1# Continuation Overview 2 3 4## When to Use 5 6As the all-scenario, multi-device lifestyle becomes popular, users have an increasing number of devices. Each device provides users with what they need in a certain scenario. For example, watches allow users to view information in a timely manner, and smart TVs bring them an immersive watching experience. However, each device has its limitation, for example, typing text on a smart TV is frustrating as it is much more difficult than on a mobile device. If multiple devices can sense each other through a distributed OS and together form a super device, the strengths of each device can be fully exerted to provide a more natural and smoother distributed experience for users. 7 8In OpenHarmony, distributed operations across devices are called continuation (previously named hopping), which is further classified into [cross-device migration](hop-cross-device-migration.md) and [multi-device collaboration](hop-multi-device-collaboration.md). To implement continuation, cross-device interaction capabilities of application components are required. Currently, these capabilities are open only to system applications. 9 10 11## Basic Concepts 12 13- **Continuation** 14 15 Continuation refers to distributed operations across devices. It breaks device boundaries and makes applications modular. For example, a user can edit the same email, carry out fitness, or play a game across devices. Continuation provides broad application scenarios, innovative product perspectives, enhanced product advantages, and superior experience. 16 17- **Cross-device migration** 18 19 When the environment changes, for example, when a user goes outdoors or when a more appropriate device is detected, the user can migrate an ongoing task to another device for better experience. The original device exits the task. A typical cross-device migration scenario is as follows: You migrate a video playback task from your tablet to a smart TV. The video application on the tablet exits. From the perspective of application development, cross-device migration migrates the UIAbility component running on device A to device B. After the migration is complete, the UIAbility component on device B continues the task, whereas that on device A exits. 20 21- **Multi-device collaboration** 22 23 Multi-device collaboration enables collaboration between multiple devices, providing users with more efficient and immersive experience than with a single device. A typical multi-device collaboration scenario is as follows: Application A on the tablet is used as the answer board, and application B on the smart TV is used for live broadcast, delivering a better online class experience. From the perspective of application development, multi-device collaboration enables different UIAbility or ServiceExtensionAbility components to run simultaneously or alternately on multiple devices to provide a complete service, or enables the same UIAbility and ServiceExtensionAbility component to run simultaneously on multiple devices to provide a complete service. 24 25 26## Continuation Architecture 27 28OpenHarmony provides a set of APIs for you to implement continuation in your applications. The continuation architecture has the following advantages: 29 30- Capabilities such as remote service invocation to facilitate service design 31 32- Simultaneous continuation of multiple applications 33 34- Different device forms supported, such as tablets, smart TVs, and watches 35 36The following figure shows the continuation architecture. 37 38 **Figure 1** Continuation architecture 39 40  41 42- Cross-device migration task management: The initiator accepts a migration request from the user, provides a migration entry, and displays the migration result. (This capability is unavailable yet.) 43 44- Multi-device collaboration task management: The initiator accepts an application registration request and provides management capabilities such as starting or stopping collaboration and status display. (This capability is unavailable yet.) 45 46- Distributed component management: provides capabilities such as remote service startup, remote service connection, and remote migration, and enables cross-device migration or multi-device collaboration of applications based on a combination of these capabilities. 47 48- Distributed security authentication: provides an E2E encrypted channel for cross-device transmission between applications to ensure that the right person uses the right data through the right device. 49 50- DSoftBus: functions as a unified communication base for a wide range of devices such as tablets, wearables, and smart TVs, and enables unified distributed communication between these devices. 51
