When testing convergence times packet loss duration is a useful attribute to have. One implementation is to use a static packet rate for example 1000 frames per second and note the number of packets lost and calculate the duration. However this can be done inside ixia itself but is tricky to enable.
Ixia has purposefully left this out of default as it can be unreliable when using a mixture of packet sizes etc in flows.
The packetloss duration can be enabled by using the Test Options button and checking the Packet Loss Duration checkbox.
IxNetwork needs to be able to track the flows in order to calculate frame loss duration: