Objectives, Goals and Assumptions

Both CDPD and Mobile IP require mobile hosts to be able to communicate with other systems that do not implement mobility functions. No changes or enhancements are required for systems that do not support mobility, to be able to communicate with mobile hosts.

Underlying Data Link Layer

Mobile IP makes no assumption about any particular link layer technology. One of the driving requirements for design of Mobile IP was that it should be completely independent of the data link. In the case of CDPD, there were no external requirements for support of data links other than the CDPD airlink (an overlay on AMPS). From the onset the CDPD architects recognized that mobility for CDPD could be independent of CDPD's airlink. To this end, CDPD was designed under a self-imposed requirement for CDPD mobility to be independent of the airlink.

Link Layer Efficiency

CDPD treats the airlink as a precious resource and minimizes the number of bytes transferred over the air. Trade-offs made between layering integrity (Layer 3 vs. Layer 2) and airlink efficiency in CDPD favor airlink efficiency.

Mobile IP is contained strictly within Layer 3. Mobile IP recognizes that the link by which a mobile node is attached to the Internet may often be a precious wireless link, which should be optimized where possible by the Layer 3 protocol (in this case Mobile IP).

Network Layer Support

CDPD was designed to not only support IP, but also to be a multi-protocol mobility solution. Mobile IP is a pure IP solution. Both CDPD and Mobile IP require that mobility be supported without the mobile system needing to change its IP address. This is a departure from existing IP networks.

Network Administration and Management

CDPD assumes that the network is centrally administered, managed and operated by cooperating cellular Service Providers. Mobile IP assumes no additional constraints beyond the existing mode of operation of the Internet. This is probably the most fundamental difference between CDPD and Mobile IP and has serious ramifications on address assignment and security.