FA-7256 / Transport flow control / Open access
Rtt estimator weights old and new samples · case 01
Rtt estimator weights old and new samples.
ROOT CAUSE
The faulty implementation uses `(old+sample)/2` for the rtt-estimator-weights-old-and-new-samples decision.
VERIFIED REPAIR
Apply the explicit rtt-estimator-weights-old-and-new-samples contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `alpha*old+(1-alpha)*sample` and still violates a separate fixture.
Case contract
Bounded offline decision model: rtt estimator weights old and new 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 rtt-estimator-weights-old-and-new-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(old, sample, alpha):
return (old+sample)/2
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 30, 0.25), 15)", "check('fixture 2', solve(10, 30, 0), 10)", "check('fixture 3', solve(10, 30, 1), 30)", "check('fixture 4', solve(0, 0, 0.5), 0)"]
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 | 20.0 | 10 | Failed |
| fixture 3 | 20.0 | 30 | Failed |
| fixture 4 | 0.0 | 0 | Passed |
| fixture 1 | 20.0 | 15 | Failed |
SHA-256 / c265cc405a1505a632e6f298b13d3925cad30f02796ffee6096ed6f4cc2885b1
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(old, sample, alpha):
return alpha*old+(1-alpha)*sample
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 30, 0.25), 15)", "check('fixture 2', solve(10, 30, 0), 10)", "check('fixture 3', solve(10, 30, 1), 30)", "check('fixture 4', solve(0, 0, 0.5), 0)"]
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 | 30 | 10 | Failed |
| fixture 3 | 10 | 30 | Failed |
| fixture 4 | 0.0 | 0 | Passed |
| fixture 1 | 25.0 | 15 | Failed |
SHA-256 / 547a01439a74ff6ec51e64f95b12f21c19aaecb84d7e2d39b9646573abbfe80d
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(old, sample, alpha):
return (1-alpha)*old+alpha*sample
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 30, 0.25), 15)", "check('fixture 2', solve(10, 30, 0), 10)", "check('fixture 3', solve(10, 30, 1), 30)", "check('fixture 4', solve(0, 0, 0.5), 0)"]
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 | 30 | 30 | Passed |
| fixture 4 | 0.0 | 0 | Passed |
| fixture 1 | 15.0 | 15 | Passed |
SHA-256 / 9300477f8b149cb32dc9d95a48d0fcfcdafcd3442fc031ad9cb23fd284fc1d9d
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 2026-09-29T14:38:09.865700+00:00.
Case digest / e1d4e643fd59e360b387edfae094880b80338e674e7c5bfaeb4ba73726a6c0dd