Lawful Interception Tagging in Packet-Switched Call Forwarding
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Solution Overview
Problem
In packet-oriented telecommunications networks, lawful interception of call forwarding is challenging as the content of forwarded connections cannot be monitored, as the subscriber ID of the call forwarding destination is not always recognized for monitoring purposes.
Innovation Solution
A method where the first switching function responsible for the called subscriber with call forwarding is informed of monitoring, and it signals call forwarding to a second switching function, which then monitors the called subscriber based on specified parameters, allowing the agency to listen to the data transmission from the call forwarding destination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If call forwarding is implemented in a packet-oriented telecommunications network, then the subscriber can forward calls to another number, but the lawful interception of the forwarded connection content cannot be performed
Solution Approach 1:
The monitoring indication is inserted into the signaling message before the call forwarding is executed. This preliminary action ensures that subsequent switching functions can recognize the monitoring requirement and forward the connection content to the monitoring entity, resolving the issue where call forwarding previously prevented lawful interception
Solution Approach 2:
A monitoring indication serves as an intermediary element in the signaling message, carrying the monitoring requirement information through the network from the first switching function through intermediate switching functions to the final destination, enabling lawful interception without disrupting call forwarding functionality
2Ease of operation
If the subscriber ID of the call forwarding destination is not recognized, then call forwarding can be established, but the monitoring agency cannot identify the connection for interception
Solution Approach 1:
The monitoring indication acts as an intermediary carrier that transports the monitoring requirement information through the signaling message, bypassing the need for intermediate switching functions to recognize or store the subscriber ID. This ensures the monitoring information is preserved throughout the call forwarding chain
Solution Approach 2:
The signaling message with the inserted monitoring indication provides feedback to intermediate and final switching functions, enabling them to recognize that the connection should be monitored and to forward the connection content accordingly, even when the destination subscriber ID is not recognized
Data Source
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AI summary
The invention relates to a method for lawful interception in the case of call forwarding (AW_TlnB) in a packet-oriented telecommunications network (TK1, TK2, TK3), in which switching functions (S-CSCF1, . . . , P-CSCF3) are made available by servers. The additional aim in this telecommunications network (TK1) is to monitor connections of a subscriber (Tln B) with call forwarding (AW_TlnB) by means of lawful interception. In this case, monitoring (ÜW_TlnB) of the connections of the subscriber (Tln B) is notified to a first switching function (S-CSCF1) which is responsible for a called subscriber (Tln B) with call forwarding (AW_TlnB). The first switching function (S-CSCF1) then writes (23) a tag for said subscriber (Tln B) to a predetermined parameter of a switching protocol. Only then is signalling of call forwarding (AW-TlnB) carried out to a second switching function (S-CSCF2) which is responsible for a calling subscriber (Tln A) and the connection is then forwarded to a third switching function (S-CSCF3). In this case, this third switching function (S-CSCF3) then identifies and initiates the monitoring (ÜW_TlnB) of the called subscriber (Tln B) on the basis of the predetermined parameter of the switching protocol. The major advantage of the method according to the invention is that it is still possible for a department or authority who is empowered to carry out monitoring to monitor (ÜW_TlnB) the contents of connections in a packet-oriented telecommunications network (TK1) even in the case of call forwarding (AW_TlnB).