SBC Attended Call Transfer With Target Session Reuse
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Solution Overview
Problem
Existing SIP call transfer methods fail when session load balancing is implemented across multiple SBCs, as the SBCs involved in the original and target sessions are different, preventing the reuse of media sessions and leading to failed call transfers.
Innovation Solution
A method and system for optimized attended inter-SBC call transfer that involves establishing media sessions between transferor, transferee, and transfer target using a first and second SBC, with signaling to reuse the target session, even when sessions are distributed across different SBCs, by using custom headers and Re-INVITE messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If session load balancing is implemented across multiple SBCs, then network scalability and call distribution are improved, but call transfer reliability deteriorates because different SBCs cannot share media session information
Solution Approach 1:
The patent introduces a session information storage mechanism (such as a database or shared memory structure) that acts as an intermediary between multiple SBCs. When an SBC establishes a media session, it stores the session information in this shared storage. During call transfer, the receiving SBC can retrieve the necessary session information from this intermediary storage, enabling successful transfers even when calls are distributed across different SBCs through load balancing.
2Productivity
If the Re-INVITE procedure is used to reuse media sessions, then call transfer optimization is improved, but compatibility deteriorates when SBCs are distributed across multiple nodes with session load balancing
Solution Approach 1:
The patent performs preliminary actions by storing complete media session information (including session identifiers, endpoint details, and media parameters) in a shared storage structure before the call transfer occurs. This preliminary storage of session data enables the receiving SBC to quickly retrieve and reuse the session without needing to establish a new media path, thus maintaining the efficiency benefits of Re-INVITE while enabling compatibility across distributed SBCs.
3Loss of time
If blind call transfer is used, then transfer speed is improved, but call quality control deteriorates compared to attended call transfer with session reuse
Solution Approach 1:
The system enables self-service by automatically retrieving and reusing existing media session information from the shared storage during attended call transfer. This automation eliminates the need for manual session establishment while maintaining the quality control benefits of attended transfer, as the system autonomously matches and reuses compatible sessions based on stored information.
Data Source
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AI summary
A first SBC establishes a first media session between a transferor and a transferee. A second SBC establishes a second media session between the transferor and a transfer target. The first SBC receives a REFER message initiated by the transferor and determines that a dialog ID in the REFER message does not correspond to a media session currently being handled by the first SBC. The first SBC sends a SIP INVITE message to a plurality of SBCs, including the second SBC, that are in a load sharing group with the first SBC. The SIP INVITE message includes the dialog ID associated with the second media session, which triggers the second SBC to re-use the second media session to establish a media session between the transferee and the transfer target.