# Does Agora have reconnection mechanisms? (/en/api-reference/faq/integration/reconnection) > For AI agents: see the complete documentation index at [llms.txt](/llms.txt). The Agora SDK has reconnection mechanisms when a user drops offline or a process gets killed. This page shows the connection state mechanism of the Agora SDK under these circumstances. This article does not apply to the Agora Video SDK Web SDK. ## User drops offline [#user-drops-offline] The Agora SDK adds the [`onConnectionStateChanged`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onconnectionstatechanged) or [`connectionStateChangedToState`](https://api-ref.agora.io/en/video-sdk/ios/4.x/documentation/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onconnectionstatechanged) callback in v2.3.2. This callback reports the current network connection state and reasons to any state change. ### Before v2.3.2 [#before-v232] The following diagram shows the callbacks received by the apps of UID 1 and UID 2 during which UID 1 joins the channel, experiences a network exception, loses connection, and rejoins the channel. ![](https://web-cdn.agora.io/docs-files/1557482391248) Where: * T0 = 0 s: The SDK receives the `joinChannel` or `joinChannelByToken` request from the app of UID 1. * T1 ≈ T0 + 200 ms: 200 ms after calling the `joinChannel` or `joinChannelByToken` method, the app of UID 1 joins the channel and receives the `onJoinChannelSuccess` or `didJoinChannel` callback. * T2 ≈ T1 + 100 ms: Due to network latency, the app of UID 2 detects UID 1 100 ms after the latter joins the channel. UID 2 receives the `onUserJoined` or `didJoinedOfUid` callback. * T3: The uplink network condition of UID 1 deteriorates. The SDK automatically tries rejoining the channel. * T4 = T3 + 4 s: If the app of UID 1 fails to receive any data from the server in 4 seconds, it receives the `onConnectionInterrupted` or `rtcEngineConnectionDidInterrupted` callback; meanwhile the SDK continues to try rejoining the channel. * T5 = T3 + 10 s: If the app of UID 1 fails to receive any data from the server in 10 seconds, it receives the `onConnectionLost` or `rtcEngineConnectionDidLost` callback; meanwhile the SDK continue to try rejoining the channel. * T6 = T3 + 20 s: If the app of UID 2 fails to receive any data from UID 1 in 20 seconds, the SDK decides that UID 1 is offline. The app of UID 2 receives the `onUserOffline` or `didOfflineOfUid` callback. * T7: If the app of UID 1 successfully rejoins the channel, it receives the `onRejoinChannelSuccess` or `didRejoinChannel` callback. * T8 ≈ T7 + 100ms: 100 ms after the app of UID 1 successfully rejoins the channel, the app of UID 2 receives the `onUserJoined` or `didJoinOfUid callback`, which means that UID 1 is online again. ### v2.3.2 and Later [#v232-and-later] The following diagram shows the callbacks received by the apps of UID 1 and UID 2 during which UID 1 joins the channel, experiences a network exception, loses connection, and eventually fails to rejoin the channel. ![](https://web-cdn.agora.io/docs-files/1557482418517) Where: * T0 = 0 s: The SDK receives the `joinChannel` or `joinChannelByToken` request from the app of UID 1. * T1 ≈ T0 + 200 ms: 200 ms after calling the `joinChannel` or `joinChannelByToken` method, the app of UID 1 joins the channel. During the process, the app of UID 1 also receives the `onConnectionStateChanged(CONNECTION_STATE_CONNECTING, CONNECTION_CHANGED_CONNECTING)` or `connectionChangedToState(AgoraConnectionStateConnecting, AgoraConnectionChangedConnecting)` callback. When successfully joining the channel, app of UID 1 receives the `onConnectionStateChanged(CONNECTION_STATE_CONNECTED, CONNECTION_CHANGED_JOIN_SUCCESS)` or `connectionChangedToState(AgoraConnectionStateConnected, AgoraConnectionChangedJoinSuccess)` and `onJoinChannelSuccess` or `didJoinChannel` callbacks. * T2 ≈ T1 + 100 ms: Due to network latency, the app of UID 2 detects UID 1 100 ms after the latter joins the channel. UID 2 receives the `onUserJoined` or `didJoinedOfUid` callback. * T3: The uplink network condition of UID 1 deteriorates. The SDK automatically tries rejoining the channel. * T4 = T3 + 4 s: If the app of UID 1 fails to receive any data from the server in 4 seconds, it receives the `onConnectionStateChanged(CONNECTION_STATE_RECONNECTING, CONNECTION_CHANGED_INTERRUPTED)` or `connectionChangedToState(AgoraConnectionStateReconnecting, AgoraConnectionChangedInterrupted)` callback; meanwhile the SDK continues to try rejoining the channel. * T5 = T4 + 10 s: If the app of UID 1 fails to receive any data from the server in 10 seconds after receiving onConnectionStateChanged(CONNECTION\_STATE\_RECONNECTING, CONNECTION\_CHANGED\_INTERRUPTED) or connectionChangedToState(AgoraConnectionStateReconnecting, AgoraConnectionChangedInterrupted), it receives the onConnectionLost or rtcEngineConnectionDidLost callback; meanwhile the SDK continue to try rejoining the channel. * T6 = T3 + 20 s: If the app of UID 2 fails to receive any data from UID 1 in 20 seconds, the SDK decides that UID 1 is offline. The app of UID 2 receives the `onUserOffline` or `didOfflineOfUid` callback. * T7 = T4 + 20 min : If the app of UID 1 fails to rejoin the channel in 20 minutes after receiving onConnectionStateChanged(CONNECTION\_STATE\_RECONNECTING, CONNECTION\_CHANGED\_INTERRUPTED) or connectionChangedToState(AgoraConnectionStateReconnecting, AgoraConnectionChangedInterrupted), the SDK stops trying. The app of UID 1 receives the onConnectionStateChanged(CONNECTION\_STATE\_FAILED, CONNECTION\_CHANGED\_JOIN\_FAILED) or connectionChangedToState(AgoraConnectionStateFailed, AgoraConnectionChangedJoinFailed) callback. UID 1 needs to leave the channel and call the joinChannel or joinChannelByToken method to join the channel. > - If UID 2 is a Web client, the behaviors of the Web app are as follows: > * When UID 1 joins and rejoins the channel, UID 2 receives the `client.on("stream-added")` callback. > * If UID 2 does not receive any data from UID 1 in 10 seconds, UID 2 receives the `client.on("stream-removed")` callback. > * If the server does not receive any data from UID 1 in 3 minutes, UID 2 receives the `client.on("peer-leave")` callback. > - Users can call `leaveChannel` to stop the retires at any time during the SDK reconnection process. ## Process Gets Killed [#process-gets-killed] This scenario involves the following situations: * Enables or disables VoIP mode. * The process gets killed. * Closes a web page. Suppose UID 1 and UID 2 are in the same channel. When the process of user A gets killed: * If UID 1 is in iOS or macOS: UID 1 calls the `leaveChannel` method and UID 2 receives a callback: * Android, Windows, or Linux: UID 2 receives the `onUserOffline` callback. * iOS or macOS: UID 2 receives the `didOfflineOfUid` callback. * The Web: UID 2 receives the `client.on("peer-leave")` callback. * If UID 1 is in Android, Windows, or Linux and user B uses the Native SDK: * If UID 1 does not restart the app and rejoin the original channel within 20 seconds, UID 2 receives a callback: * Android, Windows, or Linux: UID 2 receives the `onUserOffline` callback. * iOS or macOS: UID 2 receives the `didOfflineOfUid` callback. * If UID 1 restarts the app and rejoins the original channel within 20 seconds, UID 2 does not receive any callback function. * If UID 1 is in Android, Windows, or Linux and UID 2 uses the Web SDK: * If UID 1 does not restart the app and rejoin the original channel within 10 seconds, UID 2 receives the` client.on("stream-removed")` callback. * If UID 1 restarts the app and rejoins the original channel, UID 2 does not receive any callback. * For the Web SDK, killing a process is equivalent to a user dropping offline. * If UID 1 is the last user in the channel, the server destroys the channel in 10 seconds.