If I understood correctly "goodput" applies to application data rate (i.e 1460 byte packets) while "throughput" also includes all protocol headers (1514 byte packets).

What term should be used for throughput including Ethernet CRC and Ethernet overhead (1538 byte packets)?

EDIT: I've heard it being referred to as "Physical Throughput", "L1 Speed" or even "L0 Speed".

1 Answer 1


I simply call this link speed or L1 throughput; with Ethernet, this is the nominal speed.

You can directly calculate the maximum, effective L4 throughput for TCP over IPv4 over standard Ethernet (without any options) with (1460/1538) * link speed.

For completeness, the nominal speed doesn't include all Ethernet overhead. The physical layer encodes bits with various line codes, so for instance a 1000BASE-SX signal (1 Gbit/s over shortwave multi-mode fiber) is 8b/10b encoded with a physical signal rate of 1.25 Gbit/s.

You can find the nominal speed only in the physical layer's top sublayer (on top of PCS), but it's a very practical figure to work with.

While some might refer to the lower physical sublayer as L0, the only official use I know of is with Fibre Channel where FC-0 refers to the lowest part of the FC physical layer - PHYs, transceivers, cables and connectors. For Ethernet, this is (more or less) the PMD sublayer.

  • Just for completeness: K, M, G etc in link speeds are always powers of ten and never powers of two, ie 1 Gbit/s is 1,000,000,000 bits/sec. My calculations were off for years until I learned this.
    – jonathanjo
    Commented Jan 26, 2019 at 18:31

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