title: RMI Callbacks - what is the on the wire protocol?
body: <p>What is the "on the wire", TCP/IP level protocol when Java RMI is used with client callbacks?</p>
  
  <p>Specifically, does the server initiate a separate TCP/IP connection to the client to make the callback, or is an existing TCP/IP connection used?</p>
  
  <p>This reference: <a href="https://www.cis.upenn.edu/~bcpierce/courses/629/jdkdocs/guide/rmi/spec/rmi-protocol.doc.html" rel="nofollow noreferrer">https://www.cis.upenn.edu/~bcpierce/courses/629/jdkdocs/guide/rmi/spec/rmi-protocol.doc.html</a> indicates a HTTP POST is encapsulated in RMI to invoke the method, is the HTTP POST made by the server to the client for a callback?</p>