P-CSCF Namespace Precedence for IMS Priority Calls
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Solution Overview
Problem
Current IMS networks lack standardized solutions for maintaining uniform priority across network elements when multiple namespaces are present in SIP Resource-Priority headers, particularly in priority and emergency calls, and there is a need for defined values for DIAMETER Rx interface AVPs to ensure consistent namespace usage.
Innovation Solution
A configuration table is defined in the P-CSCF to establish precedence orders for namespaces, with the introduction of the Multiple Namespace Precedence Order (MNPO) in the SIP Resource-Priority header, ensuring that the originating and terminating P-CSCFs use the same namespace for priority handling by specifying a precedence order for namespaces and mapping AVPs accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple namespaces are present in the SIP Resource-Priority header, then the system can support multiple priority schemes, but it becomes unclear which namespace to use for determining call priority
Solution Approach 1:
The P-CSCF determines and selects a specific namespace from multiple available namespaces before processing the call priority determination. This preliminary selection action resolves the ambiguity by establishing a clear namespace choice in advance, allowing downstream network elements to consistently apply the selected namespace for priority handling.
Solution Approach 2:
The P-CSCF acts as an intermediary between the multiple namespaces and the call priority determination process. It receives the SIP request with multiple namespaces, selects the appropriate namespace based on configured precedence rules, and forwards the call with the selected namespace information to downstream elements, thereby mediating the namespace selection ambiguity.
2Adaptability or versatility
If the originating P-CSCF uses a different namespace than the terminating P-CSCF, then each can independently handle priority, but uniform priority treatment across the call path cannot be ensured
Solution Approach 1:
The patent applies local quality by configuring different precedence orders for originating and terminating P-CSCFs based on their specific roles. The originating P-CSCF uses a precedence order appropriate for call initiation, while the terminating P-CSCF uses a precedence order appropriate for call termination, allowing each to independently handle priority according to its local requirements while maintaining overall consistency.
Solution Approach 2:
The patent changes the namespace selection parameter dynamically based on the P-CSCF's role in the call path. By configuring different precedence orders (parameters) for originating and terminating P-CSCFs, the system allows each element to select namespaces appropriate to its function while ensuring that the selected namespaces are compatible for uniform priority treatment across the call path.
3Reliability
If standardized solutions are implemented for namespace precedence, then uniform priority handling is achieved, but network operator flexibility in defining custom precedence orders is reduced
Solution Approach 1:
The patent implements a universal solution by defining a standardized mechanism for namespace precedence that can be applied across all P-CSCFs and network elements. The configuration table approach provides a multi-functional framework that supports both standardized uniform handling and operator-defined custom precedence orders, making the system universally applicable while maintaining flexibility.
Solution Approach 2:
The patent makes the namespace precedence dynamic by allowing network operators to configure custom precedence orders in configuration tables. The P-CSCFs retrieve and apply these dynamically configured precedence orders rather than using fixed hard-coded rules, enabling the system to adapt to different operator requirements while maintaining standardized behavior within each operator's network.
Data Source
Figure 1
AI summary
A method of call handling when multiple namespaces are present for a call of a priority or emergency call type initiated by a subscriber of a wireless network includes: obtaining, by an originating Proxy Call Session Control Function (P-CSCF), a predetermined precedence order for the multiple namespaces; retrieving, by the originating P-CSCF, each namespace and associated priority from the subscriber's Registration Context; inserting, by the originating P-CSCF, a SIP Resource-Priority header for each namespace and associated priority; and inserting, by the originating P-CSCF, an additional SIP Resource-Priority header with an additional specified namespace (Multiple Namespace Precedence Order (MNPO)) and priority value identifying the predetermined precedence order for the multiple namespaces. The originating P-CSCF uses the namespace with the highest precedence order to select the appropriate values to fill in Reservation-Priority Attribute-Value Pair (AVP) and Multimedia-priority services (MPS) Identifier AVP in Rx interface signaling to a Policy and Charging Rules Function (PCRF).