Integration servers across a WAN


I have the following scenario, i have 2 integration servers across the the WAN(logically a LAN).I want to trasfer documents(nothing but messages).What will be the role of a broker between these 2 servers.How different is it from doing a server alias.

When I say 2 integration servers are communicating through a broker,does it use a properitory protocol or any other customer protocol that is configurable.

Thanks in advance

At first point…

What is the version of your IS/Broker server and the operating system on which the servers were installed?

So that we can suggest accordingly…