Wifi 评分机制分析
从android N开始，引入了wifi评分机制，选择wifi的时候会通过评分来选择。
android O源码
frameworks\opt\net\wifi\service\java\com\android\server\wifi\SavedNetworkEvaluator.java
private int calculateBssidScore(ScanResult scanResult, WifiConfiguration network,
WifiConfiguration currentNetwork, String currentBssid,
StringBuffer sbuf) {
int score = 0;
// 判断信号是否为5GHz
boolean is5GHz = scanResult.is5GHz();
sbuf.append("[ ").append(scanResult.SSID).append(" ").append(scanResult.BSSID)
.append(" RSSI:").append(scanResult.level).append(" ] ");
// Calculate the RSSI score.
int rssiSaturationThreshold = is5GHz ? mThresholdSaturatedRssi5 : mThresholdSaturatedRssi24;
// 根据wifi的信号等级来获取rssi
int rssi = scanResult.level < rssiSaturationThreshold ? scanResult.level
: rssiSaturationThreshold;
score += (rssi + mRssiScoreOffset) * mRssiScoreSlope;
sbuf.append(" RSSI score: ").append(score).append(",");
// 5GHz band bonus.
if (is5GHz) {
score += mBand5GHzAward; // score += 40
sbuf.append(" 5GHz bonus: ").append(mBand5GHzAward).append(",");
}
// 之前连接过会有奖励
// Last user selection award.
int lastUserSelectedNetworkId = mWifiConfigManager.getLastSelectedNetwork();
if (lastUserSelectedNetworkId != WifiConfiguration.INVALID_NETWORK_ID
&& lastUserSelectedNetworkId == network.networkId) {
// 开机时间减去连接的时间戳,得到的时间就是连接的时间到现在总共多久
long timeDifference = mClock.getElapsedSinceBootMillis()
- mWifiConfigManager.getLastSelectedTimeStamp();
if (timeDifference > 0) {
int bonus = mLastSelectionAward - (int) (timeDifference / 1000 / 60);
score += bonus > 0 ? bonus : 0;
sbuf.append(" User selection ").append(timeDifference / 1000 / 60)
.append(" minutes ago, bonus: ").append(bonus).append(",");
}
}
// Same network award.
// 当前正在连接的SSID也会有奖励
if (currentNetwork != null
&& (network.networkId == currentNetwork.networkId
//TODO(b/36788683): re-enable linked configuration check
/* || network.isLinked(currentNetwork) */)) {
score += mSameNetworkAward;
sbuf.append(" Same network bonus: ").append(mSameNetworkAward).append(",");
// 如果支持漫游，也会有漫游奖励
// When firmware roaming is supported, equivalent BSSIDs (the ones under the
// same network as the currently connected one) get the same BSSID award.
// 漫游奖励，SSID相同，BSSID不同。
if (mConnectivityHelper.isFirmwareRoamingSupported()
&& currentBssid != null && !currentBssid.equals(scanResult.BSSID)) {
score += mSameBssidAward;
sbuf.append(" Equivalent BSSID bonus: ").append(mSameBssidAward).append(",");
}
}
// Same BSSID award.
if (currentBssid != null && currentBssid.equals(scanResult.BSSID)) {
score += mSameBssidAward;
sbuf.append(" Same BSSID bonus: ").append(mSameBssidAward).append(",");
}
// Security award.
// 不是开放的网络，也会有奖励
if (!WifiConfigurationUtil.isConfigForOpenNetwork(network)) {
score += mSecurityAward;
sbuf.append(" Secure network bonus: ").append(mSecurityAward).append(",");
}
sbuf.append(" ## Total score: ").append(score).append("\n");
return score;
}
/**
* Evaluate all the networks from the scan results and return
* the WifiConfiguration of the network chosen for connection.
*
* @return configuration of the chosen network;
* null if no network in this category is available.
*/
public WifiConfiguration evaluateNetworks(List<ScanDetail> scanDetails,
WifiConfiguration currentNetwork, String currentBssid, boolean connected,
boolean untrustedNetworkAllowed,
List<Pair<ScanDetail, WifiConfiguration>> connectableNetworks) {
int highestScore = Integer.MIN_VALUE;
ScanResult scanResultCandidate = null;
WifiConfiguration candidate = null;
StringBuffer scoreHistory = new StringBuffer();
for (ScanDetail scanDetail : scanDetails) {
ScanResult scanResult = scanDetail.getScanResult();
int highestScoreOfScanResult = Integer.MIN_VALUE; // 0x80000000
int candidateIdOfScanResult = WifiConfiguration.INVALID_NETWORK_ID; // -1
// One ScanResult can be associated with more than one networks, hence we calculate all
// the scores and use the highest one as the ScanResult's score.
List<WifiConfiguration> associatedConfigurations = null;
WifiConfiguration associatedConfiguration =
mWifiConfigManager.getConfiguredNetworkForScanDetailAndCache(scanDetail);
if (associatedConfiguration == null) {
continue;
} else {
associatedConfigurations =
new ArrayList<>(Arrays.asList(associatedConfiguration));
}
for (WifiConfiguration network : associatedConfigurations) {
/**
* Ignore Passpoint and Ephemeral networks. They are configured networks,
* but without being persisted to the storage. They are evaluated by
* {@link PasspointNetworkEvaluator} and {@link ScoredNetworkEvaluator}
* respectively.
*/
if (network.isPasspoint() || network.isEphemeral()) {
continue;
}
WifiConfiguration.NetworkSelectionStatus status =
network.getNetworkSelectionStatus();
status.setSeenInLastQualifiedNetworkSelection(true);
if (!status.isNetworkEnabled()) {
continue;
} else if (network.BSSID != null && !network.BSSID.equals("any")
&& !network.BSSID.equals(scanResult.BSSID)) {
// App has specified the only BSSID to connect for this
// configuration. So only the matching ScanResult can be a candidate.
localLog("Network " + WifiNetworkSelector.toNetworkString(network)
+ " has specified BSSID " + network.BSSID + ". Skip "
+ scanResult.BSSID);
continue;
} else if (TelephonyUtil.isSimConfig(network)
&& !mWifiConfigManager.isSimPresent()) {
// Don't select if security type is EAP SIM/AKA/AKA' when SIM is not present.
continue;
}
// 计算分数
int score = calculateBssidScore(scanResult, network, currentNetwork, currentBssid,
scoreHistory);
// Set candidate ScanResult for all saved networks to ensure that users can
// override network selection. See WifiNetworkSelector#setUserConnectChoice.
// TODO(b/36067705): consider alternative designs to push filtering/selecting of
// user connect choice networks to RecommendedNetworkEvaluator.
if (score > status.getCandidateScore() || (score == status.getCandidateScore()
&& status.getCandidate() != null
&& scanResult.level > status.getCandidate().level)) {
// 重新设置candidate
mWifiConfigManager.setNetworkCandidateScanResult(
network.networkId, scanResult, score);
}
// If the network is marked to use external scores, or is an open network with
// curate saved open networks enabled, do not consider it for network selection.
if (network.useExternalScores) {
localLog("Network " + WifiNetworkSelector.toNetworkString(network)
+ " has external score.");
continue;
}
// 判断是否在扫描的列表中评分最高
if (score > highestScoreOfScanResult) {
highestScoreOfScanResult = score;
// 保存networkId
candidateIdOfScanResult = network.networkId;
}
}
if (connectableNetworks != null) {
connectableNetworks.add(Pair.create(scanDetail,
mWifiConfigManager.getConfiguredNetwork(candidateIdOfScanResult)));
}
// 根据评分以及level来判断选择最合适的candidate
if (highestScoreOfScanResult > highestScore
|| (highestScoreOfScanResult == highestScore
&& scanResultCandidate != null
&& scanResult.level > scanResultCandidate.level)) {
highestScore = highestScoreOfScanResult;
scanResultCandidate = scanResult;
mWifiConfigManager.setNetworkCandidateScanResult(
candidateIdOfScanResult, scanResultCandidate, highestScore);
// Reload the network config with the updated info.
candidate = mWifiConfigManager.getConfiguredNetwork(candidateIdOfScanResult);
}
}
if (scoreHistory.length() > 0) {
localLog("\n" + scoreHistory.toString());
}
if (scanResultCandidate == null) {
localLog("did not see any good candidates.");
}
return candidate;
}
}
2018-7-12, Shenzhen
