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. |