<remark><p>Added protocol flows for finding and joining shadow rooms, thus removing dependency on communication with firsthost; changed examples to mimic XEP-0045.</p></remark>
<p>&xep0045; defines a full-featured technology for multi-user text conferencing in XMPP. By design, <cite>XEP-0045</cite> assumes that a conference room is hosted at a single service, which can be accessed from any point on the network. However, this assumption introduces a single point of failure for the conference room, since if occupants at a using domain lose connectivity to the hosting domain then they also lose connectivity to the room. In some deployment scenarios (and even on the open Internet) this behavior is suboptimal. Therefore, this document attempts to define a technology for distributing MUC rooms across multiple services.</p>
<p>The basic approach to distribution of MUC rooms is as follows:</p>
<olstart="1">
<li>A user creates a room on a service and configures it as "distributed" (or the service assumes that the room is distributed based on local service policy); this first instance of the room is called a SOURCE and the service on which it is created is called a FIRSTHOST.</li>
<li>The firsthost can immediately request that other services (called PEERHOSTS) replicate the room by creating their own local instances (called SHADOWS); alternatively, the firsthost can wait to send the replication request until users from the peerhost have joined the room.</li>
<li>If a user from the peerhost attempts to join the source room after replication is established, the firsthost invites the user to join the shadow rather than the source by sending a direct invitation to the user.</li>
<li>As long as the peerhost and firsthost have connectivity, they share room messages, room rosters, and room configuration changes in real time. If any conflict arises, the firsthost's information rules since it is "first among equals".</li>
<li>If the peerhost loses connectivity to the firsthost, it maintains the shadow, including local room history, room roster, and room configuration, and if possible also maintains connectivity with other peerhosts.</li>
<li>Upon reconnecting to the firsthost, a peerhost exchanges room history and room rosters with the firsthost and receives room configuration data (if modified).</li>
</ol>
<p>The room IDs of source rooms SHOULD be opaque to users and unique across all possible peerhosts, for example by generating a UUID in accordance with &rfc4122; or by hashing the human-readable name of the room using the SHA-256 algorithm in accordance with &nistfips180-2;.</p>
<p>When the original room owner creates the room (or subsequently configures the room), the service MAY simply default all rooms to "distributed".</p>
<p>Alternatively, the server MAY offer the option of making the room a "distributed room". This is done by including the "muc#roomconfig_distributed" feature in the room configuration form:</p>
<p>Alternatively, the firsthost can choose to perform room distribution in the background, rather than exposing the 'muc#roomconfig_distributed' option to the user.</p>
<p>Several error cases are possible (the peerhost is resource constrained, the firsthost is forbidden to peer with the peerhost, etc.); these will be specified more fully in a future version of this specification.</p>
<p>Once the peerhost acknowledges that it is willing and able to replicate the room, four things happen:</p>
<olstart="1">
<li>The source sends the room configuration to the shadow.</li>
<li>The source sends the room roster to the shadow.</li>
<li>The shadow optinoally requests the room history from the source.</li>
<li>The firsthost informs other peerhosts about the new peerhost.</li>
</ol>
<examplecaption='Source Sends Room Configuration to Shadow'><