At present, foreign legal interception technologies mainly have two types: active (active) and passive (passive).
Active lawful interception
Active lawful interception techniques are typically implemented by devices and software built into the network of communication service providers, including two parts that are installed in traditional or software-based switches, legal listening modules and mediation devices in routers. In the active lawful interception technology, after receiving the lawful interception instruction, the communication service provider will let the professional activate the intermediary device to monitor the communication of the specific target. The monitored communication is then transmitted to the mediation device, which mediates and sends it to the law enforcement agency according to a certain protocol.
Passive lawful interception
Passive lawful interception techniques are typically implemented by probes. The probes are independent of the communication service provider network and are typically installed at the edge of the network rather than inside the network. After the communication service provider receives the lawful interception command, it activates the probe to monitor the communication of the specific target. The probes are primarily for IP communications and can also target traditional circuit switched domains. The probe can be searched for the phone number, IP address, URL, etc. mentioned in the lawful interception command, or can use the deep packet inspection (DPI) technology to "pick out" the signaling protocol such as SIP, and capture or map the communication metadata. And communication content.
A brief comparison of two types of lawful interception techniques
Active lawful interception technology and passive lawful interception technology have their own advantages. For example, in terms of cost, the former involves multiple types of equipment and huge software and hardware investments, and the cost is relatively high, while the latter is relatively low in cost; In other words, the former can easily handle the surge in network speed, while the latter is relatively less scalable.
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