What is the functional difference between Token Ring Token Bus and FDDI?
There are no purely functional differences between a token ring token bus implementation and FDDI. In fact, the token bus is defined in IEEE 802.4, and FDDI's topology derives from that very standard. Think of FDDI as being a subset of 802.4. Refer to RFC 1042 (http://www.faqs.org/rfcs/rfc1042.html) for more details.The remainder of my entry doesn't really apply to this question and is more subjective, but I do try to outline some other non-functional differences between the two standards.Apart from functional differences, the obvious ones can be broken into a couple different parts off the top of my head: physical and application. The physical difference is that Token Ring pretty much uses coax cable as its medium while FDDI conspicuously uses fiber. From an application standpoint, Token Ring is short distance (coax has a maximum attenuation distance of 500 meters) while FDDI can traverse far greater distances while attaining greater throughput. As a result, FDDI would be much more scalable, supportive of many more users, and primarily used in large geographically-demanding environments but pricey; on the other hand, token ring would be for less scalable environments but cheaper.Another non-functional difference would be noise immunizations. FDDI is inherently immune to most interferences that coax implementations would be heir to. Fluorescent lighting, various frequencies, and other causes of noise to fiber would not affect it in the same adverse manner that would apply to coax.