EATF Entity Media Negotiation for IMS Emergency Call Transfer

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Solution Overview

Problem

The existing emergency call transfer process between Packet Switched (PS) and Circuit Switched (CS) networks is lengthy, similar to ordinary call transfers, leading to inefficiencies in the Single Radio Voice Call Continuity (SR VCC) process.

Innovation Solution

The method involves an Emergency Access Transfer Function (EATF) entity that anchors or does not anchor media during the call transfer process, performing media negotiation and routing to accelerate the transfer speed by optimizing network elements such as Proxy-Call Session Control Function (P-CSCF) and Mobile Switching Center (MSC) server interactions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If the existing emergency call transfer process is used, then the call can be transferred between PS and CS networks, but the transfer process is lengthy and inefficient

Engineering Contradiction:

Improvetransfer timeVSAvoidtransfer efficiency

Core Design Contradiction:

Loss of timeVSProductivity

Solution Approach 1:

The EATF entity performs media negotiation with the far end before the actual call transfer occurs. By pre-negotiating media parameters and establishing media connectivity in advance, the system eliminates the need for lengthy media negotiation during the transfer process, thereby reducing transfer time and improving efficiency

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The EATF entity acts as an intermediary that anchors the call and facilitates direct media negotiation between the far end and the target network element. This intermediary role allows the EATF to coordinate the transfer process efficiently, enabling faster call establishment compared to the existing sequential process

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If the EATF entity follows the existing transfer mechanism, then call transfer functionality is achieved, but the process is complex and time-consuming

Engineering Contradiction:

Improvetransfer process simplicityVSAvoidtransfer duration

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

Media negotiation is performed in advance before the call transfer is initiated. This preliminary action simplifies the actual transfer process by pre-establishing media parameters, reducing the complexity and duration of the transfer operation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the sequence and timing of parameter negotiation, performing media parameter negotiation before call transfer rather than during or after. This parameter reordering simplifies the transfer process flow and reduces overall transfer time

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP2852119B1Method for switching session of IMS network and eatf

Publication Date: 2017.08.23 ZTE CORP

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AI summary

A method for switching a session of an IP Multimedia Subsystem (IMS) network and an Emergency Access Transfer Function (EATF) entity are disclosed. The method includes: the EATF entity anchoring a call sent by a network element in a call initiation domain, and routing the call to an Emergency-Call Session Control Function (E-CSCF); the EATF entity receiving call transfer invite message sent by a network element in a call termination domain; and if identifying that the call transfer invite message is an invite message inviting to perform transfer of the call, the EATF entity performing media negotiation, and sending a response message carrying media information to the network element in the call termination domain.