What does a Hub do?
A hub allows multiple applications to share a connection to the xAP network on a single PC. Only PC's running more than one xAP application need to run a xAP hub but it is recommended that a hub be installed by default on all computers on a home network that uses xAP. The hub is required because only one program on a computer is allowed to connect to an IP port and receive data. xAP data is sent over the LAN using UDP packets on port 3639. The job of a xAP hub is to listen for xAP messages on port 3639 and distribute them to the other xAP applications running on the computer. The hub and the application negotiate a local, dynamically allocated port to communicate over when the application starts up.
There are two variants of hub in common use:
Edward Pearson's .Net 2.0 based hub service for Windows available from here.
This hub replaces various earlier hubs based on xAP Framework.Net v1 and v2.
Other Non Dedicated Alternatives
Whilst operating more than a single xAP application on a single PC requires a Hub to be operational, some xAP applications offer a built-in hub role if no hub is detected when they start. Applications developed using xAP Framework gain this functionality from the framework. The preferred approach however is to install dedicated a xAP hub on all computers on the home network.