CEllular IP

Recent initiatives to add mobility to the Internet mostly focus on the issue of address translation through introduction of location directories and address translation agents. In these protocols (e.g., Mobile IP) packets addressed to a mobile host are delivered using regular IP routing to a temporary address assigned to the mobile host at its actual point of attachment. This approach results in simple and scalable schemes that offer global mobility. Mobile IP is not appropriate, however, for fast mobility and smooth handoff because after each migration a local address must be obtained and communicated to a possibly distant location directory or home agent (HA).

Cellular mobile telephony systems are based on a different concept from that of Mobile IP. Instead of aiming at global mobility support, cellular systems are optimized to provide fast and smooth handoff within restricted geographical areas. In the area of coverage, mobile users have wireless access to the mobility unaware global telephony network. A scalable forwarding protocol interconnects distinct cellular networks to support roaming between them.

Even in limited geographical areas, however, the number of users can grow to a point where using fast lookups for per user data bases is no longer viable. In addition, mobility management requires mobile hosts to send registration information after migration. The resulting signaling overhead has significant impact on the performance of wireless access networks. To overcome this problem, cellular telephony systems require mobile hosts to register after every migration only when they are engaged in `active' calls. In contrast, 'idle' mobile hosts send registration messages less frequently and as a result can roam large areas without loading the network and the mobility management system. In this case, the location of idle mobile hosts is only approximately known to the network. To establish a call to an idle mobile host, the mobile host must be searched for in a limited set of cells. This feature of passive connectivity allows cellular networks to accomodate a very large number of users at any instance without overloading the network with large volumes of mobility management signaling information.

Cellular networks offer a number of desirable features which if applied correctly could enhance the performance of future wireless IP networks without loosing any of the important flexibility, scalability and robustness properties that characterize IP networks. However, there are fundamental architectural differences between cellular and IP networks that make the application of cellular techniques to IP very challenging. Cellular telephony systems rely on the restrictive "circuit'' model that requires connection establishment prior to communication. In contrast, IP networks perform routing on a per packet basis. In addition, current cellular systems are strictly based on hierarchical networks based on costly mobile-aware nodes (e.g., MSC). COMET believe that a future ``Cellular Internet'' should be based on IP, inheriting its simplicity, flexibility and robustness. A Cellular Internet should leverage mobility management and handoff techniques found in cellular networks. A single scalable host mobility protocol should be capable of flexibly supporting pico, campus and metropolitan area networks based on a set of simple and cheap network nodes that can be easily interconnected to form arbitrary topologies and operate without prior configuration... (Go to to read rest of article....

The Cellular IP Source Code can be downloaded from here.

An interesting project here would be first of all - simply download the Linux version of the code, get it working. Then as Cellular IP protocol is implemented as extensions to the ns simulator which is widely used by the networking community to analyze IP networks - compare and contrast cellular ip with 802.11 handoffs using NS 2. The handoff performance is the key measurement that we are looking for results from. This can be easily performed using some predefined NS scripts. Call to see me in my office if you are interested at all. The only pre-requisite is that you have already installed a linux distribution on a machine. I have an NS Wireless tutorial here.