Chapter List

Overview

So far, we have concentrated our efforts on networking at Layer 2 (the Data Link Layer), and as we have seen, there are some quite major differences when we consider the topologies and access methods employed. Ethernet runs over cable plant that comprises coaxial cable, unshielded twisted pair cable, and fiber optic. It runs at 10, 100, and 1000Mbps, and is totally non-deterministic in nature. Token Ring uses no coaxial cable, but uses both shielded and unshielded twisted pair cables besides fiber. This technology runs at 4 and 16Mbps, and is highly deterministic. Vendors are moving to standardize 100Mbps Token Ring (and beyond), but today the upper limit in speed remains at 16Mbps. FDDI, like Token Ring, uses fiber and twisted pair, and works at 100Mbps only. There are no serious plans to improve on this, but again, this is a deterministic technology when viewed from the perspective of performance.

So what is Internetworking, and what relevance does this have to those technologies mentioned above? To answer this, we really need to consider networks themselves in a little more depth, and indeed the problems that they bring with them. The view that we have taken so far, is that networks are a collection of LANs and that they are always of the same basic technology.