Wire-tapping in a packetized world

Among the dozen or so external links on the to-do list for launching carrier-grade telephone service is a nine-year-old law, known as the Communications Assistance for Law Enforcement Act, or CALEA.

In general, CALEA is to modern, digital telephony, what wiretapping is to traditional analog telephony. It usually enters the life of the cable technologist on a piece of paper with the words "court order" written on it. The court order is in the clutches of a uniformed police officer, who is standing in the lobby, and who needs immediate access to the call records of a suspected criminal. In some cases, the order also requires a way to anonymously duplicate calls made by, or received from, that suspect.

The reasons for CALEA are palpable: The bottomless appetite among people to talk to each other isn't confined to the blameless. Bad guys talk to each other, too. Add in the flourish of new communication methods, and the woes of the law enforcement community intensify.

The available methods for the bad guys to talk to each other are plentiful– and increasing. Since court-ordered wiretapping began, in 1970, cellular and satellite signal paths emerged. So did call digitization, packetization and the use of the Internet as a signal path.

These days, a call from one place to another can move over any of four networks beyond the traditional Public Switched Telephone Network (PSTN). As a direct result, electronic surveillance can be a wild goose chase for police and FBI officers.

In practice, drugs are the catalyst for most telecommunication intercepts. Of 1,491 court orders issued to authorize electronic surveillance in 2001, 78 percent (1,167) targeted narcotics offenders, according to the Administrative Office of the United States Courts. A far second: Gambling offenses (82).

And, of those nearly 1,500 intercepts, most were invoked on cellular telephone users. Of those cable providers who offer residential telephone service, all say that they're ready for CALEA. Some, like Cox Communications, have assisted law enforcement officials with their electronic surveillance needs from time to time–but they say that the number of wiretaps requested remains pretty small. CALEA, they say, is the kind of thing that needs an action plan more than it needs constant attention–like fire drills.


What usually matters most to police and FBI officials, when it comes to electronic surveillance, is immediacy. When the uniformed police officer shows up in the lobby with the court order, he or she doesn't want to hear that it'll take three or so days to get the CALEA gear up, any more than the firefighter wants to hear that it'll take three days to get a bucket of water. Throughout the law itself, CALEA makes frequent use of the word "expeditiously."

And, CALEA cares little about underlying technologies. Law enforcement officials need two things: Call details, and call content. Call details are everything a phone can do–dial numbers, receive dialed numbers, forward calls, initiate or participate in three-way calls, and any of the rest of the SS7 features. Call content, in the analog world, is a wiretap. In digital telephony, call content means setting up a duplicate packet stream, which can be routed to multiple police or FBI officers.

Lastly, CALEA requires that law enforcement officers get what they need, without tipping off the suspect. Just like in the movies, when a click on the line scared off a phone conversation of nefarious intent, today's digital, packet networks can't introduce any latencies or problems that would scare off today's high-tech criminal.

The FBI, and behind it, the U.S. Attorney General, shepherds CALEA implementations. In most cases, the FBI provides CALEA software modules; when the law was introduced, $500 million was set aside to reimburse both carriers and switch manufacturers for CALEA-related expenses. (Don't get too excited. The law is nine years old; most of the CALEA disbursements have already been made.)

In its documentation about CALEA, the FBI openly favors "flexible deployment," described as "the deployment of CALEA-compliant solutions in accordance with normal generic upgrade cycles–where such deployment will not delay implementation of CALEA solutions in areas of high priority to law enforcement officials." In other words, do it when you launch phone, but don't make them wait.

New providers of residential phone service, such as cable operators, can also file a "Safe Harbor" document with the FCC, which indicates the methods by which they plan to implement CALEA. According to Section 107(a)(2) of CALEA, "a telecommunications carrier shall be found to be in compliance … if the carrier is in compliance with publicly available technical requirements or standards adopted by an industry association or standard-setting organization, or by the FCC."

To that end, both PacketCable, and ANSI/SCTE Standard 24-13, describe a functional representation of how CALEA can be implemented in cable phone environments. Traditional telcos use a standard, developed by subcommittee TR-45.2 of the Telecommunications Industry Association, known as J-STD-025. It specifies the necessary interfaces for delivering intercepted communications and call-identifying information to law enforcement agencies.


In the old days of analog telephone, two devices–the "pen register" and the "trap and trace" device–were used to help police in surveillance. Both devices are still widely used in surveillance discussions.

The term "pen register" dates back to the days of telegraphs, and describes a machine that uses ink and ticker tape to record and display telegraph pulses. Today, the "pen register" essentially references the ability to interpret outgoing information.

These days, new techniques are used to conduct electronic surveillance. Predictably, implementing CALEA differs, depending on whether a cable phone provider is using circuit switched/constant bit rate or packetized, IP-based gear.

In a circuit-switched scenario, a specifically-entrusted cable system employee provisions the switch for surveillance on a particular target. "Specifically-entrusted" usually means the person who handles security and piracy protection, or, in the case of CALEA, the person who can work quickly, intelligently, and quietly.

That person provisions the Class-5 switch so that relevant data can be diverted to an outgoing port, for collection by the FBI. Capturing call content is accomplished through a conference bridge, where one leg of the call is anonymously linked to the law.

Gathering call detail and content in a packet-based, IP environment isn't quite as straightforward. A voice call made over the public Internet uses the methods of the Internet, which break a bunch of packets into clumps, and send them over varying routes to their destination. The route itself can change from one call to the next.

The industry's PacketCable specifications include methods for dealing with CALEA. As the figure on page 10 shows, PacketCable breaks CALEA-oriented activities into functional requirements, which can be variously interpreted by suppliers. Still, though, because PacketCable essentially duplicates the PSTN in software, implementing CALEA is tricky.

One cable provider active with VoIP cites call forwarding as the trickiest task for CALEA. Consider the intercept target, active on a cable VoIP system, who forwards all incoming calls to a cell phone. In the parlance of PacketCable, it is not enough to depend on the CMTS (cable modem termination system) to capture call content.

In that scenario, the call comes in from the PSTN, to a media gateway. A call management server, provisioned for CALEA, recognizes the call as an intercept target. But, since the suspect is forwarding all calls, usually to a cell phone, the call may not ever leave the gateway. In short, relying only on a three-way bridge, or a CMTS capture, may not work–the media gateway also needs to be involved.

All vendors of VoIP equipment for cable are aware of CALEA, and offer modules or standalone servers to address the need for electronic surveillance. But, because VoIP in cable is still relatively new, it's fair to say that its CALEA efforts have yet to settle into a pattern.

Some suppliers, for example, combine CALEA directly into a softswitch. Others isolate CALEA into a separate server. PacketCable allows for integrated or standalone handling.


Cable operators getting ready for phone, whether circuit-switched or VoIP, are aware of CALEA, and are setting up methods to comply. Mostly, notes one cable MSO technologist, getting ready for CALEA means figuring out different possible scenarios, especially given the many features and routes offered by broadband, IP communication networks. Call flows can get pretty complicated, pretty fast.

But, despite the complexity, electronic surveillance appears to work. The 1,491 court-ordered wiretaps in 2001 produced 3,683 arrests, and 732 convictions–proof enough that electronic surveillance is a valuable tool in catching the bad guys.