Editing Signals intelligence (section)

===Signaling channel interception===
A given digital communications link can carry thousands or millions of voice communications, especially in developed countries. Without addressing the legality of such actions, the problem of identifying which channel contains which conversation becomes much simpler when the first thing intercepted is the ''signaling channel'' that carries information to set up telephone calls. In civilian and many military use, this channel will carry messages in [[Signaling System 7]] protocols.

Retrospective analysis of telephone calls can be made from [[Call detail record]] (CDR) used for billing the calls.