Research Challenges in Mobile Computing

Mobility implies that networks need to cope with moving users. During a single session, users may connect from different network attachment points or use different networks or even more than one network simultaneously[7]. Hence, tomorrow's network will have to support movement of users, servers, services and even infrastructures to support mobile computing.

In my view, following are the important areas of research in the area of network support for mobile computing.

• Mobility. Protocols to support routing to and from mobile hosts. IETF Mobile IP proposal is addressing the issue of unicast routing to mobile hosts. When mobility becomes the norm rather than exception, dealing with large scale mobility, location management, scalable mobile multicast routing will become important. Development of scalable and reliable multicast for mobile networks is another research problem. Design of authentication and access control schemes for mobile users. Current access control schemes allow the specification of who can do what. With mobility, we need to address the issue of who can do what and where .
• Location or position information as an additional parameter in protocol design. Providing routing protocols based on position or location [4,6]. Providing support for querying services available within a given proximity and providing services with a specific geographic scope (use of TTL can give a logical scope). Use of location in determining router functionalities, designation of responsibilities and services to entities within a geographic region.
• End-to-end QoS to moving users. Current end-to-end QoS schemes are designed to guarantee flow behavior with the assumption of relatively static route path between the sender and the receivers. With mobility, the flow path may change with each move, hence end-to-end delay will be impacted by mobility. Any contract that the network is willing to offer to a user must be valid inspite of mobility. Hence, services classes or contracts have to account for mobility[1]. Reservation schemes that support service classes in mobile networks need to consider spatial resource demands in all possible locations that a user may move during a given session[2] Solving these research problems will lead to interesting new services such as Internet Cellular Phone[3].
• Adaptive protocols. Protocols have to adapt to a different set of parameters in mobile wireless networks. Current protocols such as TCP do adapt to RTT and react to congestion in the network. However, protocols need to be designed for adaptation to parameters such as B/W, latency, burst error, disconnection during handoff, asymmetry of the link, location, and cost. Mechanisms for introducing general purpose adaptation in a secure manner are needed. Work done in the area of extensible kernels is applicable here.
• Support for data and functionality migration. In mobile environments, the capability of the client and the type of network access available vary widely. Hence, support for controlling the amount of data and reducing the dependence on a homogeneous network is absolutely critical. Network abstractions for data and functionality migration to and from the mobile host are needed. Data should be able to ``follow" the mobile host. This should be balanced against the cost of migration[5].

1. On accommodating mobile hosts in an Integrated Services Packet Network, Anup Talukdar, B. R. Badrinath, Arup Acharya, IEEE Infocom, April 1997, pp. 1048-1055.
2. MRSVP: A reservation protocol for an Integrated services packet network with mobile hosts, Anup Talukdar, B. R. Badrinath and Arup Acharya, Rutgers University Tech. report., July 1997.
3. IPv6 + Mobile-IP + MRSVP = Internet Cellular Phone, B. R. Badrinath and Anup Talukdar, In Proceedings of IWQoS, May 1997.
4. Mobile Computing: DataMan Project perspective, In Mobile Networks and applications, Tomasz Imielinski, January 1996, pp. 359--369.
5. On structuring distributed algorithms for mobile networks, B. R. Badrinath, Arup Acharya, Tomasz Imielinski, In Computer Communications, April 1996, pp. 309-320.
6. Geographic addressing and routing, Julio Navas and Tomasz Imielinski, In Mobicom 97, September 1997.
7. Vertical handoffs in wireless overlay networks, Mark Stemm, and Randy Katz, To appear in ACM/Baltzer Journal on Mobile Networks, May 1997.