Hardware Reference
In-Depth Information
DOCSIS cable modems use 6MHz channels that can carry up to 38Mbps downstream
or 27Mbps upstream. DOCSIS 2.0 and earlier allow using only a single channel each
way, meaning they are limited to 38Mbps maximum downstream. DOCSIS 3.0 allows
for bonding multiple channels, and because most DOCSIS 3.0 modems use four bonded
channels down, that would allow up to 152Mbps downstream speed. Although those are
the maximum figures, what you really get depends on your provisioned rate (that is, what
the Internet service provider [ISP] agrees to give you) and may be limited by other bottle-
necks in the network or in your system.
Cable Pricing
Mostcableprovidersofferanumberofdifferentconnectionspeedplansprovidingvarious
download and upload speeds, ranging from as slow as 2Mbps to as fast as 50Mbps or
higher. Some ISPs require you to subscribe to their cable TV service, or may provide a
lower monthly rate if you bundle cable Internet with other services such as TV or phone.
Business-class cable pricing for comparable download/upload speeds tends to be higher
because of additional services such as static IP addresses, a greater number of email ad-
dresses provided, and 24/7 customer support.
Whether you are considering residential or business-class service, keep in mind that up-
load speeds are typically much slower than download speeds, ranging from 10% to 20%
of download speeds.
There may be equipment costs in addition to the monthly fees. For example, most ISPs
provide cable modem rental for a few dollars a month, or you can purchase your modem
outright from the ISP or from other vendors. Unless you need cable Internet service for
just a few months, it makes more sense to buy a cable modem than to rent one.
Digital Subscriber Line
Thebiggestrivaltothecable modeminthebroadbandInternet businessisthedigital sub-
scriberline(DSL).DSL,likeitspredecessorIntegratedServicesDigitalNetwork(ISDN),
appeals to the telephone companies who might be able to use the existing plain old tele-
phoneservice(POTS)wiringtoprovidehigh-speedInternetaccess.DSLisalsoappealing
to businesses that don't have access to cable modems but are looking for a high-perform-
ance, lower-cost alternative to ISDN or T-1/T-3 leased line services.
Note
Some technical discussions of DSL refer to
xDSL
. The x stands for the various versions of
DSL being proposed and offered by local telephone companies and ISPs. DSL generally
refers to any type of digital subscriber line service.
