The Communication Services Layer provides transport-independent communication services. It uses Standard C++ Library iostreams and Essential Tools Module virtual streams for communication into and out of a portal. This persistence mechanism enables your application to create and use streaming operators without depending on a particular output medium or format. For example, the same output function can be used to write to a disk, memory segment, or a network, using binary, ASCII, or XDR formats, by changing the virtual stream used for output.