The central capability of CDPD is its ability to get data to a mobile device or application regardless of its location. This capability is called mobility management. CDPD mobility management is provided by two protocols: the Mobile Network Registration Protocol or MNRP and the Mobile Network Location Protocol or MNLP .
MNRP is the means by which a mobile announces its presence (including authenticating itself) to the serving system (via the End System Hello or ESH message). MNLP is the means by which the serving system notifies the home system for the mobile that it is providing service to the mobile.
The CDPD mobility management scheme is based on triangular routing of NPDUs via encapsulation from a home MD-IS (the mobile home function) to the current serving MD-IS (the mobile serving function). This packet redirection is displayed in Figure 3.9.
By using the home system as the network anchor for the M-ES, the outside world of networked applications can always access the mobile the same way they access any host-conventional routing technology is sufficient to get data packets to the home system. The CDPD mobility management scheme takes over from there, forwarding the data packets via encapsulation to the current system serving the M-ES. This solution is identical to an early Mobile IP Task Force solution, which is elegant in its simplicity.
Although there are pathological cases in which this redirection of packet traffic is highly inefficient, the CDPD specification team elected this solution because the speed of WAN networks is ever-increasing and their costs decreasing. A solution which might be more efficient in the pathological cases would be generally less efficient in accommodating moving users in the cellular environment.3.21
The CDPD mobility management scheme is defined by Parts 500 through 507 of the CDPD System Specification and is described in Chapter 4.