## Spirent TestCenter: Why does flow count change drastically when modifier is used?

 Environment/Versions VFD Frame Editor Device count 1000 VLAN increment by 1 Stream block Modifier on UDP port number count (quantity)
 Answer UDP port number count modifier set to 37 gives 37000 flows but when set to 32 gives only 4000 flows. Here is an explanation of why you are seeing the modifier behavior. You have 1000 device count. When you set the modifier on the UDP port, it will try to set the same quantity for each value. Let’s use a device count of 6 for explanation purposes. Example: UDP modifier set with a count of 3. Device 1 – UDP port 1024 Device 2 – UDP port 1025 Device 3 – UDP port 1026 Device 4 – UDP port 1024 Device 5 – UDP port 1025 Device 6 – UDP port 1026 As you can see a UDP count of 3 will give an equal number of UDP port values (2 for 1024 and 2 for 1025 and 2 for 1026). So only 6 flows with a UDP count of 3. Next Example: UDP modifier set with a count of 4 Device 1 – UDP port 1024 Device 2 – UDP port 1025 Device 3 – UDP port 1026 Device 4 – UDP port 1027 Device 5 – UDP port 1024 Device 6 – UDP port 1025 We don’t see equal number of UDP port values (2 for 1024, 2 for 1025, 1 for 1026, 1 for 1027) so we have to add another 6 devices. Device 1 – UDP port 1026 Device 2 – UDP port 1027 Device 3 – UDP port 1024 Device 4 – UDP port 1025 Device 5 – UDP port 1026 Device 6 – UDP port 1027 After adding 6 more devices (total 12) we now see equal number of UDP port values. All have 3 each. (3 for 1024, 3 for 1025, 3 for 1026, 3 for 1027) So this will result in 12 flows. If this is not the desired configuration, possibly changing the modifier such as using the repeat field may produce a more desirable set of flows. Using the repeat count will allow a configuration that can give each device the same number of UDP port values.

Product : Spirent TestCenter,PGA