Peripherals and Networking - Strata Study Guide - page 111

Not sure if you have a built-in dial-up modem in your computer? On a
desktop PC, a built-in modem is indicated by two telephone jacks, side
by side. On a notebook PC, there is typically just one telephone jack for a
modem. Look closely, because a wider-than-normal jack that looks like it's
for a telephone cord is actually for an RJ-45 connector for Ethernet.
Nowadays, most people use always-on broadband connections for Internet access.
Broadband literally means a wide pathway, capable of carrying data at a high rate of speed.
There are two major technologies in the broadband Internet service market:
Digital Subscriber Line (DSL) Carries Internet signals through telephone lines.
Cable Internet Carries Internet signals through the same cables that deliver cable TV service.
In addition, several other smaller players exist in the broadband Internet market,
including satellite Internet, Wi-Max, and broadband over cell phones (3G, 4G, and so on).
Each of these technologies requires a terminal adapter (for example, a cable modem or
a DSL modem). These boxes are loosely called modems in popular usage, but they don't
modulate and demodulate between analog and digital in the way traditional modems did.
Broadband cable or DSL network technology can theoretically operate at very fast
speeds—over 100 Mbps in some cases. However, the actual speed at which you experience
Internet connectivity depends on many factors, including the service plan you've purchased
(with faster plans being more expensive), how many other users in your area are using the
connection at the same time as you (more an issue with cable than with DSL), what sites
you're accessing, and the overall level of traffi c on the Internet at the moment.
DSL
DSL relies on the presence of an existing telephone network where the local relay (normally
a telephone exchange) has been upgraded to support DSL communication. The speeds
available on a DSL service depend on the technology implemented in the telephone
exchange as well as the quality and the distance of the telephone lines. The actual speeds
you achieve from a DSL connection depend, among other things, on the distance your
location is from the central offi ce , a switching station for your phone company from which
DSL is administered.
An old type of broadband called Integrated Switched Digital Network
(ISDN) was available in the early days of the Internet, offering
approximately twice the speed of dial-up service (56 Kbps, which is really
slow by today's standards).
DSL service is either asymmetric DSL (ADSL) or symmetric DSL (SDSL) .
Symmetric , in the context of network traffi c, means equal. A symmetric DSL connection
transfers data at the same speed whether uploading or downloading. An SDSL connection
of 2 Mbps transfers data both ways at that speed.