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(S//SI) Click ... Click ... Click ... What's the Number?
FROM: Adolf Cusmariu
Technical Director, Operational Technologies (S202B11)
Run Date: 09/21/2006
(S//SI) Attention, collectors and SIGDEV analysts: a new analog-dialing extraction capability will
soon be available for your use via BABBLEQUEST.
(S//SI) What if SIGINT collects an acoustical signature from the old analog rotary telephone
system, full of simple clicks as the mechanical dial opens and closes the circuit on its way
around? Is there any way of determining what number was dialed? The MENA target office
covering the Levant (S2E33) had just such a problem when they came across intercepts from
what appeared to be an internal communications link.
(S//SI) Background: Each Number Has a Unique Frequency
(S//SI) Dialed Number Recognition (DNR) in our modern digital age has become a problem in
frequency (or spectral) estimation; each dialed digit, regardless of standard, is uniquely
represented by a frequency doublet. For example, in the DTMF system used in the US, the digit
"5" is represented by the doublet (770Hz, 1,336Hz). Estimate the doublet sequence and you get
the dialed number. The somewhat older pulsed dialing systems again yield to spectral DNR
because the pulse stream is typically carried by line-supervision tones used by phone companies
to charge for line usage; once an appropriate pulse counter is devised the dialed number can be
estimated. Of course, dialed number databases provide critical intelligence on all targets,
helping to define social networks, patterns of communication, call origination and destination,
and tasking guidance.
(S//SI) The image below shows an example of MENA's analog dialing intercept, in the spectral
and acoustical domains.
(S//SI) The spectrogram in the top tier shows the sequence: a dial tone, then a 3-digit analog
number, ring-back, and finally voice indicating the call got through. The click sequence produced
by the dial rotation is worth examining in more detail:
(U) The New Capability
(S//SI) DNR in this case amounts to careful retention of very short pulses, as a given dialed digit
corresponds to exactly two such pulses. S202B11 (HLT Operational Technologies) has
developed an algorithm to break out the numbers. Full details about this DNR algorithm
may be found at
MENA DNR webpage
...which also contains algorithm code in MATLAB.
(S//SI) About BABBLEQUEST
(S//SI) For nearly a decade BABBLEQUEST has been a workhorse architecture processing
millions of intercepts each month, to provide DNR of several types, Facsimile Activity Detection,
and extensive speech technical exploitation using many and varied state-of-the-art algorithms of
both internal and external origin.
(U) POCs:
(U//FOUO) If you have special needs regarding these services, please contact one of the below:
Adolf Cusmariu (Technical Director, HLT Operational Technologies), at
;
(Speech Services Project Manager), at
;
(BABBLEQUEST Project Manager), at
; or
Customer Representative), at
.
"(U//FOUO) SIDtoday articles may not be republished or reposted outside NSANet
without the consent of S0121 (DL sid_comms)."
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DERIVED FROM: NSA/CSSM 1-52, DATED 08 JAN 2007 DECLASSIFY ON: 20320108