SIP Message Call Continuity in IMS Networks
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Solution Overview
Problem
Current call continuity management in networks involving circuit-switched and IP multimedia subsystem (IMS) networks faces challenges due to limitations in E.164 number length and reliance on Caller ID information, which can result in lost digits during routing and incorrect call leg establishment.
Innovation Solution
The use of a Session Initiation Protocol (SIP) Invite message with a URI in the Request-URI field to dynamically allocate a routable number, such as an IP multimedia routing number (IMRN) or Voice Call Continuity (VCC) Domain Transfer Number (VDN), for call continuity, ensuring seamless handover between domains by providing a unique identifier and alternative domain information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If call reference identity digits are appended to the E.164 number to generate IMRN, then call routing capability is improved, but the number length exceeds the 15-digit limitation causing digit loss during routing
Solution Approach 1:
The patent segments the call reference identity from the E.164 number by using separate SIP message fields (Request-URI and P-Asserted-Identity headers) instead of concatenating them into a single long number. This allows the routing information to be preserved without exceeding the 15-digit E.164 limitation, thereby resolving the contradiction between call routing capability and number length constraints.
2Device complexity
If Caller ID information is relied upon for VCC application, then call identification is simplified, but information is lost in the international ISDN infrastructure using ISUP signaling
Solution Approach 1:
The patent introduces SIP messaging as an intermediary protocol between the UE and the VCC application, replacing the direct reliance on ISUP signaling for Caller ID transmission. The SIP protocol preserves call identification information through its header fields (Request-URI, P-Asserted-Identity) without the limitations of ISUP, thereby preventing information loss while maintaining simplified call identification through standardized fields.
3Adaptability or versatility
If multiple registrations of a common Public Identity from different UE devices are supported, then network flexibility is improved, but establishing correct call legs becomes complex and error-prone
Solution Approach 1:
The patent implements a feedback mechanism where the VCC application receives SIP messages containing unique identifiers (such as device-specific URIs or correlation IDs) that allow it to track and distinguish between multiple registrations of the same Public Identity. The system uses this feedback information to automatically establish correct call legs by matching the incoming SIP message identifiers with the appropriate registered device, thereby reducing call leg establishment complexity while maintaining network flexibility.
Data Source
AI summary
In one embodiment, a scheme is disclosed for managing call continuity in a network environment including a circuit-switched (CS) network and an IP multimedia subsystem (IMS) network wherein a SIP Invite message having a Domain Transfer-URI contained in the Request-URI that is operable to trigger a return of a routable number is utilized. Responsive to the SIP Invite message from a UE device, a network node provides a SIP response message (e.g., SIP 380 (Alternative Service) Response) which includes one or more radio access technologies and an alternative domain available to the UE device for continuing a call from one domain to another domain.