Editing Network switching subsystem (section)

===Lawful interception functions===
{{main|Lawful interception}}
According to U.S. law, which has also been copied into many other countries, especially in Europe, all telecommunications equipment must provide facilities for monitoring the calls of selected users. There must be some level of support for this built into any of the different elements. The concept of ''lawful interception'' is also known, following the relevant U.S. law, as [[Communications Assistance for Law Enforcement Act|CALEA]].
Generally, lawful Interception implementation is similar to the implementation of conference call. While A and B are talking with each other, C can join the call and listen silently.