O

OAI (Open Application Interface) - A means for a computer system and a PBX to exchange information. It is an older name for CTI (Computer Telephony Integration). It allows a person in the workplace to enter information into a computer by using their telephone. Some of the information is time-reporting information, inventory information, etc.

OC (Optical Carrier) - A prefix for SONET carrier hierarchies, which is followed by a number, such as OC-1, OC-3, etc.

OC-1 (Optical Carrier 1) - The beginning of the SONET-level transmission speeds. An OC-1 is capable of carrying one DS-3 within its payload. Its transmission carrier speed is 51.840 Mbps. OC-1 can be converted into an electrical signal, which is called an STS-1 (Synchronous Transport Signal-1). For more information on OC speeds, see OC-N.

OC-12 (Optical Carrier 12) - A SONET level of transmission speed. It is capable of transporting three DS-3 signals, which is equal to 622.080 Mbps. For more information on OC speeds, see OC-N.

OC-192 (Optical Carrier 192) - A SONET level of transmission speed. It is capable of transporting three DS-3 signals, which is equal to 9.953 Gbps. For more information on OC speeds, see OC-N.

OC-3 (Optical Carrier 3) - A SONET level of transmission speed. It is capable of transporting three DS-3 signals, which is equal to 255.520 Mbps. For more information on OC speeds, see OC-N.

OC-48 (Optical Carrier 48) - A SONET level of transmission speed. It is capable of transporting three DS-3 signals, which is equal to 2.488 Gbps. For more information on OC speeds, see OC-N.

OC-N (Optical Carrier N) The N denotes a number in the SONET optical carrier hierarchy, which now extends from OC-1 to OC-192.

Octal - A numbering system. Base 8. The Base 10 system has 10 different characters to represent numbers, 0 through 9. Base eight uses only eight of those characters, 0 through 7.

Octel - A company that manufactures stand-alone voice-mail equipment. For a photo of an Octel voice-mail system, see Voice Mail. Octel is now a part of Lucent Technologies.

Octet - Another term for byte, a string of eight bits.

Octopus Cable - Also called a Y or three-way cable. An octopus cable is used to break a larger connector (usually from a bus) to two or more smaller connectors. The Nortel Meridian utilizes a cable with 50 pins on one connector that breaks out in two different RS-232 connectors. Having the single large connector plug into the back plane uses less space than three smaller connectors.

ODBC (Open Data Base Connectivity) - A standard software interface for accessing data in both relational and nonrelational data-base management systems. Using this application programming interface, data-base applications can access data stored in data-base management systems on a variety of computers—even if each data-base management system uses a different data-storage format and programming interface. ODBC is based on the call-level interface specification of the X/Open SQL access group and was developed by Digital Equipment Corporation, Lotus, Microsoft, and Sybase. See also Java Database Connectivity.

Odd Parity - A method of bit-stream checking. Parity is used in error correction. The number of logic “ones” is counted in a bit stream. There is “odd parity” and there is “even parity.” Which is used depends on if you like odd or even numbers, or if the modem you are trying to connect with likes odd or even numbers. Parity is a part of error-checking protocol. It is simply the part of the protocol where the two devices are told if they are counting odd number bits or even number bits. In odd parity, if the number of ones is odd, then a parity bit is set to “one” at the end of the bit stream. This is odd parity because the parity bit is set to one when the number of “ones” is odd. In even parity, the parity bit is set to “one” when the number of “one” bits is even. See Parity.

ODI (Open Data-Link Interface) - A Novell specification that provides a standardized interface for NICs (Network Interface Cards) that allows multiple protocols to use a single NIC. See also NIC.

OE (Office Equipment) - Also referred to as line equipment. Line equipment is the actual interface port (from a circuit card) on the centraloffice switch in a telephone-company central office. It is the equivalent to a station or IPE (Intelligent Peripheral Equipment) card in a PBX system (TN for Nortel Specifics). Each telephone line has an associated line equipment or office-equipment interface. That particular port is what defines the telephone service provided to the customer connected to it via the OSP network. The CPU (core) of the central-office switch associates a phone number with a line-equipment port (OE). When a customer of the phone company calls and requests that their phone number be changed, the service order eventually finds its way to a central-office technician or service translator that reprograms the line equipment with a new phone number.

Off-Premises Extension (OPX) - Off-premises extension adapter, also called a loop extender. An OPX adapter is an add on device for a PBX switch or central-office switch that allows operation over an abnormally long loop or twisted pair, usually more than 12,000 feet for a central-office switch and 1500 feet for a PBX. The PBX or key-system manufacturer usually offers special equipment for a long-reach application. Some OPX adapters for PBX systems can be programmed to dial digits into an outgoing trunk, which will automatically ring a telephone somewhere else, such as the CEO of a company’s home office.

Off-Sight Night Answer - A feature of PBX and some key systems that allows a main line to be forwarded to a telephone number programmed in by the user/administrator when the system is put into night mode.

OHD - Optical hard drive.

Ohm - The unit of resistance, represented by the Greek letter Omega, Ω. Resistance is just what its name depicts, resistance to electric current flow. A 100-W, 120-V household light bulb has about one ohm of resistance. The more resistance is in a circuit, the less current flows through it.

Ohm’s Law - A series of mathematical relationships for electronics. The relationships are based on voltage, resistance, power, and amperage. The two basic Ohm’s law formulas are: P (power in watts) = I (current in amps) x E (voltage in volts) E (voltage in volts) = I (current in amps) x R (resistance in ohms).

Omnidirectional - A reference to a microphone that receives sound from all directions.

On-Board Modem - A term that refers to an internal modem.

ONA (Open Network Architecture) - The architecture of the public telephone network. Under FCC rulings, the Bell operating companies must allow other companies that offer “value-added services” to connect to and offer services through the local telephone companies network. Value-added services, under open network architecture, are voice mail, operator services, and IVR telephone-shopping applications. You don’t have to use the Bell companies’ voice mail if another voice-mail service provider is available. If you order the other company’s voice mail, all of your voice-mail connections will go through the alternative value-added service provider, on their separate equipment. The problem with ONA is that from a technology sense, access is equal, but in competition for market share, it is not.

One-Ten Termination Block - A twisted-pair connectivity method. See 110 Termination Block.

One-Way Trunk - A reference to a DID (Direct Inward Dial) or DOD (Direct Outward Dial) trunk used in PBX applications.

Ones Density - A reference to the maximum number of consecutive “zero” bits can be transmitted in a row using specific transmission equipment without losing the timing of the carrier (T1). To eliminate successive zeros in T1 transmissions line/protocols, such as B8ZS, have been implemented.

ONI - Optical Network Interface.

ONU (Optical Network Unit) - A reference to an access node that converts optical signals transmitted via fiber to electrical signals. ONUs are a part of hybrid fiber/coax/twisted-pair networks that are emerging in local markets. The ONU enables mass amounts of bandwidth to be delivered to areas that are beyond electrical transmission range of a central office or head end. ONUs can be pole mounted or placed in cable vaults. See also Remote Mini Fiber Mode.

OOF (Out of Frame) - A fault condition of a T1 carrier circuit. If an OOF condition exists, the circuit is down and not operational. Many T1 carrier equipment manufacturers implement recovery measures in the operating system to help systems come back on line automatically. Open - See Open Circuit.

Open Application Interface (OAI) - See OAI.

Open Architecture - The ability of different systems to integrate with each other, such as a PBX system and a Novell LAN. The newer term for open network architecture is CTI (Computer Telephony Integration).

Open Circuit - A circuit fault. Many confuse an open with a short. An open is literally an open, a “disconnection” in a circuit. A short is a “crossed circuit,” an easier path to ground caused by a bad component, water, or other means for electricity to get to where it is not wanted.

Open Data-Link Interface (ODI) - A Novell specification that provides a standardized interface for NICs (Network Interface Cards) that allows multiple protocols to use a single NIC. See also NIC.

Open Data Base Connectivity (ODBC) - A standard software interface for accessing data in both relational and nonrelational data-base management systems. Using this application programming interface, data-base applications can access data stored in data-base management systems on a variety of computers—even if each data-base management system uses a different data-storage format and programming interface. ODBC is based on the call-level interface specification of the X/Open SQL access group and was developed by Digital Equipment Corporation, Lotus, Microsoft, and Sybase. See also Java Database Connectivity.

Open-Ended Access - A term that refers to a switched telephone line that is not restricted from any calling prefixes or area codes. Most residential customers have subscribed to service that has open-ended access, not knowing what it is called.

Open Network Architecture (ONA) - See ONA.

Open Shortest Path First (OSPF) - A standard traffic-control program used by routers. OSPF was developed by the Internet Engineering Task Force during the late 1970s. Because OSPF is one of the original routing protocols, it is supported by virtually every router manufacturer. OSPF is a link-state hierarchical routing protocol.

Open Systems Interconnection (OSI) - The latest model, or guideline for communications protocols is the OSI (Open Systems Interconnect). It is the best model so far because all of the layers (functions) work independently of each other. Older proprietary communications models are shown in the figure. The OSI model is a seven-layer or “step” process for communications. The different functions are: • Application layer The seventh and highest layer of the OSI communications protocol model. The applications layer is the function of connecting an application file or program to a communications protocol. • Presentation layer The sixth layer in the OSI. In general, the presentation layer performs the function of encoding and decoding the data to be transmitted within the communications protocol. • Session layer The fifth layer of the OSI model. In general, the session layer establishes and maintains connection to the communica tions process of the lower layers. It also controls the direction of the data transfer. • Transport layer The fourth layer or function in a communications protocol model. In general, the transport layer performs the function of error correction and the direction of data flow (transmit/ receive). • Network layer The third layer in the OSI model. In general, the network layer does the job of switching and routing of the data being transmitted within the protocol. • Data-link layer The second layer or function in the OSI model. In general, the data-link layer receives and transmits data over the physical layer media (twisted pair, fiber optic, etc.). • Physical layer The first layer in the OSI model. In general, the physical layer is the actual media of the communications transmission (twisted-pair wire, coax, air, fiber optic, etc.). It is also the types of connectors used and the pin-outs of those connectors. The 568B wiring scheme for CAT 5 wire is a physical-layer function. For a basic conceptual diagram of the OSI model, see OSI Standards.

Open Wire - Also called “C” wire. Wire that is steel strengthened for longspan aerial-plant applications. Some C wire is uninsulated, so it is also called open wire. Open wire better fits the application because it is used in wide open or very rural areas. The old telegraph system was an openwire system.

Operating System - The computer software program that controls the functions of computer hardware. Examples of operating systems are Microsoft Windows 2000, MS-DOS, Pick, UNIX, and OS/2.

Operator - An attendant that assists callers. Operators can work for telephone companies or private telecommunications service companies.

Operator Console - The huge telephone used by a PBX attendant. The console is distinguishable by its large BLF (Busy Lamp Field) and many feature keys.

Optical Attenuator - A fiber-optic attenuator works like your sunglasses, it reduces the level of light entering your eyes so that you can see more effectively. They come in various connector types. Typical fiber-optic attenuator values are 5 dB, 10 dB, and 20 dB.

Optical Drive - A term used to refer to hardware that reads and/or writes to compact discs, in general, including CD-ROM drives, DVD drives, and CD-RW drives.

Optical Fiber Patch - Panel A means of terminating fiber-optic cable. Fiber patch panels contain a fiber splice tray equipped with pigtails. The pigtails are simply fiber connectors with a piece of fiber optic connected to them so that a fiber from within a cable can be easily spliced to them. The connectors are spaced on the front of the fiber patch panel.

Optical Fiber Splice - The two types of fiber-optic splices are fusion (heat) and mechanical.

Optical Time-Domain Reflectometer (OTDR) - A testing device that measures the loss over a fiber optic and the distance from the tester. OTDRs look similar to oscilloscopes with a CRT display tube. OTDRs are a specialized optical version of a TDR (TimeDomain Reflectometer) used to test copper pairs. The way a TDR works is that it transmits a signal down a media (copper or glass), then waits for a reflection to come back. When the reflection returns to the device, the time difference is used to calculate the distance that the signal traveled. The size or power of the return signal is used to calculate loss.

Optoelectric Transducer - A class of electronic components that converts light energy into electrical energy and electrical energy into light energy.

OPX Adapter (Off-Premises Extension Adapter) - Also called a loop extender. An OPX adapter is an add-on device for a PBX switch or central-office switch that allows operation over an abnormally long loop or twisted pair, usually over 12,000 feet for a central-office switch and 1,500 feet for a PBX. The PBX or key system manufacturer usually offers special equipment for a long-reach application. Some OPX adapters for PBX systems can be programmed to dial digits into an outgoing trunk, which will automatically ring a telephone somewhere else, such as the CEO of a company’s home office.

Oscillator - An electronic circuit that produces an AC cycle from a DC power source. Oscillators are used as carrier references for transmitters and for the timing signal in clock circuits for digital instruments, such as PCs and telephone systems. Quartz crystal oscillators are the most reliable and inexpensive. For a photo, see Crystal Oscillator.

Oscilloscope - A testing device that allows a user to view a waveform on a screen (CRT). The screen is graduated to show different frequencies and voltage levels. The value of each graduation (or division) is determined by the setting of the frequency/division knob. The voltage level of each division is determined by the voltage-level selector knob. Oscilloscopes range in price from about $400 to more than $8000. The features that make an oscilloscope increase in price are the ability to read/display very fast frequencies and the ability to view more than two waveforms at a time. Some oscilloscopes are capable of being connected to plotters, which gives the user the ability to print a waveform displayed on the screen.

OSI (Open Systems Interconnect) - See Open Systems Interconnect.

OSI Model (Open Systems Interconnect Model) - See Open Systems Interconnect.

OSI Standards - An architecture set up by the ISO (International Standards Organization) that sets some broad standards for communications. The purpose of the standards is to help manufacturers make equipment that is universally compatible. The OSI is not perfectly followed by the telecommunications and data communications industry. It is used as a model in the design of communications protocols. The basic idea of the OSI is that seven functions, steps, or layers are in the successful completion of a communication transmission. The goal of the OSI is to make all of these layers separate and individual “entities” in hardware and software so that different manufacturers can integrate at different levels. Data communications is modeled after voice communications. Even though humans speak many different languages (protocols), there is still a common architecture of human communications. See Open Systems Interconnect.

OSPF (Open Shortest Path First) - A standard traffic-control program used by routers. OSPF was developed by the Internet Engineering Task Force during the late 1970s. Because OSPF is one of the original routing protocols, it is supported by virtually every router manufacturer. OSPF is a link-state hierarchical routing protocol.

OTDR (Optical Time-Domain Reflectometer) - See Optical TimeDomain Reflectometer.

Out-of-Band Signaling - In telephone circuits (DS1 to be specific), the two different ways to send signals are in band and out of band. Signals are digits that you dial, dial tone, the phone being off-hook, ringing, etc. An in-band telephone line is like the one in your home; the digits that you dial and the ringing are carried within the channel that you talk on. Out-of-band signaling is a method that telephone companies and businesses use for larger PBX applications and data-transfer applications. In an out-of-band signaled DS1, there are 24 multiplexed channels. The 24th channel carries the signaling for the other 23 channels or phone lines. The advantage of out-of-band signaling is that each channel has an increased capacity to carry data (8Kb/s more) and the 23 channels are not used to find out if a line is busy (both directions, in and out). The off-hook sensing and busy signaling are performed in the 24th channel. If you have a system that receives thousands of calls per day, this can reduce traffic.

Outdoor Jack Closure - Closures are available that help protect telephone and other jacks from moisture and other outdoor weather conditions.

Outside Plant - A term that refers to a communications utility’s twistedpair and/or coax network that winds through towns and neighborhoods. It includes terminals, pedestals, cross boxes, and vaults.

Outsource - To subcontract work to other companies, usually for their construction or technical expertise in the installation of specific electronics or software.

Outward Restriction - A feature of PBX (Private Branch Exchange) telephone systems that prevents selected telephone extensions from dialing outside the office/building. When a user of one of these extensions dials “9” for an outside dial tone, they will just get a fast busy signal.

Overhead - The part of a transmission that contains the information/signal that controls the operation of the transmission. If you are transporting yourself across town in your car, you are the payload and your car is the overhead.

O - 1. Ohm.The ASCII symbol for ohm.The preferred symbol is Ω, but it doesn’t print easily with some software programs. 2. O+ (O positive).The most common blood type. Give blood, please. Assuming that the technician is skilled and the equipment is properly sterilized, it doesn’t take long, it doesn’t hurt, and it doesn’t make you ill, but it may very well save a life.

O&M (Operations and Maintenance) - Referring to all functions associated with the ongoing operations and maintenance of a system or network.

OADM (Optical Add/Drop Multiplexer) - In wavelength division multiplexing (WDM) a device that is able to add or drop individual wavelengths without separating all wavelengths and certainly without converting them to electrical format. An OADM is a purely optical version of an ADM. See also ADM, wavelength, and WDM.

OAM&P (Operations, Administration, Management, and Provisioning) - Referring to all functions associated with the ongoing operation, administration, and management of a system or network, as well as its initial installation.

O-Band (Original Band) - The ITU-T standard optical transmission window in the wavelength range of 1,260–1,360 nm. See also wavelength and window.

oblique - Sloping, slanting, or indirect, i.e., neither perpendicular nor parallel. See also angle of incidence and obtuse.

OBRA 93 - See Omnibus Budget Reconciliation Act of 1993.

obsessive compulsive disorder (OCD) - See OCD.

obtuse - 1. In mathematics, an angle greater than 90 degrees, but less than 180 degrees. 2. A person who is slow to comprehend or understand, or who is dull or insensitive. We all know such people. See also abstruse.

OCC (Other Common Carrier) - The term applied in the United States prior to the breakup of the Bell System (January 1, 1984) to describe the long-distance carriers that competed with AT&T Long Lines.As a result of the Modified Final Judgement (MFJ) that caused the reorganization of the Bell System, AT&T and the OCCs became known as interexchange carriers (IXCs, or IECs) and initially were not allowed to provide intraLATA long distance service. See also Bell System,IXC, LATA, long distance, and MFJ.

OCD (Obsessive Compulsive Disorder) - A type of psychiatric anxiety disorder characterized by a person’s recurrent, unwanted thoughts (obsessions) and related ritualistic and repetitive behaviors (compulsions) such as counting, checking, cleaning, or handwashing in an attempt to neutralize the obsessions.The rituals, however, provide only temporary relief and, therefore, must be repeated, again and again. By the way, there are 54 words and 406 characters in this definition, including spaces and not including this sentence, or the following sentences in this definition.There are 84 words and 503 characters in the previous definition. Obsessive compulsive disorder comprises 3 words and 30 characters, with spaces. OCD is one word, although it really is not a word, and 3 letters, with no spaces. Personally, I prefer phrases that contain an even number of words and words that contain an even number of letters.Thank you. (By the way, thank you is 2 words of 5 and 3 letters, which is OK because 5 + 3 = 8, which is an even number.)

OCR (Optical Character Recognition) - Application software that allows a computer to recognize printed or written characters, e.g., letters, numbers, punctuation marks, and pictograms using an optical scanner for input. Optical mark recognition (OMR) also employs an optical scanner, but does not employ a character recognition engine. See also OMR.

octothorpe - See #.

OD (Outside Diameter) - The measure of the width of the outer surface of a circular or cylindrical object such as a hollow pipe or tube.

ODU (Optical Data Unit) - An entity for processing in an Optical Transport Network (OTN). An ODU comprises a frame or series of frames in their native protocol, encapsulated in a digital wrapper for network management purposes. See also digital wrapper, encapsulate, frame, network management, OTN, and protocol.

OEM (Original Equipment Manufacturer) - A company that builds components or products that are incorporated into products or systems sold by another company commonly referred to as a value-added reseller (VAR).An Ethernet network interface card (NIC), for example, might be built by an OEM to the specifications of a manufacturer of laptop or tablet computers.

OEO (Optical-Electrical-Optical) - Optical repeaters are characterized as being OEO in nature. Such a repeater receives an attenuated optical signal, converts it to an amplified electrical signal, reshapes and retimes it, converts it back to optical signal, and retransmits it. See also OOO and repeater.

OFC (Optical Fiber, Conductive) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying component, such as a metallic strength member or vapor barrier, and are not certified for use in interior plenum or riser applications. See also cable, conductor, current, optical fiber, plenum cable, and riser cable.

OFCP (Optical Fiber, Conductive, Plenum) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying component, such as a metallic strength member or vapor barrier, and are certified for use in interior plenum applications. See also cable, conductor, current, optical fiber, and plenum cable.

OFCR (Optical Fiber, Conductive, Riser) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain at least one electrically conductive, non–current-carrying component, such as a metallic strength member or vapor barrier, and are certified for use in interior riser applications. See also cable, conductor, current, optical fiber, and riser cable.

OFDM (Orthogonal Frequency Division Multiplexing) - Synonymous with discrete multitone (DMT). See also COFDM and DMT.

offered load - In frame relay, the data rate, as measured in bits per second (bps) offered to the network for delivery.The aggregate offered load can be less than the access rate supported by the access link and/or the port speed of the frame relay network device (FRND), but can never exceed whichever is less. See also access rate, data rate, frame relay, FRND, link, and port.

off-hook - A condition that exists when a telephone receiver or handset is lifted or removed from its cradle, thereby completing a circuit and placing the telephone in use.The term refers to the fact that early telephone handsets hung from a switch hook, a hook that activated a switch. See also on-hook.

off-hook voice announce - A key telephone system (KTS) feature that enables the system attendant to announce another incoming call even if the station user is off-hook and engaged in another call. In some implementations, the announcement is through the telephone speaker, with the station microphone muted so that the other party does not hear the announcement. In other implementations, the announcement is through the handset receiver so that the other party is not muted, as the muting is noticeable. See also KTS.

off-premises extension (OPX) - Synonymous with off-premises station (OPS). See OPX.

off-premises station (OPS) - Synonymous with off-premises extension (OPX). See OPX.

offset quadrature phase shift keying (OQPSK) - See OQPSK.

offshoring - The exporting of certain business functions to foreign countries, where either company employees or independent contractors perform the work. Offshoring commonly involves the exporting of work from developed countries to undeveloped foreign countries for reasons that include cost reduction, tax avoidance, legal liability avoidance, and strategic market expansion. If work is shifted to independent contractors, the process becomes one of offshore outsourcing. See also job security and outsourcing.

OFN (Optical Fiber, Nonconductive) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are not certified for use in interior plenum or riser applications. See also cable, conductor, optical fiber, plenum cable, and riser cable.

OFNP (Optical Fiber, Nonconductive, Plenum) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are certified for use in interior plenum applications. See also cable, conductor, optical fiber, and plenum cable.

OFNR (Optical Fiber, Nonconductive, Riser) - The designation by the National Fire Protection Association (NFPA) for fiber optic cables that contain no electrically conductive components and are certified for use in interior riser applications. See also cable, conductor, optical fiber, and riser cable.

OH - The chemical symbol for hydroxyl. See also hydroxyl.

Ohm, Georg Simon (1787–1854) - The German physicist whose research on electric currents led to the formulation of Ohm’s Law. See also Ohm’s Law.

OLT (Optical Line Terminal) - In a passive optical network (PON), the device that terminates the optical local loop at the edge of the network. In a telco PON, the OLT is housed in the central office (CO). In a CATV PON, the OLT is housed in the headend.The OLT can either generate downstream optical signals on its own, or can pass optical signals from the optical backbone through a collocated optical crossconnect or multiplexer.The OLT also receives upstream signals from the optical network terminals (ONTs) at the customer premises and optical network units (ONUs) in remote nodes. See also backbone, CATV, CO, cross-connect, downstream, headend, local loop, multiplexer, OLT, ONU, PON, telco, and upstream.

Omnibus Budget Reconciliation Act of 1993 (OBRA 93) - Also known as the Deficit Reduction Act of 1993 and the Revenue Reconciliation Act of 1993. In the United States, an act of Congress that included a provision authorizing the Federal Communications Commission (FCC) to auction domestic radio spectrum. See also FCC and spectrum.

OMR (Optical Mark Recognition) - The process of gathering data with an optical scanner by measuring the reflectivity of light at predetermined positions on a surface. OMR differs from optical character recognition (OCR), which requires a recognition engine in order to make sense of written characters. See also OCR.

ones density - The density of one (1) bits in a digital bit stream. Depending on specific nature of the Tcarrier network, 15–80 zero (0) bits can be transmitted in a row as long as the density of ones is at least 12.5 percent (1 in 8) over a specified interval of time. Ones density ensures that there are electrical pulses on a circuit with at least a minimal density in order to keep the various circuit terminating equipment and repeaters synchronized. Ones density is maintained by a channel service unit (CSU), a type of data communications equipment (DCE) that provides the customer interface to a digital circuit. In the event that the circuit is silent, i.e., there is no active data transmission, the CSU will regularly transmit one (1) bits, known as keep alive bits, for the same purpose. See also CSU, DCE, pulse, repeater, synchronize, and T-carrier.

on-hook - A condition that exists when a telephone receiver or handset is in its cradle and available to receive an incoming call. The term refers to the fact that early telephone handsets hung from a switch hook, a hook that activated a switch. See also off-hook.

ONT (Optical Network Terminal) - In a passive optical network (PON), the device that terminates the optical local loop at the customer premises in a fiber-to-the-premises (FTTP) scenario. The ONT serves as a media converter, interfacing the optical fiber to the copper-based inside wire.The ONT is an addressable device that recognizes and accepts downstream data addressed to it specifically, ignoring all other data. The ONT is synchronized with the optical line terminal (OLT) at the network edge and is assigned time slots for user-generated upstream data, which it buffers as necessary. See also buffer, downstream, FTTP, local loop, media converter, OLT, optical fiber, PON, synchronize, and upstream.

OOO (Optical-Optical-Optical) - A device that is purely optical in nature, rather than having electrical or electronic as well as optical components. The repeaters used in fiber optic transmission systems (FOTS), for example, are Optical-Electrical-Optical (OEO). Optical switches used in wavelength division multiplexed (WDM) transmission systems sometimes are purely optical. See also FOTS, OEO, optical, and WDM.

opaque OXC (opaque Optical CROSS-Connect) - A digital cross-connect (DXC) employed in an optical system. This approach requires that the optical signal be converted into electrical format before being switched by the electronic DXC, then converted back into optical format before being placed back on the fiber optic transmission system (FOTS). This optical-electrical-optical (OEO) signal conversion process adds some amount of delay to the signal, but offers the advantage of signal regeneration to deal with issues of signal dispersion and attenuation. A transparent OXC is an optical-optical-optical (OOO) device that includes an optical switching module.A translucent OXC is a hybrid that includes both electronic and optical switching modules. See also attenuation, dispersion, DXC, FOTS, OEO, OOO, OXC, translucent OXC, and transparent OXC.

The Open Group - An inter-industry forum dedicated to the development and promotion of electronic messaging, including e-mail, fax, electronic data interchange (EDI), based on open standards and global interoperability. Previously known as the Electronic Messaging Association (EMA),The Open Group is technology-neutral and vendor-neutral. See Appendix A for contact information. See also EDI, e-mail, and fax.

open-loop algorithm - In frame relay, a congestion control mechanism (or lack thereof) that permits the frame relay network device (FRND) to accept incoming frames with no prior knowledge of the likelihood of the network’s ability to deliver them successfully. See also closed-loop algorithm, congestion, frame relay, and FRND.

open source - Also known as open source software (OSS). Software distributed under a license that makes the source code (i.e., program instructions) freely available to the end user. Such a license often encourages the user to modify the source code as long as the modifications are made freely available to other users, as well. Open source software generally is available at no charge, i.e., free. Linux is a classic example of successful open source software. See also software, Linux.

open source software (OSS) - See open source.

open standard - A set of specifications that are standardized by a formal body and are then published and made freely available to the technical community. See also standard.

Open Systems Interconnection Model - See OSI Reference Model.

operations, administration, management, and provisioning (OAM&P) - See OAM&P.

operations and maintenance (O&M) - See O&M.

operations support system (OSS) - See OSS.

OPS (Off-Premises Station) - Synonymous with off-premises extension (OPX). See OPX.

optical - In physics, relating to the study of light in the infrared (IR), visible, and ultraviolet (UV) regions of the electromagnetic spectrum. See also electromagnetic spectrum, IR, light, UV, and visible light.

optical add/drop multiplexer (OADM) - See OADM.

Optical Carrier (OC) - See OC.

optical character recognition (OCR) - See OCR.

optical cross-connect (OXC) - See OXC.

optical data unit (ODU) - See ODU.

optical-electrical-optical (OEO) - See OEO.

optical fiber - A slender strand of transparent glass or plastic specially constructed to serve as a dielectric conductor, or waveguide, of infrared (IR) light in a fiber optic transmission system (FOTS).The fiber generally is one of many types of glass optical fiber (GOF) although plastic optical fiber (POF) is sometimes used. GOF offers the advantage of very low signal attenuation over long distances, in support of signaling rates that currently are as high as 40 Gbps per lambda, or wavelength. POF sometimes is used over short distances where its flexibility, general durability, and low cost are advantageous. See also GOF and POF.

optical fiber, conductive (OFC) - See OFC.

optical fiber, conductive, plenum (OFCP) - See OFCP.

optical fiber, conductive, riser (OFCR) - See OFCR.

optical fiber, nonconductive (OFN) - See OFN.

optical fiber, nonconductive, plenum (OFNP) - See OFNP.

optical fiber, nonconductive, riser (OFNR) - See OFNR.

optical isolator - 1. A device used in a high-speed, high-power fiber optic transmission system (FOTS) to isolate erbium-doped fiber amplifiers (EDFAs), laser diode light sources and other devices.The optical isolators act as diodes, preventing signals from propagating in the upstream direction and confusing the downstream signal or device generating it. See also diode, EFDA, FOTS, and laser diode. 2. A device containing a short length of optical fiber and inserted into an electrified communications link to electrically isolate the attached devices from ground loops, power spikes, and surges. Such an optical isolator can act as a repeater, as well as a protector. See also link, optical fiber, protector, and repeater.

optical line-of-sight (optical LOS) - See LOS.

optical line terminal (OLT) - See OLT.

optical mark recognition (OMR) - See OMR.

optical network terminal (ONT) - See ONT.

optical network unit (ONU) - See ONU.

optical-optical-optical (OOO) - See OOO.

optical transport network (OTN) - See OTN.

optical transport unit (OTU) - See OTU.

optics - The branch of physics dealing with the nature and properties of electromagnetic energy in the light spectrum and the phenomena of vision. In the broadest sense, optics deals with infrared light, visible light, and ultraviolet light. See also electromagnetic spectrum, infrared light, physics, ultraviolet light, and visible light.

OPX (Off-Premises eXtension) - Synonymous with off-premises station (OPS).A key telephone system (KTS) or PBX station or extension that terminates on a telephone physically located off-premises, typically on a non-contiguous property. In addition to a special line card, an OPX requires a dedicated private line, typically leased from the local exchange carrier (LEC).The OPX enjoys all of the features of an extension located on-premises, but at considerable cost. OPXs are, and always were, uncommon, but sometimes are used to connect a distant guard shack or security building to the PBX or perhaps to provide a technically challenged key executive with a PBX extension at home. See also KTS, LEC, and PBX.

OQPSK (Offset Quadrature Phase Shift Keying) - A variant of QPSK that uses a half-symbol timing offset to prevent large amplitude fluctuations in the modulated signal. See also amplitude, modulate, QPSK, signal, and symbol.

orange hose - A term used to describe the thick coaxial cable specified by the IEEE as 10Base5, for use in early Ethernet networks.The term was in reference to the orange cable sheath used by some manufacturers.The cable also was about as thick as a garden hose. See also 10Base5, coaxial cable, Ethernet, and IEEE.

orderwire - A circuit or channel used by technical personnel for coordination and control functions relating to activation, deactivation, reconfiguration, reporting, and maintenance of communications systems, networks, and services. See also channel and circuit.

.org (organization) - Pronounced dot org. Originally, the Internet generic Top Level Domain (gTLD) reserved exclusively for noncommercial (not-for-profit) organizations. The domain is now unrestricted. This is an unsponsored domain. See also Internet, gTLD, and unsponsored domain.

original band (O-Band) - See O-Band.

original equipment manufacturer (OEM) - See OEM.

orthogonal - 1. In mathematics, at right angles to or perpendicular to. 2. In telecommunications, describing radio frequency (RF) signals that are independent and mutually exclusive and, therefore, avoid intersymbol interference.Thereby, a receiver can recognize a legitimate signal and reject an unwanted signal or signal element.The concept applies to orthogonal frequency division multiplexing (OFDM), also known as discrete multitone (DMT). See also DMT, interference, RF, signal, and symbol.

orthogonal frequency division multiplexing (OFDM) - Synonymous with discrete multitone (DMT). See DMT.

OS (Operating System) - The master software program that controls the allocation and usage of all internal resources (e.g., memory, queuing, input/output, central processing unit [CPU], time, disk space, and transmission and reception processes) and, thereby, enables and controls the operation of the entire computer system.The OS forms the foundation for application software that performs end-user tasks such as word processing and mathematical calculation. An OS is largely software, although there are firmware components. See also firmware, program, and software. See Operating System.

oscillate - Vary predictably, or rhythmically, between two extremes, usually within a set period of time. An alternating current (AC) waveform, for example, oscillates between maximum and minimum electrical values, which are positive voltage (+V) and negative voltage (–V), respectively. See also AC, voltage, and waveform.

OSI Reference Model (Open Systems Interconnection Model) A layered architecture consisting of a set of international networking standards developed by the International Organization for Standardization (ISO) in 1983, and now known collectively as ITU-T Recommendation X.200.The ISO promoted the model as a full standard, and the United States federal government and many computer manufacturers invested heavily (billions in US$) in compliance.The initiative failed within a few years, at least in the United States, as SNA, TCP/IP, and a few other standards seemed to have satisfied most people’s appetite for standards and OSI seemed too complex and redundant.The European community, however, embraced OSI, at least in part because of the confusion caused by the multinational nature of the region and, therefore, the plethora of national standards.The European Union (EU) actually legally imposed the model for some applications. Eventually,TCP/IP pushed OSI aside as a standard, but the reference model remains valuable, and most manufacturers relate their products to the model in order to put them in context. So, the OSI Reference Model continues to have great value. The model is a layered architecture that defines a set of common rules that computers of disparate origin can use to exchange information.The layers serve to segment functions, so that each layer can be considered independently, yet all are interrelated, with supporting software embedded in each node providing the interface between layers. In a typical scenario, a transmitting device uses the top layer, at which point the data is placed into a packet, prepended by a header.The data and header, known collectively as a Protocol Data Unit (PDU), are handled by each successively lower layer as the data works its way across the network to the receiving node, typically with each layer adding a header. At the receiving node, the data works its way up the layered model; successively higher layers strip off the header information.While in transit, the data may work its way up and down the model as it transits different networks and subnetworks running different protocols.

Layer	Functional Focus
7 Application	Semantics: Applications and end user processes such as e-mail, file transfer, and authentication
6 Presentation	Syntax: Data format (coding) and display, code conversion, encryption, compression
5 Session	Dialog coordination: Establishing, maintaining, coordinating, and terminating dialogues and data exchanges
4 Transport	Reliable data transfer: End-to-end error detection and correction, and flow control, ensuring the integrity of the complete datastream
3 Network	Routing and relaying: Message routing, error detection, and control of internodal traffic
2 Data Link	Technology-specific transfer over a link or channel: Framing, error control, flow control, data sequencing, time-out levels, and data formatting (encoding and decoding)
1 Physical	Physical connections: Electrical and mechanical aspects of the interface of a device to a transmission medium

OSI Reference Model Layers

See also application layer, data link layer, ISO, ITU-T, network, network architecture, Network Layer, Physical Layer, Presentation Layer, protocol, Session Layer, SNA, software, standard, subnetwork, TCP/IP, Transport Layer, X.200, and x series.

OSP (OutSide Plant) - All of the telecommunications apparatus and cable systems outside (i.e., not housed in buildings) such as central offices or customer premises. OSP includes all the components of cable systems such as the aerial, buried, and underground cables, amplifiers and repeaters, cross-connect boxes, and remote neighborhood nodes, some of which may be located in vaults or sheds. See also inside plant.

OSS (Operations Support System) - 1. Referring to the system or systems that perform management, inventory, engineering, planning, and repair functions for communications service providers. Specific OSS functions can include inventory management, cost allocation, billing, service order management, trouble ticket management, traffic analysis, capacity planning, and network optimization. 2. Open source software. See open source software.

Ostrofsky, Marc - The world record holder, to the best of my knowledge, with respect to the sale price of a domain name. In the mid-1990s, Ostrofsky put a number of his employees to work searching for domain names that had e-commerce potential.They searched for just about any word in the English language, especially words preceded with e- or e. As a result of that effort, he identified and registered www.eflowers.com. In 1999, he rejected an offer of $1,000,000 from Flowers Direct, preferring to sell it to them for $25,000, plus $0.50 for every transaction generated over the Web site, plus free flowers for his wife (now ex-wife), Sarah, for the rest of her life. Given the projections of 500,000 transactions per year, Ostrofsky realized an excellent return on an investment of $70.00. Ostrofsky later sold the rights to www.business.com for $7,000,000, a domain name he had acquired a few years earlier for $250,000 for use in connection with a business he later sold for many millions of dollars. See also domain name.

OTA (over the air) - See over the air.

Other Common Carrier (OCC) - See OCC.

OTN (Optical Transport Network) - Described in the ITU-T Recommendation G.709 (2003), OTN adds operations, administration, maintenance, and provisioning (OAM&P) functionality to optical carriers, specifically in a multi-wavelength system such as dense wavelength division multiplexing (DWDM). OTN specifies a digital wrapper, which is a method for encapsulating an existing frame of data, regardless of the native protocol, to create an optical data unit (ODU), similar to that used in SDH/SONET. OTN provides the network management functionality of SDH and SONET, but on a wavelength basis.A digital wrapper, however, is flexible in terms of frame size and allows multiple existing frames of data to be wrapped together into a single entity that can be more efficiently managed through a lesser amount of overhead in a multi-wavelength system.The OTN specification includes framing conventions, nonintrusive performance monitoring, error control, rate adaption, multiplexing mechanisms, ring protection, and network restoration mechanisms operating on a wavelength basis. A key element of a digital wrapper is a Reed-Solomon forward error correction (FEC) mechanism that improves error performance on noisy links. Digital wrappers have been defined for 2.5-, 10-, and 40- Gbps SDH/SONET systems. SDH/SONET operation over an OTN involves additional overhead due to encapsulation in digital wrappers.The resulting line rates are defined as optical transport units (OTUs). See also digital, DWDM, error control, FEC, ITU-T, link, multiplexer, ODU, OTN, OTU, rate adaption, ReedSolomon, and wavelength.

OTU (Optical Transport Unit) In an optical transport network (OTN), an optical channel for transporting optical data units (ODUs), which comprise native frames encapsulated in digital wrappers. ITU-T Recommendation G.709 specifies three line rates alongside their corresponding SDH/SONET line rates.

G.709		SDH/SONET
Interface	Line Rate	OC/STM Level	Line Rate
OTU-1	2.666 Gbps	OC-48/STM-16	2.488 Gbps
OTU-2	10.709 Gbps	OC-192/STM-64	9.953 Gbps
OTU-3	43.018 Gbps	OC-768/STM-256	39.813 Gbps

G.709 Line Rates and Corresponding SDH/SONET Line Rates

G.709 also specifies an interface for 10 GbE clients, utilizing the same digital wrapper, which results in a line rate of 11.095 Gbps. See also 10GbE, channel, digital wrapper, encapsulate, frame, ITU-T, line rate, ODU, OTN, SDH, and SONET.

out-of-band signaling and control - Signaling and control that takes place over frequencies (e.g., in guard bands) or in time slots separate from those that carry user payload. In an analog context, out-of-band signaling can take place over the guard bands that separate channels.T-carrier signaling clearly is in-band rather than out-of-band, as it involves bit robbing, which periodically replaces payload bits with signaling bits. E-carrier signaling and control occurs exclusively in time slots reserved for that purpose. Packet technologies such as frame relay, Internet Protocol (IP), asynchronous transfer mode (ATM), and X.25 variously include headers and trailers that support out-of-band signaling, and use separate signaling packets for various network management purposes.Truly out-of-band signaling takes place over an entirely separate path and even a separate network, as is the case with Signaling System 7 (SS7). In any case, out-of-band signaling and control does not directly compete with payload for bandwidth. See also analog, ATM, digital, E-carrier, frame relay, guard band, header, in-band signaling and control, IP, network management, packet, payload, SS7, T-carrier, trailer, and X.25.

out-of-phase - 1. A signal that has suffered phase distortion so that the sinusoidal waveform has been unintentionally altered in phase, or periodic angle. See also phase and sine wave. 2. Someone who is outof-sync or out-of-step with the normal world, whatever that is. Such people may be crazy as loons, but they seem to get by, and some even thrive, in spite of it. See also normal.

outside vapor deposition (OVD) - See OVD.

outsourcing - The transferring of certain business functions from internal staff to outside contractors. Outsourcing commonly is applied to non-core functions, such as accounting, information technology, human resources, facilities management, fleet management, parts manufacturing, payroll, press relations, and real estate management for reasons that include lowering costs, avoiding liabilities, and allowing management to focus on the core business. Outsourcing also is an excellent way for management to shift or even avoid responsibility. See also job security and offshoring.

OVD (Outside Vapor Deposition) - A commonly used technique for the mass production of glass optical fiber, OVD begins with heating silica and germanium to the point of vaporization. As the glass vapor cools, it is deposited as layers of soot on the outside of a rotating hollow ceramic bait rod to create a glass cylinder.The first layer is the core material of germanium-doped silica. On top of the core material, many layers of slightly purer silica soot, i.e., silica with lower levels of dopants, are deposited to form the cladding. If the end product is to be a step-index fiber, there is an abrupt change in the chemical composition between the core and cladding. If the end product is to be a graded-index fiber, there will be many graded layers of silica of slightly different chemical compositions deposited on the core to yield slightly and successively purer layers of cladding surrounding the fiber axis.The composition of the glass layers in a graded-index fiber is much like the arrangement of the annular rings of a tree.When the deposition process is complete, the bait rod is slipped out of the glass cylinder, which is then sintered and collapsed into a preform cylinder, which is cooled and stored.The tip of the preform cylinder is reheated to a temperature of 2,500 degrees in a drawing tower.The resulting gob of molten glass is carefully drawn by gravity, in a process known as broomsticking, into a fiber as long as 20 kilometers. As the fibers cool, an acrylate coating is applied to protect the raw glass from physical damage. As is the case with all of these techniques, OVD takes place in a vacuum environment, as it is the exposure to oxygen that makes glass so brittle. Inside vapor deposition (IVD) is a similar process, with the soot deposited on the inside of a rotating glass tube that becomes the outside cladding. See also cladding, core, graded-index fiber, IVD, sinter, and step-index fiber.

overlay - In telecommunications, a deployment in which the new infrastructure parallels that of existing infrastructure. In a passive optical network (PON) deployment, for example, this approach enables the service provider to construct the new system and provide enhanced broadband service to PON subscribers as required, while continuing to serve others subscribing to more basic services from the old cable plant. See also brownfield, greenfield, infrastructure, and PON.

overlay area code - An area code that covers the same geographical area as an existing area code. As a result, callers within the area must dial a full 10-digit number (NNX-NNX-xxxx) to reach any other number within the area.The concept of the overlay area code was developed as a means of avoiding forcing subscribers to change telephone numbers after an area code split. Such telephone number changes cause great disruption, result in lost business and otherwise cost businesses great amounts of money for advertising, re-printing of business cards and letterhead stationary, and so on. See also area code.

overlay carrier - A carrier that builds a network that overlays, or approximately follows the same physical layout as, the traditional PSTN. Competitive carriers sometimes deploy microwave or other wireless systems, for example, that duplicate the physical topology of the incumbent carrier

over-over - Synonymous with push-to-talk (PTT). See PTT.

oversubscribe - To place potentially greater demands on a device or circuit than it is capable of handling at one time.A T1 circuit, for example, supports a data rate of 1.536 Mbps, which commonly is subdivided into 24 voice grade channels of 64 kbps. So, the circuit can support 24 voice or data calls of 64 kbps each. If more than 24 calls are offered to the T1, it is said to be oversubscribed. If the calls are all uncompressed voice calls truly requiring continuous bandwidth of 64 kbps, the 25th call must be denied. If the calls are data calls supporting bursty applications, such as e-mail, that do not require continuous bandwidth of 64 kbps, the TDM multiplexer may be able to manage the contention by buffering some of the data and sharing bandwidth among multiple such calls.Thereby, the circuit may be able to support considerably more than the 24 calls supported by a more rigid approach. Oversubscription is the economic foundation of carrier services. For example, a neighborhood of 96 phone lines may be served well by two oversubscribed T1 lines because the probability of all users placing calls at one time is very small (less than 1 percent). See also bandwidth, carrier, channel, circuit, and voice grade.

over the air (OTA) - 1. Referring to broadcast airwave radio and television transmission. See also airwave, broadcast radio, broadcast television, and broadcast transmission. 2. Referring to methods of distributing software updates and application settings to cellular telephones.

OXC (Optical CROSS-Connect) - A network device used to switch high-speed optical signals (e.g., SDH/SONET OC-3, OC-12, and OC-48).An OXC can switch the signal in its entirety, or can demultiplex it and switch its component signals. For example, an OXC can receive an OC-48 signal and demultiplex it into four constituent OC-12 signals, each of which it forwards through a separate OC-12 port. An opaque OXC is essentially a digital cross-connect (DXC) employed in an optical system. This approach requires that the optical signal be converted into electrical format before being switched by the electronic DXC, then converted back into optical format before being placed back on the fiber optic transmission system (FOTS). This optical-electrical-optical (OEO) signal conversion process adds some amount of delay to the signal, but offers the advantage of signal regeneration to deal with issues of signal dispersion and attenuation. A transparent OXC, also known as a photonic cross-connect (PXC), is characterized as optical-optical-optical (OOO), as it performs the switching function without converting the signal to electronic format.This approach does not impose the same level of signal processing delay as the OEO process employed in an opaque OXC, but neither does it provide signal visibility. In other words, it is not possible to monitor the signal quality or determine the nature of the higher layer protocols employed.A translucent OXC is a hybrid that includes both optical and electronic switching modules and operates in both opaque and transparent mode. If signal visibility or regeneration is desirable, the electronic module is employed. See also attenuation, cross-connect, dispersion,DXC,OC-3,OC-12,OC-48,OEO,OOO, optical, protocol, regenerator, SDH, signal, and SONET.