EXFO ETS-1000 - Manual (Page 43)

Typical Tasks and Solutions
Ethernet Tester Analyzer 35
RFC 2544 Methodology
Latency
This test allows to analyze the time it takes for a frame to be transmitted
from the source to destination and then back to the source. The latency is
one of the major parameters for real-time applications running over
Ethernet networks.
When analyzing the latency, the throughput for DUT at each of the listed
frame sizes is determined first. Then, a stream of frames at a particular
frame size is sent through the DUT at the determined throughput rate to a
specific destination. The minimum duration of the stream transmission is
set as 120 seconds (user can specify alternative value in the range of 1–
2886 seconds). In a specific time, an identifying tag is included into one
frame with the type of tag being implementation dependent. The time at
which this frame is fully transmitted is recorded as a tag time stamp value.
The receiver port of the analyzer then recognizes the tag information in the
frame stream and records the time at which the tagged frame was
received (Tb value).
The latency value is the difference between time stamp Tb and time stamp
Ta values.
The test is repeated at least 20 times (user can specify alternative value
from 1 to 30).