Hi Andy,
AB> My initial thought was to do it in seaside. However, I then AB> wondered whether it would be better to build it all in Squeak. AB> The benefit of the Squeak approach (I am guessing) is that I could AB> somehow broadcast to the listening images that I wanted them to AB> start/stop, rather than have them polling every second. Obviously, AB> the app is tiny, so in practical terms it doesn't matter either AB> way, but I am now curious about how I might communicate the AB> start/stop messages over the network to the images. Is this AB> relatively easy in Squeak?
at the end of this message you'll find a copy of a workspace which I used to test network communication. I can help out with more code.
I have no knowledge about Seaside but in AidaWeb a real time clock is part of the demos. Basically the Browser updates parts of the page via Ajax. Dunno how stable that is (Browser side), if it runs for hours.
In class Socket you'll also find TCP communication, I used UDP because I controlled an Asteroids game at a frame rate of 50 per second. TCP will make sure the packet is received or notify the sender, with UDP you have to make sure yourself.
Can't help you with broadcasts (I guess it's a matter of the address you send to) but there you definitely will have no knowledge if your data was received.