ADSL Asymmetric Digital Subscriber Line
Asymmetric Digital Subscriber Line is what brings you broadband. It uses
software based at your local phone exchange to make your standard phone line
behave like a high-bandwidth line. It's 'asymmetric' because it allocates more
bandwidth downstream from the Internet to your desktop than upstream.
ADSL2+
ADSL2+ has only been available since it was approved for use in September
2005. ADSL2+ means you can now get even higher speeds than ever before. ADSL2+
(G.992.5), more than doubles the downstream data rate (bandwidth) of ADSL to as
much as 25M bit/sec. (25 Mbps)
ALWAYS-ON
You don't have to dial into a broadband connection. If your PC is on and
you're logged on to your broadband service, you're online
ATM Asynchronous Transfer Mode
This high speed network protocol is composed of 53 byte "cells" having 5 byte headers and 48 byte payloads. Because of its short packet length, it is especially good for real time voice and video.
ATU-C ADSL Termination Unit - Central Office
The device at the end of an ADSL line that stands between the line and the first item of equipment in the telephone switch. It may be integrated within an access node.
ATU-R ADSL Termination Unit - Remote
The device at the end of an ADSL line that stands between the line and the first item of equipment in the subscriber's premises. It may be integrated within an access node.
AWG American Wire Gauge
A measure of the thickness of copper, aluminum and other wiring in the U.S. and elsewhere. Copper cabling typically varies from 18 to 26 AWG. The higher the number, the thinner the wire. The thicker the wire, the less
susceptible it is to interference. In general, thin wire cannot carry the same amount of electrical current the same distance that thicker wire can.
BERT Bit Error Rate Test
A test that reflects the ratio of errored bits to the total number transmitted. Usually shown in exponential form (10^-6) to indicate that one out of a certain number of bits are in error.
bps Bits Per Second
A measurement of transmission speed
BRI Basic Rate Interface
This is an Integrated Services Digital Network (ISDN) interface
typically used by smaller sites and customers. This interface consists
of a single 16 Kbps Data (or "D") channel plus 2 Bearer (or
"B") channels for voice and/or data. Also known as Basic Rate
Access, or BRA
BRIDGE TAP
An accidental connection of another local loop to the primary local
loop. Generally it behaves as an open circuit at DC, but becomes a
transmission line stub with adverse effects at high frequency. It is
generally harmful to DSL connections and should be removed. Extra phone
wiring within one's house is a combination of short bridge taps. A POTS
splitter isolates the house wiring and provides a direct path for the
DSL signal to pass unimpaired to the ATU-R modem.
BROADBAND
Broadband refers to a type of network connection that supports a very high
bit rate. The higher the bit rate, which is a measure of speed of transmission
of bits per second (bps), the faster the transmission will occur in a given
period of time. Typical types of broadband are cable internet, DSL, satellite
...
CABLE INTERNET
Cable Internet is a broadband method which uses the local coaxel cable TV
line to receive (broadband) Internet to your home or office via a cable modem.
Speeds vary due to being a shared line opposed to DSL being a dedicated line,
but speeds can be as fast or much faster depending on the ISP
CAP
- Carrierless Amplitude
A version of QAM in which incoming data
modulates a single carrier that is then transmitted down a telephone
line. The carrier itself is suppressed before transmission (it contains
no information, and can be reconstructed at the receiver), hence the
adjective "carrierless."
CBR - Constant Bit Rate
CCITT
- Consultative Committee for International Telegraph and Telephone
CLEC - Competitive Local Exchange Carrier
CO - Central Office
A circuit switch that terminates all the local access lines in a
particular geographic serving area; a physical building where the local
switching equipment is found. xDSL lines running from a subscriber’s
home connect at their serving central office.
CODEC -
an abbreviation for coder/decoder.
Specifically it converts a voice
grade analog signal to u-law or A-law encoded samples at an 8KHz
sampling rate. DSL bypasses the CODECs at the central office by
separating the frequencies in a POTS splitter and passing the DSL signal
to a DSLAM, the DSL equivalent of a CODEC.
CPE -
Customer Premise (or Provided) Equipment
A wide range of customer-premises terminating equipment which is
connected to the local telecommunications network. This includes
telephones, modems, terminals, routers, settop boxes, etc.
CSU - Channel Service Unit
DCE - Data Communication (or Circuit-Terminating) Equipment
DMT
- Discrete Multi-tone
DOWNSTREAM -
Transmission of data from the Internet to your computer
DSL - Digital Subscriber Line
DSL is a technology for providing a dedicated digital circuit between
one location (home, office ...), and the telephone company's central
office, allowing high-speed simultaneous voice and high-speed data
services, such as super fast Internet access, over existing twisted
copper telephone lines.
DSLAM - Digital Subscriber Line Access Multiplexer
DSU - Data Service Unit
A digital interface device that connects end user data communications
equipment to the digital access lines, and which provides framing of
sub-64Kbps customer access channels onto higher rate data circuits. A
DSU may be combined with a CSU into a single device called a CSU/DSU.
See Channel Service Unit/Data Service Unit.
DTE - Data Terminal (or Termination) Equipment
Typically the device that transmits data such as a personal computer or data terminal.
ECHO SUPPRESSOR/ECHO CANCELLER
These are active devices used by the phone company to suppress positive feedback
(singing) on the phone network. They work by predicting and subtracting a
locally generated replica of the echo based on the signal propagating in the
forward direction. Modems deactivate these devices by sending the 2100Hz answer
tone with 180 phase reversals every 450msec at the beginning of the connection.
FDM - Frequency Division Multiplexing
FIBER OPTIC - See
Optical Fiber
FIREWALL
Software or hardware that is designed to prevent unauthorised access to a
network. This can be either a piece of software or a standalone piece of
equipment.
FTTC - Fiber To The Curb
Network
Where an optical fiber runs from the
telephone switch to a curbside distribution point close to the
subscriber where it is converted to copper pair.
FTTH- Fiber To The Home Network
Where an optical fiber runs from the telephone switch to the
subscriber's premises.
HDSL - High bit-rate Digital Subscriber Line
Modems on either end of one or more twisted wire pair that deliver T1 speeds. At present, this requires two lines.
HFC - Hybrid Fiber-Coax
IEC
- Inter-Exchange Carrier
ISDL - ISDN Digital Subscriber Line
Uses ISDN transmission technology to
deliver data at 128 kbps in an IDSL modem bank connected to a router.
ISDN - Integrated Services Digital Network
Gives a user up to 56 kbps of
data bandwidth on a phone line that is also used for voice, or up to 128
kbps if the line is only used for data.
ISO - International Organization for Standards
ISP - Internet Service Provider
An entity that provides commercial access
to the Internet. These can range in size from someone operating dial-up
access with a 56 kilobit line and several dozens of customers to
providers with multiple pops in multiple cities and substantial
backbones and thousands or even tens of thousands of customers.
ITU - International Telecommunications Union
IXC - Inter-exchange Carrier Post
1984 name for long distance phone
companies in the United States. AT&T is the largest, followed by MCI
and Sprint, but several more small IXCs exist.
Kbps - Kilobits Per Second
LATA - Local Access and Transport Area
This was created by the 1984
divestiture and defines the geographic area over which the LEC may
provide toll calls. The area is often smaller than that covered by a
long distance area code. Even though ten or twenty LATAs are
normally to be found within the territory of a LEC, the LEC may not
provide calls that cross LATA boundaries. Such inter-LATA traffic is the
exclusive domain of the IXC.
LEC - Local Exchange Carrier
One of the U.S. telephone access and service
providers that have grown up with the recent deregulation of
telecommunications.
LOADING COIL
A device used to
extend the range of a local loop for voice grade communications. They
are inductors added in series with the phone line which compensate for
the parallel capacitance of the line. They benefit the frequencies in
the high end of the voice spectrum at the expense of the frequencies
above 3.6KHz. Thus, loading coils prevent DSL connections.
LOCAL LOOP
A pair of wires, moderately twisted for the entire length between the
telephone company's end office and the user premises (the common
telephone set) form a loop, so it is referred to as the local loop. This
loop provides a user with access to the global telecommunications
infrastructure that is installed all over the world. The local loop has
been historically designed to provide voice grade audio service. The
circuit is powered from the central office with 48V (open circuit
voltage) limited in current to a value somewhat higher than 20mA. This
current is used for signaling phone access, burning off moisture,
breaking through metalic oxides caused by corrosion, and powering a
carbon microphone. The original telephone equipment contained no active
electronics. The actual wiring of the local loop may be considered to be
a lossy transmission line. DSL uses whatever frequencies will propagate
on this line for purposes of digital data transmission. T1 modulation
(alternate mark inversion) has been doing this for years. DSL extends
the capability by using modern technology to increase the data rates and
distances spanned.
Mbps - Megabits Per Second
MDF - Main Distribution Frame
MICROFILTER
A small device that you plug into your phone socket and your computer
communications cable which stops your broadband connection being disrupted by
telephones connected to the same line
MODEM
The device which modulates or converts your computer's digital signals
device to analogue signals suitable for carrying over a normal phone line and
vice versa. Modem is short for modulation/demodulation.
MODULATION
The prescribed method of encoding digital (or analog) signals on a
different waveform (the carrier signal). Once encoded, the original
signal may be recovered by an inverse process, demodulation. Modulation
is performed to adapt the signal to a different frequency range (and
medium) than that of the original signal.
MVL - Multiple Virtual Line
NARROWBAND
A service or connection allowing only a limited amount of information to be
conveyed such as dial up internet access
NAT -
Network Address Translation
The translation of an Internet Protocol
address (IP address) used within one network to a different IP address
known within another network. One network is designated the inside
network and the other is the outside. Typically, a company maps its
local inside network addresses to one or more global outside IP
addresses and unmaps the global IP addresses on incoming packets back
into local IP addresses. This helps ensure security since each
outgoing or incoming request must go through a translation process that
also offers the opportunity to qualify or authenticate the request or
match it to a previous request. NAT also conserves on the number of
global IP addresses that a company needs and it lets the company use a
single IP address in its communication with the world.
NEBS -
Network Equipment Building Standards
NEXT - Near-end Crosstalk
Interference between pairs of lines at the
telephone switch end.
NID
- Network Interface Device
A device that terminates copper pair from the serving central office at
the user’s destination and which is typically located outside that
location.
OPTICAL FIBER -
Optical fiber (or "fiber optic") refers to the medium and the technology
associated with the transmission of information as light pulses along a glass or
plastic wire or fiber. Optical fiber carries much more information than
conventional copper wire and is in general not subject to electromagnetic
interference and the need to retransmit signals. Most telephone company
long-distance lines are now of optical fiber.
Transmission on optical fiber wire requires repeater at distance intervals.
PCM
- Pulse Code Modulation
POP
- Point of Presence
A node of an ISP containing a DSU-CSU, terminal
server and router and sometimes one or more hosts, but no network
information center or network operations center.
POTS
- Plain Old Telephone Service
Basic voice service available in
residences throughout the United States.
PPP
- Point to Point Protocol
PRI
- Primary Rate Interface
This is an Integrated Services Digital Network (ISDN) interface
typically used by larger customers. This interface consists of a single
64 Kbps Data (or "D") channel plus 23 or 30 Bearer (or
"B") channels for voice and/or data. Also known as Primary
Rate Access, or PRA.
PSTN
- Public Switched Telephone Network
PTT -
Postal, Telegraph and Telephone
Generic European name usually used to
refer to state-owned telephone companies.
PVC
- Permanent Virtual Circuit
Connection-oriented circuit that may be
set up by software between any two nodes of a switched network.
QAM
- Quadrature Amplitude Modulation
QoS
- Quality of Service
RADSL
- Rate Adaptive Digital Subscriber Line
A version of ADSL where modems
test the line at start up and adapt their operating speed to the fastest
the line can handle.
RBOC
- Regional Bell Operating Company
One of the seven U.S. telephone
companies that resulted from the break up of AT&T
ROUTER
A device which decides where to send packetised information, so essential if
you have more than one computer on a network
SDSL - Symmetrical Digital Subscriber Line
HDSL plus POTS over a single
telephone line. This name has not been adopted by a standards group but
is being discussed by ETSI. It is important to distinguish, however, as
SDSL operates over POTS and would be suitable for symmetric services to
premises of individual customers.
SELF-INSTALL
You are responsible for installing software (using a wizard) and plugging in
the microfilter and modem yourself
SNR - Signal-to-Noise Ratio
SOHO - Small Office Home Office
A type of DSL connection possessing qualities better than ADSL.
Designed especially for smaller businesses
SONET - The Synchronous Optical Network
SONET includes a set of signal rate multiples
for transmitting digital signals on optical fiber. The base rate (OC-1) is 51.84
Mbps. OC-2 runs at twice the base rate, OC-3 at three times the base rate, and
so forth. Planned rates include OC-1, OC-3 (155.52 Mbps), OC-12 (622.08 Mbps),
and OC-48 (2.488 Gbps). Asynchronous transfer mode (ATM) makes use of some of
the Optical Carrier levels.
SVC
- Switched Virtual Circuit
A term found in frame relay and ATM networking in which a virtual
connection, with variable end-points, is established through an ATM
network at the time the call is begun; the SVC is de-established at the
conclusion of the call. See also Permanent Virtual Circuit.
T1
A T1 transfers data between two points at 1.544 Mbps symmetrically, and
is ideal for customers who need a high-speed Internet connection. A
T1 connection provides roughly 60 times more data than a normal
residential modem and is also extremely reliable.
TELCO- Telephone Company
Generic name for telephone companies throughout the
world which encompasses RBOCs, LECs and PTTs.
TDM - Time Division Multiplexing
UBR
- Unspecified Bit Rate
UPSTREAM
Transmission of data from your computer to the Internet
UTP - Unshielded Twisted Pair
A cable with one or more twisted copper wires bound in a plastic sheath.
Preferred method to transport data and voice to business workstations
and telephones. Unshielded wire is preferred for transporting high speed
data because at higher speeds, radiation is created. If shielded cabling
is used, the radiation is not released and creates interference.
VBR
- Variable Bit Rate
VDSL- Very high bit-rate Digital Subscriber Line
Modem for twisted pair
access operating at data rates from 12.9 to 52.8 Mbps with corresponding
maximum reach ranging from 4500 to 1000 feet of 24-gauge twisted pair.
XDSL
Refers collectively to all types of digital subscriber lines, the two main
categories being ADSL and SDSL. Two other types of xDSL technologies are
High-data-rate DSL (HDSL) and Very high DSL (VDSL). xDSL is similar to ISDN
inasmuch as both operate over existing copper telephone lines (POTS) and both
require the short runs to a central telephone office (usually less than 20,000
feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream
traffic, and from 32 Kbps to over 1 Mbps for downstream traffic.
-----------------------------------------------------
