Each message is sent to the recipient using some transport. Transports differ in the way they work and in supposed location of sender and recipient. For example, Direct Transport class can place "fake" (local) messages right to the messenger's input queue. Memory-Mapping File Transport is a quick way to transfer information between processes on the same computer. Socket Transport is a full-featured TCP-based transport that connects different computers over internet or local network. HTTP Transport is a network transport that connects computers, PDAs and cell phones over internet or local network using standard HTTP protocol. More transport classes are to appear in future.
All transport classes descend from one class, BaseTransport and so they have common properties. Each transport also has it's own properties, specific to the way this transport delivers messages.