http://telepathy.freedesktop.org/xmpp/tubes is the XML namespace for Telepathy Tubes as implemented over XMPP or link-local XMPP.
http://telepathy.freedesktop.org/xmpp/tubes.html contains some protocol documentation. The source code for this document is docs/tubes.xml in telepathy-gabble.
When used as an XMPP capability, http://telepathy.freedesktop.org/xmpp/tubes indicates support for D-Bus and Stream Tubes compatible with Gabble 0.7.x.
Strings of the following forms indicate support for particular tube services: