This document is an index of the STANAG 5066 Extension Protocol (S5066-EP) series. The complete set of documents in this series are:

  1. STANAG 5066 Extension Protocol Index (S5066-EP1)
  2. STANAG 5066 Padding DPDU (S5066-EP2)
  3. Pipelining the CAS 1 Linking Protocol (S5066-EP3)
  4. Data Rate Selection in STANAG 5066 for Autobaud Waveforms (S5066-EP4)
  5. STANAG 5066 Large Windows Support (S5066-EP5)
  6. Slotted Option for STANAG 5066 Annex K (S5066-EP6)
  7. Advertising Extended Capabilities (S5066-EP7)
  8. Block Based EOTs (S5066-EP8)
  9. Compact Acknowledgement (S5066-EP9)
  10. Extension DPDU (S5066-EP10)
  11. Variable C_PDU Segment Size (S5066-EP11)
  12. HF Wireless Token Ring Protocol (S5066-EP12)
  13. STANAG 5066 Routing Sublayer (S5066-EP13)
  14. STANAG 5066 TRANSEC Crypto Layer using AES and other Protocols (S5066-EP14)
  15. AES Key Distribution for TRANSEC and Half Loop (S5066-EP15)

1. S5066-EP Series Goals

STANAG 5066 is a NATO Standard "PROFILE FOR HF RADIO DATA COMMUNICATIONS" providing a link level service for HF Radio. The latest version is Edition 3 of December 2010.

There are a number of issues with the current STANAG 5066 specification, particularly in relation to its use with the new Wideband HF (WBHF) specifications. NATO is aware of the need to update STANAG 5066 and has expressed intention to do so. The S5066-EP series is intended to address the open issues prior to STANAG 5066 official update.

This series of documents provides a set of extensions that can be used in conjunction with STANAG 5066 edition 3. The intent is that vendors and those procuring systems can reference these specifications, prior to this capability being available to NATO.

It is anticipated that this functionality will be folded into a future update of STANAG 5066 and at that point the series can be obsoleted.

Isode is managing the S5066-EP series and this index as a community service. The initial S5066-EP documents are written by Isode. Isode encourages other individuals, organizations and vendors to contribute documents to this series.  

2. Exchange of Information on STANAG 5066 EPs

The STANAG 5066 are all published on this website and can be reached using the links in the table at the bottom of this document.

There is an open mailing list for discussion of current and new S5066-EPs: s5066-ep (at) To join this list or manage your subscription, please send a message to s5066-ep-request (at)

3. Document Requirements

S5066-EPs must be openly available specifications that NATO may incorporate into a future edition of STANAG 5066.  They must be free of IPR or Patent restrictions that would prevent this.

These specifications are intended for implementation and must provide sufficient clear information to be implemented in context of STANAG 5066 Ed3.

S5066-EPs must have a clear publication date, and (apart from this document) a referenceable version number. S5066-EPs must have a status value which is one of:

  • Experimental: A new proposal for consideration.
  • Implemented: A specification that has at least one implementation that has demonstrated viability of the proposal.
  • Interoperable: A specification with two independent implementations that have been shown to inter-operate.   
  • Informational: A document that does not have interoperability considerations.

4. Index

Number Title Status Last Edit Date Summary
S5066‑EP1 STANAG 5066 Extension Protocol Index Informational 18‑01‑2017 This Document
S5066-EP2 STANAG 5066 Padding DPDU Implemented 16-01-2017 New PDU to improve performance
S5066-EP3 Pipelining the CAS 1 Linking Protocol Experimental 14-01-2017 Optimizes  CAS-1, which is important for small data transfers in particular.
S5066-EP4 Data Rate Selection in STANAG 5066 for Autobaud Waveforms Experimental 14-02-2017 This document specifies an approach to
STANAG 5066 Data Rate Selection, to address some significant problems with
Data Rate Change in the current standard.
S5066-EP5 STANAG 5066 Large Window Support Implemented 06-12-2017 This specification addresses performance problems caused by window exhaustion which impacts WBHF and faster speeds for standard HF.
S5066-EP6 Slotted Option for STANAG 5066 Annex K Experimental 04-05-2017 This document specifies an a Slotted option for STANAG 5066 Annex K (CSMA Access) as an alternative to the Jitter approach specified.
S5066-EP7 Advertising Extended Capabilities Experimental 07-12-2017 This document specifies a mechanism for STANAG 5066 implementations to specify which STANAG 5066 Extensions (S5066-EP series) they support.
S5066-EP8 Block Based EOTs Experimental 24-07-2017 This document specifies a mechanism for using block count to determine end of transmission.
S5066-EP9 Compact Acknowledgement Experimental 24-07-2017 This document specifies a mechanism for client acknowledgement of STANAG 5066 APDUs that improves efficiency and reliability of the current mechanism.
S5066‑EP10 Extension DPDU Experimental 15‑09‑2017 This document provides a framework for specifying future DPDUs.
S5066-EP11 Variable C_PDU Segment Size Experimental 06-12-2017 This document specifies a modification of STANAG 5066 to allow more flexibility in selection of C_PDU segment size. This enables performance improvements.