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DSL Glossary
xDSL (Digital Subscriber Line)
DSL is a dedicated, always on (except for MegaBit 256 Select),
high-speed connection to the Internet. xDSL utilizes more of the
bandwidth on copper phone lines than what is currently used for plain old
telephone service (POTS). By utilizing frequencies above the telephone
bandwidth (300Hz to 3,200Hz), xDSL can encode more data to achieve higher
data rates than would otherwise be possible in the restricted frequency
range of a POTS (Plain Old Telephone System) network. In order to utilize
the frequencies above the voice audio spectrum, xDSL equipment must be
installed on both ends and the copper wire in between must be able to
sustain the higher frequencies for the entire route. This means that
bandwidth limiting devices such as loading coils must be removed or
avoided.
ADSL (Asynchronous DSL)
Asymmetric Digital Subscriber Line (ADSL) is the most popular form of
xDSL technology. The key to ADSL is that the upstream and downstream
bandwidth is asymmetric, or uneven. In practice, the bandwidth from the
provider to the user (downstream) will be the higher speed path. This is in
part due to the limitation of the telephone cabling system and the desire
to accommodate the typical Internet usage pattern where the majority of
data is being sent to the user (programs, graphics, sounds and video) with
minimal upload capacity required (keystrokes and mouse clicks). Downstream
speeds typically range from 256Kbps to 1.5Mbps. Upstream speeds typically
range from 64Kbps to 1Mbps. ADSL also allows the sharing of a single
voice line. With ADSL, and RADSL, you can talk on the phone and be on
the Internet at the same time with only one phone line. Saves the
cost of a second phone line dedicated for an Internet connection.
RADSL (Rate Adaptive DSL)
Rate Adaptive Digital Subscriber Line (RADSL) refers to Qwest supplied ADSL lines
that have rated speeds starting at 256Kbps up and down and goes up to
7.1Mbps down and 1Mbps up. RADSL also allows the sharing of a single
voice line. With RADSL, and ADSL, you can talk on the phone and be on
the Internet at the same time with only one phone line. Saves the
cost of a second phone line dedicated for an Internet connection.
SDSL (Synchronous DSL)
Symmetrical Digital Subscriber Line (SDSL) runs at the same speed for
uploads or downloads. SDSL speeds range from 192Kbps up to 1.5Mbps.
SDSL is a common choice for businesses who upload or trade a lot of data
using their Internet connection.
IDSL (ISDN DSL)
IDSL service runs over an ISDN line and is currently a data only
connection to the Internet. IDSL has a longer reach that other flavors of
xDSL, so some customers out of reach from ADSL or SDSL may still be able to
receive IDSL service. IDSL service is rated at 144Kbps upload and
download.
DSL Line Requirements:
DSL pushes existing copper phone lines to the limit. Because of this, the
qualifications are very stringent. Lines must meet all of the following
conditions:
- The local loop from the CO to customers’ premise can be no longer
than 18,000 feet of 26-gauge copper.
- The loop must be directly fed by copper from the central
office.
- The loop must not have any load coils on it.
- All bridge taps must be counted in total loop length.
- There cannot be a "pair gain" present on the line.
CPE (Customer Premise Equipment)
CPE is the equipment located at the customers site. This typically
only includes the DSL modem, whether it is an internal PCI card or external
Ethernet router. It may include other pieces of equipment as well,
such as separate routers, hubs, or other modems.
Line Sharing
Line sharing allows an ADSL signal to share the phone line with regular
telephones and fax machines allowing the use of your high-speed Internet
connection and telephone at the same time. DSL uses a higher
frequency than that of standard voice communications. All that is
necessary is for microfilters to be installed on the phone lines going to
telephones and fax machines.
Microfilter
Also called an in-line filter, this piece of equipment plugs into the
phone line to your telephone, fax machine, or other equipment other than
the DSL modem or router. It prevents the frequency the DSL is running
on from polluting the frequency your regular voice or fax line, and vice
versa. It is necessary to place one of these on every phone line
going to a telephone, fax machine, etc.
Router
On the Internet, a router is a device or, in some cases, software in a
computer, that determines the next network point to which a packet should
be forwarded toward its destination. The router is connected to at least
two networks and decides which way to send each information packet based on
its current understanding of the state of the networks it is connected to.
A router is located at any gateway, where one network meets another.
Hub
A hub connects devices together. Hubs used to be expensive pieces of
equipment used only in larger computer rooms, but now mini hubs of just 4
or 8 ports can be had cheaply. The key characteristic of hubs is whether or
not they are switched, and whether they support 100mbps or not. For home
use, unless you are doing some really strange stuff, the cheapest hub from
a name brand is adequate. For DSL, one port will be used by the DSL modem,
leaving the rest free for your computers.
Ethernet
Ethernet is the most widely-installed local area network (LAN)
technology. The most commonly installed Ethernet systems are called
10BASE-T and provide transmission speeds up to 10 Mbps.
Network
Two or more computers connected together to share data or resources.
Kbps
Kilobits per second.
One thousand bits per second. Most
common measurement of speed of a DSL line.
Mbps
Megabits per second.
One million bits per second. Used
to measure very high-speed DSL connections.
Speeds in this range are close to T-1.
Central
Office (CO)
A local telephone company switching center. It
is here that DSLAM’s are installed to enable DSL services in an area.
DSLAM
A central office (CO) device for ADSL service that intermixes
voice traffic and DSL traffic onto a customer's DSL line.
It also separates incoming phone and data signals and directs them
onto the appropriate carrier's network.
Also used to serve SDSL and IDSL, though it does not intermix voice
onto these lines.
PCI
An internal expansion slot inside a computer to allow a new
“device card” to be added to a computer to give it added functionality. Considered an “upgrade” path.
USB
An external port that allows USB devices to be added to a
computer that will typically give added functionality to a computer.
Ethernet
The most widely used local area network (LAN) access method
typically uses CAT-5 cable with RJ-45 connectors (like a large phone jack) (see
networking definition of service for more information).
Ethernet is not just used to create networks, but also to connect to
the Internet via various DSL or cable modems, which may require it.
Typically requires an Internal PCI network interface card (NIC) with
an RJ-45 connection jack.
Loop pre-qualification
Because
DSL requires the above conditions, the local loop must undergo
pre-qualification to determine if it meets the above requirements.
This requires checking the pre-qualification status against a
database held by the DSL provider.
Call 1-888-841-4DSL (4375) for more information, or
send an email to dslsales@cybertrails.com.
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