First of all, I would like to apologize for yet another question that has nothing to do with programming. I don't know of any good networking forums on the web. I did register an account at networking-forum.com a few months back, only to have my first question rejected by the spam filter (which may have been either a bot or a human mod), despite it being a legitimate question about how to learn networking skills and not anything even remotely resembling spam. So yeah, once again, the Internet has proven that CodeCall is the only decent forum for computer nerds aside from vintage-computer.com, Unix.com, and a few user/support groups.
Second of all, I would like to apologize for that off-topic rant. I get pissy about stuff like this.
Third of all, I would like to apologize for the fact that my recent forum activity has consisted entirely of asking questions rather than contributing answers. I haven't been as active on CodeCall as I would like, mostly just checking back every couple weeks or so to ask a question or post an update on my blog. I've also found that in most cases I simply don't know the answers to the questions posted here, or they're just obvious beginner questions that have already been answered by ten different people. There are other members here who are far more knowledgeable than I am who can provide far better answers than I can for technical questions. As for me, I've had mostly questions lately, since I'm trying to learn about a lot of different areas right now.
tl;dr I apologize for being off-topic and not contributing answers.
Now on to my actual question. I have realized that I don't actually understand what an ISP does. I know what they do in layman's terms - that is, they provide Internet access to customers. But why do you need an ISP for that? Use of the Internet predates the first ISPs by at least a decade. In pre-ISP days, you could connect to Usenet or to a BBS simply by hooking a modem to your computer and plugging it into the telephone line. Logically speaking, it seems you could probably do the same thing today to connect to the World Wide Web. Where does the ISP come in? I don't get it.
I'm wondering if anyone can provide a technical explanation, or a link to a technical explanation, of the function of ISPs and how they operate. I've tried the Wikipedia entry on ISPs, but it doesn't help. I'm kind of at a loss here, as well as somewhat dumbstruck by my own ignorance of something so fundamental to the understanding of networks. I've taken a networking class in college and I've read multiple books on Internet protocols, and yet I still don't know the basics.