The layering of the Communications Subsystem provides several ways to write applications that use communications protocols. The approach you choose depends on which layer will best serve your purposes. Many applications can be written entirely by using the dialog layer, which offers greater simplicity, higher productivity, and network-protocol independence. However, if you are implementing new dialog types or applications that require close control over their network connections, you'll need to use classes at the system layer.

In order to use the system layer, you need to understand its classes and how to use them. The classes at this layer map closely to the concepts of the system's implementation of each of the supported protocols. It is helpful to have a full understanding of the concepts and usage of your protocol when programming to the system layer. In addition, when you are debugging programs that have been written to this layer, you might find it helpful to use the debugging aids provided with the system implementation of your protocol.