While the CDPD network provides an NPDU routing service, support protocols are used and routed in parallel to enable mobility. This set of support protocols is illustrated in Figure 4.4.
The Mobile Network Registration Protocol (MNRP) operates over the airlink and is used by the M-ES to identify itself to the network. It is also used by the serving MD-IS to inform the M-ES of its intent to provide service. MNRP also allows the serving MD-IS to query the mobile device and the device to perform a clean deregistration (disconnection) from the network. MNRP is defined by Part 507 of the CDPD System Specifications.
Within the infrastructure, the home MD-IS (which functions as the M-ESs routing anchor) and the serving MD-IS communicate through the Mobile Network Location Protocol (MNLP). The serving MD-IS and the home MD-IS must cooperate to provide mobile network routing. This is achieved through location information and authentication information sharing using the MNLP. MNLP PDUs are transported via CLNP PDUs. MNLP is defined by Part 501 of the CDPD System Specifications.