Distribution of end user traffic by conversation shows with whom, over what service and protocol did the user talked to during specified time window. This is useful if you want to look into how much traffic has been generated by end to end conversation by a certain user. Data which was sent by the End user is classified as Upload traffic, while data which was received by the end user is classified as Download traffic.
To see traffic by conversation for specific user:
Choose End Users node from the accordion in the Menu Panel
Search and select desired user from the Node Tree
Choose Conversation from the Tab panel
In the screenshot above you can see that the selected user mostly uses mail service, since POP3 protocol consumes most of the traffic.