Glossary [ Comprehensive PDF Glossary ]

4ESS - Class 4 toll switch made by Lucent (see Tandem Network, ESS).

5ESS - End Office switch made by Lucent (see End Office, ESS).

Access Tandem - A tandem switch that is used to interconnect between carriers for equal access. Typically, this used to interconnect ILECs with IXCs, but now also includes CLECs.

Advanced Intelligent Network (AIN) - An evolving, service-independent architecture that allows a carrier to quickly and economically create and modify telecommunication services for its customers.

A-Link - In the Signaling System 7 (SS7) world, an A-link is a signaling link that connects a signal transfer point (STP) to a service switching point (SSP) or service control point (SCP). A-links operate at a transmission speed of 56 Kbps.

ATM - Asynchronous Transfer Mode. An international standard for high-speed broadband packet-switched networks operating at broadband digital transmission speeds. The technology is based on fixed-length, 53-byte cells. ATM includes protocols that specify how diverse kinds of traffic are transformed into standardized packets whose transport can be managed uniformly within the network.

AAL2 - ATM Adaptation Layer 2. Used for carrying voice over ATM.

Backbone - Part of a network used to connect smaller segments of networks together.

Bandwidth - The relative range of frequencies that can be passed by a transmission medium. Greater bandwidths mean a higher information carrying capacity of the transmission circuit. Usually measured in Hertz, bandwidth is assessed as the number of bits that can be transferred per second.

B-ISDN - Broadband Integrated Services Digital Network. An evolving standard for the second generation of integrated services digital networks. Broadband ISDN services employ packet switching to integrate voice and data services over a high-speed, packet-based infrastructure.

Bit Rate - The number of bits transmitted over a telephone line per second.

BLES - Broadband Loop Emulation Service. Standard that defines a mechanism for transporting Class 5 switch subscriber line services through the broadband access network to the end user.

BRI - Basic Rate Interface. The ISDN interface standard for single-line ISDN service. This standard provides for two message-bearing 64 Kbps B channels for speech and data, plus a 16 Kbps D channel for network signaling and data.

Broadband - A term used to describe a channel with more bandwidth than a standard voice grade channel. Broadband channels are used to carry multiple high-speed voice and data transmissions on a common communications path.

Busy Hour - An uninterrupted 60-minute period during which the average volume of telecommunications traffic is at its maximum.

Busy Hour Call Attempts (BHCA) - A measure of dynamic traffic calls that can be attempted in an average Busy Hour.

Busy Hour Call Completion (BHCC) - A measure of dynamic traffic calls that can be completed in an average Busy Hour.

Carrier Access Code (CAC) - The sequence that an end user dials in order to access the carrier's switch service. The codes are composed of 7 digits in the form of 101xxxx, where xxxx is the Carrier Identification Code.

CCS - In telecommunications traffic engineering terminology, CCS represents centi call seconds and is a unit of traffic quantity equivalent to a phone call lasting 100 seconds.

Central Office (CO) - The facility of a telecommunications common carrier where calls are switched.

Centrex - A type of phone service offered by local exchange carriers that provide PBX like functions to a group of users without the need of a PBX. Despite having individual single line phones connected to the central office, users are able to dial each other by extensions, transfer calls, etc.

CIC - 1.) Circuit Identification Code. An SS7 term used to identify a particular circuit within a trunk group. 2.) Carrier Identification Code. A four-digit code that is used to identify each carrier within North America.

Circuit Switch - A switching system that establishes a dedicated physical connection between end points for the duration of that communication session.

Class 4 Office - A switching center for toll calls. A class 4 office switches toll traffic originating at class 5 offices to other class 4 offices, or offices of a higher class. In addition, a class 4 office relays toll traffic from class 4 toll offices to the class 5 end office serving the destination address.

Class 5 Office - The lowest level in a hierarchy of central offices. Class 5 offices serve as the network entry point for user access lines and are a switching center for local calls.

CLASS - Custom Local Area Signaling Services. A grouping of optional features to basic local exchange telephone service. CLASS provides subscribers with the ability to screen and selectively reject, forward, trace, and redial incoming calls.

CLEC - Competitive Local Exchange Carrier. These are new local carriers, typically formed after the US Telecommunications Act of 1996, to compete with the incumbent RBOCs.

CTI - Computer Telephony Integration. The combining of data with voice systems in order to enhance telephone service. Examples include the delivery of Caller ID information via a PC, and the ability to access voice mail via the PC.

DMS 100 - Class 5 end office switch made by Northern Telecom (Nortel).

DMS 250 - Access tandem switch made by Nortel.

Point Code - A network address used within the SS7 network to represent a Service Switching Point (SSP) for routing purposes. Typically, each SSP switch within an SS7 network has at least one point code.

DS-0 - Digital signal level "zero." A single digital 64 Kbps, pulse code modulated, transmission channel which represents the starting point for a digital multiplexing hierarchy.

DS-1 - Digital signal level one. A 1.544 Mbps digital signal comprised of 24 multiplexed 64 Kbps DS-0 digital channels.

DS-3 - Digital signal level three. A 44.6 Mbps digital signal comprised of 28 multiplexed DS-1 signals that is carried over a T-3 facility.

Digital Subscriber Line (DSL) - A generic name for a family of digital lines (also called xDSL) being provided by CLECs and local telephone companies to their local subscribers. xDSL services include Asymmetric Digital Subscriber Line (ADSL), High Bit Rate Digital Subscriber Line (HDSL) and single twisted-pair Symmetrical Digital Subscriber Line (SDSL). DSL lines typically operate on one pair of wires, like a normal analog phone.

DSLAM - Digital Subscriber Line Access Multiplexer. A network device at a telephone company central office that receives signals from multiple customer Digital Subscriber Line (DSL) connections and puts the signals on a high-speed backbone line using multiplexing techniques.

Echo Cancellation - A technique that allows for the isolation and filtering of unwanted signals caused by echoes from the main transmitted signal.

End Office - The location where carriers place telecom equipment closest to the customer. Typically, this is where customers are provisioned. Class 5 switches are typically located here.

Equal Access - A condition where the local exchange access service offered by a carrier is made available in equal kind, quality, and price to all long distance companies.

ESS - Electronic Switching System. One of AT&T/Lucent's family of stored, program-controlled (SPC) central office switches, including the 4ESS and 5ESS switches.

EWSD - Switching system made by Siemens.

Feature Group - In switched access tariffs, a Feature Group denotes a specific and uniform type and quality of local exchange access available to inter-exchange carriers and other types of telecommunications companies.

Feature Group A - A line-side switched access connection for originating and terminating traffic. Customers of a long distance company that use Feature Group A for originating access must dial a seven-digit local number to reach an inter-exchange carrier, and then use a tone phone or tone dialer to dial an identification code plus the phone number they want to reach. In areas where equal access is not available, Feature Group A is provided at discounted rates.

Feature Group B - A trunk-side switched access connection for originating and terminating traffic. Transmission quality is superior to that of Feature Group A. Customers of a long distance company using Feature Group B for originating access must dial "950" followed by a "1" or a "0" and the three-digit carrier identification code of their chosen company. Mostly superseded by Feature Group D.

Feature Group C - A trunk-side switched access connection that directly links local phone company end offices with the long distance network of AT&T. Only AT&T has Feature Group C access connections, which offer the highest transmission quality and a complete array of access features for originating and terminating long distance traffic.

Feature Group D - The equal access connection; a trunk-side switched access connection equal in quality, features, and price to the Feature Group C connection of AT&T. Customers in exchanges where Feature Group D is available can pre-subscribe to any one long distance company. They can reach their chosen company by dialing "1" plus the phone number they want to reach. Customers in an equal access area can use other long distance companies by dialing "1" and "0" and the five-digit carrier identification code of the carrier they want.

Frame Relay - A packet-switched method of data communications provided by telecommunications carriers and Internet service providers. Frame relay can provide guaranteed bandwidth at no additional charge if the lines are open during periods of low traffic.

GR-303 - A set of technical specifications from Bellcore that define the interface between the Digital Loop Carrier (DLC) and a Class 5 switch.

H.323 - A framework of protocols for inter-working voice, video and data across an IP network.

IAD - Integrated Access Device. A customer located access device that can handle both voice and data services on the same access line to a carrier.

ILEC - Incumbent Local Exchange Carrier. Typically an RBOC, this is usually the incumbent local phone company, which owns most of the local loops and facilities in a serving area.

IMT - Inter-Machine Trunk. These are switch-to-switch trunks that are used to carry calls between carriers. Signaling is not performed in-band on these trunks; instead, they are coordinated via the overlaid SS7 network.

Intelligent Network (IN) - A telecommunications network architecture in which processing capabilities for call control and related functions are distributed among specialized network nodes rather than concentrated in a switching system. The SS7 network forms part of the IN infrastructure.

Internet Protocol (IP) - A network layer (Layer 3) standard for data transmission that performs the addressing function and contains some control information to allow packets to be routed through networks.

Internet Service Provider (ISP) - A vendor who provides access for customers (companies and private individuals) to the Internet and the World Wide Web.

ISDN - Integrated Services Digital Network. A switched network providing end-to-end digital connectivity for simultaneous transmission of voice and/or data over multiple multiplexed communications channels and employing transmission and out-of-band signaling protocols that conform to internationally-defined standards.

ISUP - ISDN User Part. The portion of SS7 that handles call control for ISDN-type calls.

IXC - Inter-eXchange Carrier. A carrier that is allowed to carry traffic from one LATA to another, typically long distance inter-state traffic, but can also include intra-state toll traffic.

Local Area Network (LAN) - A short distance data communications network (typically within a building or campus) used to link computers and peripheral devices (such as printers, CD-ROMs, modems) under some form of standard control.

LATA - Local Access and Transport Area. A geographical area within which a divested RBOC is permitted to offer exchange telecommunications and exchange access services.

LNP - Local Number Portability. The ability of telephone subscribers to maintain their phone numbers when they change local telephone companies. Dependent on SS7 in order to implement.

Local Exchange - The telephone company exchange where subscribers lines are terminated. Also called an "End Office."

Local Exchange Carrier (LEC) - The local phone companies, which can be either a Bell Operating Company (BOC) or an independent (for example, GTE) which traditionally had the exclusive, franchised right and responsibility to provide local transmission and switching services.

Local Loop - The physical connection from the subscriber's premises to the carrier's Point of Presence (POP). The local loop can be provided over any suitable transmission medium, including twisted pair, fiber optic, coax, or microwave.

Media Gateway - Communications switch equipment operating at the edge of multi-service packet networks.

Media Gateway Control Protocol (MGCP) - An Internet Engineering Task Force (IETF) draft standard for a protocol that allows voice gateways to control external call control elements. MGCP assumes a call control architecture where the call control "intelligence" is outside the gateways and handled by external call control elements.

MFJ - Modified Final Judgment. The 1984 US Department of Justice ruling that resulted in the divestiture of the Bell Operating Companies from AT&T.

North American Numbering Plan (NANP) - The numbering architecture in which every station in an NANP area is identified by a unique 10-digit address consisting of a three-digit area code, a three-digit central office code, and a four-digit subscriber number.

N-ISDN - Narrowband Integrated Services Digital Network. Standards-based voice and data network that operate over today's TDM-based switches and provides 144K and 1.544 Mbps interfaces.

OSS - Operations Support System. Methods and procedures that support the daily operation of a carrier's infrastructure, including order processing, equipment assignment, etc.

PacketCable - A set of protocols developed to deliver Quality of Service enhanced communications services using packetized data transmission technology to a consumer's home over a cable network.

Packet Switching - The technique by which a stream of data is broken into standardized packets, each of which contains an address, sequence, control, size, and error checking information, in addition to user data. Packet switches operate on this added information to move the packets to their destination in the proper sequence and again present them in a correct continuous stream.

PIC Code - Pre-subscribed/Primary Inter-LATA Carrier Code. This code is associated with the customer profile of every phone subscriber, and is used to route to the customer's pre-selected long distance carrier.

POI - Point of Interface. The point in a network at which carriers interface with one another.

Point of Presence (POP) - A long distance company's switch that is connected to the local telephone company's central office. The POP is the point at which telephone and data calls are handed off between local telephone companies and long distance telephone companies.

POTS - Plain Old Telephone Service. The traditional telephone service for the transmission of human speech across the telephone network.

PRI - Primary Rate Interface. This is the narrowband ISDN interface standard for high-speed ISDN service. Within the US, this provides 23 channels of data and/or voice traffic.

PSTN - Public Switched Telephone Network. The current narrowband-based telephone network that was designed for voice traffic.

RBOC - Regional Bell Operating Company. Regional companies formed after the divestiture of AT&T in 1984. At the time of the divestiture, there were seven companies, but now that number has been reduced to four. In today's competitive environment, they are typically referred to as Incumbent Local Exchange Carriers (ILECs).

Reciprocal Billing - A process by which the carrier who locally terminates a call to a customer gets compensated by the carrier who delivered the call to him for termination.

SAC - Service Access Code. These are the special codes that replace the area code and are used for special network services. (Examples include 500, 700, 800, 888, 877, and 900)

SAM - Service Access Multiplexer. Generic name for a central office located multiplexer that aggregates multiple customers via lower speed line to a higher speed trunk connection.

SCP - Service Control Point. A remote computer database within the SS7 network that receives queries from SSPs in order to process applications such as 800 and LNP number lookups and calling card verification.

Signaling System 7 (SS7) - The current international signaling standard for all digital exchanges with integrated services. The SS7 network allows call control and transaction messages from the integrated voice and data network to be transferred on communications paths that are separate from the voice and data connections. It delivers out-of-band signaling that provides fast call setup by means of high-speed, circuit-switched connections and transaction capabilities which deal with remote database interactions. SS7 also plays an integral role in the deployment of ISDN. The SS7 protocol consists of four basic sub-protocols:

• Message Transfer Protocol (MTP) - Provides functions for basic routing of signaling messages between signaling points.
• Signaling Connection Control Part (SCCP) - Provides additional routing and management functions for transfer of messages other than call setup between signaling points.
• Integrated Services Digital Network User Part (ISUP) - Provides for transfer of call setup signaling information between signaling points.
• Transaction Capabilities Application Part (TCAP) - Provides for transfer of non-circuit related information between signaling points.

Softswitch - As defined by the International Softswitch Consortium, a softswitch (call agent, caller server or media gateway controller) is a device that provides, at a minimum:

• Intelligence that controls connection services for a media gateway, and/or native IP endpoints.
• The ability to select processes that can be applied to a call.
• Routing for a call within the network based on signaling and customer database information.
• The ability to transfer control of the call to another network element.
• Management functions such as provisioning, fault, billing, etc.
  
  

SSP - Service Switching Point. Within the SS7 network, an SSP is a telephone central office switch that inter-works with the network.

STP - Signaling Transfer Point. An STP is a packet switch within the SS7 network that routes network call information among other circuit switches and between SSPs and SCPs.

Tandem Network - An arrangement of voice switches that enables calls to be routed through two or more switching centers in tandem fashion, such that each end office switch does not need to be directly connected to each other.

Tandem Switch - A voice switch that is designed primarily with trunk interfaces rather than subscriber interfaces.

TCAP - Transaction Capabilities Application Part. The portion of the SS7 protocol that is used to make database queries to SCPs. It is used to support services such as 800 and LNP number translation, as well as other functions.

TDM - Time Division Multiplexing. A multiplexing scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is broken up into many segments, each having a very short duration and specific time slots within the channel. The slots are assigned whether or not any signals are available for transmission.

Telephony-Grade - 99.9994% uptime or the higher reliability standard circuit switches require (translating into 3 minutes of downtime a year), as opposed to the "carrier-class" reliability standard of 99.999% (called "five-nines").

TR-303 - A Bellcore standard for communication between telephony switches and Digital Loop Carrier systems.

US Telecommunications Act of 1996 - As part of telecom deregulation, this ruling required ILECs to unbundle their network elements and lease them at wholesale rates to CLECs, in order to be allowed into the long distance market. While no ILEC has so far satisfied the 14-point rule that proves that they have enabled competition in their markets, many CLECs have been formed as a result of this act.

Voice over ATM (VoATM) - The process of transmitting voice traffic across an ATM-based packet network.

Voice over IP (VoIP) - The process of transmitting voice traffic across an IP-based packet network.

Voice over Packet (VoP) - The process of transmitting voice traffic across any kind of packet network.