metrotek ETS-1000, Руководство по эксплуатации

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20 Analysis. Typical tasks and solutions
imum interframe gap is sent to DUT
2
(fig. 5.1
3
). Then, the analyzer
counts the frames that are transmitted by the DUT. If the fewer frames
are received than transmitted, the interframe gap is increased and the
test reruns.
Note:
relation between interframe gap and load is inverse,
thus, the bigger gap value is, the lesser the load is.
.
.
..
1
2
Figure 5.1. Throughput
2. Latency. This test allows to analyze the time during which a frame will
be transmitted from the source to destination and then back to source.
The latency is one of the major parameters for the real-time services
operation.
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
Ta 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.
2
For the current test and tests described further, all steps are performed automatically.
3
At the figures, only one of connection type is shown. For other possible connection
schemes please refer to the see section 5.3.
ETS-1000. Operations manual