How do the Layers communicate with each other in N-Tier application?

Each Layer comprises of one or more components. Each component being a part of the app may communicate with one or more component. The component may "speak"to the other components using one of the many protocols, HTTP, FTP, TCP/IP and mechanisms such as XML/RPC, SOAP, REMOTING etc. The data as such may be “passed” across in many formats such as binary, string , XML.