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<header>
  <title>Server to Server communication over STANAG 5066 ARQ</title>
  <abstract>
  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.

  </abstract>
  &LEGALNOTICE;
  <number>0365</number>
  <status>Experimental</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XEP 0361</spec>
    <spec>STANAG 5066</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>S5066</shortname>
  <author>
    <firstname>Steve</firstname>
    <surname>Kille</surname>
    <email>steve.kille@isode.com</email>
    <jid>steve.kille@isode.com</jid>
  </author>
  <revision>
    <version>0.1</version>
    <date>2015-09-17</date>
    <initials>XEP Editor (mam)</initials>
    <remark><p>Initial published version approved by the XMPP Council.</p></remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2015-08-19</date>
    <initials>sek</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>
   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.   <span class='ref'><link url='http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf'>STANAG 5066</link></span> <note>STANAG 5066 C3B (EDITION 3): PROFILE FOR HF RADIO DATA COMMUNICATIONS &lt;<link url='http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf'>http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf</link>&gt;.</note>
 is a widely used link level protocol.   Direct use of <strong>STANAG 5066</strong> enables elimination of all extraneous end to end handshaking, which is important to optimize performance.  It also enables use of <strong>STANAG 5066</strong> flow control, which is important for reslience.
  
  </p>
<p> 
  The solution is based on &xep0361; and requires peer configuration to be established according to <strong>XEP-0361</strong>.  The data exchanged between the XMPP servers follows exactly what is specified in <strong>XEP-0361</strong>.    The data is transferred using <strong>STANAG 5066</strong> rather than using TCP.    
 
</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
  <p>
    This specification can be considered as a profile for server to server XMPP communication, to enable XMPP deployment over HF Radio using <strong>STANAG 5066</strong>.   This profile MUST only be used where its use has been pre-agreed and configured for both participating servers.  
  </p>
</section1>

<section1 topic='Use Cases' anchor='usecases'>
  <p>
    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 <strong>STANAG 5066</strong> and XMPP communicated efficiently and reliably.
 
  </p>
</section1>
<section1 topic='Business Rules' anchor='rules'>
 
  <section2 topic="General Operation"> 
  <p>
    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.
  </p>
    <p>
      Applications sending data over <strong>STANAG 5066</strong> need to be aware of increased delays and any application level timers (e.g., IQ response timers) need to be set accordingly.
    </p>
  </section2>
  <section2 topic="Stream Fragmentation">
    <p>
      <strong>XEP-0361</strong> 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 <strong>STANAG 5066</strong>, 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.
      
      
    </p>
    <p>
      &xep0198; MUST not be used over <strong>STANAG 5066</strong>, as reliability of stanza transfer is handled by use of <strong>STANAG 5066</strong>.  Application-layer keepalives and timeout detection such as white-space pings and &xep0199; MUST NOT be used.
    </p>
   
  </section2>

<section2 topic="Mapping onto STANAG 5066">
  <p>
    Each stanza is transferred using the RCOP (Reliable Connection Oriented Protocol) defined in Section F.8 of Annex F of <strong>STANAG 5066</strong>.   This reliably transfers the block of data to the destination.   If a soft link needs to be established this will be done by the <strong>STANAG 5066</strong> service.  The <strong>XEP-0361</strong> 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 <strong>XEP-0361</strong>.
  </p>
  <p>
    <strong>STANAG 5066</strong> 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 <strong>XEP-0361</strong> support.     In the event of delivery failure, the whole RCOP PDU (Stanza) MUST be retransmitted.
  </p>

</section2>
  <section2 topic="Addressing">
    <p>  
  The peer addressing of the <strong>STANAG 5066</strong> end points will be configured as part of the <strong>XEP-0361</strong> peer agreement.
    </p>
    <p>
 The <strong>STANAG 5066</strong> SAP MAY be set to any mutually agreed value.   It is RECOMMENDED that 2 is used.  This is the standard SAP for RCOP.
    </p>
<p>
  The RCOP connection ID number will be set to a mutually agreed value.  It is RECOMMENDED that 0 is used as the preferred value.
</p>
  </section2> 
</section1>


<section1 topic='Security Considerations' anchor='security'>
  <p>
    Security Considerations of <strong>XEP-0361</strong> apply.   <strong>STANAG 5066</strong> will frequently be employed in conjunction with link level crypto devices, which SHOULD be done when appropriate to provide data confidentiality.       
  </p>
  
</section1>
<section1 topic='STANAG 5066 Standard' anchor='iana'>
  <p>This specification uses STANAG 5066 Edition 3 "PROFILE FOR HF RADIO DATA COMMUNICATIONS" (December 2010). </p>
  <p><strong>STANAG 5066</strong> is a NATO UNCLASSIFED  (Releasable to the Public) document that may circulated freely. It is available on <link url='http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf'>http://nso.nato.int/nso/zPublic/stanags/CURRENT/5066Ed03.pdf</link>.</p>
</section1>
  
  <section1 topic="Acknowledgements">
    <p>
      Curtis King designed and validated the approach documented in this XEP.
    </p>
    <p>
      Kevin Smith provided useful comments on this specification.
    </p>
    <p>
      Dave Cridland asked NATO about STANAG 5066 publication, leading to its availability on the Web.
    </p>
  </section1>
</xep>
