Expert Column / IPv6 The writer is a senior member of the research staff in the Mobile Convergence Laboratory of Samsung Electronics, Korea. He is a member of the IPv6 International Forum....Ed. By Daniel Soohong Park Mobile Convergence Laboratory, Samsung Electronics. The next few years promise to be truly revolutionary, with the introduction of broadband wireless services. With the global deployment of 3G and WiFi networks now under way, users will be able to experience a new range of mobility and multimedia services - but as separate networks. Unfortunately one major function that has not been developed is a roaming solution to allow users to move in and out of various public 3G/WiFi and private WiFi networks without session restarts. However this is where Mobile IPv6 can play a powerful role. Built on IPv6, Mobile IPv6 enables the creation of always-on IP sessions that keep users connected as they travel from their home to office to hot spots without having to restart an application. Unlike Mobile IPv4, which is based on resource intensive signaling and tunneling, mobility was designed into IPv6 protocol to enable instant connectivity with minimal overhead. Mobile IPv6 also features route optimization that helps ensure that the best path between the user and home network is established so that backbone bandwidth is never wasted. And finally because Mobile IPv6 enables end-to-end connectivity, users are assured security without the fear of NAT (Network Address Translation). For service providers and more importantly users 3G-WiFi roaming promises to enable always on broadband wireless connectivity. To achieve a seamless mobility requires us to solve a number of problems before broadband wireless roaming becomes a reality. First, different signaling protocols are being used by 3G and WiFi. Second the very high scale of the problem, with millions of mobile user needs to be addressed. And third, security issues surrounding the transmittal of corporate data need also to be solved. We also need to be address different usage scenarios including when a mobile node roams into a 3G domain or when a 3G node roams into an unknown WiFi network. In summary 3GWiFi roaming has the dynamics of very complex problems. Mobile IPv4 was developed as an addon feature to the IPv4 protocol. Thus its deployment requires the use of overlay Mobile IPv4 routers, compute intensive signaling to set up a connection and the use of tunnels once a connection is set up. In addition to the obvious problem of having to buy hardware, Mobile IPv4's signaling and tunneling cost increase proportionally with the number of mobile users and their throughput requirement. Subsequently on reason why service providers stayed away from Mobile IPv4 deployments was that users would likely start experiencing long delays and/or temporary disconnections as the performance limit of the protocol was reached. Another problem with Mobile IPv4 is that IPv4 addresses are logical Identifiers that are used to represent at the same time the destination host and its topological position on the whole network. Topological addressing simplifies routing in a fixed network environment but becomes a big problem in a mobile one. Mobile IP permits users to remain connected across wired (e.g., Ethernet, xDSL) and wireless (e.g., 802.11, Cellular, Satellite, 3G) networks while roaming from one network to another. This permits the user to stay connected in route to the airport from home, rather that shutting down their PDA/Laptop at home, and reconnecting at the WiFi location at the airport. Mobility in Mobile IPv6 is facilitated by having the Mobile Node contact its Home Agent with its current location. The Home Agent is a router that maintains the location state for the Mobile Node as it moves and stores the information as a Care-of-Address. This simple but powerful feature which is built into the IPv6 protocol enables all mobile hosts to be reachable without the need of the service provider to purchase/deploy extra devices or waste bandwidth due to tunneling. Another powerful feature of Mobile IPv6 is that it enables a Mobile Node and the IP service host also referred as a Correspondent Node to communicate directly without going through a Home Agent by the use of the Mobile IPv6 Route Optimization. This is done using a procedure defined as Return Routability (RR) within the Mobile IPv6 protocol in which the network path between the Mobile Node and Correspondent Node is secured through the RR procedure. Once this happens packets can be directly forwarded between the communicating parties without the need for the Home Agent. In summary, Mobile IPv6 offers to revolutionize the telecommunications and consumer products by enabling truly always-on broadband connectivity for mobile computing devices. When 3G is combined with WiFi ones' office LAN can now have a global footprint. Looking to the future, Mobile IPv6 promises to help create a new generation of consumer and enterprise application like personal content delivery services, multimedia e-collaboration and virtual Private Mobile Radio replacement just to name a few. The elegance and cost effectiveness of Mobile IPv6 is certain to be an important element of tomorrow's mobile multimedia networks.