Spirent SmartBits System, Reference Manual

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Chapter 9: Ethernet Cards
Standard Ethernet Features
116 SmartBits System Reference
Incrementing and Decrementing patterns chosen from the drop down list restart their
count at the beginning of each packet transmitted.
You can design custom background patterns in Hex format with the Frame Editor . The
data pattern entered in the Frame Editor is used as the background data pattern.
•
Figure 9-1 illustrates two methods of placing the background pattern in a frame: The
ML-7710 method begins the pattern starting with the first byte of the IP header, and is
then overwritten by the IP header.
•
The other method is shown with the Gigabit and POS cards. This method places the
pattern in the payload data field only.
Figure 9-1. Variations in Background Fill Pattern
Background Fill Pattern Automatically Offset with Certain Cards
The ML-7710 example, shown in Figure 9-2 , displays the initial background fill pattern
and the subsequent frame content:
•
The background pattern is 8 bytes of ff, followed by 8 bytes of 00 = 16 bytes.
•
The IP header is 34 bytes (takes 2 sets of the pattern plus 2 bytes of the third pattern
set).
•
The payload is 64 bytes (continues with the third pattern set, and adds 3+ pattern sets).
•
The signature field and CRC are 22 bytes (continues the pattern from the payload
data).
After the IP header, signature field, and CRC are written into the frame, the payload data
maintains the offset of the pattern based on the initial background fill pattern.