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  is a widely used 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 reslience.
The solution is based on Zero Handshake Server to Server Protocol (XEP-0361)  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 STANAG 5066 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.
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.
XEP-0361 transfer of data between a pair of XMPP servers is a byte stream flowing in each direction over TCP. There is no other protocol or hand shaking. When carried instead over STANAG 5066, these byte streams are transmitted as a sequence of blocks transferred in order Each block is an XML stanza, holding message, presence or iq. Essentially the stream is broken into blocks (stanzas) at natural boundaries XMPP boundaries, and then reassembled on reception into the original stream.
Stream Management (XEP-0198)  MUST not be used over STANAG 5066, as reliability of stanza transfer is handled by use of STANAG 5066. Application-layer keepalives and timeout detection such as white-space pings and XMPP Ping (XEP-0199)  MUST NOT be used.
Each stanza is transferred using the RCOP (Reliable Connection Oriented Protocol) defined in Section F.8 of Annex F of STANAG 5066. This reliably transfers the block of data to the destination. If a soft link needs to be established this will be done by the STANAG 5066 service. The XEP-0361 peer agreement is supported by a flow of stanzas in each direction being transferred by RCOP. The peer agreement will use this flow of stanzas to provide a service equivalent to the TCP connection or connections of XEP-0361.
STANAG 5066 SIS Delivery Confirmation MAY be set to NODE DELIVERY, as this gives optimum network performance. CLIENT DELIVERY MAY be used, which increases reliability as stanza delivery to the peer XMPP server is guaranteed and the sending server will receive acknowledgements equivalent to XEP-0361 support. In the event of delivery failure, the whole RCOP PDU (Stanza) MUST be retransmitted.
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 2 is used. This is the standard SAP for RCOP.
The RCOP connection ID number will be set to a mutually agreed value. It is RECOMMENDED that 0 is used as the preferred value.
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 3 "PROFILE FOR HF RADIO DATA COMMUNICATIONS" (December 2010).
STANAG 5066 is a NATO UNCLASSIFED (Releasable to the Public) document that may circulated freely. It is available on http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf.
Curtis King designed and validated the 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.
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <email@example.com> discussion list.
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The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. STANAG 5066 C3B (EDITION 3): PROFILE FOR HF RADIO DATA COMMUNICATIONS <http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Replace references to draft-ietf-xmpp-websocket with RFC7395 (XMPP over WebSocket).
Initial published version approved by the XMPP Council.