IMS Lawful Interception via MRF SIP Session
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Solution Overview
Problem
Current methods for lawful interception of multimedia services in telecommunication systems face challenges in correlating Interception Related Information (IRI) and Content of Communication (CC) without post-processing, especially in roaming scenarios and across different access networks, leading to increased costs and complexity for operators and Law Enforcement Agencies.
Innovation Solution
Activating interception of Content of Communication in the service domain by establishing a new SIP session between IMS nodes and the Law Enforcement Monitoring Facility (LEMF), allowing for direct transportation of media flow and correlation of IRI and CC without post-processing, using a generic IMS-based Lawful Interception (LI) reference model that operates independently of core and access networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Content of Communication is intercepted in the GSN according to 3GPP standards, then interception of bearer streams is achieved, but correlation between IRI and CC requires complex post-processing and is not fully specified
Solution Approach 1:
The patent applies preliminary action by establishing a SIP session between the MRF and LEMF before content interception occurs. The MRF is pre-configured with the target subscriber's identity and is ready to intercept and forward content immediately when the media flow passes through it, eliminating the need for complex post-processing correlation activities.
Solution Approach 2:
The MRF acts as an intermediary between the GSN and LEMF. It receives the media flow from the GSN, intercepts the content, and forwards it to the LEMF through an established SIP session. This intermediary simplifies the correlation process by centralizing the interception and forwarding function in a single entity that has access to both the media flow and the target subscriber's identity.
2Adaptability or versatility
If a generic LI solution is implemented in the service domain independent of access network, then access independence is achieved, but existing standards require separate LI activation in multiple domains
Solution Approach 1:
The MRF is designed as a universal entity that can intercept content from any access network (UMTS, GSM, fixed broadband, etc.) through a single SIP-based interface. By establishing a SIP session between the MRF and LEMF, the system achieves access independence while consolidating the LI function in the service domain, eliminating the need for separate LI activations in different access networks.
3Ease of operation
If media session passes through service domain gateway, then monitoring can be implemented by assigning extra port, but this requires the media session to pass through service domain which may not always be the case
Solution Approach 1:
The MRF serves as an intermediary that the CSCF can invoke to intercept content. When the CSCF detects a session involving a monitored subscriber, it sends a SIP message to the MRF, which then establishes a SIP session with the LEMF and intercepts the content. This approach maintains session routing flexibility while enabling easy monitoring implementation through the standardized SIP interface.
Data Source
AI summary
A method in a telecommunication system for monitoring a communication by a Law Enforcement Monitoring Facility (LEMF). The LEMF sends a request for monitoring of a first party to a Call Session Control Function (CSCF) in a service domain of the telecommunication system. When the CSCF detects a SIP session event due to a setup of a media-flow connection between the monitored party and a second party, the CSCF sends Interception Related Information (IRI) toward the LEMF, and sends a resource setup message to a Multimedia Resource Function (MRF), also in the service domain. A Gateway GPRS Support Node (GGSN) routes the Communication Content (CC) to the MRF. The MRF copies the CC and routes one copy back to the GGSN and routes the other copy to the LEMF via a Delivery Function utilizing a SIP session with the LEMF.