Communications intelligence depends for its success on tactical
as well as strategic elements. When an intercept station has been
put in the right location, operates at the right time of the day,
points its antenna in the right direction, and tunes its radio to
the right frequencies, it is rewarded with a flood of traffic too
large to record, let alone analyze. The process of examining
intercepted traffic to determine what is to be retained and what is
not may be as "simple" as detecting which channels within a trunk
are active or as complex as recognizing the topic of a conversation.
Typical selection processes include active channel detection, called
and calling number identification, speaker identification, keyword
spotting (in either text or voice), fax recognition, and semantic
information processing.
The difficulty of locating and isolating just the right messages
is an intrinsic consequence of the volume of traffic in modern
communications. Communications intercept equipment must decide
in a faction of a second whether to record a message it has
detected or to permit the message to escape. Often it must make
the decision to record communications of which it has only one
part. If, for example, the two directions of a telephone call
are carried on separate facilities, an individual intercept
point may have access to only one side of the conversation.
Although the entire call may in fact be recorded, so that both
sides of the conversation will ultimately be available to an
analyst, it wil be recorded by two devices acting independently.
Should either fail to detect that the call is of interest, and
therefore fail to record it, the utility of the other component
will be vastly reduced. The problem of identifying traffic of
interest among all possible traffic is the problem of 'search'.
Custom Search
The 'sine qua non' of communications intelligence is acquisition of signals. Without communications in the form of radio waves, electrical currents in wires, written materials, or copied disks and tapes, there can be no work for cryptographic or intelligence analyst. The interception of communications presents both a strategic and a tactical aspect.
Strategically, it is crucial to learn as much as one can about an opponent's communications infrastructure. The first step is to come up with the most precise possible description of the target--what the military call the 'order of battle'. If the target is a country, it may have millions of residents who in turn make millions of phone calls every days. Most of these calls are not of interest; the people who make them do not work for the
government or in critical industries and say little of intelligence value.
Describing the target is one of the many areas where 'collateral intelligence-information from sources other than covert interception of communications plays a vital role. Most of the information about a country and its government can be learned from open sources, such as phone books, newspapers, histories, and government manuals. Some, however, will come from covert sources such as spies, and some will come from communications intelligence itself.
Strategically, it is crucial to learn as much as one can about an opponent's communications infrastructure. The first step is to come up with the most precise possible description of the target--what the military call the 'order of battle'. If the target is a country, it may have millions of residents who in turn make millions of phone calls every days. Most of these calls are not of interest; the people who make them do not work for the
government or in critical industries and say little of intelligence value.
Describing the target is one of the many areas where 'collateral intelligence-information from sources other than covert interception of communications plays a vital role. Most of the information about a country and its government can be learned from open sources, such as phone books, newspapers, histories, and government manuals. Some, however, will come from covert sources such as spies, and some will come from communications intelligence itself.
Once the targets have been precisely identified, it is necessary to discover how they communication with one another. Are their communications carried by high-frequency radio, by satellite, or by microwave? How accessible the communications are and how they can be acquired is a function of the means
chosen. High-frequency radio and satellite transmissions are the most accessible.
At the time of World War II, most radio communications and thus most of what was intercepted was HF. Such signals bounce back and fourth between the ionosphere and the ground and can travel thousands of miles. This property
makes intercontinental radio communication possible; at the same time, it makes it essentially impossible to keep HF signals out of the hands of opponents. Today a large fraction of radio communication is carried by satellite. Satellite downlinks typically have 'footprints' thousands of miles across that spread over more than one country. Terrestrial microwave
communications are significantly harder to intercept. They travel between towers a few miles or tens of miles apart. Intercept facilities on the ground must generally be located within a few tens of miles of the micro-wave path and often require facilities in the target country. In the 1970s
and the 1980s, there was a war of words between US and Soviet diplomats over Soviet microwave interception activities from a residence the Soviet maintained at Glen Cove, New York (Broad 1982).
As with the organization structure, a target's communication practices can often be derived from open sources. Since national and international organizations cooperate in allocating the radio spectrum, it is easier to identify the frequencies used for military, police, or air traffic control communications by consulting regulations and standards than by direct spectrum monitoring.
chosen. High-frequency radio and satellite transmissions are the most accessible.
At the time of World War II, most radio communications and thus most of what was intercepted was HF. Such signals bounce back and fourth between the ionosphere and the ground and can travel thousands of miles. This property
makes intercontinental radio communication possible; at the same time, it makes it essentially impossible to keep HF signals out of the hands of opponents. Today a large fraction of radio communication is carried by satellite. Satellite downlinks typically have 'footprints' thousands of miles across that spread over more than one country. Terrestrial microwave
communications are significantly harder to intercept. They travel between towers a few miles or tens of miles apart. Intercept facilities on the ground must generally be located within a few tens of miles of the micro-wave path and often require facilities in the target country. In the 1970s
and the 1980s, there was a war of words between US and Soviet diplomats over Soviet microwave interception activities from a residence the Soviet maintained at Glen Cove, New York (Broad 1982).
As with the organization structure, a target's communication practices can often be derived from open sources. Since national and international organizations cooperate in allocating the radio spectrum, it is easier to identify the frequencies used for military, police, or air traffic control communications by consulting regulations and standards than by direct spectrum monitoring.
