metrotek Bercut-ET, Руководство по эксплуатации

Страница: 20 / 116

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 par-
ticular frame size is sent through the DUT at the determined through-
put 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 record-
ed 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.
Bercut-ET. Operations manual