Wi-Fi网络评分机制00_(WiFi选网/自动连接)

评分机制简介

当扫描到多个wifi网络时，系统又是如何确定到底连接哪一个AP呢，在Android WiFi Framework中，存在一套评分机制，它会对每一个扫描到的AP进行打分，最后选择一个最优的进行连接。

以WifiConnectivityManager的handleScanResults()方法为入口。当收到扫描结果后，现通过WifiNetworkSelector的getCandidatesFromScan()方法生成所有待评分的candidates，随后再通过WifiNetworkSelector的selectNetwork()方法对每个candidate进行评分并选择最优的一个candidate。

// packages/modules/Wifi/service/java/com/android/server/wifi/WifiConnectivityManager.java
private void handleScanResults(@NonNull List<ScanDetail> scanDetails,
        @NonNull String listenerName,
        boolean isFullScan,
        @NonNull HandleScanResultsListener handleScanResultsListener) {
    // ... ...
    List<WifiCandidates.Candidate> candidates = mNetworkSelector.getCandidatesFromScan(
        scanDetails, bssidBlocklist, cmmStates, mUntrustedConnectionAllowed,
        mOemPaidConnectionAllowed, mOemPrivateConnectionAllowed,
        mRestrictedConnectionAllowedUids, isMultiInternetConnectionRequested());
    mLatestCandidates = candidates;
    mLatestCandidatesTimestampMs = mClock.getElapsedSinceBootMillis();
    // ... ...
    handleCandidatesFromScanResultsForPrimaryCmmUsingMbbIfAvailable(
                listenerName, candidates, handleScanResultsListener);
}

private void handleCandidatesFromScanResultsForPrimaryCmmUsingMbbIfAvailable(
        @NonNull String listenerName, @NonNull List<WifiCandidates.Candidate> candidates,
        @NonNull HandleScanResultsListener handleScanResultsListener) {
    WifiConfiguration candidate = mNetworkSelector.selectNetwork(candidates);
    if (candidate != null) {
        localLog(listenerName + ":  WNS candidate-" + candidate.SSID);
        connectToNetworkForPrimaryCmmUsingMbbIfAvailable(candidate);
        handleScanResultsWithCandidate(handleScanResultsListener);
    } else {
        localLog(listenerName + ":  No candidate");
        handleScanResultsWithNoCandidate(handleScanResultsListener);
    }
}

selectNetwork()的步骤如下:

1. 获取评分器CandidateScorer

   final WifiCandidates.CandidateScorer activeScorer = getActiveCandidateScorer();
   

   目前系统默认的评分器是ThroughputScorer

   public static final String PRESET_CANDIDATE_SCORER_NAME = "ThroughputScorer";
   private WifiCandidates.CandidateScorer getActiveCandidateScorer() {
           WifiCandidates.CandidateScorer ans = mCandidateScorers.get(PRESET_CANDIDATE_SCORER_NAME);
   

2. 运行所有评分器

   其实对最后结果产生影响的只有ThroughputScorer

   for (WifiCandidates.CandidateScorer candidateScorer : mCandidateScorers.values()) {
           WifiCandidates.ScoredCandidate choice;
           try {
               choice = wifiCandidates.choose(candidateScorer);
           } catch (RuntimeException e) {
               Log.wtf(TAG, "Exception running a CandidateScorer", e);
               continue;
           }
   

总结

Android的WiFi选择器功能是通过WifiNetworkSelector实现的。

WifiNetworkSelector通过通过打分算法对每一个scan result进行打分，最终选择分数最高的进行连接。

目前支持的评分器有:

• BubbleFunScorer

  只关心信号强度rssi(received signal strength indicator)

• CompatibilityScorer

• ScoreCardBasedScorer

• ThroughputScorer

WifiNetworkSelector的selectNetwork()方法会运行所有的评分器，但是有效(active)的评分器只有ThroughputScorer。