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Server to Server communication over STANAG 5066 ARQ This specification defines operation over XMPP over the NATO STANAG 5066 data link service for point to point links (ARQ). This enables optimized XMPP performance over HF Radio (which STANAG 5066 was designed for) and over other data links using STANAG 5066. &LEGALNOTICE; 0365 Experimental Standards Track Standards Council XEP 0361 STANAG 5066 SLEP S5066 Steve Kille steve.kille@isode.com steve.kille@isode.com 0.3 2022-03-28 sek Make use of SLEP Streaming service, which was not available for 0.1. This provides a better service mapping than direct use of 5066 and provides compression. 0.2.1 2018-07-21 egp

Replace references to draft-ietf-xmpp-websocket with RFC7395 (XMPP over WebSocket).

 0.2 2017-09-11 XEP Editor (jwi) Defer due to lack of activity. 0.1 2015-09-17 XEP Editor (mam)

Initial published version approved by the XMPP Council.

 0.0.1 2015-08-19 sek

First draft.

This specification arose from requirements to operate over HF Radio, which has exceedingly high latency (sometimes minutes) low data rates (down to 75 bits/second) and poor reliablity. STANAG 5066 STANAG 5066 C3B (EDITION 3): PROFILE FOR HF RADIO DATA COMMUNICATIONS <https://www.isode.com/documentation/S5066Edition4ratification.pdf>. is a widely used HF link level protocol. Direct use of STANAG 5066 enables elimination of all extraneous end to end handshaking, which is important to optimize performance. It also enables use of STANAG 5066 flow control, which is important for resilience.

The solution uses the streaming service specified by SLEP SIS Layer Extension Protocol (SLEP) (S5066-APP3) <https://www.isode.com/whitepapers/S5066-APP3.html>. - SIS Layer Extension Protocol. SLEP specifies three layer services that operate over STANAG 5066, including a streaming service which provides an equivalent service to TCP. SLEP also provides compression, which is mandated for use by this specification.

The solution is based on &xep0361; and requires peer configuration to be established according to XEP-0361. The data exchanged between the XMPP servers follows exactly what is specified in XEP-0361. The data is transferred using SLEP rather than using TCP.

This specification can be considered as a profile for server to server XMPP communication, to enable XMPP deployment over HF Radio using STANAG 5066. This profile MUST only be used where its use has been pre-agreed and configured for both participating servers.

An example scenario where this protocol is important is where two ships connected by HF Surface Wave communication only need to exchange XMPP messages. A reliable link (Soft Link) can be established using STANAG 5066 and XMPP communicated efficiently and reliably over SLEP.

Because of potentially very low bandwidth sending server MAY perform traffic optimisation, such as selective removal of stanzas that are not adding sufficient value, like CSNs, or strip selected elements such as xhtml-im.

Applications sending data over STANAG 5066 need to be aware of increased delays and any application level timers (e.g., IQ response timers) need to be set accordingly.

&xep0198; MAY be used over SLEP. Although reliability of stanza transfer is provided by use of STANAG 5066 and SLEP, use of &xep0198; is RECOMMENDED to monitor link latency.

Application-layer keepalives such as white-space pings are NOT RECOMMENDED.

The stanza stream is transferred using SLEP. SLEP compression is mandatory.

The peer addressing of the STANAG 5066 end points will be configured as part of the XEP-0361 peer agreement.

The STANAG 5066 SAP MAY be set to any mutually agreed value. It is RECOMMENDED that 6 is used which is the value specified in STANAG 5066 for use by this XEP.

Security Considerations of XEP-0361 apply. STANAG 5066 will frequently be employed in conjunction with link level crypto devices, which SHOULD be done when appropriate to provide data confidentiality.

This specification uses STANAG 5066 Edition 4 "TECHNICAL STANDARDS FOR HF RADIO LINK LAYER AND APPLICATION SUPPORT PROTOCOLS FOR SINGLE CHANNEL WAVEFORMS" (November 2021).

STANAG 5066 is a NATO UNCLASSIFED (Releasable to the Public) document that may circulated freely. It is available on https://www.isode.com/documentation/S5066Edition4ratification.pdf.

This specification uses the streaming service specified by SIS Layer Extension Protocol (SLEP) (S5066-APP3).

SLEP is an openly available protocol specification with no license restrictions. It is available on https://www.isode.com/whitepapers/S5066-APP3.html.

Curtis King designed and validated the original approach documented in this XEP.

Kevin Smith provided useful comments on this specification.

Dave Cridland asked NATO about STANAG 5066 publication, leading to its availability on the Web.

Edwin Mons implemented and validated the SLEP mapping.