Workshop

use this common connection “gets on” or “gets off” the bus.
Because NICs share a common bus, each NIC can “hear” other NICs. NICs have built-in rules for using
this common area, which is discussed further in Hour 9, “Ethernet Basics,” and Hour 10, “Token-Ring
Basics.” For the moment, you just need to know that each NIC has been schooled in “netiquette” and has
been taught in the factory to play well with others and to share the wire nicely—that is, most of the time.
Be aware that if a network card does not obey these rules, this can cause problems on the entire shared
segment. (See Figure 1.2 for an illustration of shared versus dedicated telephone lines and network
segments.)
Figure 1.2 Shared versus dedicated lines.
Computers on older networks were actually connected together on the same wire, much like older
Christmas lights used to be. Therefore, a physical break in the wire meant that all the computers on one
side of the break went down. A hub-based segment fixes this, because each computer has its own physical
connection, and the hub ties them all together. The newer method of sharing the wire is called a star
topology, because it looks like a star. The older method is called bus topology—the line from PC to PC is
the common bus area.
A new technology called switching allows each network card to have its own private line; however, a lot
of hub-based shared networks are still in existence (and don’t look for them to go away any time soon).
You’ll find switching to be more and more exciting as you get into network troubleshooting. Similar to
the way hubs allow users to get away from the “Christmas light bulb” problem, switches allow users to
get away from many of the problems of shared networks. Instead of each computer having to compete for
the right to talk when it wants to, each computer can transmit pretty much when it needs to—as long as
the computer on the other end is available, of course. Others in the network neighborhood no longer
compete for the right to talk on the wire, because each computer has its own connection.
How does this work? In a nutshell, a switch looks at the MAC addresses of two workstations on the
network that want to communicate, and it opens up a high-speed private channel for them. A hub has one
common channel, but a switch has many, many channels, as well as the intelligence to switch
conversations between them. With a fast enough switch (called a wire speed switch), workstations
conversing on the switch are not affected whatsoever by other workstations talking away at full speed.
Although prices on hubs are very low, switching has become very cheap as well; you can look to this