Spirent SmartBits System, Reference Manual

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Chapter 9: Ethernet Cards
Standard Ethernet Features
122 SmartBits System Reference
Frame Transmit Modes
The following transmit modes are available on all cards:
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Continuous. Constant frame transmit with a constant/random interframe gap (IFG).
Transmission is stopped by application request.
•
Single burst. A single burst with a constant or random IFG. Transmission stops at the
end of the burst.
•
Multiburst. Repetitive bursts with a user-defined delay between bursts. The IFG may
be constant or random; the IBG is constant. Transmission stops at the end of the final
burst.
•
Continuous Multiburst. Runs multi-burst mode continuously with a constant or
random IFG. Transmission is stopped by application request.
Frame Sizes, Legal Ethernet
It is important to note the following standard minimum and maximum legal (or valid)
frame sizes; any frame sizes higher or lower than these sizes are counted as undersize or
oversize frames.
•
Legal (valid) minimum frame lengths: 40 bytes including CRC.
•
Legal (valid) maximum frame lengths: 1518 bytes including CRC or 1522 bytes
including CRC and VLAN tag.
•
For enabled jumbo frames , the maximum length is 9018 bytes including CRC, or
9022 bytes including CRC and VLAN tag.
Interface
The physical connector/media to the card.
Interpacket Gap (Tx min/max/Increments)
Defines the minimum and maximum interpacket gaps allowed per card, and the allowed
increments (resolution).
Interpacket Gap or Inter Frame Gap (IFG) specifies the amount of time between
successive frame transmissions in continuous or burst transmit modes.
Valid ranges for the IFG rate depend upon the network specifications.
Packets per Second and % Utilization allows corresponding IFGs to be calculated from the
rate or utilization chosen assuming 100% medium availability. If transmitting on a
congested or contended medium, the actual transmit rate may be lower.
Each transmit mode essentially sets the inter-frame gap (IFG) timer value between frames.
When bursty-oriented transmission styles are in use, the gap timer is loaded with an
alternate value, called the inter-burst gap (IBG), between bursts.