To estimate the exact measurement loss, we needed to use reliable application-generated sequence numbers. We conducted a two-way UDP packet exchange experiments using an end-to-end traffic measurement tool, NetDyn 3 (3). As shown in Figure 2, our NetDyn setup consisted of three different processes, Source, Echo and Sink. Source inserted a sequence number in the payload, sent the packet to Echo, which also added a sequence number before forwarding it to Sink. The Source and Sink processes ran on a wireless station, while the Echo process ran on a server connected to the wired LAN. Using the sequence numbers generated by the Source and Echo, we were able to determine which packets were lost in the path from the Source to the Echo and vice versa.
In our experiment, Source sent 20,000 1500-byte packets at 100 packets/second. We ensured that no fragmentation occurred on either side of the AP. Therefore, for each NetDyn frame on the wireless side, there was a corresponding frame on the wired side.