76 Part I • Information Technology
where very high data rates are required. Moreover, 40-gbps
Ethernet (40 GbE) and 100-gbps Ethernet (100 GbE) are
just around the corner, with standards currently under
development by IEEE. These ultrahigh speed networks
have been designed to run over fiber-optic cables, but,
amazingly, they can also run over twisted-pair cables.
Most of these Gigabit Ethernet networks are configured to
use full-duplex communication. Ethernet speeds keep
going up, suggesting that Ethernet will continue to be the
preferred networking approach for high-speed LANs and
backbone networks for the foreseeable future.
BACKBONE NETWORKS Backbone networksare the
in-between networks—the middle distance networks that
interconnect LANs in a single organization with each
other and with the organization’s WAN and the Internet.
For example, the corporate headquarters of a large firm
might have multiple buildings spread out over several city
blocks. Each floor of a large building might have its own
LAN, or a LAN might cover an entire smaller building.
All these LANs must be interconnected to gain the
benefits of networking—enhanced communications, the
sharing of resources and data, and distributed data
processing. In addition, the LANs must also be connected
to the company’s WAN and, in most cases, to the Internet.
A backbone network is the key to internetworking
(see Figure 3.8).
The technology involved in backbone networks is
essentially the same as that described for LANs but at
the high end. The medium employed is either fiber-optic
cabling or twisted-pair cabling, providing a high data
transmission rate—100 mbps, 1 gbps, or more. The
topology is usually a bus (Fast Ethernet or Gigabit
Ethernet). The only new terminology we need to intro-
duce relates to the hardware devices that connect net-
work pieces together or connect other networks to the
backbone network.
We have already introduced the hub, the switch,
and the WAP. A hub, we know, is a simple device into
which cables from computers are plugged; it can also be
used to connect one section of a LAN to another. Hubs
forward every message they receive to all devices or sec-
tions of the LAN attached to it, whether or not they need
to go there. Awireless access pointis the central device
in a wireless LAN that connects the LAN to other net-
works. A bridgeconnects two LANs, or LAN segments,
when the LANs use the same protocols, or set of rules
(more on this later); a bridge is smart enough to forward
only messages that need to go to the other LAN. A
router, or a gateway(a sophisticated router), connects
two or more LANs and forwards only messages that need
to be forwarded but can connect LANs that use different
protocols. For example, a gateway is used to connect an
organization’s backbone network to the Internet. AClearwire and 4G Networks
The Clearwire story is an interesting one that is still unfolding. Clearwire was founded by entrepreneur
Craig McCaw, who in the 1980s built a cellular phone business that he sold to AT&T for $11.5 billion.
In 2008, Clearwire obtained $3.2 billion in investment funding from Sprint Nextel, Intel, Comcast, and
Google, among others. Another $1.6 billion in funding was obtained in 2009, with $1 billion of that
from Sprint Nextel, which holds a 51 percent interest in Clearwire. With that funding, Clearwire
continues to build its 4G WiMAX wireless network.
However, there is competition in terms of the technology that will be used to build 4G networks.
Both AT&T and Verizon Wireless—the two largest cellular providers in the United States—have decided
to develop their 4G networks based on a cellular technology called Long Term Evolution (LTE).Some
commentators think that there is room for both WiMAX and LTE technologies in the 4G world, with
WiMAX favored for “local nomads” who want fast Internet access anywhere in their local region and
LTE favored for national roamers who regularly travel around the country. Even if the dual 4G approach
does not work, Clearwire does not see the 4G battle as a big issue—Clearwire insists that its equipment
can be shifted from WiMAX to LTE technology relatively easily. The important point is that WiMAX and
other 4G networks have the potential to do for broadband Internet access what cell phones have done
to phone access. In the same way that many users have given up on wired phone service in favor of cell
phones, the 4G networks could replace cable and DSL services and provide Internet access just about
anywhere you go.
[Based on Ante, 2009; Clearwire, 2010; Kapustka, 2008; and Perez, 2009b]