A repository of notes and comments that will eventually make their way into the documentation. Please treat the information here with caution, it has often not been verified.
What is meant by the 'wire protocol' or 'protocol' for remote EJB?
Unfortunately, there's quite a bit of EJB documentation that seems to hide the fact the remote method calls need to use some wire protocol. So some of the books and tutorials will just use RMI and not explain that RMI is only one possible protocol for remote EJB.
Resin's preferred protocols are Hessian and Burlap. It does support CORBA/IIOP, only because the spec requires it, but the support is pretty minimal and it's not recommended. The upcoming J2EE 1.4 spec might require RMI and does require SOAP (but only for session interfaces.)
(So why does Sun require specific wire protocols for EJB, when it doesn't even require that you support SQL or databases for the CMP. As far as I can tell, it's all Sun politics, where the CORBA and RMI groups think that by forcing the app servers to use their lame protocols, they'll finally get somewhere in the marketplace.)
Should I use Burlap or Hessian?
Burlap and Hessian are almost identical. Most of the files just globally replace Burlap with Hessian.
Hessian is marginally better, since it doesn't have an issue with binary data or utf-8. i.e. there's no encoding of the stream necessary.
On the other hand, Burlap is easier to debug if that's ever necessary. But it should be trivial to swap out Hessian for Burlap if you ever need to look at the stream.
If you wanted an XML-based protocol for some reason you would use Burlap. It's easier to look a the burlap data to try and debug what it's sending back and forth.
Also, for something like Flash, it might be easier to parse XML rather than a binary protocol.
Should I use Corba/IIOP?
You don't want to use IIOP unless you really need to.
Unless you are forced by some external requirement to use IIOP, use something else. Pretty much anything else is better than IIOP.
CORBA/IIOP is a massively over-complex, confused, poorly designed, unwieldly behemoth that only has some success because of huge amounts of pressure and advertisement from big companies like Sun and IBM.
Even SOAP is better than CORBA/IIOP and SOAP is also overly-complex and unwieldly.