The RC12 integrates an embedded STANAG 5066 ARQ stack, which includes STANAG 5066 embedded required by most users. Fully compliant with all mandatory requirements of STANAG 5066 Edition 4, the RC12 is designed to operate in conjunction with the RM12 Wideband SDM & ALE, creating a secure HF data communications solution when paired with an external cryptographic unit.

The RM12 is a rack-mounted unit with a software option for embedded wideband HF data modem waveforms that adhere to MIL-STD-188-110D and STANAG 5069 (Block 4), as well as wideband ALE (WALE) controller functions defined in MIL-STD-188-141D. It delivers provides raw over-the-air (OTA) data speeds of up to 240,000 bps for both surface wave and beyond-line-of-sight (BLOS) HF communication links.

The RC12 supports direct connectivity to external email servers and military message handling systems (MMHS), offering robust functionality for military communications. A key feature is its IP client, enabling efficient IP-over-HF applications.

The RC12 platform features embedded software for the Mobile Ad-Hoc Relay Line-of-Sight Networking (MARLIN) protocol, as defined by the NATO ACompP-4691/STANAG 4691 Annex A (Version 1) specification. Designed to complement the RM12 Wideband SDM & ALE, the RC12 provides a secure, IP-based data communication solution over HF extended line-of-sight (ELOS) radio links when paired with an external cryptographic unit.

In environments where SATCOM is unavailable due to equipment limitations, cost considerations or operations in satellite-denied areas, MARLIN’s use of HF ELOS becomes a practical and cost-effective alternative.

The MARLIN protocol leverages the widespread availability of legacy tactical voice radios capable of operating in HF bands, enabling these radios to transport IP data utilising STANAG 4691. MARLIN radio circuit networks enhance interoperability among allied forces by facilitating the exchange of tactical data across various platforms, including sea-surface, sub-surface, airborne (mobile), and land (fixed) platforms.

This capability is particularly valuable for task force-based ship-to-ship command and control (C2) operations over HF ELOS, where direct UHF line-of-sight (LOS) or multi-hop relay communication is not feasible due to distance, MARLIN ensures reliable connectivity.

The RC12 is designed for installation on naval and maritime below-deck platforms, including surface, sub-surface and airborne systems, due to its compact form factor and robust environmental specifications, especially its wide operating temperature range. It is also equipped to operate in high-power NATO shore stations, supporting broadcast and ship-shore (BRASS) configurations, including BRASS Initial Core Capability (BICC) and BRASS IP Enhanced System (BRIPES), BRASS Enhancements 1 Technical Architecture (BRE1TA) and BRASS Enhancements 2 Technical Architecture (BRE2TA). Additionally, the RC12 can operate in either fixed-frequency or multi-frequency networks and provides interoperability with other STANAG 5066-compliant products such as the RC66, BFEM66, 4KMA and RIFAN.

The RC12’s STANAG 5066 ARQ protocol stack supports multiple operational modes, including automatic repeat request (ARQ), non-ARQ (broadcast) and operation under conditions of radio silence. With its support for the Subnetwork Interface Sublayer (SIS) protocol, the RC12 enables multiple applications to send and receive data simultaneously. Each application’s data is prioritised, ensuring higher-precedence data is transmitted first through efficient multiplexing and prioritisation. The stack also facilitates bidirectional communication on a given link, enhancing data transfer efficiency across the network.

To optimise network performance, the RC12 incorporates advanced collision avoidance and recovery mechanisms and a listen-before-transmit function to improve overall network throughput. It can also automatically adjust the transmitter data rate through its DRC functionality when modem control is available.

The STANAG 5066 Edition 4, also known as wideband ARQ (WB-ARQ), addresses data operations at speeds of up to 240 kbps. The RC12 provides data operation from 75 bps up to a maximum of 240 kbps, aligning with the capabilities of wideband HF radio systems offering a maximum bandwidth of 48 kHz.

The RC12 fully complies with the mandatory requirements outlined in STANAG 5066 Edition 4 Annexes A, B, C, D, F and S, and supports a subset of the optional requirements specified in these annexes. Annexes E, G, H, I and M have been removed in Edition 4 and are therefore not applicable.

Media Access Control (MAC) capabilities are addressed in Annexes J, K, and L. The RC12 complies with the requirements of Annexes J and K. Annex L, which covers the WTRP function, was extensively revised in Edition 4, making interoperability with Edition 3 implementations unachievable. The RC12’s WTRP implementation is fully compliant with the Edition 4 specification.

Edition 4 introduced Annexes R and T, which specify optional Routing and TRANSEC crypto sublayers, respectively. RapidM plans to implement these features in the future. The majority of clients defined in Edition 3 remain part of the Edition 4 specification but have been moved from Annex F into their own dedicated annexes. While no new clients were added in Edition 4, updates were made to the S4406 Annex E client and IP clients. Additionally, some clients were removed from the specification.

The RC12 supports networks consisting of both STANAG 5066 Edition 3 and Edition 4 nodes concurrently. As part of the RC12 addressing configuration, it is specified on a per-node-basis whether the node is Edition 3 or Edition 4 capable. The default configuration assumes an Edition 3 capability when communicating with nodes not yet added to the routing table.

When the RC12 is configured for Edition 4, it will only be able to concurrently communicate with nodes being Edition 3 or Edition 4 capable. As part of the link request, the Edition 4 node determines whether a remote node is Edition 4 capable or not. If it is determined that the remote node is not Edition 4 capable, then all ensuing STANAG 5066 data exchanges will be completed using Edition 3 functionality thus without the use of any features associated exclusively with Edition 4.

Alternatively, if via the STANAG 5066 link request, it is determined that the remote node is indeed Edition 4 capable, then all ensuing STANAG 5066 data exchanges can make use of the Edition 4 functionality. When the RC12 is configured for Edition 3 only, it will only be able to communicate using Edition 3 features. Note that no Edition 4 features will be used if communicating with Edition 3 nodes.

The STANAG 5066 Edition 3, referred to as narrowband ARQ (NB-ARQ), addresses data operation up to a maximum data rate of 9.6 kbps in 3 kHz and 19.2 kbps in 2 × 3 kHz (ISB). STANAG 5066 Edition 3 Annexes A, B, C and D are marked as mandatory annexes. The RC12 complies with these requirements. STANAG 5066 Edition 3 Annexes E, G, H and M contain important implementation guidelines, whilst Annex N is a placeholder to provide TDMA operation in future. The latter annexe is empty and therefore not applicable. STANAG 5066 Edition 3 Annexes J, K and L address the Media Access Control (MAC) capabilities. The RC12 complies with the requirements of Annexes J, K and L. The applicable data clients are specified in Edition 3 as part of Annex F.

The RC12 offers as a software option, the standards-based MARLIN controller as specified in the NATO STANAG 4691 Annex A, used for fixed frequency ad-hoc V/UHF LOS and HF ELOS networks. The RC12’s MARLIN controller conforms to the STANAG 4691, Annex A, by providing functionalities, such as automatic network discovery, collision avoidance, error-free data delivery using the embedded ARQ protocol, multi-hop Mobile Ad-hoc Networking (MANET) operation and slot merging for adaptive data throughput control. For the Rapid Mobile STANAG 4691 MARLIN HF and V/UHF solution, the RC12 is utilised in conjunction with the HF and V/UHF waveforms provided by the RM12. A link encryption module may be connected between the controller and modem. Typically, an IP router connects to the RC12 controller, while an HF radio interfaces with the RM12 modem.

The RC12’s utilises the following RM12 embedded HF waveforms during STANAG 4691 network controller operations:

• HF ELOS MIL-STD-188-110D (48 kHz), ≤ 240 000 bps

The RC12 unit has a bit-exact synchronous DCE interface compliant with the EIA 530A standard. The interface is intended to connect to the RED side of standardised cryptographic equipment. The DCE interface supports all the modem data rates required by MIL-STD-188-110D (Blocks 1, 2, 3 and 4) up to 240 kbps. Please note that this standard includes several very unusual rates not normally found on serial interfaces.

In addition, the RC12 unit has three Ethernet interfaces for data transfer and management functions via UDP/IP and TCP/IP as summarised below.

• J13 DATA LAN port is used for the protocol data unit transfers via TCP/IP between the RC12 and the RM12 when synchronous serial transfers are not required.
• J14 CTRL LAN port is used for device management. The J14 CTRL LAN port supports up to three logical connections. The J14 CTRL LAN port is also used to interface with an external Network Time Protocol (NTP) server for accurate system time.
• J35 AUX LAN port is used to interface with the data applications used with the embedded STANAG 5066 stack or STANAG 4691 controller functions.

The RC12 also provides a serial interface for remote control and connections to an external GPS device for accurate system time. The RC12 units can also be configured and controlled via the front panel interface.