# Improving network reliability using Multipath TCP Use the available radios in iOS devices to improve your app’s network reliability and performance. ## Discussion When using your app on an iOS device, users are likely to move in and out of range of Wi-Fi, switching to cellular networks and back again. Multipath TCP improves the performance of your app when a user is in a location with limited Wi-Fi and while their device is transitioning to and from cellular data usage. In its default configuration, a URL session uses a single radio for a network call, preferring Wi-Fi over cellular. However, with Multipath TCP enabled, the URL session initiates the request on both radios and selects the more responsive of the two with a preference for Wi-Fi. ### Enable Multipath TCP in your app These steps are required: - Enable the in the Xcode Capabilities pane for your app target. - Set the [`multipathServiceType`](/documentation/Foundation/URLSessionConfiguration/multipathServiceType-swift.property) property in [`URLSessionConfiguration`](/documentation/Foundation/URLSessionConfiguration) to a mode other than `none`. For most cases, the handover mode is the best option. This mode provides your users with a seamless transition between Wi-Fi and cellular, allowing uninterrupted usage of your app. (For information about other modes, see [`URLSessionConfiguration.MultipathServiceType`](/documentation/Foundation/URLSessionConfiguration/MultipathServiceType-swift.enum).) While the user’s device is connected to a reliable Wi-Fi network, your app uses only Wi-Fi, and no cellular data is consumed. As the user leaves the range of the Wi-Fi network and the signal starts to deteriorate, Multipath TCP begins transitioning data usage to the cellular network to provide a seamless transition. > Important: > Multipath TCP requires the destination server to have Multipath TCP enabled. Many commercial load balancers already support Multipath TCP, and you can enable it in the configuration. For Linux-based servers, the Linux kernel with Multipath TCP is available at the [Multipath TCP](https://multipath-tcp.org) website. ### Limitations when using Multipath TCP with Wi-Fi Assist Because Wi-Fi Assist is a user selectable, device-wide option, there are a few limitations when using Multipath TCP with that option enabled: - Wi-Fi Assist prevents flows from using cellular data when your app is in the background. - Wi-Fi Assist limits the amount of data that your app can send over cellular networks. When the limit is reached, Multipath TCP is disabled. Wi-Fi Assist is integrated into the [`URLSession`](/documentation/Foundation/URLSession) API and doesn’t require any changes to the session configuration. At the start of each URL session task, Wi-Fi Assist determines whether to use Wi-Fi or cellular data for the connection. After the URL session task begins, Wi-Fi Assist doesn’t change from Wi-Fi to cellular or from cellular to Wi-Fi. Multipath TCP extends the performance-improving capabilities of Wi-Fi Assist to provide seamless radio transition and improved throughput. > Note: > When using a developer-enabled device for testing, you can disable the Wi-Fi Assist data limitation in the developer section of the Settings app. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)