Path measurement: Difference between revisions

The main (or master) device captures packet meta data from the remote (or client) device which takes only a fraction of the total traffic.  

Approximately 5% additional bandwidth is required for this capture connection.  

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* Enable analysis: This will disable or enable the path measurement feature. When disabled, no additional memory is used. When enabled, memory for the packet buffer is used which cannot be used for other analyzing modules thus reducing the maximum time the device can go back in time.

The settings must be saved but to actually take effect, a restart of the packet processing is necessary. If this step is required will tell so at the bottom of the page under '''Required actions'''.

This section shows the current state of the measurement engine. The engine might be inactive even if the feature is enabled. Usually a restart is required to actually make it active. If active, the current packet delay is shown. It might be different from the selected value in the configuration above, but if so a note appears that a restart is required.

An info box appears if the a restart of the packet processing is required. The shown link leads to the page '''Settings → Administration''' where the restart can be triggered. The device itself does not need to be rebooted, only the packet processing must be restarted which usually takes only a few seconds.

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The first graph shows the latency measured from the master device to the remote device and back.  

The second and third graph show the number of lost packets in each direction. Lost packets are only accounted for connections that have been seen on both devices.  

The second tab shows packet loss information for each pair of IP addresses. This statistic covers all IP connections that has been seen on both measurement sides. The table shows the number of packets that have been counted for each communication pair. Additionally the number of packets seen on the master device and the corresponding packet loss is shown. The same statistics are shown for the client device too. You can click on the IP address to go to the detailed statistics of the IP module to check which kind of traffic was happening for that IP. Two graphs are shown for each IP pair which shows the packet loss for both direction on one graph and the total packets in the second graph.

The toggle buttons above the graphs allow to switch the graph modes from absolute values to relative values. This setting will show the lost packets in relation to the total (monitored) traffic.  The second option allows to show mbit/s throughput instead of the packet rate.

There are some limitations about the path measurement:

See [[Analyze connections between remote sites]] to get a detailed overview of use cases and device setup.

The debug information tab shows additional statistics which are usually only relevant for identifying problems in the path measurement, either program errors or test setup errors.

# What does the note '''Network setup problem detected: Packet modification or complete loss''' means?

#:This message box appears if flows have been identified for which not a single packet could be seen on both sides. Usually this means that there is some device in between both measurement points that modifies the packet. This can be WAN optimizer which rewrite TCP connection for improved network performance. Such setup is not supported.