As mentioned earlier, CDPD defines an accounting scheme which is very general and capable of supporting many kinds of service provider and customer relationships. The basic idea is to functionally separate accounting (business) relationships from networking relationships-i.e., the accounting home for a CDPD subscriber need not be the same as the networking home for that subscriber.
The flow of accounting information is capable of supporting mobile users, while minimizing the coordination between service providers. Usage information such as packets and bytes transferred at Layer 3 is captured by the serving MD-IS. Each CDPD service provider only needs to know the presentation title of the HAD associated with each block of Layer 3 addresses which are in use by M-ESs. X.400 provides the basis for ensuring reliable delivery of accounting data from one accounting server (the SAD) to another (the HAD).
CDPD accounting is defined by Parts 630 and 1023 in the CDPD System Specification and Implementor's Guidelines, respectively, and is also described in Chapter 7.