Information Technology Reference
In-Depth Information
LAN topology is the logical and physical system of interconnection of devices in a
LAN. In a Structured Cabling installation, we provide the “highways” to move the
data from one location to another. The topology of the LAN describes how each
device will interact with others, and how the sum of all devices will be intercon-
nected to function as a network. An understanding of LAN topology—how the
wires are hooked up—will be very useful in our discussion of LAN wiring.
In this topic, we cover structured wiring suitable for many of the popular types
of LAN topologies used today. Most of the other chapters are concerned with gen-
eral-use wiring devices and installation techniques that are not specific to any par-
ticular LAN topology. This chapter will detail the two most popular types of LANs:
Ethernet and Token-Ring. We will show several of their variations and show you
how our system of structured cables can be used for each LAN.
We will explain the wiring patterns and interconnections, called the topology,
that are needed to support each type of network. We will not be covering the inti-
mate details of a LAN's protocols, as this is not our topic; we will just show you
how to connect them over Structured Cabling to make the “net work.”
If you are generally familiar with common LANs or with the Open Systems
Interface (OSI) model, you will recognize the LAN topology as Layer 1, the Physical
layer. Layer 1 is subdivided into additional layers. Part of Layer 1 comprises the
actual wire, connectors, and hubs that must be connected properly for the rest of
the protocol model to function. This wiring layer is critical to the functioning of the
network. If the wiring fails, the network fails. Nothing else in the protocol stack
matters. This may be held over the head of the nearest cable installer (perhaps your
own head), if it gives you any comfort (or motivation).
Most types of modern LAN topologies can be supported on the twisted-pair wiring
described in this topic. In addition, there are a number of older, legacy topologies. Some
of these legacy networks work great over twisted pairs, but many older LAN topologies
function on other types of wiring. Those older (in some cases, obsolete) technologies are
important for understanding the development of modern wiring, and some may still be
in use. For completeness, we will cover legacy topologies in Appendix B. Although some
of these older technologies can use twisted-pair cabling, many use coax, twinax, and the
like. So, in this chapter, other than a very brief history of Ethernet cabling, we will stick
to more modern shielded and unshielded twisted-pair copper, optical-fiber cabling, and
the corresponding Ethernet and Token-Ring networks that use these types of cabling.
The three basic types of network topologies are
bus
,
ring
, and
star
. Some LANs,
such as Ethernet, use more than one basic type. The three topologies are illustrated
in Fig. 2.1. Each topology has its advantages and disadvantages.
