I am a long time telephone company COT (central office tech). I have some insight into our government's Homeland Security call "tapping" and I am getting more and more frustrated at people throughout the political spectrum who have stong opinions about it, yet they are uninformed.
The equipment used to "tap" phones resides in telephone central offices and within the last few years I have seen equipment labelled CALEA. I knew from the location of the equipment that it is associated with the SS7 network and was told that it was Homeland's spy gear. This information was already enough for me to know that phones are not being "tapped".
SS7, or Signalling System Seven, is strictly a signalling network. Thirty plus years ago, in the copper wire era, telephone signalling was carried on the same trunk (line) that the caller would be talking on. The caller would pick up the phone, get dial tone, and perhaps dial a long distance number, ie grandma. The local switch office would set up a talk path to the nearest toll (long distance) office and pass the dial pulses (not tones) on to the next toll office, etc, etc, until the talk path and dial pulses got to grandma's local telephone central office where, due to grandma being deaf and physically slow, the phone rings for thirty minutes before the caller gives up because grandma was actually at the doctor's office.
The talk path, perhaps from New York to California, was tied up for a very long time and there were zero billable minutes. With a very expensive line being tied up, this was no good. If instead, grandma had been talking on her phone, the caller would still have tied up the talk path while getting a busy signal from the California central office, again with no money for Ma Bell.
The situation is different today. Now when you dial grandma, the signal tones are converted to data that is sent out on the SS7 network. The SS7 network is similar to the ethernet and carries packets of data to addresses. Each local and toll office is on the SS7 network and each has a unique address.
Your request to ring grandma instantly goes to grandma's local telephone office which there starts to ring grandma's phone. Grandma's phone office also sends back a signal to your local office which puts ringing tone on your line so that you know granny's phone is ringing. No talk path is set up yet, all that is in play is the ringing circuit in granny's office and a ring tone circuit in yours.
When the phone is finally answered, SS7 signalling is exchanged and a talk path is nearly instantaneously set up. Nearly 100% of the talk path useage is now billable, with this scheme new facilities did not need to be added because existing facilities were better utilized. (this, with fiber and multiplexing, has driven long distance rates from a dollar plus per minute to nearly free in the last sixty years)
The Homeland's CALEA equipment is tapped on to the SS7 network, which carries signalling only, no voice or customer data of any kind. The information obtained is only of the who-called-who type and the Supreme Court has ruled that you should have no expectation that the fact that you made a call is secret (after all you know that records are kept for billing purposes).
Homeland has no way of knowing content from this information but can use it to develop leads and support requests for search warrants (ie taps). When someone says they are opposed to warrantless call tapping, let them know that this is not the case and explain that signals are being intercepted and not content. Absent some other information, the fact that you made a call doesn't mean anything.
In researching (the little I did) for writing this I found that CALEA stands for "Communications Assistance for Law Enforcement Act" and newly installed telephone switches (central offices) were required to be CALEA compliant by 01-01-1995. This ability predates Nine Eleven and Homeland itself by a great deal so it isn't new anyway. The central offices that I work in are older so they are now being CALEA retrofitted, post Nine Eleven. I did searches in this and other forums and found nothing on CALEA, SS7, or CCIS thus prompting me to write this tome, the free membership here being attractive. Information can be found on the web quite easily, searching for CALEA, SS7 (or "Signalling System 7"), and CCIS (common channel interface signalling, which still exists but predates SS7).
I hope this was informative- Bob
I thought that I had paragraphs. This was my first post so I don't know why the returns disappeared.