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Q6-3 How Does the Cloud Work?

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.
Cable Line

A cable line is the second type of WAN connection. Cable lines provide high-speed data
transmission using cable television lines. The cable company installs a fast, high-capacity optical
fiber cable to a distribution center in each neighborhood it serves. At the distribution center, the
optical fiber cable connects to regular cable-television cables that run to subscribers’ homes or
businesses. Cable signals do not interfere with TV signals.
Because as many as 500 user sites can share these facilities, performance varies depending
on how many other users are sending and receiving data. At the maximum, users can download
data up to 50 Mbps and can upload data at 512 Kbps. Typically, performance is much lower than
this. In most cases, the download speed of cable lines and DSL lines is about the same. Cable lines
use their own protocols.

WAN Wireless Connection

A third way you can connect your computer, mobile device, or other communicating device
is via a WAN wireless connection. Amazon.com’s Kindle, for example, uses a Sprint wireless
network to provide wireless data connections. The iPhone uses a LAN-based wireless network
if one is available and a WAN wireless network if not. The LAN-based network is preferred
because performance is considerably higher. As of 2015, WAN wireless provides average per-
formance of 1.0 Mbps with peaks of up to 3.0 Mbps, as opposed to the typical 50 Mbps for LAN
wireless.

Q6-3 How Does the Cloud Work?

Mateo and Joni are flabbergasted at the low cost of the cloud. They doubt that it’s real. They would
be less cautious if they understood how the cloud operates. This section will give you the basic
understanding they lack and enable you to be an effective consumer of cloud services.
The cloud resides in the Internet. So, in order to learn how the cloud works, you need a
basic understanding of how the Internet works. With that background, you will learn how it
is possible for a cloud vendor to provide dramatic elasticity to support the workload shown in
Figure 6-1.
The technology that underlies the Internet and the additional technology that enables the
cloud to work are complicated. Here, we will stay at a high level and help you learn overarching
concepts and basic definitions. We begin with a simple example.

An Internet Example

Figure 6-7 illustrates one use of the Internet. Suppose you are sitting in snowbound Minneapolis,
and you want to communicate with a hotel in sunny, tropical northern New Zealand. Maybe you
are making a reservation using the hotel’s Web site, or maybe you are sending an email to a res-
ervations clerk inquiring about facilities or services.
To begin, note that this example is an internet because it is a network of networks. It consists
of two LANs (yours and the hotel’s) and four networks. (In truth, the real Internet consists of tens
of thousands of networks, but to conserve paper, we don’t show all of them.) A hop is the move-
ment from one network to another. As drawn, in Figure 6-7, the shortest path from you to the
hotel’s LAN consists of four hops. This term is frequently used by cloud vendors when they discuss
provisioning servers to minimize the number of hops.