Overhead of Mobility

We now analyze the effect of mobility at a micro-level on the performance of SSCH. Ideally, SSCH should be able to detect a link breakage due to movement of a node, and subsequently re-synchronize to other neighbors. We show that SSCH can indeed handle this scenario with an experiment comprising 3 nodes and 2 sessions, and in Figure 7 we present a moving average of each session throughput, averaged over a period of 280 ms.

Node 1 is initially sending a maximum rate UDP stream to Node 2. Node 1 initiates a second UDP stream to Node 3 at around 20.5 seconds. This bandwidth is then shared between both the sessions (as in the experiment of Section 4.1.3) until 30 seconds, when Node 3 moves out of the communication range of Node 1. Our experiment configures Node 1 to continue to attempt to send to Node 3 until 43 seconds, and during this time it continues to consume a small amount of bandwidth. In contrast, the experiment in Section 4.1.2 measured the overhead of enqueueing a single packet to an absent node. When the stream to Node 3 finally stops, Node 2's received throughput increases back to its initial rate.

Figure 7: Overhead of Mobility: Node 1 is sending a maximum rate UDP stream to Node 2. Node 1 starts another maximum rate UDP session to Node 3. Node 3 moves out of range at 30 seconds, while Node 1 continues to attempt to send until 43 seconds.