Chapter 9: Ethernet Cards
Gigabit Frame Rate Calculation
130 SmartBits System Reference
VLAN Tagging
Refers to frames that are tagged in accordance with IEEE 802.1q. The VLAN type field
(0x8100) and VLAN tag field are inserted between the source MAC address and existing
Ethernet type field, effectively shifting the Ethernet payload right by four bytes.
On the receiver side, each port supports a counter indicating the number of VLAN tagged
frames received. The maximum allowable frame size for counting oversize VLAN frames
is 1522 bytes (or 9022 bytes if the jumbo option is enabled).
VFD 3 Size
Memory allocated for VFD 3; see glossary page 342 for VFD details.
Gigabit Frame Rate Calculation
The LAN-3200A, LAN-3201A, and LAN-301As modules operate at 1000 Mbps.
Payload Capacity Utilization
The payload capacity utilization is calculated on how frequently frames are generated. In
other words, the higher the frame rate, the higher the payload capacity utilization. The
maximum frame rate is achieved with the minimum inter-frame gap. In SmartMetrics
Gigabit, the minimum gap allowed is 12-bytes and the preamble minimum is 8-bytes.
Thus, the maximum payload capacity utilization, measured in bytes per second for a given
frame size is: Max. Payload Capacity Utilization (Bps) = (max. frame rate) * (frame size
+ 12 (inter-frame gap) + 8 (minimum preamble) + 4 (CRC)
Conversely, you can calculate the frame rate from the Payload Capacity Utilization as
follows: (Max. frame rate) = Max. Payload Capacity Utilization (Bps) / (frame size + 12
(inter-frame gap) + 8 (minimum preamble) + 4 (CRC)
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