Routing vs. broadcasting in message-oriented services
I've recently taken up desktop and network programming after years of doing web-only work. My first big hobbyist-research-just-to-impress-myself project is doing a peer-to-peer app - an instant messaging client. Just something quirky for my friends an I to keep in touch with each other, hopefully based on some new, custom protocol I'll roll. As such, I've been reading a lot about routing vs.broadcasting from an application layer perspective.
(Needless to say, I'm swimming in an unfamiliar pond, this not being HTTP.)
Can anyone shed some light on the major difference(s) and/or considerations when dealing with message routing vs. broadcasting? Thanks!