STANAG 5066 is the NATO standard for link level over HF. Thales/French MoD have proposed STANAG 5070 a new link level standard derived in part from STANAG 5066. Having multiple standards for the same purpose (or overlapping purposes) is generally undesirable for users, nations and vendors. This paper considers how to converge ongoing activity onto a single standard.



An overview of STANAG 5066 is given in the Isode whitepaper [STANAG 5066: The Standard for Data Applications over HF Radio]. The most recent edition (STANAG 5066 Ed3) is a ratified NATO standard. STANAG 5066 is widely deployed by many nations and implemented by multiple vendors.

There is current consideration of update to provide a new Ed4, to address support of contiguous Wideband HF and other improvements.


STANAG 5070 is an initiative from Thales and French MoD to facilitate deployment of non-contiguous wideband HF. Drafts of the specification are available for review. It is unclear of there is support from other nations for this work. There is no visible vendor activity beyond Thales and Thales partners.

Why One Standard is Desirable?

A key attraction of STANAG 5066 is that it provides a single interface to all HF infrastructure. Having separate interfaces, with some applications using STANAG 5066 and others using STANAG 5070 is going to be confusing and complex for deployment, create work for vendors, leading to delay and cost for end users.

This paper explores how all proposed functionality could be provided by a single standard.


This paper looks at how a combined single standard could be built based on STANAG 5066. This direction is chosen (rather than taking STANAG 5070 as the base) because:

  • STANAG 5066 is the ratified standard.
  • The STANAG 5066 base is stable.
  • There are less technical features to review (in STANAG 5070).

Capabilities of STANAG 5066 Not in STANAG 5070

This section lists capabilities in STANAG 5066 that are not provided in the current STANAG 5070. This is essentially a check list that the converged protocol needs to address.

  1. EMCON, multicast and broadcast support.
  2. Multi-node support using CSMA (Annex K).
  3. Multi-node support using Wireless Token Ring Protocol.
  4. Support for contiguous Wideband HF. (Not in Ed3, but a key goal of Ed4)
  5. Operation at low narrowband speeds down to 75bps (the STANAG 5070 TDD design will not support this).

How STANAG 5070 Capabilities could be incorporated into STANAG 5066

This section looks at the capabilities of STANAG 5070 that are not provided in STANAG 5066, and looks at how they could be provided as updates to STANAG 5066.


This is a desirable capability for STANAG 5066. [STANAG 5066 TRANSEC Crypto Layer using AES and other Protocols (S5066-EP14)] shows how this could be added to STANAG 5066 with an open specification.

IP Crypto

There is interest in using IP Crypto.   The Isode whitepaper [Using IP Crypto over HF] explains an approach with STANAG 5066, which has benefits relative to the STANAG 5070 approach.  This references four open specifications:

Non-Contiguous ALE

STANAG 5070 includes specification of ALE and ALM for use with non-contiguous HFXL. This is a necessary specification for deployment of non-contiguous. There is no reason why this needs to be bundled with HF link layer protocols. Other ALE specifications are independent and this one should be too.


STANAG 5070 uses a TDD (Time Division Duplex) approach, although reference is made to TDMA (Time Division Multiple Access).

STANAG 5066 has a Media Access Framework, and a placeholder for a TDMA protocol. It would be clean to add a TDD or TDMA MAC access mechanism to STANAG 5066 as a new Annex. Probably using the Annex M placeholder.

Isode view on TDD/TDMA

STANAG 5066 provides CSMA and WTRP MAC mechanisms. Isode believes that these are good options and there is no reason to introduce another option.   However, if the option is going to be introduced, it is best achieved as a new MAC layer and not as a new standard.

‘“IMPACT OF TURNAROUND TIME ON WIRELESS MAC PROTOCOLS” -Eric E. Johnson, Manikanden Balakrishna, and Zibin Tang’ compares TDMA, CSMA and WTRP. It concludes that CSMA is best for lightly loaded networks and WTRP is best for heavily loaded networks.

Use of Non-Contiguous Wideband

STANAG 4539 Annex H specifies non-contiguous wideband. This could be supported by defining an annex to STANAG 5066 to enable it.  There does not seem to be a reason why a new standard is needed. Two approaches are noted: one or both could be standardized.

Use with STANAG 5066 ARQ

There would need to be a clear definition as to how the service interface is presented to STANAG 5066. In particular, to specify if it controlled as a single channel or multiple independent channels.

There would need to be a rate change mechanism, This might be based on [Data Rate Selection in STANAG 5066 for Autobaud Waveforms (S5066-EP4)].

Use with Modem Level ARQ

Use the mechanism specified in STANAG 5070. Downsides of this approach:

  • This is tied to the TDD algorithm, so cannot be used with CSMA or WTRP.
  • The efficiency of the rate change mechanism is questionable.   See Nordic HF 16 Paper “Optimizing applications and data links for HF radio intermediate term variations: Can you ride the wave?” (Steve Kille).
  • Application QoS requirements cannot be taken into consideration when determining speed.


It is clear from this analysis that a single converged HF link standard which is an update to STANAG 5066 could be provided to address all of the STANAG 5070 functions, apart from ALE, which needs to be a separate specification.

Merging both standards as part of STANAG 5066 Ed4 is the recommended course of action.