Ad hoc mobility management with uniform quorum systems

A distributed mobility-management scheme using a class of uniform quorum sy stems (UQS) is proposed for nd hoc networks. In the proposed scheme, locati on databases are stored in the network nodes themselves, which form a self- organizing virtual backbone within the flat network structure. The database s are dynamically organized into quorums, every two of which intersect at a constant number of databases. Upon location update or call arrival, a mobi le's location information is written to or read from all the databases of a quorum, chosen in a nondeterministic manner. Compared with a conventional scheme [such as the use of home location register (HLR)] with fixed associa tions, this scheme is more suitable for ad hoc networks, where the connecti vity of the nodes with the rest of the network can be intermittent and spor adic and the databases are relatively unstable. We introduce UQS, where the size of the quorum intersection is a design parameter that can be tuned to adapt to the traffic and mobility patterns of the network nodes. We propos e the construction of UQS through the balanced incomplete block designs. Th e average cost, due to call loss and location updates using such systems, i s analyzed in the presence of database disconnections. Based on the average cost, we investigate the tradeoff between the system reliability and the c ost of location updates in the UQS scheme. The problem of optimizing the qu orum size under different network traffic and mobility patterns Is treated numerically. A dynamic and distributed HLR scheme, as a limiting case of th e UQS, is also analyzed and shown to be suboptimal in general. It is also s hown that partitioning of the network is sometimes necessary to reduce the cost of mobility management.