====================
Testing leg latency
====================

In addition to testing throughput, SD-WAN speed tests can also
be used to test leg latency. To test leg latency, follow these steps:

#. Determine the download speed of the leg using normal speed testing
   procedures.
#. Run a TCP download test with a rate limit of 25% of the total bonded
   speed. For example, if the total speed is 6.0 Mbps, set the TCP
   download rate limit to 1.5 Mbps.

   |image0|

   This ensures that the latency checks during the speed test measure
   the propagation latency of the leg (the latency seen due to the
   distance between the CPE and aggregator), not the queueing latency
   (the latency seen due to packets being placed in large queues).
#. Review the test results. Note the reported latency.
   |image1|
   The latency chart should be fairly uniform, as in this example below:
   |image2|

   If the latency chart shows a lot of variation, the test result is
   invalid and the leg should be tested further to determine why the
   latency varies.


.. |image0| image:: /attachments/1639516/1933401.png
.. |image1| image:: /attachments/1639516/1933402.png
.. |image2| image:: /attachments/1639516/1933403.png
