SOAP Message Exchange Model

SOAP messages are one-way transmissions. But, they are often combined to form patterns such as request/response.
A SOAP implementation can optimize for a particular transport medium.
SOAP nodes can be the sender, receiver, or any intermediary. SOAP does not provide a routing mechanism.
When processing a message, a node is said to take the role of a SOAP actor specified by the URI http://www.w3.org/2001/12/soap-envelope/actor/actorname.
Every SOAP node must be able to act as http://www.w3.org/2001/12/soap-envelope/actor/next.
No SOAP node should act as none, these are meant for the final receiver.