Overhead of an Absent Node

SSCH requires more re-transmissions than IEEE 802.11 in order to prevent logical partitions. These retransmissions waste bandwidth that could have been dedicated to a node that was present on the channel. To quantify this overhead, we initiated a CBR stream between two nodes, allowed the system to quiesce, and then initiated a send from the first node to a non-existent node. We present a moving average of the throughput over 80 ms in Figure 5. It shows that the sender takes 530 ms to timeout on the non-existent node. During this time the session throughput drops by 550 Kbps, which is a small fraction (4.6%) of the total throughput.

Figure 5: Overhead of an Absent Node: Node 1 is sending a maximum rate UDP stream to Node 2. Node 1 then attempts to send a packet to a non-existent node.