S-CSCF P-CSCF Failure Detection and Failover Mechanism

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Solution Overview

Problem

In IP Multimedia Services (IMS) networks, there is no mechanism to detect Proxy-Call Session Control Function (P-CSCF) failures in fixed networks, leading to call failures since user equipment (UE) waits for registration refresh or new call initiation when P-CSCF is down.

Innovation Solution

A Serving-Call Session Control Function (S-CSCF) proactively detects P-CSCF failures by sending status messages, marking the P-CSCF as unavailable and setting a timer for recheck, and informs the device management system to force devices to register with a different P-CSCF, thereby mitigating call failures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If no P-CSCF failure detection mechanism is implemented, then device complexity is reduced, but call reliability deteriorates due to inability to detect and respond to P-CSCF failures

Engineering Contradiction:

Improvecall reliabilityVSAvoiddetection mechanism complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The S-CSCF performs preliminary health checks of P-CSCFs by sending test messages before actual call processing occurs. This allows the system to detect potential failures in advance and trigger failover procedures before calls are affected, thereby improving call reliability without requiring complex real-time monitoring during call processing

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback mechanism where the S-CSCF monitors P-CSCF responsiveness through periodic health checks. When a P-CSCF fails to respond or returns negative responses, the S-CSCF receives feedback about its unhealthy state and automatically initiates failover procedures, creating a closed-loop system that improves reliability while maintaining manageable complexity

Inventive Principle:

Principle #23Feedback

2Reliability

If UE waits for registration refresh or new call initiation to detect P-CSCF failure, then detection timing is delayed, but this causes call failures and worsens user experience

Engineering Contradiction:

Improvecall success rateVSAvoidfailure detection time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent implements preliminary health check actions by having the S-CSCF send test messages to P-CSCFs before actual call processing occurs. This allows failure detection to happen in advance during a dedicated health check phase rather than waiting for call processing to reveal the failure, thereby reducing detection time and preventing call failures

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system establishes continuous health monitoring as an ongoing useful action between S-CSCF and P-CSCFs. By maintaining continuous or periodic connectivity checks as a standard operational procedure, the system ensures that P-CSCF failures are detected immediately when they occur, rather than waiting for intermittent registration refreshes or call initiation events

Inventive Principle:

Principle #20Continuity of useful action

3Speed

If S-CSCF proactively checks P-CSCF availability continuously, then failure detection speed improves, but system complexity and resource consumption increase

Engineering Contradiction:

Improvefailure detection speedVSAvoidmonitoring system complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

Instead of continuous real-time monitoring, the patent implements periodic health checks where the S-CSCF sends test messages to P-CSCFs at scheduled intervals. This periodic action provides sufficient failure detection speed for practical purposes while dramatically reducing system complexity and resource consumption compared to continuous monitoring, as the system only needs to manage timing information rather than maintain constant connection states

Inventive Principle:

Principle #19Periodic action

4Speed

If P-CSCF is marked unavailable immediately upon first negative response, then failover speed increases, but false positives may occur reducing system stability

Engineering Contradiction:

Improvefailover speedVSAvoidP-CSCF status stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent implements beforehand cushioning by requiring multiple negative responses or a timer-based confirmation before permanently marking a P-CSCF as unavailable. This cushioning mechanism protects against false positives caused by temporary network issues or transient failures, while still enabling relatively fast failover by using timers that can be configured based on operational requirements. The system balances speed and stability by allowing immediate failover detection while requiring confirmation before final status change

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS11252200B2Apparatus and method for P-CSCF failure detection and processing

Publication Date: 2022.02.15 CHARTER COMM OPERATING LLC

AI summary

Described herein are apparatus and methods for detecting and handling Proxy-Call Session Control Function (P-CSCF) failures. A method may include sending, by a serving-CSCF (S-CSCF), a message to the P-CSCF to check operability. The S-CSCF may mark in a list that the P-CSCF is unavailable if a negative response or no response is received from the P-CSCF and may set a timer to recheck availability of the unavailable P-CSCF. A message is sent by the S-CSCF to a device management system to force a user device to stop using the unavailable P-CSCF and register with a different P-CSCF. The S-CSCF may recheck availability of the unavailable P-CSCF upon expiration of the timer and may remove the unavailable P-CSCF from the list when a positive response is received from the unavailable P-CSCF.