Restoring Mobile Terminating CS Services via Alternative MME
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Solution Overview
Problem
The deployment of LTE/EPC in mobile communication systems can impair the delivery of mobile terminated CS services, such as CS calls and SMS, due to the risk of prolonged service disruption when the MME fails without restart, leading to delayed or failed service delivery to users.
Innovation Solution
A method is introduced where an alternative MME within the MME pool is contacted instead of the original failed MME, and is forced to accept paging requests with a 'restoration indicator' parameter, allowing CS services to be delivered even if the UE is unknown to the alternative MME, mimicking the behavior of an MME that has recently restarted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LTE/EPC is deployed with MME for mobility management, then packet-switched services are improved, but mobile terminated CS services delivery is impaired due to MME failure without restart
Solution Approach 1:
The network pre-configures alternative MME entities and their associated TACs before failure occurs. When the original MME fails, the MSC/VLR can immediately redirect paging requests to pre-identified alternative MMEs without needing to discover them during the failure recovery process, reducing service disruption time
Solution Approach 2:
The system establishes backup MME entities that can serve as cushioning resources before failures occur. These alternative MMEs are kept ready with their TAC configurations so that when the original MME fails, the network can immediately switch to alternatives, preventing service disruption rather than recovering from it
2Reliability
If alternative MME is contacted for paging request when original MME fails, then service continuity is improved, but network complexity increases due to MME pool management
Solution Approach 1:
Multiple MME entities within the pool are configured with universal capability to handle paging requests for any TAC. Each alternative MME can accept paging requests not only for its own associated TACs but also for TACs associated with other MMEs in the pool, eliminating the need for complex TAC-to-MME mapping during failure scenarios
Solution Approach 2:
The MSC/VLR acts as an intermediary that manages the MME pool. It maintains knowledge of alternative MME entities and their capabilities, and intelligently routes paging requests to appropriate alternatives when the original MME fails, shielding the complexity of MME pool management from the rest of the network
3Reliability
If MME-Reset parameter is set to true for restored MME, then service restoration is enabled, but false restoration issues occur when MME fails without restart
Solution Approach 1:
The alternative MME is pre-configured with TAC associations and paging capabilities before being needed. When selected to handle paging requests, it can immediately function with MME-Reset=true behavior without needing to undergo a restart process, avoiding the information loss issues that would occur with actual MME restarts
Solution Approach 2:
The alternative MME effectively copies the functionality and configuration of the original MME for the purpose of handling paging requests. It assumes the role of the failed MME by processing paging requests as if it were the original MME, without needing to actually restart or retrieve real UE context information
Data Source
Figure 1~2
Figure 3
AI summary
In an embodiment, a method for restoration of MT (Mobile Terminating) CS services in case of failure of a PS Core Network CN entity, referred to as original CN entity, originally identified as to be contacted for a paging request towards a User Equipment UE for said MT CS services, in a mobile communication system, comprises a step of: - providing that an alternative CN entity is contacted instead of said original CN entity, and that said alternative CN entity is forced to accept said paging request even if said UE is unknown to said alternative CN entity.