Ethernet Frame - Maximum Throughput

Maximum Throughput

We may calculate the protocol overhead for Ethernet as a percentage

We may calculate the protocol efficiency for Ethernet

Maximum efficiency is achieved with largest allowed payload size and is:

for untagged Ethernet packets, since the frame size is maximum 1500 byte payload + 8 byte preamble + 14 byte header + 4 byte trailer + minimum interframe gap corresponding to 12 bytes = 1538 bytes. The maximum efficiency is:

when 802.1Q VLAN tagging is used.

The throughput may be calculated from the efficiency

,

where the physical layer net bit rate (the wire bit rate) depends on the Ethernet physical layer standard, and may be 10 Mbit/s, 100 Mbit/s, 1 Gbit/s or 10 Gbit/s. Maximum throughput for 100BASE-TX Ethernet is consequently 97.53 Mbit/s without 802.1Q, and 97.28 Mbit/s with 802.1Q.

Channel utilization is a concept often confused with protocol efficiency. It considers only the use of the channel disregarding the nature of the data transmitted – either payload or overhead. At the physical layer, the link channel and equipment do not know the difference between data and control frames. We may calculate the channel utilization:

The total time considers the round trip time along the channel, the processing time in the hosts and the time transmitting data and acknowledge packets. The time spent transmitting data includes data and acknowledge packets.