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One slot uses the equivalent bandwidth of 6.25 kHz. In comparison,
NXDN uses discrete 6.25 kHz channels, whilst TETRA uses a four-slot
TDMA in a 25 kHz channel.
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- Licence-free PMR446 use (2005)
Products for licence-free use inthe Euopean PMR446 band.
To be used without an existing infrastructure (repeaters) for low-power
commercial applications. The maximum RF output is 0.5 Watt.
- Conventional licenced use (2005)
Products for licenced conventional radio systems operating in the
PMR frequency bands between 66 and 960 MHz. Targeted at users who require
spectral efficiency, advanced voice features, integrated IP data services and
high power output.
- Trunking network (2012)
Trunking operation in the 66-960 MHz frequency bands. It supports voice
and short messaging handling similar to TETRA, and packet data service
in a variety of formats, including IPv4 and IPv6.
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TS 102 361-1 Air Interface Protocol TS 102 361-2 Voice and General services and facilities TS 102 361-3 Data protocol TS 102 361-4 Trunking protocol
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By default, DMR is not secure. Although eavesdropping is more complex
than with analogue radio systems (e.g. FM), there are
radio scanners on the market that
can readily decode a DMR audio stream. For enhanced security, some
manufacturers offer encryption as an additional feature [3]. The following
types of encryption are currently recognised:
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- Basic encryption
This is the simplest implementation that is basically a
voice scrambler that is intended for analogue mode operation. It uses a 10, 32 or 64 character KEY.
Note that voice scramblers are inherently insecure.
- Enhanced encryption
This type of encryption is endorsed by the DMR Association and uses
ARC4 with a 40-bit key. Although it offers better security than Basic Encryption
(see above), A 40-bit key is considered insufficient by today's standards (2023).
As a result, a brute-force attack is considered realistic.
Several attacks against RC4/ARC4 are known [4].
- Advanced encryption
This encryption type uses the
Advanced Encryption Standard (AES)
with a 128 or 256 bit key. AES was established in 2001 by the US
National Institute of Standards (NIST) and is considered very secure.
- Customised encryption
This type of encryption allows the use of a proprietary encryption
algorithm by installing a customised SIM or SD card in the radio.
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© Crypto Museum. Created: Thursday 02 November 2023. Last changed: Thursday, 16 November 2023 - 08:02 CET.
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