R&S M3SR 4100 Series, Operating Manual

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M3SR Series 4100 Automatic Link Establishment 3
rd
Generation (ALE-3G)
4.70 Operating Manual 6175.4760.02 – 01
4.4.1.8 Automatic Link Maintenance (ALM)
The ALE-3G Automatic Link Maintenance (ALM) function is responsible for monitoring the
quality of an established link, and for initiating corrective action when necessary.
In the R&S M3TR, Late Link Entry LLE is mutually integrated into the ALM functionality. The
LLE allows unlinked stations to enter existing links at a later phase. The LLE feature is only
available for HF modem and voice transmission.
After a Link Setup the ALM function will calculate the channel quality of the link and compare
it against a configured ALM threshold. If the channel quality is below the configured thresh-
old, a relink operation will be issued on a different channel to find a channel with a quality
above the threshold. If the channel quality of all channels are below the threshold, the ALM
function will relink on the best available channel in the scan group. During an active 3G link
the ALM function can monitor the channel quality based on SNR information of HF-Modem
receptions and trigger an automatic ALM relink if necessary.
For successful operation it is important that the slave doesn’t send any data for 1.5 seconds
after the masters starts with relink operation.
4.4.1.9 Communication Security (COMSEC)
If COMSEC is activated for an ALE-3G network, all communication is secured and unse-
cured communication will be avoided. All data transmitted with xDL will be encrypted. More-
over, two additional secure voice transmission modes are available: Last Ditch Voice and
Secure Digital Voice.
4.4.1.10 Last Ditch Voice (LDV)
With the Last Ditch Voice mode the operator is able to transmit a 60 s voice message via the
ARQ Protocols. This guarantees that the voice message reaches the recipient under almost
all circumstances, but not in real-time like a conventional voice call. Each station can store
one LDV message. A new received LDV message is indicated to the user at the MMI and via
an audio indication. The user has also the ability to play back the received LDV message
until a new LDV message is received.
4.4.1.11 Secure Digital Voice (SDV)
In mode ALE-3G the feature Secure Digital Voice can be used for encrypted voice commu-
nication under highly degraded shortwave channel conditions. For details see
sect. 4.7 Secure Digital Voice. Additionally to the security features described at Secure Dig-
ital Voice operation mode, Secure Digital Voice with ALE-3G provides a replay protection.
The replay protection avoids the decryption of old waveform signals.