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ATM Operation
Setting Foreground and Background Distributions
Setting up foreground
How to
1 Set up the Transmitter for ATM (See "Setting up the Transmitter for ATM
Payloads " page 154).
2 In the
STREAM as
Channel (VC) under test can be set up.
3 Service Selections:
For Constant Bit Rate (CBR) traffic, select the PEAK CELL RATE and CDV
tolerance.
For Variable Bit Rate (VBR) traffic, select the SUSTAINABLE CELL RATE,
PEAK CELL RATE, MAXIMUM BURST SIZE and CDV tolerance. The
OmniBER then automatically generates worst case user traffic for the VC under
test using the 0.191 enhanced traffic generator algorithm.
For error performance measurement, set the CDV tolerance value to its minimum
value.
Select SINGLE BURST to transmit a burst of cells at the selected cell rate.
N O T E
The CDV tolerance value cannot be set to zero. The minimum value reflects the
inherent CDV that is generated due to the segmentation and mapping of the ATM cell
stream into the physical interface.
To fully stress the policing functions of the VC under test, the CDV tolerance can be
set to the value used in the policing function.
Peak Cell Rate
For CBR, the peak cell rate is the average rate at which cells will be transmitted.
Because the selected cell rate is implemented by a series of discrete cell events, for
arithmetical reasons there will be some unavoidable deviation from ideal periodic
timing. This effect is small.
Cell Delay Variation Tolerance (CDVT)
The transmitter will generate a signal which has a cell delay variation as set by the
user in order to test a receiver's cell delay variation tolerance.
Sustainable Cell Rate
For VBR, this is the long term average cell rate being transmitted.
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folder select SETUP as
ATM SETTINGS
and then the traffic parameters for the Virtual
DISTRIBUTION
, CELL
FOREGROUND
163
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