Methods and apparatus for resolving data inconsistencies in an ims network

An apparatus configured to operate as a Home Subscriber Server, HSS, within an IP Multimedia Subsystem, IMS, core network, the apparatus comprising:

• a memory for storing users' IMS registration states;
• an interface for receiving from a Serving Call Session Control Function, S-CSCF, of the IMS core network, notifications indicating IMS registration state changes of users to new IMS registration states;
• and
• a state synchronization handler for determining that a notification received from the S-CSCF contains an indication of a previous loss of IMS registration state synchronization for a given user between the S-CSCF and the HSS, and for responding by updating the given user's IMS registration state in the memory to the new IMS registration state contained in the received notification.

A method of handling a communication failure between a Serving Call Session Control Function, S-CSCF, and a Home Subscriber Server, HSS, of an IP Multimedia Subsystem, IMS, network, the method comprising:

• at the S-CSCF:
• detecting delivery failure of a notification sent by the S-CSCF to the HSS and relating to an IMS registration state change for a given user;
• recording an indication of the delivery failure in association with said given user in order to indicate a loss of IMS registration state synchronization for the given user between the S-CSCF and the HSS;
• detecting an event relating to said given user, the event requiring an IMS registration state change for the user to a new state;
• determining that a delivery failure indication is currently associated with the user;
• and
• sending a further notification to the HSS, the further notification including both an indication of the required IMS registration state change and an indication of a previous loss of IMS registration state synchronization for the user between the S-CSCF and the HSS;
• and
• at the HSS:
• receiving said further notification;
• determining that the notification includes said indication of a previous loss of IMS registration state synchronization for the user;
• and
• updating an IMS registration state for the given user to said new IMS registration state included within the notification.

A system comprising:

• a first apparatus configured to operate as a Serving Call Session Control Function, S-CSCF, within an IP Multimedia Subsystem, IMS, core network, the first apparatus comprising:
• an interface for sending to a Home Subscriber Server, HSS, of the IMS core network, notifications indicating IMS registration state changes of users;
• a detector for detecting delivery failure of a notification of an IMS registration state change sent to a HSS and relating to a given user;
• a memory and memory controller for storing in said memory an association between an identifier of said given user and an indication of said delivery failure in order to indicate a loss of IMS registration state synchronization for said given user between the S-CSCF and the HSS;
• and
• an event handler for:
• detecting an event relating to said given user, the event requiring an IMS registration state change for the user;
• determining that said memory currently stores a delivery failure indication associated with the user's identifier;
• and
• causing said interface to send a further notification to the HSS, the further notification including both an indication of the required IMS registration state change and an indication of a previous loss of IMS registration state synchronization for the user between the S-CSCF and the HSS;
• and
• a second apparatus configured to operate as a Home Subscriber Server, HSS, within an IP Multimedia Subsystem, IMS, core network, the second apparatus comprising:
• a memory for storing users' IMS registration states;
• an interface for receiving from a Serving Call Session Control Function, S-CSCF, of the IMS core network, notifications indicating IMS registration state changes of users to new IMS registration states;
• and
• a state synchronization handler for determining that a notification received from the S-CSCF contains an indication of a previous loss of IMS registration state synchronization for a given user between the S-CSCF and the HSS, and for responding by updating the given user's IMS registration state in the memory to the new IMS registration state contained in the received notification.

A non-transitory computer-readable storage medium storing computer program instructions which, when executed by a processor in a Serving Call Session Control Function, S-CSCF, cause the processor to perform a method of handling a communication failure between the S-CSCF and a Home Subscriber Server, HSS, of an IP Multimedia Subsystem, IMS, network, the method comprising:

• detecting delivery failure of a notification sent by the S-CSCF to the HSS and relating to an IMS registration state change for a given user;
• recording an indication of the delivery failure in association with said given user in order to indicate a loss of IMS registration state synchronization for the given user between the S-CSCF and the HSS;
• detecting an event relating to said given user, the event requiring an IMS registration state change for the user to a new state;
• determining that a delivery failure indication is currently associated with the user;
• and
• sending a further notification to the HSS, the further notification including both an indication of the required IMS registration state change and an indication of a previous loss of IMS registration state synchronization for the user between the S-CSCF and the HSS.

A non-transitory computer-readable storage medium storing computer program instructions which, when executed by a processor in a Home Subscriber Server, HSS, cause the processor to perform a method of handling a communication failure between a Serving Call Session Control Function, S-CSCF, and the HSS of an IP Multimedia Subsystem, IMS, network, the method comprising:

• receiving, from the S-CSCF, notifications indicating IMS registration state changes of users to new IMS registration states;
• determining that a notification received from the S-CSCF contains an indication of a previous loss of IMS registration state synchronization for a given user between the S-CSCF and the HSS;
• and
• updating the given user's IMS registration state in the memory to the new IMS registration state contained in the received notification.