Distribution by QoS shows specific traffic in the terms of service quality. This is interesting in particular to companies that provide a QoS based service or use such services themselves.
To view traffic distribution by QoS:
Choose a section (Exporters, Traffic Patterns or End Users) in the Menu Panel
Select desired node in the Node Tree
Choose QoS in the Tab panel
The screenshot above indicates two main QoS used on the New York's router's St. Louis interface - Default and CS6. It is also noted that at 12h when major increase of Default traffic occurred, CS6 traffic simultaneously experienced a significant drop.
Quality of Service is used for prioritization of critical applications and/or network users (transferring data across the network is prioritized). You can think of these demands as tolerance a certain application or protocol has towards the amount of data loss (packet dropping), delay, jitter... E.g. providing low-latency voice or streaming media, while providing simple best-effort for web traffic or file transfers.
QoS was initially implemented via ToS and Precedence (IP Prec) 3-bit field, and now via Differentiated Services Code Point (DSCP) 6-bit field and Explicit Congestion Notification (ECN) 2-bit field. Read more about Configuring DSCP.