diff options
| -rw-r--r-- | core/java/android/net/SntpClient.java | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/core/java/android/net/SntpClient.java b/core/java/android/net/SntpClient.java index 28134b29156d..550cc24db1db 100644 --- a/core/java/android/net/SntpClient.java +++ b/core/java/android/net/SntpClient.java @@ -103,13 +103,22 @@ public class SntpClient long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET); long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET); long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime); - long clockOffset = (receiveTime - originateTime) + (transmitTime - responseTime); + // receiveTime = originateTime + transit + skew + // responseTime = transmitTime + transit - skew + // clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2 + // = ((originateTime + transit + skew - originateTime) + + // (transmitTime - (transmitTime + transit - skew)))/2 + // = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2 + // = (transit + skew - transit + skew)/2 + // = (2 * skew)/2 = skew + long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2; if (Config.LOGD) Log.d(TAG, "round trip: " + roundTripTime + " ms"); if (Config.LOGD) Log.d(TAG, "clock offset: " + clockOffset + " ms"); - // save our results - mNtpTime = requestTime + clockOffset; - mNtpTimeReference = requestTicks; + // save our results - use the times on this side of the network latency + // (response rather than request time) + mNtpTime = responseTime + clockOffset; + mNtpTimeReference = responseTicks; mRoundTripTime = roundTripTime; } catch (Exception e) { if (Config.LOGD) Log.d(TAG, "request time failed: " + e); |