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216 Chapter 6 The Cloud
Connecting Your LAN to the Internet

Although you may not have realized it, when you connect your SOHO LAN, phone, iPad, or
Kindle to the Internet, you are connecting to a WAN. You must do so because you are connect-
ing to computers that are not physically located on your premises. You cannot start running
wires down the street to plug in somewhere.
When you connect to the Internet, you are actually connecting to an Internet ser-
vice provider (ISP). An ISP has three important functions. First, it provides you with a
legitimate Internet address. Second, it serves as your gateway to the Internet. The ISP re-
ceives the communications from your computer and passes them on to the Internet, and
it receives communications from the Internet and passes them on to you. Finally, ISPs pay
for the Internet. They collect money from their customers and pay access fees and other
charges on your behalf.
Figure 6-6 shows the three common alternatives for connecting to the Internet. Notice that
we are discussing how your computer connects to the Internet via a WAN; we are not discuss-
ing the structure of the WAN itself. WAN architectures and their protocols are beyond the scope
of this text. Search the Web for “leased lines” or “PSDN” if you want to learn more about WAN
architectures.
SOHO LANs (such as that in Figure 6-5) and individual home and office computers are
commonly connected to an ISP in one of three ways: a special telephone line called a DSL line, a
cable TV line, or a wireless-phone-like connection.

Digital Subscriber Line (DSL)
A digital subscriber line (DSL) operates on the same lines as voice telephones, but it operates so
it does not interfere with voice telephone service. Because DSL signals do not interfere with tele-
phone signals, DSL data transmission and telephone conversations can occur simultaneously. A
device at the telephone company separates the phone signals from the computer signals and sends
the latter signal to the ISP. Digital subscriber lines use their own protocols for data transmission.

Figure 6-6
Summary of LAN Networks

Transmission Transmission Equipment Protocol
Type Topology Remarks
Line Speed Used Commonly Used
Local area UTP or optical Common: Switch IEEE 802.3 Switches connect devices,
network ber 10/100/1000 Mbps NIC (Ethernet) multiple switches on all but
Local area Possible: 1 Gbps UTP or optical small LANs.
network Local area UTP or optical for Up to 600 Mbps Wireless IEEE 802.11n, Access point transforms
network with nonwireless access point (802.11ac not yet wired LAN (802.3) to wireless
wireless connections Wireless NIC common) LAN (802.11).
DSL modem to DSL telephone Personal: DSL modem DSL Can have computer and
ISP Upstream to 1 Mbps, DSL-capable phone use simultaneously.
downstream to telephone line Always connected.
40 Mbps (max 10
likely in most areas)
Cable modem Cable TV lines to Upstream to Cable modem Cable Capacity is shared with other
Connections to ISP optical cable 1 Mbps Cable TV cable sites; performance varies
to the Downstream depending on others’ use.
Internet 300 Kbps to 10 Mbps
WAN wireless Wireless 500 Kbps Wireless One of several Sophisticated protocols
connection to to 1.7 Mbps WAN modem wireless enables several devices to
WAN standards use the same wireless
frequency.