VoLTE Roaming Emergency Call Support via S8 Home Routing
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Solution Overview
Problem
In the S8 Home Routing architecture for VoLTE roaming, emergency calls from visiting users cannot be properly established due to the lack of a Network-to-Network Interface (NNI) between the home and visited IMS, preventing the visited IMS from obtaining the Mobile Station International Subscriber Directory Number (MSISDN) of the visiting UE, which is necessary for callback purposes in case of call disconnection.
Innovation Solution
The visiting Mobility Management Entity (MME) obtains user profile data, including the MSISDN, from the Home Subscriber Server (HSS) and provides it to the location server, which then communicates this data to the Emergency Call Server (ECS) and Public Safety Access Point (PSAP), ensuring that callback information is available for re-establishing emergency calls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If S8 Home Routing architecture is used for VoLTE roaming, then service coverage is extended to visited networks, but emergency call functionality is lost due to lack of NNI interface
Solution Approach 1:
The patent introduces an intermediary mechanism where the visited MME acts as a mediator to obtain MSISDN from the home HSS and provide it to the visited IMS and location server. This intermediary approach bypasses the missing NNI interface between home and visited IMS, allowing emergency call information to be transmitted through the core network's existing interfaces (S6a between MME and HSS, and Slc between location server and visited IMS).
Solution Approach 2:
The patent segments the emergency call information transmission path into separate functional components: (1) MSISDN acquisition by visited MME from home HSS, (2) MSISDN storage in visited network's location server, and (3) MSISDN provision to visited IMS. This segmentation allows each component to operate independently using available interfaces, circumventing the need for direct NNI between home and visited IMS.
2Device complexity
If NNI interface between home and visited IMS is not provided, then network complexity is reduced, but MSISDN cannot be obtained for callback purposes
Solution Approach 1:
The patent makes the visited MME perform multiple functions: it not only handles mobility management but also acts as a query interface to the home HSS for obtaining subscriber information (MSISDN). This multi-functionality eliminates the need for a dedicated NNI interface between IMS entities, as the MME's existing S6a interface to HSS is reused for information retrieval.
Solution Approach 2:
The visited network autonomously obtains and stores the MSISDN information without requiring direct interaction with the home IMS. The visited MME queries the home HSS and stores the MSISDN locally in the visited network's location server, enabling the visited network to self-serve the emergency call information requirement without depending on home IMS capabilities or NNI interface.
Data Source
AI summary
A method, a device, and a non-transitory storage medium provide an emergency call support service in which a network device of a visited network obtains user profile data of a wireless device from a home network of the wireless device, and provides the user profile data to a location server of the visited network. The emergency call support service allows an emergency call, when initiated by a roaming subscriber of the wireless device via the visited network, to include the user profile data and be provided to a public safety access point.