1 <!-- 2 Copyright 2012 The Android Open Source Project 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15 --> 16 17 18 In Android 4.0, statistics reported by Linux network interfaces are 19 recorded over time, and are used to enforce network quota limits, 20 render user-visible charts, and more. 21 22 Each network device driver (Wi-Fi included) must follow the standard 23 kernel device lifecycle, and return correct statistics through 24 `dev_get_stats()`. In particular, statistics returned must remain 25 strictly monotonic while the interface is active. Drivers may reset 26 statistics only after successfully completing an `unregister_netdev()` 27 or the equivalent that generates a `NETDEV_UNREGISTER` event for 28 callbacks registered with `register_netdevice_notifier()` / 29 `register_inetaddr_notifier()` / `register_inet6addr_notifier()`. 30 31 Mobile operators typically measure data usage at the Internet layer 32 (IP). To match this approach in Android 4.0, we rely on the fact that 33 for the kernel devices we care about the `rx_bytes` and `tx_bytes` 34 values returned by `dev_get_stats()` return exactly the Internet layer 35 (`IP`) bytes transferred. But we understand that for other devices it 36 might not be the case. For now, the feature relies on this 37 peculiarity. New drivers should have that property also, and the 38 `dev_get_stats()` values must not include any encapsulation overhead 39 of lower network layers (such as Ethernet headers), and should 40 preferably not include other traffic (such as ARP) unless it is 41 negligible. 42 43 The Android framework only collects statistics from network interfaces 44 associated with a `NetworkStateTracker` in `ConnectivityService`. This 45 enables the framework to concretely identify each network interface, 46 including its type (such as `TYPE_MOBILE` or `TYPE_WIFI`) and 47 subscriber identity (such as IMSI). All network interfaces used to 48 route data should be represented by a `NetworkStateTracker` so that 49 statistics can be accounted correctly. 50
