VIAVI TestCenter: Why are there no multicast traffic seen between IGMP Join and Leaves in IPTV packet captures?

VIAVI TestCenter: Why are there no multicast traffic seen between IGMP Join and Leaves in IPTV packet captures?

On the VIAVI TestCenter, there are two different capture buffers for dataplane traffic, and for control plane traffic.   The dataplane capture buffer wraps/overwrites once the buffer limit is reached.   This is not the case with the control plane capture buffer.    For example consider the below shown packet capture:   Packet # 51 - Join. Packet #52 - Second Join. Packet #53 - At 5th second channel change interval leave   The above screenshot shows there are no multicast traffic seen between IGMP Join/Leave (packets 52 and 53). This is because the mutlicast traffic which was supposed to be in between IGMP Join/Leave has been overwritten. The final packet capture presented to the user is a combination of dataplane and control plane packets.   As the dataplane traffic is pumped more and more, the control plane packets in the capture file starts accumulating towards the beginning of the capture file. When the load on the streamblock is reduced making the traffic to be sent at a lower rate, the packet capture will be able to show that there are multicast packets seen between the IGMP Join/Leaves. This is the same reason why there might be differences between Join/Leave latencies in the IPTV results and when calculated manually.