After you’ve installed WebSphere ESB, go to First Steps and run the supplied sample.
You have a single-server bus environment with an external requester and provider.
You will find that, rather than having a single-server bus environment with an external requester and provider, you will have a requester "client" servlet and a Web service provider running in the same application server as a mediation module. This is possible because WebSphere ESB is built on top of WebSphere Application Server.
But the ESB could be more distributed. You can connect one mediation module to another. You can distribute the ESB over more than one server, or specify cluster servers to achieve either failover, workload sharing, or both.
This topology is adequate for some application integration scenarios, but you may want to change WebSphere ESB to suit your needs.