Finally, keep in mind that technology changes rapidly in the computer and networking fields. Although hubs might have been sufficient a few years ago, today these are now legacy devices that have been replaced by switches that operate much faster and cost about the same as a hub used to cost. Although Bill Gates might have thought (way back when) that no one would ever need more than 640KB of memory, that prediction proved false almost as soon as it left his mouth. As we all know, change is the only constant thing in this universe. With technology, this is especially the case today.
If you are about to set yourself on a course of designing a network, become familiar with all the latest technologies, and don't depend solely on past experience. The best way to keep up with new technologies is to read about them. You can use books, such as this one, and resources on the World Wide Web, and you can also talk to knowledgeable consultants who are experts in their field.
Finally, Appendix C, "Internet Resources for Network Administrators," can point you to some interesting books and Web sites that contain helpful information. You'll find links in the appendix to sites that specialize in security, network protocols, and so on. You'll also find sites that maintain copies of Internet Request for Comments (RFC) documents, which spell out standards that are used on the Internet.