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Telecom carriers are required to provide a means to collect call data and call content (voice streams) from their customers in response to lawful authorization. The core of this ability is provided by an Intercept Server (IS) at the carrier's premises that formats call content and data according to various national standards. The IS is provisioned with specific targets, typically, subscriber phone numbers. When the carrier equipment detects the start of a call, it sends messages to the IS at various stages of the call. It can tap into the voice streams and sends copies of them to an IP address designated by the IS. The IS then forwards call data and call content on to law enforcement Delivery Function (DF) devices at the LEA premises, which filters as appropriate as per outstanding warrants.

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