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You can call the cloud-based flow from your on-premises flow, and the flow in the cloud does not use any of your on-premises resources. 

If you are splitting processing between different integration servers, your flows communicate by using a Switch server technology and connectivity agents. As shown in Figure 7-104, the Switch server communicates to the appropriate connectivity agents. The Switch server is a special type of integration server that routes data. You cannot deploy anything to the Switch server. 

The connectivity agents contain the certificates that your flows require to communicate securely with the Switch server. The connectivity agents for connecting to a Switch server, must be running in the integration servers where you have deployed your on-premises message flows. 

<img src='content_image/997292.jpg'>

Notice that if both of your callable flows are both deployed on IBM Cloud, they can communicate with each other as soon as you deploy them as the Switch server is automatically started for you. You do not need to set up communication between them. 

Similarly, you also do not need to set up communication if both flows are deployed to the same IBM App Connect integration server. 

You can split processing synchronously between message flows by using the CallableFlowInvoke  node in the calling flow, and CallableInput and CallableReply  nodes in the callable flow. Alternatively, you can split processing asynchronously between message flows, by using the  CallableFlowAsyncInvoke  node in the calling flow, CallableInput  and CallableReply nodes in the callable flow, and the CallableFlowAsyncResponse  node in the response flow. You can also choose to share data between the flows that contain these asynchronous nodes (the calling flow and the response flow) by storing and retrieving data in the UserContext folder in the environment tree. 

## 7.9.2 Using callable flows with IBM App Connect Designer 

Flows created on the cloud in IBM App Connect Designer have the ability to call flows on App Connect integration servers in other environments. Here are some examples of the powerful integrations that are now possible: 

