Passive Monitoring of Telephone Lines
The possibility to passively monitor a huge number of telephone lines has become more and more important as it provides a full history of telephone data for a predefined timeframe (e.g. last six month). In this case, all communications are passively intercepted without active intervention by the communications network. This is an ideal method to collect information for intelligence agencies, and also to identify targets for use in a Lawful Interception (LI) based system. The number of intercepts in the case of passive Interception is much larger than in the case of LI. The aim of passive surveillance is to intercept all traffic (voice, faxes, data-sessions, email, internet sessions, etc) on: International gateways: This point provides all land-based communication across the borders of a country. The same technology can equally be used to intercept within the country or in a specific area. Mobile Networks (PLMN) From a passive perspective, this is the interception between PSTN and PLMN as well as within PLMN systems themselves on the level of the communications between the MSC and BSC. The demands of passive surveillance are:
- Large volumes of traffic need to be intercepted (e.g. 1000s of E1s)
- Different types of interfaces are required (E1/T1; STM1/STM4, etc.)
- Large storage capacity (Petabytes) and vast processing & filtering are required
- Changes in protocols or telecommunication environments continue
