Description
Add or subtract the four-byte FCS according to includesFcs and return both length conventions.
A wire-format length may count headers, payload, padding, or only part of an enclosing message. Offsets and exclusive ends must use a clearly stated byte convention.
Add or subtract the four-byte FCS according to includesFcs and return both length conventions.
When to use this tool
Use Ethernet Fcs Excluded Frame Length when you need a field-level byte count or boundary check.
How to use the tool and how it works
- Enter frameBytes, includesFcs. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read withoutFcs, withFcs. Use the output convention below.
Add or subtract the four-byte FCS according to includesFcs and return both length conventions.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| frameBytes | Frame Bytes | Required. Safe integer. |
| includesFcs | Includes Fcs | Required. Boolean. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| withoutFcs | Without Fcs | Required. Safe integer. |
| withFcs | With Fcs | Required. Safe integer. |
{
"input": {
"frameBytes": 64,
"includesFcs": true
},
"output": {
"withoutFcs": 60,
"withFcs": 64
}
}Limitations and assumptions
- Other wire overhead is unchanged; includesFcs requires at least four reported bytes.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Compare the computed span with the actual captured buffer and validate its contents separately.
References
Similar or alternative tools
- Ethernet Preamble Included Length Flag
Subtract eight bytes when reportedBytes includes preamble and SFD, otherwise retain it as frameBytes.
- Ethernet Padding Payload Shortfall
Use a header of 14 + 4 × vlanTags bytes for zero through two tags.