Selective Call Routing for Circuit-Switched Fallback Phaseout
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Solution Overview
Problem
In mixed networks where LTE/5G and legacy 2G/3G circuits coexist, the phased-out support for circuit-switched fallback (CSFB) leads to unnecessary signaling overhead and resource waste due to inconsistent tracking of CS support deprecation, causing network disturbances during the transition to packet-switched networks.
Innovation Solution
Network nodes in the core network track the deprecation of CS support by maintaining locational records, allowing them to determine whether CS retry attempts are necessary based on the subscriber's location, thereby reducing unnecessary CS retry attempts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CS retry attempts are made in all locations during network transition, then call connectivity is maintained for legacy devices, but signaling overhead and network resources are wasted in areas where CS support is deprecated
Solution Approach 1:
The patent applies local quality by implementing location-specific CS support policies. The network server determines whether to allow CS retry attempts based on the subscriber's current location and the CS support status of that specific location. This resolves the contradiction by enabling CS retries only in locations where CS infrastructure exists (maintaining reliability) while blocking retries in locations where CS is deprecated (reducing signaling overhead).
Solution Approach 2:
The patent implements preliminary action by pre-determining CS support status for various network locations before actual call attempts. The network server maintains information about which locations support CS and which do not, and uses this information to make routing decisions in advance. This prevents unnecessary CS retry attempts before they occur, eliminating wasted signaling overhead while preserving connectivity where needed.
2Productivity
If CSFB is phased out to transition to PS networks, then network resources are optimized for packet switching, but inconsistent tracking of CS support leads to network disturbances
Solution Approach 1:
The patent implements feedback by continuously tracking and updating information about CS support status across different network locations. The network server receives location information from the HSS and maintains an updated record of which locations support CS and which have deprecated it. This feedback mechanism ensures consistent routing decisions throughout the network transition, preventing disturbances while optimizing resource allocation for PS networks.
3Loss of energy
If location tracking is implemented to manage CSFB attempts, then unnecessary signaling is reduced, but network infrastructure complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a network server that acts as a mediator between the mobile device and the core network elements (HSS, MSC). This server consolidates the logic for determining CS support status and makes routing decisions based on location information. While this adds a network component, it centralizes the complexity in a manageable location rather than distributing it across multiple network elements, and the complexity is justified by the significant reduction in signaling overhead achieved.
Data Source
AI summary
Systems, methods, and devices that relate to staged discontinuation of the circuit-switched fallback are disclosed. In one example aspect, a method for wireless communication includes receiving, by a network server configured to manage subscriber data, a request from a telephony application server requesting a routing of a call or a message for a mobile subscriber and transmitting, by the network server to the telephony application server, a response indicating that the packet-switched network is not available for routing the call or the message. The response comprises a value that identifies the location of the mobile subscriber to enable the telephony application server to refrain from transmitting a subsequent request requesting the routing of the call or the message using the circuit-switched network.