XEP33 and Server Active Multicasting

XEP-0033: Extended Stanza Addressing specifies how Jabber entities can define multiple destination addresses on a XMPP stanza.

This is interesting when a user wants the destinations to know that he sent the same message to all the other destinations (Carbon Copy), or to send a copy to a supervising user (Blind Carbon Copy). The current version of XEP33 explains this basic usage, including an example.

XEP33 can also be used by Jabber servers, MUC services... to reduce bandwidth consumption. This possibility is hinted on the introduction of XEP33, but is not further described on the content of the document. I call this usage Server Active Multicasting, since the server (or a server component) is actively determined to use multicasting, and instead of sending individual stanzas to each destination, tries to send stanzas to groups of users.

There are many opportunities on the server side to use XEP33 to reduce traffic, for example:

• On the Jabber/XMPP server: to send presence changes
• MUC service: to send chatroom messages, subject changes, presence changes, join, leaves, nick changes...
  
• Pubsub/PEP service
  
• Subscription/group list service
  
• RSS transport
  

As part of my GSoC project, my next steps are to define some guidelines to implement
Server Active Multicasting. And of course implement this on ejabberd.