Glossary of Telecommunications Terms

This glossary provides definitions of some common of the terms that are used in the telecommunications industry.

Term

Definition

10Base-T

10 Mbps
Ethernet over twisted-pair copper cable.

100Base-T

100 Mbps
Ethernet over twisted-pair copper cable.

1000Base-T

1000 Mbps
Ethernet over twisted-pair copper cable.

4E

Class 4 switch from Lucent Technologies. One that generally provides call routing between carriers.

5E

Class 5 switch from Lucent Technologies. One that generally provides connectivity to end users.

ACD

Automatic Call Distribution. A telephone system feature which distributes incoming calls to an agent or representative and keeps statistics on each call. Typically used in high-volume call center environment.

Analog
Line

Phone line using an
analog wave form for transmission of speech.

ANI

Automatic number
identification. Used in telco networks to identify the calling party.

Automated Attendant

 Voicemail-based menu tree that helps direct
callers to appropriate information or destinations.

Automatic Call Distribution

See ACD.

Blue Lights

Slang; see Emergency Phones. Also, the actual blue light on top of an Emergency phone.

Call Forwarding

Service to send calls to another location, available in
several forms, generally Busy, Don’t Answer, or All. The form describes the
condition under which calls are sent to an alternate telephone number.

Centranet

Phone switching
system, usually installed in a service provider’s central office that provides
dial tone and features to customers. The name is unique to Verizon.

Centrex

Phone switching
system, usually installed in a service provider’s central office that provides
dial tone and features to end user customers. The name is unique to AT&T.

CSU

Channel service unit. Used
to terminate a T1 facility.

DHCP

Dynamic Host Configuration
Protocol.

DID

Direct Inward Dialing. The service provided by a network service vendor (like AT&T), which allows a caller to dial a 10-digit telephone number and reach an individual extension of a business communications system.

Direct Inward Dialing

See DID.

Direct Outward Dialing

See DOD.

DOD

Direct Outward Dialing. A feature that allows telephone system users to dial an access code and a telephone number from their desk.

DS0

Network facility with
bandwidth of up to 64kb.

DS1

Network facility with
bandwidth of 1.544 MB, sometimes channelized to provide 23 or 24 channels.

DS3

Network facility with
bandwidth of 45 MB, sometimes channelized to provide multiple T1 facilities.

DTMF

Dual-tone multi-frequency
standard signaling used for touch-tone dialing.

E Phone

Slang. See Emergency
Phones.

Elevator Phones

Phones on the same system
as Emergency Phones. Located in the elevator.

Emergency Phones

Specialized phones that will automatically call the Department of Public
Safety (DPS) when the handset is lifted. They are strategically located around campus.

EPN

Extended Port Network. A remote switching module of a telephone switch. Different vendors use different names. EPN is specific to Avaya and our Definity line of PBXs.

ESF

Extended Super Frame T1
framing scheme.

Ethernet

Local area network used
for connection computers, printers, workstations, or terminals. Generally
provided over twisted pairs or coaxial cable, offering speeds of 10 Mbps or
100 Mbps. 1 and 10 Gbps are possible.

Extended Port Network

See EPN.

Ground Start

Way of signaling
initiation of a call from a PBX to the CO by briefly grounding one side of a
line.

IP

Internet Protocol. A standard addressing scheme and message routing protocol for communication between nodes of a data network.

ISDN Line

Integrated Services
Digital Network. ISDN lines are generally either BRI (2b+d) or PRI (23b+d),
where b = the number of bearer channels and d = a control channel. BRI
service is usually provided to a telephone-type end point, whereas PRI is
usually used to connect two switches.

Loop Start

Way of signaling
initiation of a call by creating a loop across the two wires of a telephone
pair.

MLHG

Multi-Line Hunting. The
ability of a switching system to connect calls to another phone in a group
when other numbers in the group are busy. Types include serial or circular.
Serial always begins with the number originally dialed and hunts to the next
in line until the end of the group is reached. Circular, begins with the
number originally dialed and hunts to the next through the entire group even
if the originally dialed number is in the middle.

OC-1

Optical Carrier using a
SONET Optical signal, capacity of 51.840 Mbps.

OC-3

Optical Carrier using a
SONET Optical signal, capacity of 155 Mbps.

OC-12

Optical Carrier using a
SONET Optical signal, capacity of 622.08 Mbps.

OC-48

Optical Carrier using a
SONET Optical signal, capacity of 2.4 Gbps.

PBX (also called PABX)

Private Branch Exchange. A telephone switching system usually installed at a business location as opposed to a service providers central office.

PDN

Primary Directory Number. The telephone number that the physical telephone set is associated with. Generally, the first telephone number listed on a multi-line set.

PDN (alt.)

Public Data Network. A digital data network, usually X.25 protocol that is accessible by dialing a public telephone number.

Primary Port Network

See PPN.

Private Branch Exchange

See PBX.

SDN

Secondary Directory Number. A telephone number that is picked up on a telephone set, but which is a PDN on another instrument.

SDN (alt.)

Software Defined Network. A virtual private network.

SLA

Service-Level Agreement

SNI

Switch Node Interface. The link(s) between a PPN and an EPN over which control information is passed. Phone calls can be routed over these facilities as well, but this is generally not the case at USC.

Sonet

Synchronous Optical
Network

Stations

In the voice world, a
station is any terminal equipment that utilizes a port on the switch. Generally,
one port is used by one station.

Switch module

Generic term
used to describe a cabinet(s) containing the memory, processors, circuitry,
and equipment necessary to support a group of stations.

Switch Node Interface

See SNI.

T1

Network facility with
bandwidth of 1.544 MB, often channelized to provide 23 or 24 channels of
voice traffic.

T3

Network facility with
bandwidth of 44.736 MBPS, channelized to provide 28 T1s.

TCO

Total Cost of Ownership.

TCP/IP

Transmission Control
Protocol / Internetworking Protocol. A protocol developed to allow dissimilar
devices to communicate across many kinds of networks.

TG

Trunk Group. A quantity of network facilities that complete calls.

Tie

Also, Tie Line. A specific type of trunk that is used to connect two switches.

Trunks

Individual channels or circuits that can be grouped. This is the smallest denominator for a network facility.

Umbilicals

Specialized connections between a remote module(s) and the main host in the 5ESS switch. Similar to a SNI facility, these carry control information.

Voicemail System

System that specifically
supports the voice mail application and is connected to the telephone switch.
Calls are passed between the two systems, which communicate with each other
to light the light on your telephone when you have a message.

VoIP

Voice over IP. A technique
that allows voice to be carried in a portion of the bandwidth of an Ethernet
signal that is carrying IP traffic.

VPN

Virtual Private Network.

WAN

Wide Area Networking.