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Technical Glossary

4 Electronic Switching System - Class 4 stored, program controlled central office switch made by Lucent.

5 ESS - 5 Electronic Switching System - A digital central office manufactured by Lucent.


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

Access Tandem - A Local Exchange Carrier (LEC) switching system that provides a concentration and distribution function for originating and/or terminating traffic between a LEC end office network and IXC POPs.

ACELP (Adaptive Code Excited Linear Prediction) - ACELP improves on the efficiency of CELP voice compression by a factor of 2:1.

ADSL (Asymmetric Digital Subscriber Line) - A technology for transmitting digital information at high bandwidths on existing phone lines to homes and businesses. Unlike regular dialup phone service, ADSL provides continuously available, "always on" connection.

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.

Aggregation - Simplifying and facilitating convergence.

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.

Analog System - the simple way to transmit speech. The first networks for mobile phones were analog. Analog systems include AMPS, NMT, and ETACS.

ARP (Address Resolution Protocol) - A protocol used to query IP hosts about their physical (L2) addresses. If ARP is unavailable, the IP addresses must be manually mapped to their L2 addresses by the network administrator.

AS (Application Server) - An application server is a server program in a computer in a distributed network that provides the business logic for an application program.

Asynchronous - A type of transmission in which each character is transmitted independently without reference to a standard clock. It can also mean that there are different capacities for data transfer in each direction, for example the old 90/200 baud modems and the new ADSL.

Asynchronous Mode - a standard for data transmission where each data package has a start and stop bit. See also Synchronous Mode.

ATM (Asynchronous Transfer Mode) - A high speed switching system that uses 53-byte size cells to transmit voice, data and video. A cell in analogous to envelopes that each carry the same number of bits.


Backbone - A segment of a network used to connect smaller segments of networks together. Backbones carry high concentrations of traffic between on and off ramps of networks.

Bandwidth - The capacity in a network for data transmission. Bandwidth is measured in the number of data bits that can be handled per second (bps, Kbps, Mbps or Gbps).

BICC (Barrier Independent Call Control) - A standard that focuses on switch-to-switch communication to enable communication between VoPacket nodes and allow the termination of a TDM call without using SIP. BICC is favored by larger carriers such as AT&T.

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 - The smallest unit of data in a computer. A bit has a single binary value, either 0 or 1.

bps (bits per second) - data transmission speed, the number of pieces of information transmitted per second.

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 Technology - The technology for data and telecommunication with high transmission capacity.

Broadcast - To transmit data that is addressed to all members of a local networking group. For example, "browsing" the Network Neighborhood sends broadcast packets to all local devices.

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.

Byte - A unit of information that is eight bits long. In most computers a character, such as a letter, a number or a typographic symbol is represented by a byte. It can assume a value from 0 (0000 0000) to 255 (1111 1111).


Call Progress Tone - a tone sent from the telephone switch to tell the caller of the progress of the call. Common tones are dial tone, busy tone, ring back tone, reorder tone, recall dial tone.

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.

Carrier Backbone Switch - A switch for data traffic used in a backbone network.

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.

CDMA Code Division Multiple Access - A digital cellular communications technique used as a multiplexing and multiple access technique in which multiple calls are individually coded for transmission over one channel simultaneously.

Cell Delay Variation - A component of cell transfer delay, induced by buffering and cell scheduling.

Central Office (CO) - telephone company facility where subscribers' lines are joined to the switching equipment for connecting other subscribers to each other, locally and long distance. Sometimes central office has the same meaning as telephone exchange o public exchange, which are commonly used outside North America. Sometimes central office means a wire center in which there might be several switching exchanges.

Centrex - A type of phone service offered by local exchange carriers that provides 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 Switching - A switched circuit is only maintained while the sender and recipient are communicating, as opposed to a dedicated circuit which is held open regardless of whether data is being sent or not.

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.

Communications Protocol - Standards for the way in which data is transmitted within a network, for example: TCP and IP.

Constant Bit Rate - A data service where the bits are conveyed regularly in time and at a constant rate, carefully timed between source and sink.

CORBA (Common Object Request Broker Architecture) - An architecture and specification for creating, distributing and managing distributed program objects in a network. It allows programs at different locations and developed by different vendors to communicate in a network through an "interface broker."

Core Network - A combination of high-capacity switches and transmission facilities that form the backbone of a carrier network.

CPECustomer Premise Equipment -Telephone systems, modems and terminals installed at customer sites.

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.


Data Exchange - The enabling of data traffic within or between networks.

Digital - where information - speech, for example - is encoded before transmission. Digital networks are rapidly replacing analog ones as they offer improved sound quality, secure transmission and can handle data as well as voice. Digital networks include mobile systems GSM 900, GSM 1800, GSM 1900, D-AMPS and the cordless DECT system.

DS-0 (Digital Signal Level Zero) - A single digital 64 Kbps, pulse code modulated, transmission channel that 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.

DSL (Digital Subscriber Line)- A technology for bringing high-bandwidth information to homes and small businesses over ordinary copper telephone lines.

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.

Drivers - Software that links the hardware to the operating system. Good drivers are usually developed by the chip manufacturers and make the hardware easy to use.

DTMF (Dual Tone Multi Frequency) - A fancy term describing push button or touchtone dialing. In DTMF, when you press a button on a touchtone pad of a telephone, it makes a tone, actually the combination of two tones, one high frequency and one low frequency, thus the name Dual Tone Multi Frequency. The eight possible tones that comprise the DTMF signalling system were specially selected to easily pass through the telephone network without attenuation and with minimum interaction with each other. Since these tones fall within the frequency range of the human voice, additional considerations were added to prevent the human voice from inadvertently imitating or falsing DTMF signalling digits. One way this was done was to break the tones into two groups, a high frequency group and a low frequency group. A valid DTMF tone has only one tone in each group. The following is a table of the DTMFdigits/characters with their respective frequencies in Hertz. A, B, C, and D are used for specialized applications and cannot be generated by standard telephones.


















Low Frequency

















High Frequency

















Duplex: Full and Half - Full duplex allows data to be transmitted and received at the same time, so doubling the potential throughput. Half duplex allows data to be either transmitted or received, but not both, at the same time.

DWDM (Dense Wavelength Division Multiplexing) - A technique by which multiple light signals (generally using four or more signals) of different wavelengths are simultaneously transmitted in the same direction over a single optical fiber.


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.

Enterprise Switch - A switch linking a network that may be geographically dispersed, but is controlled by one organization.

Erlang - An erlang is a number between 0 and 1 that indicates how busy a telephone facility is over a period of time. An erlang of 1 applied to a particular telephone circuit would indicate busy 100% of the time. An erlang can be applied to the group of lines in a telephone trunk line or to the traffic in a telephone call center.

Ethernet - Ethernet is the most widely installed Local Area Network (LAN) technology. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Fast Ethernet and gigabit Ethernet evolved from Ethernet and provide transmission speeds up to 100 Mbps and 1,000 Mbps.

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.

Extranet - the extension of a company's intranet out onto the Internet, for example, to allow selected customers, suppliers, and mobile workers to access the company's private data and applications via the World Wide Web. Generally an extranet implies real-time access through a firewall of some kind.


Fast Ethernet - Fast Ethernet is a Local Area Network (LAN) transmission standard that provides a data transmission rate of 100Mbps.

Fast Packet Switching - an emerging, packet-orientated, digital technology that differs from traditional packet switching in a number of ways. The most obvious is that it transmits all data in a single packet format whether the information is video, voice or data. Fast packet switching uses short, fixed length packets (cells) and - via hardware switching - is capable of speeds between 100,000 and 1,000,000 packets/second.

FDMA (Frequency Division Multiple Access) - A multiplexing and multiple access technique for sharing of a spectrum band where each user is assigned a single transmission channel.

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.

Fiber Optics - Thin transparent fibers of glass or plastic that are enclosed by material of a lower index of refraction and in which Light Emitting Devices (LEDs) send light through the fiber to a detector that turns the light into an electrical signal.

FX (Foreign Exchange) - A central office trunk that has access to a distant central office. It has a FXO interface on one side and a FXS interface on the other. See FXO and FXS.

FXO (Foreign Exchange Office) - It has the appearance of a terminal equipment. CO lines or PBX extensions are connected to FXO ports.

FXS (Foreign Exchange Station) - It has the appearance of a CO line. Telephones, fax machines, PBX CO ports, and other terminal equipment are connected to FXS ports.


Gbps (Gigabits per second) - Billions of bits per second.

GHz (Gigahertz) - a frequency measurement which equals one billion hertz. One hertz equals one cycle per second.

Gigabit Ethernet - Gigabit Ethernet is a local area network (LAN) transmission standard that provides a data transmission rate of 1 billion bits per second (1 Gbps).

GMII (Gigabit MII) - A standard, 125MHz interface with 8-bit wide data busses between the Gigabit MAC and PHY. Compliant with the IEEE 802.3ab.

Ground Start - A signaling method for seizing a CO line. Some PBXs use ground start lines to prevent glare. When the CO wants to signal an incoming call on a ground start line, it grounds one of the wires of the line. Before the PBX tries to use a ground start line for an outgoing call, it checks that the wire has not been grounded. See Loop Start.

GSM (Global Standard for Mobile Telecommunications) - A TDMA standard set by the European Union for all European countries and increasingly used throughout the world for two-way digital cellular systems. It operates in the 1.8 to 1.9 GHz band in North America.


HDSL (High Data Rate DSL) - A digital subscriber line technology that allows for upstream data transmission at full-duplex T-1 line.

Hub - A place of convergence where data arrives from one link and is sent out on all other links within a network.

Hz (Hertz) - radio frequency measurement. One hertz equals one cycle per second.


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.

ICMP (Internet Control Message Protocol) - A protocol providing diagnostic and control functions such as sending IP redirect messages to an IP host.

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.

IMX (Intelligent Multiservice Switch) - A combination of multiservice edge switches and softswitch technology.

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 - A worldwide system of computer networks in which connected computers can exchange data. World Wide Web and e-mail are the most common applications on the Internet.

IP (Internet Protocol) - A communications protocol by which data is sent from one computer to another on the Internet. The IP provides the traffic with address information and is responsible for ensuring that data is sent to the correct destination. Most commonly used is version 4 (IPv4). Version 6 (IPv6) will allow more IP addresses.

IP Host (Internet Protocol Host) - A node in the network that has an IP address (for example, a networked PC).

ISP (Internet Service Provider) - An organization that provides access to the Internet.

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.

IT (Information Technology) - A term that encompasses all forms of technology used to create, store and exchange information in its various forms (business data, voice, still images, motion pictures, multimedia presentations and other forms, including those not yet conceived).

ITU (International Telecommunications Union) - The ITU, based in Geneva, Switzerland, is the most important telecom standards-setting body in the world. If its members agree on a standard, it effectively becomes a world standard.

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.


Kbps (Kilobits per second) - Thousands of bits per second.

KSU (Key Service Unit) - The main cabinet containing all the equipment, switching, and electronics necessary to run a KSU. See KTS.

KTS (Key Telephone System) - Similar to a PBX but typically does not have all the switching capability and functionality of a PBX. For example, a KTS might require the extension user to select a specific CO line for making an outgoing call whereas a PBX can select the CO line automatically when the extension user dials 9 (or 0). See PBX.


L2 Address - A unique number assigned to a networking device (such as a NIC) by the manufacturer.

L2TP (Layer 2 Tunneling Protocol) - An Internet Engineering Task Force standard tunneling protocol for VPNs. L2TP is implemented by ISPs to provide secure, node-to-node communications in support of multiple, simultaneous tunnels in the core of the Internet or other IP-based network. - An Internet Engineering Task Force standard tunneling protocol for VPNs. L2TP is implemented by ISPs to provide secure, node-to-node communications in support of multiple, simultaneous tunnels in the core of the Internet or other IP-based network.

L3 Address - A networking number assigned to a networking node (such as a PC) by the user. For example, IP or IPX addresses.

LAN (Local Area Network) - A network that connects workstations, printers, file servers etc. within a relatively small geographic area such as a small office or an office building.

Layers, L1 to L7 - The 7 layers of the OSI model.

LED (Light Emitting Diode) - A semiconductor diode that emits light when an electrical signal is applied. They need a relatively low current, so can be driven by chip outputs. For example, can be used to indicate at what speed a port is operating.

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.

Loop Start - A signaling method for seizing a CO line. Most single line telephones and KTSs use loop start lines. The telephony equipment starts (seizes) a line by going off-hook. Glare may occur on loop start lines. Glare occurs when the CO and the user seize the line at the same time. At the moment the CO signals an incoming call, the user goes off-hook to make an outgoing call and gets connected to the incoming call instead. See Ground Start.


MAC (Media Access Controller) - Controls the interface between the switch fabric and the PHY. Larger ICs often have the MACs integrated with the switch fabric or PHY to improve cost efficiency and make boards smaller and easier to design.

MAN (Metropolitan Area Network) - A network that interconnects users with computer resources in a region larger than that covered by a large local area network (LAN) but smaller than the area covered by a Wide Area Network (WAN). The term is applied to the interconnection of networks in a city into a single larger network.

Mbps (Megabits per second) - Millions of bits per second.

Media Gateway/MGCP (Media Gateway Control Protocol) - A protocol designed to bridge between current circuit-based PSTNs and emerging IP technology based networks.

MIB (Management Information Base) - Standard registers storing statistics on the local device. Makes network monitoring possible as the MIB is used by RMON, SMON, SNMP, etc.

MII (Media Independent Interface) - Used in 10M and 100M Ethernet. A 2.5MHz or 25MHz interface with 4 bit wide data busses, between the MAC and the PHY as defined in the IEEE 802.3u standard. This interface is media independent i.e., it is the same whether the data is carried over copper or fiber cables.

Modem - abbreviation of modular/demodulator. The modem converts digital computer signals into analog form for transmission over analog telephone systems.

MPLS (Multi-Protocol Label Switching) - A standard under development by the IETF. It is proposed that a label with various attributes, such as routing and QoS information, is attached to each packet. The label is used by the routers in the core of the network.

Multicast Traffic - Network traffic that is copied and distributed to several recipients on the network.

Multilayer Switch - A switch that can direct a packet to its next destination in the network based on either the local or global address held within the packet.


Narrowband - Lines or circuits able to carry up to and including T-1 or 1.544 Mbps.

NEBS (Network Equipment Building Standards) - A rigid and extensive set of performance, quality, environmental and safety requirements that is often required by telecommunications service providers for equipment installed in their switching offices.

Network Stack - The term used to describe the software layers that computers use to communicate with each other.

NIC (Network Interface Card) - A PCB that is plugged into a computer to interface it to the network.

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.

Normalize - To change an unusual call statistic reported by the automatic call distributor so as to reflect what would have been usual for that period of the day or that day of the week. Normalizing is something done before updating historical patterns so that the patterns will not be distorted by the unusual data.

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.


OA and M (Operations, Administration and Maintenance) - The specifics of managing a system or network. Typically a group of network management functions that provide network fault indication, performance information and data and diagnosis functions.

Off-hook - When the telephone handset is lifted off its cradle. When the handset is removed from its cradle, it completes the electrical loop, thus signaling the CO that it wishes dial tone.

On-hook - When the telephone handset is resting in its cradle. The telephone is not connected to any particular line. Only the bell is active, i.e., it will ring if a call comes in.

Operator - company that operates a telephone network, for example AT&T, Vodaphone and British Telecom.

OSI Model (Open Systems Interconnection Model) - The standard for transmitting messages between any two points in a network. Its purpose is to guide product developers so that their products will consistently work with other products. The model defines seven layers of functions that occur at each end of a communication link: 7--application, 6--presentation, 5--session, 4--transport, 3--network, 2--data link and 1--physical.

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

OSPF (Open Shortest Path First) - Ensures that the best path is taken through the TCP/IP network whenever possible. Involves less protocol traffic between routers than RIP and is therefore more efficient.


Packet - The unit of data that is routed between its origin and its destination on the Internet or on any other packet-switched network. An Ethernet packet can hold between 64 and 1518 bytes. In ATM, packets are called cells. All cells hold exactly 53 bytes.

Packet Switching - a method of switching data in a network where individual packets of a set size and format are accepted by the network and delivered to their destinations. The sequence of the packets is maintained and the destination established by the exchange of control information (also contained in the packets) between the sending terminal and the network before the transmission starts. The network is open to all users, all the time, with packets from the various nodes being interleaved throughout the network. The packets can be sent in any order, as the control information sent at the beginning of the transmission ensures they are interpreted in the correct order at the receiving end. Because each packet carries its own control instructions, it can use any route to reach its destination.

PBX - Private (it is owned by you not the telephone company) Branch (it is a small phone company central office) eXchange (another term for central office). It is like a small version of the telephone company's larger central switching office. A PBX is connected to CO lines and extension telephones. Generally, outgoing calls from extensions are made by dialing a digit (usually 9 or 0) to get a CO line and then dialing the destination number. Calls can be made from one extension to another. A PBX provides call hold, transfer, forward, conference, and other features. See KTS.

PCS (Personal Communications Service) - A wireless service concept that allows users to communicate with the combination of terminal and personal mobility. The allocation of spectrum in the 1800-1900 MHZ band is called the PCS band.

PHY - The Physical (PHY) device interfaces the controller to the copper or fiber medium. Up to 8 PHYs are available on a single IC for 10/100 Ethernet over copper media.

PIC (Primary Interexchange Carrier) - The long distance company to which traffic from a given location is automatically routed when dialing 1+ in equal access areas.

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.

PIN (Personal Identification Number) - a code used to establish authorization for access to certain functions or information.

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

POP (Point of Presence) - The location at which a line from a long distance carrier (IXC) connects into a local telephone carrier's switching network facility.

Port - A connection point for the network cable on, for example, a switch or router.

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

PPP (Point-to-Point Protocol) - A data link protocol that is popular for Internet access and for carrying higher level protocols, while supporting both asynchronous and synchronous lines.

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.

PTT - Historically, the Ministry of Post, Telecommunications and Telegraph. Now a term to describe the incumbent, dominant operator in a country, many of which are being or have been privatised.

PVC (Permanent Virtual Connection) - A point-to-point virtual connection scheduled ahead of time for a long-term connection between data terminal equipment.


QoS (Quality of Service) - QoS denotes the ability to provide some guarantee and differentiation of performance between different classes of traffic on a network. This is becoming very important over IP, especially for voice and video applications.


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.

Remote Concentrator - A device which places more than one distant user on two cable pairs.

Ringback Tone - The sound you hear when you are calling someone else's telephone. The tone you hear is generated by a device at your CO (central office) and may bear no relationship to the sound that the telephone you are calling makes - or does not make.

RIP (Routing Information Protocol) - Protocol used by routers to determine the best path through the network. The best path is determined as the path with the fewest routers. Protocol traffic is high when using RIP, so is being replaced with OSPF.

RMII (Reduced MII) - Used in 10M and 100M Ethernet. Lower pin count than MII (2-bit wide data bus), but twice as fast (5 MHz or 50 MHz).

RMON (Remote Monitoring) - Part of the MIB used to monitor port statistics such as number of packets input on port, number discarded on port etc. Uses the SNMP 2 protocol to read/write data and deliver alarms.

Router - A piece of networking equipment that determines the next network point to which a packet should be forwarded toward its destination. A router usually consists of hardware and software working together to process the packets. Using custom designed hardware the routing process can be significantly accelerated.

RSVP (Resource Reservation Protocol) - Routers use the RSVP protocol to communicate with each other in order to reserve resources such as bandwidth.


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.

SAR (Segmentation and Reassembling) - A process of segmenting relatively large data packets into smaller packets for purposes of achieving compatibility with a network protocol relying on a smaller specific packet size.

SCE (Service Creation Environment) - Allows outside developers to define and create new value added services by connecting pre-existing blocks of code into a flow chart that describes the logical processes the service will use to handle calls.

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.

SDSL (Symmetrical Digital Subscriber Line) - Also known as HDSL2, although the local loop length is limited to about 10,000 feet. Speeds of up to one megabit per second are still possible both ways.

Segment Switch - A switch that connects several workgroup switches to build a larger network. It switches traffic in a LAN.

Semi-Custom Design - A method for designing integrated circuits. Computer programs automatically generate the patterns needed for manufacturing.

SIP (Session Initiated Protocol) - A protocol for transporting call setup, routing, authentication and other feature messages to endpoints within the IP domain, whether those message originate from outside the IP cloud over PSTN resources or within the cloud.

SIP+ (Session Initiated Protocol+) - An extension of SIP, favored by greenfield carriers.

SMII (Serial MII) - Used in 10M and 100M Ethernet. Lower pin count than RMII and MII (serial data buses), but very fast interface (10MHz or 100MHz).

SMON (Switch Monitor) - Defines switch statistics such as number of packets switched, number discarded etc. As networks become larger, and ISPs start charging for bandwidth used, it becomes important to be able to do accounting on the traffic through switches and routers.

SMS (Service Management System) - A system that coordinates all of the national 800 telephone numbers for all the US telephone companies through service control points.

SNMP (Simple Network Management Protocol) - The protocol used to extract the data monitoring and controlling the network activity from the MIB and pass it to the IS manager. SNMP 2 offers greater security and RMON support.

Softswitch - Separates the call control functions of a phone call from the media gateways (transport layer) that carry it. Call control features can vary, but call routing, admission control, connection control (such as creating and tearing down sessions), and signaling interworking-such as from SS7 to SIP-are usually the minimum requirements.

SONET (Synchronous Optical Network) - An American National Standards Institute (ANSI) standard for high speed, fiber optical transmission on the network.

SS7 (Signaling System 7) - 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.

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.

Switch - A network device that directs data traffic to its destination within a network.

Synchronous - type of transmission in which the transmission and reception of all data is synchronized by a common clock, and the data is usually transmitted in blocks rather than individual characters. It can also mean that the data stream has the same capacity in both directions.

Synchronous Mode - standard for data transmission. Data is transferred without start and stop bits together with a clock signal to synchronize the receiver. This mode gives higher data throughput than asynchronous mode but can be less secure.


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.

TCP (Transmission Control Protocol) - A communications protocol used along with the Internet Protocol (the two together are called TCP/IP) to send data over the Internet in the form of packets between computers. TCP divides the data into packets and takes care of keeping track of them.

Tele/Data Communications Network - A system of wires, optic fibers and satellite links, where hardware (such as hubs, routers and switches) directs information between one or several senders/receivers.

TOS (Type Of Service) - A TOS is assigned to a data packet to enable differentiation between packets of different priorities.

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").

Twisted Pair - two insulated copper wires twisted together with the "twists" or "lays" varied in length to reduce potential signal interference between the pairs. Where cables comprise more than 25 pairs, they are usually bundled together and wrapped in a cable sheath. Twisted pair is the most commonly used medium for connecting telephones, computers and terminals to PABXs, supporting speeds up to 64kbits/sec.


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.

UDP (User Datagram Protocol) - A communications protocol used to send data over the network in the form of packets between network devices. There is no feedback to acknowledge that the data has arrived. UDP is fast, but can be unreliable. Voice and video are usually sent as UDP traffic.

Unicast - A type of data packet addressed to a single destination. Most traffic is unicast.

Unified Messaging - Software that allows you to see your voice mail, email and faxes that have been received by your telephone system.


VCC (Virtual Circuit Channel) - Generic name for a central office located multiplexer that aggregates multiple customers via lower speed line to a higher speed trunk connection.

VLAN (Virtual LAN) - A method of grouping together computers so that they can communicate with each other without interference from computers outside the VLAN. They do not have to be on the same physical network (hence "virtual" LAN). VLANs can also separate computers that may be on the same physical network. This is a very powerful tool for network managers.

Voice Over ATM (Voice over Asynchronous Transfer Mode) - The process of transmitting voice traffic across an ATM-based packet network.

Voice Over DSL (Voice over Digital Subscriber Line) - The process of transmitting voice phone calls over DSL.

Voice Over IP (Voice over Internet Protocol) - Voice traffic is encoded and passed over the network as IP data packets. Currently, traffic priority (and hence audio quality) can only be guaranteed over private networks.


WAN (Wide Area Network) - A geographically dispersed telecommunications network (nationally or globally). The term usually connotes the inclusion of public (shared user) networks.

WCDMA (Wideband Code Division Multiple Access) - A part of the new world-encompassing standard for mobile telephony - the Universal Mobile Telephone Standard (UMTS), which enables wireless transmission of data traffic at speeds up to 2 Mbps.

Wire Speed Router/Switch - A switch or router that can handle the switching of data traffic at the highest speeds within the connected networks.

W-LAN (Wireless-Local Area Network) - a wireless version of the LAN. It provides access to the LAN even when the user is not in the office.

Work Group Switch - The simplest switch that is positioned closest to the user's computer in the network.