Mobile Intelligence

4.4 CLIENT MOBILITY

Cugola et al. were among the first to support mobility in distributed publish/subscribe systems [10]. They introduce the “movein” and “moveout” operations that offer clients the ability to disconnect from and reconnect to the system. However, these standard distributed publish/subscribe algorithms may not perform well when the clients in the system experience frequent mobility [5, 20]. Various algorithms to address client mobility are presented below. We distinguish between subscriber and publisher mobility as the solutions to deal with each are different.

4.4.1 Subscriber Mobility

We first describe the subscriber mobility algorithm proposed by Cugola et al., which we refer to as the STANDARD algorithm [10]. Then we present a set of optimizations to this algorithm.

4.4.1.1 Standard Algorithm

Figure 4.4 illustrates a timeline of a subscriber going into a period of disconnection and reconnecting to a different broker. During period t₁, the client is connected to Broker 1 and can receive events. At the end of period t₁, the client disconnects from Broker 1 and reconnects after period t₃ to Broker 2. Period t₂ is used by an optimization described in Section 4.4.1.2. Period t₄ is required to complete the reconnection phase, which involves retrieving and playing back events that the client missed while disconnected. Finally, during period t₅, the client receives newly published events as in period t₁.

The objective of the algorithm is to reconfigure the event multicast ...