Android TrafficStats.getTotalRxBytes () is less than expected

Question

I am trying to get real traffic statistics data. But TrafficStats.getTotalRxBytes () is less than the sum of TrafficStats.getUidRxBytes () for each installed application. I found this by running this code every 30 seconds (while on a Wi-Fi network):

long total = TrafficStats.getTotalRxBytes(); long mobileTotal = TrafficStats.getMobileRxBytes(); long wifiTotal = (total - mobileTotal); Log.v("SSS", "total=" + total + " mob=" + mobileTotal + " wifi=" + wifiTotal); ArrayList<Integer> uids = new ArrayList<Integer>(); int cnt = 0; for (ApplicationInfo appInfo : packageManager.getInstalledApplications(0)) { long bytes = TrafficStats.getUidRxBytes(appInfo.uid); if (!uids.contains(appInfo.uid)) { // few applications can refer to same uid - sum each uid stats only once uids.add(appInfo.uid); if (bytes > 0) cnt += bytes; } } Log.v("SSS", "sum traffic stats = " + cnt); 

And this is in the logs:

 12-12 19:43:18.798: V/SSS(4772): total=4245863 mob=0 wifi=4245863 12-12 19:43:19.569: V/SSS(4772): sum traffic stats = 9313461 12-12 19:43:49.628: V/SSS(4772): total=4245915 mob=0 wifi=4245915 12-12 19:43:50.459: V/SSS(4772): sum traffic stats = 9314216 12-12 19:44:20.518: V/SSS(4772): total=4246524 mob=0 wifi=4246524 12-12 19:44:21.439: V/SSS(4772): sum traffic stats = 9320030 

The difference between the totals is less than the difference between the amounts:

 9320030 - 9314216 = 5814 bytes // sums of traffic stats by uid 4246524 - 4245915 = 609 bytes // total traffic stats 

1) Why? 2) How to get the correct value for general traffic statistics - should I just summarize traffic statistics using uids?