Icon-5066 is a modem-independent STANAG 5066 server. It enables applications to work efficiently over HF Modems/Radios and allows multiple applications to work simultaneously.

STANAG 5066 provides a link layer optimized for HF Radio as described in the whitepaper [STANAG 5066: The Standard for Data Applications over HF Radio]. Icon-5066 will connect to one or two HF modems, either through a Crypto box or directly, and provides a single interface to an HF network, which can be shared by multiple applications.

The diagram below shows how Icon-5066 is deployed in conjunction with an HF network and two peers, which may use Icon-5066 or another product compliant to STANAG 5066.


Icon-5066 runs as two services, which may be Windows services or Linux processes, as shown in the diagram below:

  1. The Icon-5066 Core service runs one or more independent Icon 5066 nodes. Each of these nodes implements the STANAG 5066 protocols and connects to a modem. This enables multiple STANAG 5066 services to be conveniently run on a single server.
  2. Icon-5066 Distributed Data Service communicates with the core service and provides configuration and monitoring management capabilities. Management is via Web Browser connecting to this service, which enables management of all of the nodes on the core service.

Each Icon-5066 node can have one or more drivers configured that support a variety of capabilities. These drivers are implemented in the Lua scripting language. This has a number of advantages:

  • It enables Isode to offer a selection of drivers to address different configuration requirements.
  • It allows Isode customers and partners to easily develop custom drivers to meet specific needs.

The main drivers in Icon-5066 are:

  • Modem Driver. This is the most likely driver that Isode customers will provide, in order to support additional modem types.
  • Rate Change Driver. This controls selection of transmission parameters.
  • Transmission Control. This controls choice of half-duplex/full-duplex/broadcast and whether transmission terminated when there is not more data to send.

Key Features

Full Duplex & Broadcast

The most common form of HF communication is Half-duplex, where a modem is either transmitting or receiving at any time. This is often used for reliable (ARQ) transmission between a pair of nodes where each node alternately transmits and receives. Icon-5066 supports two additional modes of STANAG 5066 compliant communication:

  1. Broadcast. Where a node continuously sends non-ARQ traffic and never receives any data. This will typically be used at fixed frequency from a transmit-only site.
  2. Full-duplex. Simultaneous transmission and reception on two separate frequencies. Full-duplex gives significant performance benefits, but can only be used in configurations were sufficient separation can be achieved between transmit and receive sites. Icon-5066 provides two modes of full-duplex operation; Single modem (where the modem is operating in full-duplex) and Two modems, independently configured, where one is used for Transmit and the other for Receive.

Data Rate Selection

Data Rate selection is the choice made before transmission of parameters affecting the transmission; in particular speed and interleaver. This is a critical choice for optimizing performance and Quality of Service for the data being handled. Icon-5066 offers a choice of drivers for different rate selection (in addition to customer rate change drivers):

  • Fixed: A simple fixed setting for use when fixed parameters are desired or where it is not possible to change them dynamically.
  • Signal to Noise Ratio (SNR): This is the best option for most deployments. This uses the mechanisms described in [Data Rate Selection in STANAG 5066 for Autobaud Waveforms (S5066-EP4)] to enable sender selection of best parameters for either latency or throughput.
  • Frame Error Rate (FER). Useful when SNR information is not available from the modem. This optimizes for throughput using the "Trinder/Gillespie" algorithm.

Multi-Node Networks

Icon-5066 supports multi-node HF networks operating over a single HF Channel following STANAG 5066 Annex K, providing CSMA (Carrier Sense Multiple Access) using jitter. This is appropriate for networks with large numbers of nodes sharing a single HF frequency.

Support for S5066-EP6 “Slotted Option for STANAG 5066 Annex K” provides a more efficient and robust option for networks with a small number of nodes, by use of a configured transmission slot for each node. S5066-EP6 also enables:

  • Operation with single CAS-1 soft link, which is important for interoperability and some traffic patterns.
  • Operation with multiple CAS-1 soft links, which improves sharing the HF channel and reduces soft link setup overhead.


Icon-5066 provides support for ALE (Automatic Link Establishment) by use of ALE drivers.   This enables use of 2G, 3G and 4G (WALE) from different vendors.  Icon-5066 configures ALE by mapping peer STANAG 5066 addresses to ALE.

An ALE driver is provided for MoRaSky, so that Icon 5066 configurations using ALE can be demonstrated and tested. Isode plans to add drivers to support for Rockwell Collins 4G ALE and RapidM 2G ALE in a future release.

Modem Support

Icon-5066 can be configured with either one modem or two (one for transmission, one for reception). Communication with each modem uses two independent channels; Data, which is mandatory, and Control. Control is optional and will use protocol specific to the chosen modem. Most modems can be used fixed speed without control.

Icon-5066 supports STANAG 4415, 4285, 4539 and 5069 (Wideband HF) waveforms.

Modem Data Support

Icon-5066 supports the following three modem data communication options. These can be used with or without modem control. Use without modem control allows support of any HF modem at fixed speed:

  • Synchronous Serial: Required by STANAG 5066 Annex D and used operationally to communicate with Crypto devices, Icon 5066 support the SeaLevel family of cards on Windows. Support for other serial cards will be added in order to address emerging customer requirements.
  • Asynchronous Serial: Icon-5066 supports Aysnc Serial on Windows using Windows COM ports and Linux TTY. Aysnc serial is not useful with common Crypto boxes, as they encrypt to stop bits, and so this does not follow the standard. However, it can often be useful for operation without Crypto, as many modems provide an Async Serial interface.
  • TCP using MIL-STD-188-110D Appendix A: Defines a TCP protocol to communicate data to a modem.  This is a very useful option for operation without Crypto.

Modem Control Support

Icon-5066 currently supports control for the following RapidM and Rockwell Collins modems:

  • RapidM RM6
  • RapidM RM8
  • Rockwell Collins Q9600
  • Rockwell Collins Q9604
  • Rockwell Collins HSM 2050
  • Rockwell Collins RT-4800
  • Rockwell Collins RT-2200A

These drivers are written using the Lua scripting language. This approach enables straightforward development of custom drivers for other modems.

Management and Monitoring

Icon-5066 is configured and monitored using a web interface. The configuration interface allows for the creation of new Icon-5066 nodes, setting of detailed parameters and the selection/configuration of drivers.

Web monitoring is provided for all of the configured nodes and includes information on:

  • Modem status (Transmit/Receive/Idle)
  • Current (or most recently used) modem parameters, including speed, interleaver and bandwidth (for STANAG 5069 WBHF)
  • Frame Error Rate for received transmissions
  • SNR measured on reception
  • STANAG 5066 send and receive transmissions with progress bar
  • Status of CAS-1 soft links established for ARQ communication.

Test Tools

Isode provides three test tools with Icon-5066 to assist partners in testing Icon-5066 deployments.

HF Tool

Isode partners will often need to test modems, for example to test with a modem variant that Isode does not have in house. HF Tool is an Isode application that directly uses the Icon-5066 modem drivers. It can be operated in three modes:

  1. Controlling two connected modems, so that HF tool can control what is sent and measure what is received.
  2. Controlling two modems with a channel simulator between them. This enables controlled measurements of performance with varying link conditions.
  3. Use of separate HF Tool instances for send and receive. This is useful for Over the Air testing where a single HF Tool instance cannot be connected at both ends. HF tool works in a way that enables the receiver to interpret what is sent.

HF Tool runs a range of tests to ensure good performance and operation of modem drivers in a range of conditions. It also gives a clear measure of modem performance:

  1. Basic data tests to show data transfer and data loss.
  2. Timing tests to show delays and turnaround times.
  3. Sequenced tests, so that varying speeds and interleavers can be tested with a single HF Tool run.

STANAG 5066 Console

STANAG 5066 Console is a GUI tool providing STANAG 5066 server discovery (running S5066 Console on the same HF network), HF Operator Chat (as per STANAG 5066 Annex F.7) and throughput measurements to peer S5066 Consoles with ARQ and non-ARQ traffic to measure network performance.


MoRaSky (Modem Radio Sky) is a software tool provided by Isode to help test Isode HF products. MoRaSky provides a service equivalent to HF modems connected to Radios and operating over the Ionosphere. It enables sophisticated testing of Icon-5066 and the applications it supports, without use of hardware or Over the Air transmission. MoRaSky can be used in one of two ways:

  1. Emulating a modern modem with data and control interfaces.
  2. Emulating a serial interface (synchronous or asynchronous) connection to a data connection to a modem with fixed parameters.

Capabilities include:

  • Emulation of one or more HF networks (multiple networks can be used for ALE and Duplex testing) with support for two or more connection points to each network.
  • Choice of geographical locations, with delays matching distance.
  • Emulation of the waveforms supported by Icon-5066 (STANAG 4415; STANAG 4285; STANAG 4539; STANAG 5069 – this is repetition if mentioned earlier).
  • Choice of interleaver corresponding to each waveform
  • Choice of bandwidth from 3kHz to 48kHz for STANAG 5069
  • Option to simulate clear channel.
  • Configurable Bit Error Rate (BER) on output.
  • Configurable Error Clustering.
  • Option to drop initial bytes.
  • Option to emulate operation at selectable SNR value, with channel variation according to various channel models (CCIR Good; CCIR Moderate; CCIR Poor; AWGN (additive white gaussian noise)).
  • Emulation of delays corresponding to two types of Crypto.
  • Intermediate Term Variation (ITV) following Walnut Street model.
  • Variation of SNR at intervals based on specified list.
  • Simulate regular on/off interference.
  • Simulate Markov chain on/off interference.
  • Modem failure to configurable pattern.

Open Standards

Icon-5066 follows STANAG 5066 - Edition 3 "Profile for HF Radio Data Communications”, December 2010. This section gives conformance notes on the various Annexes which Icon-5066 supports.

Annex Title Notes
A Subnetwork Interface Sublayer Fully supported, except for Hard Links. Isode is not aware of any STANAG 5066 applications that make use of hard links.
B Channel Access Sublayer Fully Supported.
C Data Transfer Sublayer Fully supported apart from Data Rate Change. Icon 5066 uses S5066-EP4 which provides superior functionality and WBHF support. Icon 5066 will add standard Data Rate Change to support interoperability in a future update.
D Interface between Data Transfer Sublayer and Communications Equipment Supported using Icon-5066 synchronous serial driver.
E HF modem Remote Control Interface Not supported. Obsolete and does not appear to be useful.
F HF Subnetwork Client Requirements Annex F mainly covers applications (see page section). F.16 defines the SIS Protocol ("Raw SIS Socket Server") which Icon 5066 fully supports.
G Use of Waveforms at Data Rates Above 2400 bps Fully Supported.
H Implementation Guide and Notes Guidance is followed where appropriate.
I Messages and Procedures for Frequency Change Not supported.
J General Requirements for Enhanced Media-Access-Control (MAC) Capabilities in Multi-Node STANAG 5066 Networks The model of Annex J is supported. MAC Discovery for Annex L will be implemented in parallel with Annex L (there is no discovery for Annex K, and Annex M is not yet specified).
K High-Frequency Carrier-Sense Multiple-Access (CSMA) Protocols Fully Supported.
L High-Frequency Token-Ring Protocol (WTRP) Requirements. Planned for future release.
M Adaptive Time-Division Multiple-Access (ATDMA) Protocols using STANAG 5066 DTS Layer Messaging Annex M is a placeholder with no technical content.
N Guidance on Address Management in STANAG 5066 Networks. Relevant for deployment but does not apply to products.

STANAG 5066 Extension Protocols

Isode has led community specification of a series of extensions to STANAG 5066 to address a number of deficiencies in Ed3, in particular problems relating to use of STANAG 5069 (WBHF). An index of these specifications is available in the whitepaper [STANAG 5066 Extension Protocol Index]. These specifications have been made available to NATO, so that they can be incorporated into STANAG 5066 Ed4. Icon-5066 makes optional use of these specifications, so can be conformant to Ed3.

Extension Title Notes
S5066-EP2 STANAG 5066 Padding DPDU This uses "spare" transmission space to enable improved resilience and protocol communication of status information.
S5066-EP4 Data Rate Selection in STANAG 5066 for Autobaud Waveforms This provides a modern approach to Data Rate Selection, enabling optimization for both Latency and Throughput. It also provides support for STANAG 5069.
S5066-EP5 STANAG 5006 Large Window Support This addresses ARQ window exhaustion, which will impact ARQ usage with STANAG 5069 (WBHF) and at faster narrowband HF speeds.
S5066-EP6 Slotted Option for STANAG 5066 Annex K This provides high performance and resilience for multi-node networks with a small number of nodes.  It also enables options to support single or multiple concurrent CAS-1 soft links. This provides high performance and resilience for multi-node networks with a small number of nodes.  It also enables options to support single or multiple concurrent CAS-1 soft links.

Application Support

Applications connect to Icon-5066 using the STANAG 5066 SIS (Subnet Interface Service) protocol. Each application uses one of 16 SAP IDs (Service Access Point Identifier). The diagram below shows the Isode products that operate over the SIS Protocol, using the recommended SAP ID for each application. These applications will communicate with peer applications connected to remote STANAG 5066 servers.

Icon-5066 can be used with any application that uses the STANAG 5066 SIS protocol. The following two sections set out applications supported by Isode products.

STANAG 5066 Annex F

Section Title Isode Product
F.2 Subnet management client This management client is a reserved port with no protocol defined. Icon-5066 uses HTTP Web based management.
F.3 Character-Oriented Serial Stream (COSS) Client COSS is for ACP127. It is supported by the M-Switch ACP127 add-on.
F.4 STANAG 4406 Annex E - Tactical Military Message Handling (T-MMHS) Client

This protocol is supported by the ACP 142 channel in M-Switch. This can be used with:

  • STANAG 4406 Annex E.
  • MULE (Multicast Email) to support SMTP based messaging.
F.5 HMTP (HF Mail Transfer Protocol) HMTP has been replaced operationally by CFTP (F.14)
F.6 HFPOP (HF Post-Office Protocol) HFPOP does not appear to be used operationally.
F.7 Operator orderwire (HFCHAT) Also known as Operator Chat. Supported by Isode STANAG 5066 Console.
F.8 Reliable Connection-Oriented Protocol (RCOP) w/ Extended Client RCOP is a layer protocol, used in M-Switch (ACP 142) and M-Link (XEP-0365).
F.9 Unreliable Datagram Oriented Protocol (UDOP) w/ Extended Client UDOP is a layer protocol, used in M-Switch (ACP 142).
F.11 ETHER client 8 We have not identified any market requirements for Ether Client.
F.12 IP Client IP Client will be supported in a new future Isode product.
F.14 Compressed File Transport Protocol (CFTP) CFTP, also known as BFEM (Battle Force Email) is supported by M-Switch. Isode recommends use of MULE over ACP 142 (see F.4 above) which is provides additional functionality and higher performance for SMTP over HF.

Other Applications

In addition to the STANAG 5066 protocols defined in STANAG 5066 Annex F, there are two other Isode applications which operate directly over STANAG 5066 SIS.

M-Link supports operation over STANAG 5066. This conforms to:

  • XEP-0365: Server to Server communication over STANAG 5066 ARQ

STANAG 5066 Console supports node discovery and throughput testing. This uses a protocol that is aligned to:

  • HF Discovery, Ping and Traffic Load (S5066-APP2)