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 for Windows [xFx-Express Hub]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.