XEP-0047: In-Band Bytestreams
"IBB as specified in this document defines two protocol aspects:
How to set up and tear down an IBB session using <open/> and <close/> elements sent within IQ stanzas.
How to send chunks of IBB data using IQ (or message) stanzas containing <data/> elements."
Once this is completed, the whole file transfer episode is done, and files can be transferred between two clients.