CS to IMS Call Forwarding via SIP-URI Signaling
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Solution Overview
Problem
Current mobile networks lack the capability to forward calls from a circuit-switching domain to a packet-switching Internet Protocol Multimedia Subsystem domain, preventing mobile subscribers with devices registered in the IMS domain from being reached from the CS domain and limiting call forwarding options.
Innovation Solution
The method involves using an extended MAP signaling protocol to send a Session Initiation Protocol - Uniform Resource Identifier from the subscriber profile home server to the gateway mobile switching center, enabling the detection and forwarding of calls from the CS domain to the IMS domain, with minimal changes to the existing core network infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the network uses traditional circuit-switching domain only, then call forwarding capability is limited to CS domain, but subscribers with IMS-registered devices cannot be reached from CS domain
Solution Approach 1:
The patent introduces the HSS as an intermediary component that stores both CS and IMS domain routing information for subscribers. The HSS acts as a mediator between the GMSC and IMS domain, enabling the GMSC to obtain routing information for both domains and forward calls appropriately. This intermediary resolves the contradiction by bridging the gap between CS domain call forwarding capabilities and IMS domain reachability.
Solution Approach 2:
The patent extends the MAP signaling protocol to carry SIP-URI redirection parameters, making the signaling system universal across both CS and IMS domains. The GMSC is enhanced to handle both traditional CS domain forwarding and new IMS domain forwarding using the same infrastructure. This multi-functionality allows the network to support both CS-domain-only subscribers and IMS-registered subscribers through a unified call forwarding mechanism.
2Adaptability or versatility
If the network is extended to support CS to IMS domain forwarding, then subscriber reachability is improved, but network infrastructure complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-storing both CS domain and IMS domain routing information in the HSS before any call forwarding is needed. The HSS maintains subscriber profiles that include both traditional routing information and SIP-URI redirection parameters. This preliminary preparation eliminates the need for complex real-time conversions or additional signaling exchanges during call setup, thereby reducing infrastructure complexity while enabling cross-domain forwarding.
Solution Approach 2:
The patent changes the parameter structure of existing signaling messages by extending the MAP protocol to include SIP-URI redirection parameters. Instead of creating entirely new signaling paths or protocols, the invention modifies existing message parameters to carry additional routing information. This parameter extension approach allows CS to IMS domain forwarding without requiring fundamentally new infrastructure components, thus limiting the increase in network complexity.
3Ease of manufacture
If traditional MAP signaling protocol is used, then existing network compatibility is maintained, but SIP-URI redirection cannot be transmitted
Solution Approach 1:
The patent segments the routing information into two distinct parts: traditional routing information (handled by existing MAP protocol) and SIP-URI redirection parameters (added as extensions). This segmentation allows the network to process both types of information separately through the same signaling infrastructure. The MAP protocol continues to carry traditional routing information unchanged, while additional fields carry SIP-URI parameters, thus maintaining compatibility while preventing information loss.
Solution Approach 2:
The patent adds another dimension to the existing MAP signaling protocol by introducing SIP-URI redirection parameters as additional message fields. Rather than replacing or fundamentally changing the protocol structure, the invention extends the protocol into a new dimension where both traditional and IMS-specific routing information can coexist. This dimensional extension maintains backward compatibility with existing networks while enabling transmission of SIP-URI information that was previously impossible.
Data Source
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AI summary
The invention relates to a method and devices for a mobile network (10) for forwarding a call from a circuit-switched domain (24) to a packet-shifting Internet Protocol Multimedia Subsystem domain (40). An incoming call is detected by a gateway mobile exchange (28), which verifies the subscriber profile home server (48) for the called subscriber. The gateway mobile exchange (28) then requests information from the subscriber profile home server (48) for forwarding the called subscriber's call. The subscriber profile home server (48) then sends a Session Initial Protocol - Uniform Resource Identifier (105) as a forwarding parameter to the gateway mobile exchange (28).The gateway mobile switching center (28) determines whether a Session Initial Protocol - Uniform Resource Identifier (105) is present as a redirection parameter and forwards the call to the packet-switching Internet Protocol Multimedia Subsystem domain (40).