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Paradigm Shift in IP Mobility (CMIP to PMIP)

Mobile operators and service providers have been looking for efficient solutions to the inter-system IP mobility for the past fifteen years or so. The main motivation for starting that effort was the ability to continue an IP session when a host IP address had to change. The targeted IP sessions were those involving a transport level connection. This effort resulted in a new mobility protocol so called Client Mobile IP or CMIP. CMIP is a host-based protocol that allows a mobile terminal to keep its transport connection opened and continue to be reachable while moving. CMIP is a key component of the all-IP network today and it’s designed to provide a common IP layer mobility across different access technologies. Mobile operators owning several access networks of different types are allowed to provide their users with global mobility and session continuity via CMIP.While ensuring seamless continuity for the user session via CMIP, other objectives are to be fulfilled. Such objectives can include but not limited to the following:

  • Efficient use of scarce airlink capacity
  • Use broadband wireless access technologies such as WiFi and WiMAX to relieve cellular systems and provide multimedia services;
  • Guaranteeing service level for the users by helping them determine the best system for the service they want to access to;
  • Optimizing the use of the radio resources (especially on cellular), so as to dedicate the radio spectrum to serving more data/voice by lowering the signaling overhead;
  • Making integrated (and therefore already composite architectures less complex, as well as minimizing protocols to render overall systems more scalable;
  • Lowering requirements and constraints on hosts for an easier support of inter-system mobility.

There is considerable evidence that mobility for IP nodes can be more efficiently handled if mobility management is broken down into localized mobility management and global mobility management. Local mobility involves movements across some administratively and geographically contiguous set of subnets, while global mobility involves movements across broader administrative, geographical, and topological domains. As mentioned above CMIP requires mobile node-side support at the IP layer which is not desirable plus CMIP registration eats up a measurable fraction of the airlink capacity.To alleviate this problem work in the IETF is currently underway to develop a solution based on the localized mobility management approach. This is decoupled from the global mobility management protocol which might result in a more modular mobility management system design and therefore more longevity and an easier evolution path. In the WLAN infrastructure market, WLAN switches, which perform localized mobility management without any mobile node involvement, have seen widespread deployment, indicating the technical feasibility and positive user acceptance of this approach. This suggests a design paradigm that could be used to accommodate global mobility management protocols of different types while not increasing software complexity: a network-based, localized mobility protocol with no mobile node software to specifically implement localized mobility management and no requirement for a network interface to change IP address when the mobile node changes to a new router. This is based on Proxy Mobile IP or PMIP championed by Cisco IP mobility experts and SP network architects. Both PMIPv4 and PMIPv6 standards are near completion

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