OnTheAir Switch can be used to control a Video router using RS232, but typically, you will have one computer connected to the video router, and all the other computer that need to control the same video router connected to that computer which then is used as a Server.
Here are some explanation on how it works.
Let's say Computer 1 is the one connected to the Video router, and Computer 2 the one connecting to Computer 1 to control the Video Router.
First, of course, make sure that Computer 1 is properly configured and can communicate with the Video Router.
When OnTheAir Switch is started on Computer 1, it will "publish" its service using Bonjour, making it available to all computers that are in the same local network.
On Computer 2, in OnTheAir Switch preferences, instead of selecting a Serial Port to connect to, select a TCP/IP connection, and there you will have a popup list with Computer 1 Bonjour name, select it and you'll be able to control the video router from Computer 2.
Be aware that of course if you quit OnTheAir Switch on Computer 1, Computer 2 will not be able to communicate with the Video router.