SANs, LANs, MANs, and WANs

SANs, LANs, MANs, and WANs

Characterize Network

One way to characterize networks is according to their size. Two wellknown examples are LANs (local area networks) and WANs (wide area networks); the former typically extend less than 1 km, while the latter can be worldwide. Other networks are classified as MANs (metropolitan area networks), which usually span tens of kilometers. The reason such classifications are interesting is that the size of a network often has implications for the underlying technology that can be used, with a key factor being the amount of time it takes for data to propagate from one end of the network to the other; we discuss this issue more in later articles.

An interesting historical note is that the term “wide area network” was not applied to the first WANs because there was no other sort of network to differentiate them from. When computers were incredibly rare and expensive, there was no point in thinking about how to connect all the computers in the local area—there was only one computer in that area. Only as computers began to proliferate did LANs become necessary, and the term “WAN” was then introduced to describe the larger networks that interconnected geographically distant computers.

Another kind of network that we need to be aware of is SANs (system area networks). SANs are usually confined to a single room and connect the various components of a large computing system. For example, HiPPI (High Performance Parallel Interface) and Fiber Channel are two common SAN technologies used to connect massively parallel processors to scalable storage servers and data vaults. (Because they often connect computers to storage servers, SANs are sometimes defined as storage area networks.) Although this article does not describe such networks in detail, they are worth knowing about because they are often at the leading edge in terms of performance, and because it is increasingly common to connect such networks into LANs and WANs.