Page 119 - Electronic Commerce

Chapter 2

provider greatly affects net bandwidth, which is the actual amount of data that is
transmitted per second. When few people are competing for service from an ISP, net
94 bandwidth approaches the carrier’s upper limit. On the other hand, users experience
slowdowns during high-traffic periods.
Bandwidth can differ for data traveling to or from the ISP depending on the user’s
connection type. Connection types include:
• Symmetric connections that provide the same bandwidth in both directions.
• Asymmetric connections that provide different bandwidths for each
direction.
The two bandwidth types in an asymmetric connection are as follows:

• Upstream bandwidth, also called upload bandwidth, is a measure of the
amount of information that can travel from the user to the Internet in a given
amount of time.
• Downstream bandwidth, also called download bandwidth or downlink
bandwidth, is a measure of the amount of information that can travel from
the Internet to a user in a given amount of time (for example, when a user
receives a Web page from a Web server).

Voice-Grade Telephone Connections
In the early days of the Web, most individuals connected to their ISPs through a modem
connected to their local telephone service providers. Plain old telephone service (POTS)
uses existing telephone lines and an analog modem to provide a bandwidth of between 28
and 56 Kbps. Today, most people use other connection methods, including a higher grade of
telephone service called Digital Subscriber Line (DSL) protocol. DSL connection methods
do not use a modem. They use a piece of equipment that is a form of network switch, but
most people call this piece of equipment (incorrectly) a “DSL modem.” Integrated Services
Digital Network (ISDN) was the first technology developed to use the DSL protocol suite and
has been available in parts of the United States since 1984. ISDN is more expensive than
regular telephone service and offers bandwidths of between 128 and 256 Kbps.

Broadband Connections
Connections that operate at speeds of greater than about 200 Kbps are called broadband
services. One of the newest technologies that uses the DSL protocol to provide service in
the broadband range is asymmetric digital subscriber line (ADSL, usually abbreviated
DSL). It provides transmission bandwidths from 100 to 640 Kbps upstream and from 1.5
to 9 Mbps (million bits per second) downstream. For businesses, a high-speed DSL
(HDSL) connection service can provide more than 768 Kbps of symmetric bandwidth.
Cable modems—connected to the same broadband coaxial cable that serves a
television—typically provide bandwidths between 300 Kbps and 1.5 Mbps from the client
to the server. The downstream bandwidth can be as high as 10 Mbps. In recent years, DSL
monthly fees have been slightly lower than those of cable companies in markets where
they compete. Virtually all companies and organizations of any size have some type of
broadband Internet connection.

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