P-CSCF Dual IMPU Format Generation for Emergency Callback Reliability

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Solution Overview

Problem

In the IMS emergency call system, if the PSAP is located in the PS domain and does not save the IMPU in SIP URI format, it may fail to initiate an emergency callback due to lack of ENUM support or inability to find the SIP URI format, leading to call failures.

Innovation Solution

The P-CSCF generates both IMPU in SIP URI and TEL URI formats and sends them to the PSAP, allowing the PSAP to initiate callbacks even without ENUM support, and enables direct callback initiation if ENUM is supported, thereby ensuring successful emergency calls.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the PSAP is located in the PS domain and does not save the IMPU in SIP URI format, then the PSAP cannot initiate emergency callback, but providing both TEL URI and SIP URI formats ensures successful callback

Engineering Contradiction:

Improveemergency callback reliabilityVSAvoididentity format complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The P-CSCF performs preliminary action by converting the IMPU to both TEL URI and SIP URI formats before the PSAP needs to initiate a callback. This advance preparation ensures that regardless of whether the PSAP supports ENUM or has saved the SIP URI format, the necessary identity information is already available, eliminating callback failure risks.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies parameter changes by transforming the IMPU parameter into two different format representations (TEL URI and SIP URI). This allows the system to adapt to different PSAP configurations and capabilities, ensuring compatibility and successful callback initiation regardless of the PSAP's ENUM support status or saved identity format.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the P-CSCF only provides IMPU in TEL URI format, then the system works for basic emergency calls, but fails when PSAP needs to initiate callback without ENUM support

Engineering Contradiction:

Improveemergency callback success rateVSAvoidsystem implementation complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The P-CSCF performs the identity format conversion in advance during the emergency call setup phase, generating both TEL URI and SIP URI formats of the IMPU. This preliminary action ensures that when the PSAP needs to initiate a callback, the appropriate format is already available, eliminating the need for complex runtime ENUM queries or format conversions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The P-CSCF acts as an intermediary between the UE and the PSAP by performing the identity format conversion and providing both TEL URI and SIP URI formats. This intermediary function simplifies the overall system implementation by centralizing the conversion logic in the P-CSCF, rather than requiring each PSAP to implement complex ENUM support or format conversion capabilities.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If the PSAP supports ENUM and can find SIP URI format, then direct callback initiation is possible, but without dual format provision the callback may fail

Engineering Contradiction:

Improvecallback initiation speedVSAvoidcallback establishment reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9001835B2Method and system for establishing emergency call

Publication Date: 2015.04.07 HUAWEI TECH CO LTD

AI summary

A method for establishing an emergency call includes: if an emergency call request message sent by a User Equipment (UE) contains an Internet Protocol Multimedia Subsystem Public User Identity (IMPU) in a TEL URI format, a Proxy-Call Session Control Function entity (P-CSCF) generates an IMPU in a Session Initiation Protocol (SIP) URI format according to the IMPU in the TEL URI format, sends both IMPUs to a Public Safety Answering Point (PS AP), and receives an emergency callback initiated by the PSAP. The PSAP initiates the emergency callback according to one of the two IMPUs. A system for establishing an emergency call includes a UE, a P-CSCF and a PSAP. The PSAP can always acquire the IMPU in the TEL URI format and the IMPU in the SIP URI format of the UE, and initiate an emergency callback to the UE according to the IMPU in the SIP URI format.