FA-7251 / Transport flow control / Open access
Retransmitted segments do not supply ambiguous rtt samples · case 01
Retransmitted segments do not supply ambiguous rtt samples.
ROOT CAUSE
The faulty implementation uses `sample` for the retransmitted-segments-do-not-supply-ambiguous-rtt-samples decision.
VERIFIED REPAIR
Apply the explicit retransmitted-segments-do-not-supply-ambiguous-rtt-samples contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `None` and still violates a separate fixture.
Case contract
Bounded offline decision model: retransmitted segments do not supply ambiguous rtt samples. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.
Why this case matters
This deterministic transport flow control model isolates the retransmitted-segments-do-not-supply-ambiguous-rtt-samples policy at a network component boundary.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(retransmitted, sample):
return sample
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 10), None)", "check('fixture 2', solve(False, 10), 10)", "check('fixture 3', solve(False, 0), 0)", "check('fixture 4', solve(True, 0), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 2 | 10 | 10 | Passed |
| fixture 3 | 0 | 0 | Passed |
| fixture 4 | 0 | None | Failed |
| fixture 1 | 10 | None | Failed |
SHA-256 / 9284af5d5f5be49d27ee2a0dc400de130d072b96740369ff554be9d3e3708169
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(retransmitted, sample):
return None
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 10), None)", "check('fixture 2', solve(False, 10), 10)", "check('fixture 3', solve(False, 0), 0)", "check('fixture 4', solve(True, 0), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 2 | None | 10 | Failed |
| fixture 3 | None | 0 | Failed |
| fixture 4 | None | None | Passed |
| fixture 1 | None | None | Passed |
SHA-256 / 59aaaa5152f50633d05908bdbc29c105fdfa3ca65ca9d629de123d72091aa318
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(retransmitted, sample):
return None if retransmitted else sample
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 10), None)", "check('fixture 2', solve(False, 10), 10)", "check('fixture 3', solve(False, 0), 0)", "check('fixture 4', solve(True, 0), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
exec(_line)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| fixture 2 | 10 | 10 | Passed |
| fixture 3 | 0 | 0 | Passed |
| fixture 4 | None | None | Passed |
| fixture 1 | None | None | Passed |
SHA-256 / 4de81e1a35c2524f9b709d503029c7c85cae9ec01ca2a46b94ad0879a4ca19ae
Verification & scope
Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:38:09.835179+00:00.
Case digest / 096a5432fba27b13a1f46503f60dd51cbac80021abf580e72a05ce968e88c85b