IMS HSS Home Subscriber Server

- IMS HSS - Home Subscriber Server details, structure, and operation within the overall IMS architecture.

The IMS HSS or home subscriber server is the main subscriber database used within IMS.

The IMS HSS provides details of the subscribers to the other entities within the IMS network, enabling users to be granted access or not dependent upon their status.

IMS HSS basics

When a subscriber registers onto an IMS network, the subscription data is retrieved from the HSS by the Serving-CSCF, S-CSCF that has been assigned to the subscriber.

A block diagram of a simplified view of the IMS artictecture showing the IP-CAN
Simplified view of the IMS architecture showing IP-CAN

The actual registration process has various stages to it. The primary communications occur between the HSS and the S-CSCF, but other IMS entities are also involved.

The following data transfers occur:

  • Subscription data is transferred from the HSS to the S-CSCF. This includes items such as the IMS public user identity (public identifiers used for identifying he subscriber for originating and terminating media sessions), and the service trigger data.
  • Charging subscription data is sent from the HSS to the P-CSCF via the S-CSCF.
  • IMS public user identity data which is also kept in the S-CSCF is forwarded to the user equipment
  • Service subscription data is forwarded from the HSS to the SIP-AS via the S-CSCF. This enables charging for the services to be managed.

By Ian Poole

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