Information Technology Reference
In-Depth Information
LAN wiring technology has become increasingly complex as network speeds have
increased. The proper installation of any type of network cabling requires a substan-
tial amount of knowledge and experience. This chapter will outline the skill sets
needed in the LAN wiring business and will describe the levels of education, as well
as the certification process.
The complexity of modern LAN wiring is most obvious to those of us who have been
in the computer-networking field since its infancy and have observed its evolution,
depicted in Fig. 18.1. One could well assert that the first computer networking began
with the computer-terminal systems of the '60s and '70s. Initially, these computer ter-
minals connected to the mainframe computer using home runs of coaxial cable. Runs
of up to 2000 ft (615 m) were common, and network speed actually seemed light-
ning fast, since the line rate of several megabits per second was used merely to paint
plain text to the screen (usually no more than 2000 characters per screen).
This direct connection of cable could produce a rather massive concentration
of cable as the cable runs neared the computer room, if the terminal controllers were
centralized. You can imagine the bulk and the sheer weight of 500 to 1000 coax
cables if run together into the computer room. Such a bundle was several feet in
diameter and had to be supported structurally. In those days, computer managers
were as often worried about the weight of their network as its speed!
In some installations, the controllers were placed on each floor to minimize the
cable runs. This arrangement was essentially the precursor of modern telecommuni-
cations rooms, as the controllers were often placed in the same utility room or closet
as telephone cross-connects and electrical distribution panels. A driving motivation
was the sheer cost of hundreds of lengthy coax runs (at plenum-rated cable prices),
plus the very high costs of moves, adds, and changes.
Twisted-pair
hubs and
switches
Star
3270
terminals
RS-232
terminals
Coaxial
Ethernet
Home-run
coax
Home-run
multiwire
Coaxial
bus
Distributed computing
(Networks)
Centralized computing
FIGURE 18.1
The emergence of network wiring.
