RTT Values Not Available
When you run a report with RTT columns, sometimes the included rows do not show data. Some of the reasons data might not be available include the following:
• Non-TCP flow - The NetProfiler calculates RTT information only for TCP-based flows. Any flow that is not TCP-based (ICMP, UDP, and so on) does display RTT information.
• Flow not seen by the NetShark or NetExpress - The flow must be detected by a NetShark or NetExpress to calculate RTT information. If a flow is reported only from a network router through NetFlow, there is not any RTT information available.
If the flow is only partially seen (for example, due to asymmetric routing) by the NetShark, or NetExpress, the RTT information is not valid and is discarded.
• Retransmits during the initial flow setup - The NetProfiler does not show RTT information if there is retransmitted information during the initial flow setup. If the NetProfiler does not know which packet is the correct packet to use, there is no way to accurately calculate RTT information.
• Delay between the packets - If the delay between the SYN, SYN-ACK, ACK, and DATA packets is too great (multiple minutes), the RTT timer might expire and RTT information is not calculated.
• Drops questionable values - The NetProfiler takes a conservative approach and drops values that are questionable.
• Flows that start before the initial startup time - Because RTT information is calculated only during the initial flow setup, any flows that started before the beginning of the report time frame do not include RTT information: for example, a report from 14:00:00-15:00:00 that includes flows that started prior to 14:00:00 do not show RTT information.