iOS Development environment Xcode 16.4, macOS 15.6.1 (24G90) Run-time configuration: iOS 17.2+ Short Description After having successfully established an NWConnection (either as UDP or TCP), and subsequently receiving the error code: UDP Connection failed: 57 The operation couldn't be completed. (Network.NWError error 57 - Socket is not connected), available Interfaces: [enO] via NWConnection.stateUpdateHandler = { (newState) in ... } while newState == .failed the data connection does not restart by itself once cellular (RF) telephony coverage is established again. Detailed Description Context: my app has a continuous cellular data connection while in use. Either a UDP or a TCP connection is established depending on the user settings. The setup data connection works fine until the data connection gets disconnected by loss of connection to a available cellular phone base station. This disconnection simply occurs in very poor UMTS or GSM cellular phone coverage. This is totally normal behavior in bad reception areas like in mountains with signal loss. STEPS TO REPRODUCE Pre-condition App is running with active data connection. Action iPhone does loss the cellular data connection previously setup. Typically reported as network error code 57. Observed The programmed connection.stateUpdateHandler() is called in network connection state '.failed' (OK). The self-programmed data re-connection includes: a call to self.connection.cancel() a call to self.setupUDPConnection() or self.setupConnection() depending on the user settings to re-establish an operative data connection. However, the iPhone's UMTS/GSM network data (re-)connection state is not properly identified/notified via NWConnection API. There's no further network state notification by means of NWConnection even though the iPhone has recovered a cellular data network. Expected The iPhone or any other means automatically reconnects the interrupted data connection on its own. The connection.stateUpdateHandler() is called at time of the device's networking data connection (RF) recovering, subsequently to a connection state failed with error code 57, as the RF module is continuously (independently from the app) for available telephony networks. QUESTION How to systematically/properly detect a cellular phone data network reconnection readiness in order to causally reinitialize the NWConnection data connection available used in app. Relevant code extract Setup UDP connection (or similarly setup a TCP connection) func setupUDPConnection() { let udp = NWProtocolUDP.Options.init() udp.preferNoChecksum = false let params = NWParameters.init(dtls: nil, udp: udp) params.serviceClass = .responsiveData // service type for medium-delay tolerant, elastic and inelastic flow, bursty, and long-lived connections connection = NWConnection(host: NWEndpoint.Host.name(AppConstant.Web.urlWebSafeSky, nil), port: NWEndpoint.Port(rawValue: AppConstant.Web.urlWebSafeSkyPort)!, using: params) connection.stateUpdateHandler = { (newState) in switch (newState) { case .ready: //print("UDP Socket State: Ready") self.receiveUDPConnection(). // data reception works fine until network loss break case .setup: //print("UDP Socket State: Setup") break case .cancelled: //print("UDP Socket State: Cancelled") break case .preparing: //print("UDP Socket State: Preparing") break case .waiting(let error): Logger.logMessage(message: "UDP Connection waiting: "+error.errorCode.description+" \(error.localizedDescription), available Interfaces: \(self.connection.currentPath!.availableInterfaces.description)", LoggerLevels.Error) break case .failed(let error): Logger.logMessage(message: "UDP Connection failed: "+error.errorCode.description+" \(error.localizedDescription), available Interfaces: \(self.connection.currentPath!.availableInterfaces.description)", LoggerLevels.Error) // data connection retry (expecting network transport layer to be available) self.reConnectionServer() break default: //print("UDP Socket State: Waiting or Failed") break } self.handleStateChange() } connection.start(queue: queue) } Handling of network data connection loss private func reConnectionServer() { self.connection.cancel() // Re Init Connection - Give a little time to network recovery let delayInSec = 30.0. // expecting actually a notification for network data connection availability, instead of a time-triggered retry self.queue.asyncAfter(deadline: .now() + delayInSec) { switch NetworkConnectionType { case 1: self.setupUDPConnection() // UDP break case 2: self.setupConnection() // TCP break default: break } } } Does it necessarily require the use of CoreTelephony class CTTelephonyNetworkInfo or class CTCellularData to get notifications of changes to the user’s cellular service provider?