D-4 (or Super Frame SF)
transmission format comprised of 12 frames of 192 bits each. A single 193rd
bit is used for link control and error
checking. As an industry standard, D4, also known as SF, has been superseded by the Extended Super Frame (ESF) format.
However because ESF is not backward compatible and
there continues to be a large installed base of channel banks and DS-1
Multiplexers that are based upon D4, it is still the
default private line formatting technique.
D-4 Channel Bank
A multiplexer used
to convert 24 voice grade analog or data channels into a DS-1. The D-4 is
not equipped for software-controlled
provisioning or remote circuit testing.
DA - Directory Assistance
number lookup service.
DACS - Digital Access Cross-Connect System
A digital switching facility interconnection
device. A DACS allows reconfiguration of lower levels
of capacity, within a circuit, without the need for manual changes in
the interconnections. A DACS is similar to a Mux, but
a DACS permits software changes which would require physical changes with a MUX. Also known as DCS.
DAL - Dedicated Access Line
non-switched access line that connects an inter-LATA or interstate user
directly to his long
distance carrier's point
of presence. The carrier performs no switching or call-screening functions on this line.
An inactive fiber-optic
strand without electronics or optronics, (i.e., no connected transmitters, receivers, regenerators, etc.)
A multiuse collection of
information (on a computer). Often supports random access selectivity (via "Keys") and multiple
"Views" or levels of abstraction of the underlying data.
that are optimized for digital transmission of computer information.
Day of Week Routing
Route calls based
on day of week (e.g. single weekday, list of week days, range of weekdays or combinations).
Day of Year Routing
Route calls based
on month/day of the year (e.g. single day, list of days, range of days or
DCE - Data Communications Equipment
generic definition of computing equipment that attaches to a network via a
The signaling and data
transmission channel specified in ISDN standards, which is packed switched and used to transmit network control signals for
setting up hone calls. It also carries information about incoming and outgoing calls that is displayed on the
screens of ISDN desktop terminal devices. In the
1.544 Mbps ISDN primary rate interface standard, this channel occupies 64
Kbps of bandwidth.
Digital European Cordless Telecommunications
A wireless standard for communications,
operating at 1,88-1,9 GHz. The system is developed for high traffic rates and small cells. Applications are
private, residential and business telephone and data
DDD - Direct Distance Dialing
switched telecommunication service (like 1+, 0++, etc.) that allows a call
originator to place long distance calls
directly to telephones outside the local service area without an operator.
A digital multiplexer manufactured
by Lucent Technologies Network, that interfaces DS-1 signals with either electrical DS-3 signals and/or optical signals
such as OC-3, OC-12, etc..
DDS - Digital Data Service
digital data transmission service that offers transmission speeds of 2.4,
4.8, 9.6 or 56 Kbps over interconnected
point-to-point digital private lines.
DE - Discard Eligible
frame indicator that identifies that the frame may be discarded in the case
of network congestion.
A request to terminate
service (or the process of terminating service)
Decibel - Db - db
A unit of power
(sound, electrical or optical) increase (amplification) or loss
(attenuation) that is proportional to the
exponential increase or decrease in power.
A private line leased
from a telecommunications carrier for the exclusive use of a particular
Demarcation Point - Demarc
(such as a jack or cross-connect panel) at which ownership or responsibility
for operating and maintaining facilities passes
from one party to another.
Design Layout Record - DLR
the layout (path through locations and equipment) for the local
portion of a circuit at a particular location.
To place a call on a switched
network. The term "dial" is obsolete - based on rotary dial phones
and electromechanical relay switches (which are
nearly non-existent in modern telephone systems.)
Touch Tone service recognizes dual tones that
are generated as each telephone key is pressed.
Where Touch Tone service is not available, telephones and switches
electronically "pulse" signals that
emulate the older rotary dial telephones. The terms "place" a call
or "originate" a call are more
accurate than "dial".
When the off hook
indication is received at a central office, a dial tone signal is sent to
the originating caller on a switched network to
indicate that the switch is ready to accept a number. At ELI, this equals Local Telephone Service (LTS).
Dialed Number Identification Service - DNIS
An optional feature on dedicated access lines
(DALs). DNIS delivers identifying digits (up to 14 digits) that distinguishes incoming calls. This allows
CPE to identify which number was dialed when multiple
numbers terminate on the same trunk group.
Equipment that pulses out a
standard dial protocol signal.
A device or method that uses
discrete variations in voltage, frequency, amplitude, location, etc. to
encode, process, or carry binary (zero or one)
signals for sound, video, computer data or other information. For example, a digital clock displays the time as
discrete numeric values, rather than angular displacement of analog hands. Digital communications
technology generally permits higher speeds of transmission with a lower error rate than can be achieved with analog
technology. When analog signals are received and amplified at each repeater station, any noise is also
amplified. A digital signal, however, is detected and regenerated (not amplified). Unlike
amplification, any noise (less than a valid signal) is eliminated by digital regeneration.
Digital Loop Carrier - DLC
outside the central office that concentrates analog local loop lines, and
digitizes and multiplexes the calls for transport to
the central office.
Digital Switching System
systems that use Time-Slot-Interchange as opposed to older analog switching
systems that use Space-Division-Multiplexing.
Digital Systems Access Bay - DSAB
interconnection bay-frame designed specifically to provide a cabling
interface to DACS. Usually one DSAB bay is
installed for each DACS interface bay in separate lineups.
Digital Transmission System
A set of
equipment and facilities used to transmit digital signals in both the loop
and interoffice plant. Repeaters, which provide
signal equalization and regeneration, may be deployed in these systems.
The switch signaling
protocol that contains information such as information digits, destination
number, originating ANI, etc. The digit stream
is defined by Bellcore standards.
A fiber optic system in
which the carrier provides regenerators, but does not originate the optical
signals at one-or-both ends.
Refers to database queries in the LNP
process. Query by a local switching office or toll switching office to a remote database.
Direct Inward Dialing - DID
A PBX or
Centrex optional feature that permits outside calls to be placed directly to
a station line without use of an operator.
Direct Inward System Access - DISA
The ability to access a PBX from an outside telephone number. For example, a
caller might dial an assigned number, input a
security code and then use the PBX to place a long distance call.
Directory Assistance - DA
information service whereby operators assist customers in obtaining the
telephone number(s) they wish to call.
Direct Trunk Transport
(DS-3, etc.) that an IXC will lease so they can avoid the usage charges
coming from the LEC's Access Tandem. Usually
runs from the IXC's POP to the co-locate space at the LEC's End Office.
Call termination and the
information associated with it such as time of day, who disconnected
(originator, destination, etc.)
Special pricing flexibility
used to encourage increased use of products, or to improve competitive
A change (other than
attenuation or noise) in the characteristics of a signal due to the distance
of transmission or equipment problems or
Distributed Network Computing - DNC
Separation of the elements of an application into sub component objects that
can be implemented on multiple collaborative
computers on a common network. Objects are designed to optimize local processing and storage capabilities and to
minimize the slower overhead of remote communication.
A manual connection
system for physically connecting customers' phone lines to a switch in a
central office; or, for making cable connections
between switches in a central office. Designed to make it easy for telco craftspeople to make, break or rearrange
wiring connections in a central office. May also describe the Fiber Distribution Frame.
DLCI - Data Link Connection Identifier
A frame relay header field that identifies the
destination of the packet. A unique number assigned to a PVC end point in a frame relay network.
In SS7, a digital circuit
interconnecting mated pairs of signal transfer points that are at different
hierarchical levels (i.e. local and regional D-links
now operate at a transmission speed of 56 Kbps).
Switch Profile Loading.
Northern Telecom DMS-250 process for performing Network Database Updates. Defines the network configuration, valid user
ANIs, alternate routing tables, service classes, etc.
DMS - Digital Multiplex System
product name for Northern Telecom's family of digital central office
switch which contains both the DMS-100 local telephone service switch and the DMS-250 long distance switch.
DN - Directory Number
Usually 7 or 10
digits and equates to your telephone number.
DNIC - Data Network Identification Code
A four digit number used to identify public
A carrier with
marketing power and the ability to control overall price levels. LECs and
AT&T, are considered dominant.
DPC - Destination Point Code
The part of a
routing label that identifies where the CCS/SS7 signaling message should be
Drop and Insert
The ability to add
and remove lower-level capacity from a higher-level circuit at an equipment
location. Lower-level capacity may be
interconnected at an intermediate point of a higher-capacity circuit. For example, a Chicago to Los Angeles DS-3
might have DS-1 level drop and insert capability at
Salt Lake City. this would provide DS-1 service from Los Angeles to
Salt Lake and from Salt Lake to Chicago.
DS - Digital Signal
transmission rates and coding schemes in the time-division multiplex
The base unit of digital transmission capacity.
1 communication channel = 1 simultaneous voice grade
equivalent with a communication capacity of 64 thousand bits per
second (64 Kbps).
T1- The equivalent of
24 multiplexed voice grade channels (DS-0s). 1.544 million bits per second
T2 - The equivalent
of 4 multiplexed T1 channels. 6.312 million bits per second (6.3Mbps).
T3 - The equivalent
of 28 multiplexed T1 channels. 44.736 million bits per second (45Mbps).
T4 - The equivalent
of 6 multiplexed T-3 channels. 274.176 million bits per second (274Mbps).
DSU - Digital Service Unit
interface device between the CSU and the customer's DTE (Digital Terminal
Equipment). Basically, equipment used to attach
users' computing equipment to a public network. Usually associated with a CSU, the DSU has a V.35, RS232,
RS449, or other interface to the customer equipment.
The DSU is also a multiplexer for FT1 circuits.
DSX - Digital Signal Cross-Connect
centralized termination, interconnection, and test point for digital
equipment at a particular digital signal bit rate.
These capabilities enable a DSX frame to provide several operational
functions, including equipment interconnection, test
access and patching. DSX-1 handles DS-1 signals and DSX-3 handles DS-3 signals.
One or more contiguous DSX bays
that are equipped with the necessary jumper pathways to provide the ability to do all required DSX functions.
DTE - Data Terminal Equipment
definition of external networking interface equipment such as a modem.
DTMF - Dual Tone Multi Frequency
to the phone company that you generate when you press an ordinary
telephone's touch keys. Each key you press on your
phone generates two tones of specific frequencies. So that a voice
can't imitate the tones, one tone is generated from a
high-frequency group of tones and the other from a low frequency group.
The length of a call
(switched communication connection) or the effective length of a Contract,
Product Offering, etc.
DXI - Data eXchange Interface
ATM forum, a specification developed by the SMDS interest group to define
the interaction between inter networking devices and
DSUs/CSUs that are transmitting over an SMDS access line.