WS-Routing
Web Services Routing Protocol (WS-Routing) is a SOAP-based, stateless protocol for exchanging one-way SOAP messages from an initial sender to the ultimate receiver, potentially via a set of intermediaries. In addition, WS-Routing provides an optional reverse message path enabling two-way message exchange patterns like request/response, peer-to-peer conversations, and the return of message acknowledgements and faults. WS-Routing is expressed as a SOAP header entry within a SOAP envelope making it relatively independent of the underlying protocol.
Please see http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnglobspec/html/ws-routing.asp for more information.