SIP Contact Header Routing for Circuit Switched IMS Calls
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Solution Overview
Problem
Current communication systems face challenges in seamlessly routing calls between packet-switched and circuit-switched networks, particularly in identifying and setting up bearers over the circuit-switched domain using Session Initiation Protocol (SIP) messages.
Innovation Solution
The method involves sending a SIP INVITE message with a URI that identifies the need for a bearer setup over the circuit-switched domain, determining a digit string associated with the URI, and using a SIP informational response message with a contact header to carry the dynamic routing number, allowing the UE to set up the call using an E.164 number or Private Number Plan (PNP) number.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a SIP INVITE message is sent with a URI to initiate a call to a circuit-switched subscriber, then the call can be routed to the correct destination, but the system needs a mechanism to dynamically allocate and transport circuit-switched routing numbers (E.164/PNP) back to the user equipment
Solution Approach 1:
The system pre-allocates circuit-switched routing numbers (E.164/PNP) in the IMS network before the call is initiated. When a SIP INVITE message is received, the system has already prepared the corresponding routing number in advance, eliminating the need for complex real-time allocation and reducing routing number management complexity while ensuring accurate call routing.
Solution Approach 2:
The SIP 183 Session Progress message acts as an intermediary carrier to transport the allocated circuit-switched routing number from the IMS network back to the user equipment. This intermediary message format provides a standardized mechanism for bidirectional information exchange between the network and UE, simplifying the routing number management process while maintaining reliable call routing.
2Adaptability or versatility
If the system maintains a pool of E.164 numbers as IMRNs for mapping to called party URIs, then call routing to circuit-switched subscribers is enabled, but dynamic allocation and tracking of these numbers adds system complexity
Solution Approach 1:
The system implements automatic self-service mechanisms for the E.164 number pool, where the network node autonomously allocates, tracks, and manages the availability of routing numbers without requiring manual intervention. The system automatically matches available E.164 numbers with incoming SIP INVITE requests based on the called party URI, providing flexible call routing while minimizing management complexity through automated processes.
Solution Approach 2:
The system employs feedback mechanisms where the SIP 183 message carries information about the allocated routing number back to the user equipment, and subsequent call setup messages include feedback about the routing number usage. This feedback loop enables the system to dynamically adjust and optimize the E.164 number pool allocation, maintaining high adaptability for various call routing scenarios while simplifying management through automated feedback-driven adjustments.
3Productivity
If SIP informational response messages are used to carry dynamic routing numbers in contact headers, then efficient call setup is achieved, but the system must parse and process SIP headers to extract routing information
Solution Approach 1:
The SIP 183 Session Progress message is designed to serve multiple functions simultaneously: it confirms call setup progress, transports the allocated circuit-switched routing number (E.164/PNP) in the contact header, and provides a standardized interface for further call setup. This multi-functionality enables efficient call setup by consolidating multiple information exchanges into a single message, while the standardized SIP header format simplifies parsing and processing compared to custom protocols.
Data Source
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AI summary
A method of call routing is provided. The method comprises receiving a session initiation protocol (SIP) INVITE message that contains a uniform resource identifier (URI) of a called party and that identifies that a bearer for a call to the called party is to be set-up at least in part over the circuit switching domain. The method also comprises determining a digit string associated with the URI. The method also comprises sending a SIP informational response message having a contact header that contains information based on the digit string.