Stateful I-CSCF Reselection for IMS Session Reliability
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Solution Overview
Problem
In IP Multimedia Subsystems (IMS) networks, the stateless Interrogating-Call Session Control Function (I-CSCF) module may fail to await responses to SIP messages, leading to session timeouts and call losses due to device failures or communication interruptions, resulting in unregistered services not being executed properly, causing prolonged service outages for users.
Innovation Solution
Implementing a stateful I-CSCF module that inquires the Home Subscriber Server (HSS) about user registration status, awaits responses to SIP requests, and reselects a Serving-Call Session Control Function (S-CSCF) if the initial one does not respond, ensuring that the required S-CSCF capabilities are obtained and used to process unregistered services.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the I-CSCF operates as a stateless module, then the device complexity is reduced and processing efficiency is improved, but the reliability deteriorates because the I-CSCF cannot await responses to SIP messages, leading to session timeouts and call losses
Solution Approach 1:
The patent transforms the I-CSCF from a static stateless module to a dynamic stateful module that can maintain session state and Await responses. The I-CSCF now tracks SIP message states and can actively monitor for responses, enabling it to detect failures and trigger reselection procedures dynamically based on actual response conditions.
Solution Approach 2:
The stateful I-CSCF implements feedback mechanisms by monitoring response status from S-CSCFs and using this information to determine whether to trigger reselection procedures. The system continuously monitors the state of SIP messages and adjusts its behavior based on whether responses are received or not, creating a closed-loop control system.
2Reliability
If the I-CSCF awaits responses to SIP messages, then the reliability is improved by detecting S-CSCF failures, but the processing time increases and productivity decreases
Solution Approach 1:
The system performs preliminary actions by pre-configuring multiple S-CSCFs with their capabilities in the HSS before actual call processing. When a failure is detected, the I-CSCF can immediately initiate reselection using pre-fetched capability information, avoiding the need to query the HSS again and reducing the time penalty of stateful operation.
Solution Approach 2:
The I-CSCF implements partial awaiting by monitoring only for critical response indicators rather than waiting for complete SIP message processing. This allows the system to detect failures at key decision points without requiring full message processing completion, balancing reliability monitoring with processing efficiency.
3Reliability
If the I-CSCF implements stateful operation with response awaiting, then the reliability improves, but the device complexity increases
Solution Approach 1:
The I-CSCF integrates multiple functions into a single stateful module: it performs initial SIP message routing, monitors response status, detects failures, and triggers reselection procedures. By consolidating these functions in one module rather than distributing them across separate components, the patent manages complexity while achieving stateful operation.
Solution Approach 2:
The HSS serves as an intermediary that stores S-CSCF capability information and provides it to the I-CSCF during reselection procedures. This externalizes the complexity of capability management from the I-CSCF itself, allowing the stateful I-CSCF to focus on monitoring and decision-making while the HSS handles the storage and retrieval of capability data.
4Device complexity
If unregistered services are not processed due to S-CSCF unavailability, then the device complexity is reduced, but the loss of time increases as users experience prolonged service outages
Solution Approach 1:
The system performs preliminary actions by pre-storing S-CSCF capability information in the HSS before failures occur. When an S-CSCF becomes unavailable, the I-CSCF can immediately initiate reselection using pre-fetched capability data, eliminating the need to query the HSS during the outage period and significantly reducing service disruption duration.
Solution Approach 2:
The stateful I-CSCF maintains continuous monitoring of S-CSCF availability and keeps reselection procedures ready to execute immediately upon failure detection. This continuous readiness ensures that service disruption is minimized and unregistered services can be restored quickly, maintaining business continuity during and after outages.
Data Source
AI summary
A method of session processing in the Internet Protocol (IP) Multimedia Subsystem (IMS) comprises: Interrogating-Call State Control Function (I-CSCF) accessing the Home Subscriber Server (HSS) to query the registration location of the called user, the I-CSCF sending the Session Initiation Protocol (SIP) request to the Serving-Call State Control Function (S-CSCF) based on the response of the HSS; when the response time of the S-CSCF to the SIP request sent from the I-CSCF has expired, the I-CSCF re-selecting the S-CSCF, and sending the SIP request to the S-CSCF. And an Interrogating-Call State Control Function is provided. According to the present invention, if the S-CSCF returned by the HSS to process the unregistered service of the IMS user does not responded because of the device failure or communication interruption or the like, the I-CSCF can re-select other S-CSCF to process the unregistered service of the IMS user, so as to improve the quality of service and to increase the satisfaction of user.