16 February 2017

STANAG-4538 "Circuit Mode" (a 3G-2G switching)

an interesting sample of a 3G-2G switching copied on 7780.0 KHz/USB: the handshake is performed with FLSU bursts (ie 3G-ALE) and user data are sent using MIL 188-110A serial (a 2G HF waveform), last FLSU bursts terminate the link (Fig. 1).

Fig. 1

In this scenario the traffic service is termed “Circuit Mode” in STANAG-4538 and  is used when an HF data continuous waveform (not a burst waveform) will be used to convey traffic after link establishment. The FLSU_Request specifies the traffic waveforms that will be used during circuit mode, for example MIL 188-110A (as in this recording), STANAG 4285, STANAG-4539 or other. Once circuit mode begins, any station can initiate transmissions using the specified traffic waveform. A CSMA/CA process is recommended to avoid collisions (Fig. 2)

Fig. 2

Same operational contest was copied on 11132.0 KHz/USB (Figs. 3a, 3b): these are more likely  test sessions that involves both the packet mode (the used datalink protocols are HDL+ and LDL over BW3-BW4 burst waveforms) and the circuit mode (the HF waveform is MIL 188-110A serial). These (test?) transmissions are probably from Algerian Military.

Fig. 3a
Fig. 3b

A STANAG-4538 circuit mode traffic was also copied by my friend Mike (ak mco) on 9003.0 KHz/USB (Fig. 4) who sent me his recording.  The sample consists of n-transmissions, each composed of a MIL 188-110A transfer running at 300bps, preceeded and terminated by BW5 bursts which control the link. More precisely, 188-110A frames transport Harris proprietary Citadel encrypted data, Fig. 5, so it's difficult to say what sits behind.

Fig. 4
Fig. 5

(9003.0 KHz)

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