To understand asynchronous modem communication using RAS, you need to understand the following four compatibility levels in relation to RAS:
Figure E.1 shows these four compatibility levels being implemented during a WAN connection. The different levels are shown below the section of the asynchronous RAS link to which they apply:
In the diagram, the RAS client is on the right side and the RAS server on the left side, and they are connected over external modems.
Notice that a RAS client or server acts as Data Terminal Equipment (DTE), and a modem acts as Data Communications Equipment (DCE).
Figure E.1 Modem Compatibility Standards