IMS Session Restoration via HSS AVP Pre-storage

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Solution Overview

Problem

Current Internet Protocol Multimedia Subsystem (IMS) restoration procedures disrupt communication sessions due to node unavailability, causing service disruptions, unnecessary network bandwidth consumption, and data duplication issues.

Innovation Solution

Storing attribute-value pairs (AVPs) at a Home Subscriber Server (HSS) during registration, allowing IMS nodes to directly retrieve information for session restoration without tearing down sessions or issuing unnecessary communications, thereby selecting backup nodes without re-registering the UE.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If existing IMS restoration procedures are used when an IMS node becomes unavailable, then the communication session can be restored by re-registering the UE with an available node, but the service is disrupted causing phone calls to be dropped and users to be forced to re-dial

Engineering Contradiction:

Improvecommunication session restorationVSAvoidservice continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies preliminary action by pre-storing the UE's registration information and binding data in the HSS before any node failure occurs. When an S-CSCF or AS becomes unavailable, the backup node can directly retrieve this pre-stored information from the HSS and immediately restore the communication session without requiring the UE to re-register, thus maintaining service continuity while ensuring reliable restoration

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The HSS acts as an intermediary that mediates between the UE and the IMS nodes. By storing the UE's registration information and bindings centrally in the HSS, it enables backup S-CSCF or AS nodes to quickly retrieve necessary data and restore sessions without direct communication with the UE or other IMS nodes, avoiding service disruption

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If backup IMS nodes transmit requests to other IMS nodes for additional information during restoration, then the backup node can discover a new available AS to serve the UE, but network bandwidth is consumed and delay is caused that is noticeable to the end user

Engineering Contradiction:

Improverestoration capabilityVSAvoidrestoration delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The HSS pre-stores the UE's binding information including the assigned AS identifier during the initial registration procedure. When restoration is needed, the backup S-CSCF or AS can directly retrieve this information from the HSS without needing to issue TPR messages or communicate with other IMS nodes to discover the AS, thereby eliminating restoration delay while maintaining reliable restoration capability

Inventive Principle:

Principle #10Preliminary action

3Reliability

If backup IMS nodes transmit requests to other IMS nodes for additional information during restoration, then the backup node can obtain profile recovery requests and discover new nodes, but unnecessary network bandwidth is consumed due to added load on the network

Engineering Contradiction:

Improverestoration functionalityVSAvoidnetwork bandwidth consumption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent extracts the necessary restoration information (UE registration data and bindings) from the complex IMS node communication process and stores it centrally in the HSS during initial registration. This extraction eliminates the need for backup nodes to communicate with multiple other IMS nodes during restoration, significantly reducing network bandwidth consumption while maintaining full restoration functionality through direct HSS queries

Inventive Principle:

Principle #2Taking out (Extraction)

4Reliability

If existing restoration procedures are used, then the UE can be re-assigned an available node, but stale bindings remain in data repositories creating data duplication where the repository data indicates the UE is assigned to multiple IMS nodes of the same type

Engineering Contradiction:

Improvenode assignmentVSAvoiddata accuracy

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The HSS serves as a central intermediary that maintains the single source of truth for UE bindings. When a backup node restores a session, it retrieves the current binding information directly from the HSS, which ensures that the repository data accurately reflects the current node assignment. This eliminates stale bindings and data duplication because all nodes query the HSS for the latest binding information rather than maintaining their own potentially outdated records

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11659469B2Restoration of serving call session control and application server function

Publication Date: 2023.05.23 T MOBILE US INC

AI summary

A communication session for a UE can be restored in the event of serving call session control function (S-CSCF) node unavailability and/or application server (AS) unavailability by storing, prior to IMS unavailability, attribute-value pairs (AVPs) at a home subscriber server (HSS). These AVPs can be used independently by individual IMS nodes to restore a communication session for a UE due to an unavailable IMS node. When a first S-CSCF node becomes unavailable, a proxy CSCF (P-CSCF) node can send a SIP request originating from the UE to a second S-CSCF node. The second S-CSCF node can then send a request to the HSS for an identifier of an AS associated with the UE. Upon receipt of the AS identifier (e.g., an active AS name AVP) from the HSS, the second S-CSCF node can send the SIP request to the AS in order to restore the communication session for the UE.