / EPS networks.

Hardware & Software

Solution can be deployed on a hardware platform HP NonStop Server NS-series or NB-series.

HP Integrity NonStop Server – a server that belongs to the category of High-End. It is based on the use of HP NonStop Kernel operating system, ServerNet architecture and fully redundant elements, which ensures the highest levels of availability and fault tolerance. Integrity NonStop Server is ideal for operation of the most critical business applications.

Technical Description

HSS application is cross-platform and can be deployed on different hardware platforms, with different operating systems. The figure below shows the architecture of the HSS application. Specialized Platform abstraction layer isolates the HSS application components from the characteristics of supported platforms, protocol stacks, and hardware / OS. Depending on the platform environment platform abstraction interface can have several implementations, but the interface to HSS application is always the same.

Architecture of HSS application:

Platform abstraction layer

Platform abstraction layer provides the interface between the application and the underlying OS HSS. This layer insulates the HSS from operating system:

  • IPC (interprocess communication) enables the processing of messages between different processes;
  • External Protocol Support is an application component with a common interface and a model for communications with other entities in network. Interface provides full access to the message, including the message address block and protocol-specific information;
  • Context Facility provides access to a temporary operational storage of transaction information loaded into memory
  • OS facilities provide transparent access to the system resources: a process environment, time function, task scheduler, time synchronization, shared memory, etc.
  • Control and configuration subsystem provides access to configuration application and platform
  • Event Management provides HSS application with a single interface for creating and logging and error messages
  • Statistics collection provides a single interface to the subsystem statistics, which provides the ability to collect and display statistical information
  • Overload subsystem allows to determine whether corrective action is needed based on the current load conditions and to apply such actions as necessary
  • Licensing manager provides application with an interface to the license repository to determine which features are licensed
  • Network Data Manager allows application to access the data
Diameter protocol components

Application Programming Interface (API) provides the HSS application HSS with access to incoming messages and the formation and routing outbound messages.

The parser supports parsing and formatting of all command codes and AVP Diameter base protocol and advanced application-specific command codes and AVP.

Peer State Machine component implements the internal logic of the protocol.
In the context of connection management Diameter distinguishes connection and session. One connection can support multiple sessions.

  • Exchange features: HSS acts as Diameter-server, that is, supports receiving messages Capabilities-Exchange-Request and responds with a Capabilities-Exchange-Answer
  • Disconnection of the final connections: HSS supports receiving messages Disconnect-Peer-Request and responds with a Disconnect-Peer-Answer
  • Detection of traffic problems: HSS supports receiving messages Device-Watchdog-Request and responds with Device-Watchdog-Answer

Application subsystems

HSS consists of set of subsystems:

  • Message processing subsystem provides a scalable messaging environment that is always available for business-critical real-time applications. Real-time processes that send and receive messages to and from the signaling network are configured specifically for performance in this environment
  • DPA – Dynamic Provisioning Architecture is a component for reading and writing records from HSS database, including the graphical user interface (GUI) and command line interface (CLI)
  • ADS (Application Database Synchronization) is used to support the mated-pair function for interaction with the second HSS server uses. It provides a distributed database replication in real time
  • Keys Manager controls access to storage-keys that protect subscriber authentication data
  • A set of specialized tools allows specific operations on the database, such as report generation and data modification

HSS IMS application interacts with the AS application server and the element with the functions of calls and sessions control CSCF via Cx, Sh, Si interfaces. SLF interacts with the CSCF and AS via Dx and Dh protocols. To interact with AAA HSS uses the Wx. All of these protocols are extensions of Diameter. Diameter protocol uses TCP (Transmission Control Protocol) or SCTP (Stream Control Transmission Protocol) as the transport for messages. At the network level IPv4 and IPv6 are supported.
HSS EPS has the following functionality:

  • S6a support
  • S6d support
  • 3G AKA authentication support for S6a interface
  • Diameter Server support
  • DRA support
  • Diameter messages routing(S6a, S6d) to an external HSS
  • Integration with custom APN for a more flexible configuration of APN information
  • Supports for ISR mechanism (Idle mode Signalling Reduction). Allows the subscriber to be simultaneously registered in UTRAN / GERAN Routing Area (RA), and E-UTRAN Tracking Area (TA)
  • Supports for CALEA mechanism (Communication Assistance for Law Enforcement Act). Supports HI2 interfaces and option for the U.S. (including support TCP / IP)