It was decided that the only way to be sure was to have packet traces both on the ground and onboard. Vytek set about creating some onboard packet capture code, and set the retransmission timeout maximum down to 3 seconds. Again, because of the large quantity of data, it has been organized onto a separate page . This time, however, a Java viewer applet has been supplied to allow panning and zooming the data. Data was collected for 3 'puts' and 5 'gets'.
Packet loss seems to occur primarily on the downlink, as it has less signal margin than the uplink.
What this means is that 'puts' to the spacecraft work very well, because only Acks get lost on the downlink and the next Ack 'catches up' the sequence number without slowing down. On 'gets' from the spacecraft, data packets get lost on the downlink. In our case, because of memory model limitations onboard, the window is only big enough to hold 4 packets. Thus, if more than one packet is lost within a window, the timeout comes into play. Performance was measured for both 'puts' and 'gets'.