# Network Measurement and Performance Analysis at Server Side
## 6 Observations  
We apply EVA to the three packet traces and show the result in Figures 8-10. Figure 8 shows the percentage of flows for each limiting factor. Remember that a flow may suffer several performance problems during its lifetime, especially long-lived TCP connections. For example, for a file transferring flow, it saturates the bottleneck link after slow start, and finally ends up with network congestion. For simplicity, we use the most  
**Flow statistics for each limiting factor.** The flow size distribution is reported by Figure 11. Overall, bandwidth limited flows have the largest average size, followed by congestion limited, while application limited flows have the smallest average size, followed by slow start limited. The results are easy to understand: flows that transfer bulk data are more likely to cause network performance problems than others. The flow duration distribution is plotted by Figure 12, which shows that slow start limited flows have the shortest average lifetime and congestion limited flows have the longest average lifetime. We also notice that application limited flows are not necessarily short-lived and bandwidth limited flows are not necessarily long-lived. In other words, big size does not mean long lifetime and vice versa. Finally, we show the flow rate distribution in Figure 13. Unsurprisingly, bandwidth limited flows have the largest average rate and application limited flows have the smallest average rate.  
**CDN packet trace.** As shown in Figure 8, more than 71% of the flows are slow start limited, i.e., they are short-lived flows. This is not surprising since most images the CDN server delivered were small. However, when turning our eye to the fraction of bytes for each limiting factor, we find that bufferbloat and congestion account for 48% of the traffic. More surprisingly, only 7% of the flows are identified as bufferbloat or congestion limited. Therefore, we suggest to first find the source of the network problem. If the problems are self-inflicted, better congestion controls can alleviate this. Otherwise, ISPs that provide better network environments should be considered.  
**Website packet trace.** Similar to CDN packet trace, slow start limited accounts for 61% of the flows. We also notice that application limited accounts for 34% and 60% of the bytes and duration, respectively. This is mainly because many HTTP sessions are long-lived and interactive. In addition, Figure 9 shows that 22% of the bytes are congestion control limited, which implies the congestion control could have used network bandwidth more efficiently.  
Figure 11: Flow size distribution for each limiting factor (CDN trace).  
Figure 10: Percentage of duration for each limiting factor.  
**P2P packet trace.** Interestingly, even though 79% of the flows are application limited, this limitation only accounts for 5% of the traffic. This means that most TCP connections are not used for file transfers. Unsurprisingly, bandwidth limited accounts for 47% of the traffic. In other words, P2P performance can be further improved if more bandwidth is available. It is worth noting that receive window limited accounts for 47% of the duration. This is probably not a performance problem since P2P users may deliberately limit download speed.