---
title: "Packet Latency"
-weight: 8
+weight: 2
---
# Packet Latency
- Only NDRPDR test type measures latency and only after NDR and PDR
values are determined. Other test types do not involve latency
streams.
+
- Latency is measured at different background load packet rates:
- No-Load: latency streams only.
- Latency is measured for all tested packet sizes except IMIX due to
TRex TG restriction.
+
- TG sends dedicated latency streams, one per direction, each at the
rate of 9 kpps at the prescribed packet size; these are sent in
addition to the main load streams.
+
- TG reports Min/Avg/Max and HDRH latency values distribution per stream
direction, hence two sets of latency values are reported per test case
(marked as E-W and W-E).
+
- +/- 1 usec is the measurement accuracy of TRex TG and the data in HDRH
latency values distribution is rounded to microseconds.
+
- TRex TG introduces a (background) always-on Tx + Rx latency bias of 4
usec on average per direction resulting from TRex software writing and
reading packet timestamps on CPU cores. Quoted values are based on TG
back-to-back latency measurements.
+
- Latency graphs are not smoothed, each latency value has its own
horizontal line across corresponding packet percentiles.
+
- Percentiles are shown on X-axis using a logarithmic scale, so the
maximal latency value (ending at 100% percentile) would be in
infinity. The graphs are cut at 99.9999% (hover information still
- lists 100%).
\ No newline at end of file
+ lists 100%).