S102 Link Failure Detection in CSFB MSC Pools

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Solution Overview

Problem

The existing standards for Circuit Switched Fallback (CSFB) in a pooled Mobile Switching Center (MSC) environment lack mechanisms to detect S102 link failures and update the Evolved Packet Core (EPC) network with IWS re-assignment due to load-balancing, leading to inefficiencies and potential service disruptions.

Innovation Solution

Implementing a 'heartbeat' message mechanism to detect link failures and sending notification messages for IWS relocation, allowing the EPC network to reroute messages to alternate links or newly assigned IWSs, thereby improving system robustness and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a pooled MSC environment is deployed to improve network robustness and resource utilization, then network reliability is improved, but link failure detection capability deteriorates because existing CSFB standards lack mechanisms to detect S102 link failures

Engineering Contradiction:

Improvenetwork robustnessVSAvoidlink failure detection

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent implements a feedback mechanism where the MME sends heartbeat messages to IWS nodes and waits for acknowledgments. When an acknowledgment is not received within a predetermined time, the MME detects the link failure and switches to an alternate IWS node. This feedback loop enables continuous monitoring of link status in pooled MSC environments.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent establishes alternate IWS nodes in advance within the pooled MSC environment. When a link failure is detected, the system can immediately switch to the pre-configured alternate node without waiting for discovery or configuration, thereby minimizing service disruption and improving detection effectiveness.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If load-balancing is implemented within MSC pool to improve resource distribution, then resource utilization is improved, but IWS re-assignment notification capability deteriorates because existing standards lack mechanisms to update EPC network with IWS re-assignment

Engineering Contradiction:

Improveresource utilizationVSAvoidIWS re-assignment information

Core Design Contradiction:

ProductivityVSLoss of information

Solution Approach 1:

The patent implements a notification mechanism where the serving IWS node sends feedback information to the MME about its assignment status. This allows the EPC network to be updated when load-balancing causes IWS re-assignment, ensuring the MME has current information about which IWS node is serving which MSC.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The IWS nodes autonomously manage their own assignment status and proactively notify the MME when re-assignment occurs due to load-balancing. This self-service approach ensures that the system automatically maintains accurate routing information without requiring manual intervention.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If CSFB is used to enable voice calls in LTE networks, then service coverage is improved, but system complexity increases due to the need for interworking between EPC and CS domains

Engineering Contradiction:

Improveservice coverageVSAvoidnetwork interworking complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the CSFB functionality by separating the voice call handling path from the data path. The MME manages CSFB signaling and IWS selection independently from the user plane traffic routing. This segmentation simplifies the interworking complexity by allowing independent optimization of control and data functions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces IWS nodes as intermediary elements between the EPC network and CS domain. These intermediaries handle the complexity of CS domain interworking and translation, shielding the EPC network from the intricacies of circuit-switched protocols while enabling seamless voice service integration.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8964698B2Link failure detection and interworking system relocation in circuit switched fallback

Publication Date: 2015.02.24 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method and mechanism to detect failure of an S102 link between an Evolved Packet Core, EPC, network based Mobility Management Entity, MME, and an Interworking System, IWS, in a Mobile Switching Center, MSC, pool deploying Circuit Switched Fallback, CSFB, for the EPC network. A heartbeat message exchange between an MME-IWS pair augments the current standards to provide a simple and direct method to monitor the application layer status of the S102 link between the EPC-based MME and the MSC pool-based IWS. Upon detecting a link failure, message flows can be quickly re-routed to another S102 link or MSC. Reverse use of an A21 Event Notification message from an IWS to MME, or a re-assigned IWS's delayed acknowledgement of an initial call-related message from an MME also augment the current standards to address IWS relocation related message-bouncing in MSC pool-based deployments of CSFB, thereby allowing efficient routing of messages.