A B C D E F G H I J K L M N O P R S T U V W Y

Absorption

This is where light signals are absorbed into the glass when light/data is being transferred.

Acceptance Testing
The testing of an optical network system to make sure that it performs as required.

Active Device
A device that requires a source of energy to function, unlike passive devices.

Adaptor - A device used to interconnect two different connector types.

Add/Drop
The process by which a part of the information carried in a transmission system is demultiplexed (dropped) at an intermediate point and different information is multiplexed (added) for subsequent transmission. The remaining traffic passes straight through the multiplexer without additional processing.

ADM (Add/Drop Multiplexer)
A multiplexer capable of extracting and inserting lower-rate signals from a higher-rate, multiplexed signal, without completely demultiplexing the signal.

AIS (Alarm Indicating Signal)
A code sent downstream indicating an upstream failure has occurred. SONET defines four categories of AIS: Line AIS, STS Path AIS, VT Path AIS, and DSn AIS.

American National Standards Institute (ANSI)
The coordinating body for voluntary standards groups within the United States. ANSI is a member of the International Standards Organization for Standardization (ISO).

Amplified Spontaneous Emission (ASE)
Buildup of unwanted spontaneous emission in an optical fiber amplifier. ASE is an undesirable effect and adds “noise” to the amplifier system.

Amplifier/Repeater/Optical Amplifier
Device that boosts the power of an optical signal. An optical amplifier does this without any conversion of the light into an electrical signal.

ANSI (American National Standards Institute)
A membership organization that develops U.S. industry standards and coordinates U.S. participation in the International Standards Organization (ISO).

APS
Automatic Protection Switching.

A 1+1 protection switch architecture is one in which the head end signal is permanently bridged (at the electrical level) to service and protection equipment to enable the same payload to be transmitted identically to the tail end service and protection equipment. At the tail end , each service and protection optical signal is monitored independently and identically for failures. The receiving equipment selects either the service or protection channel based upon the switching criteria.

A 1:N protection switch architecture is defined as an architecture in which any one of N service channels can be bridged to a single optical protection channel. Head end to tail end communications are accomplished by using the SONET APS channel, bytes K1 and K2.

Arrayed Waveguide Gratings (AWGs)
Integrated optical circuits formed by a series of curved silica waveguides that can combine (multiplex) or separate (demultiplex) different wavelength signals in an optical network.

Asynchronous
A network in which transmission system payloads are not synchronized and each network terminal runs on its own clock.

ATM (Asynchronous Transfer Mode )
A multiplexing/switching technique by which information is organized into fixed-length cells with each cell consisting of an identification header field and an information field. The transfer mode is asynchronous in the sense that cell use depends on the required or instantaneous bit rate.

Attenuation / Loss
In an optical fiber, the absorption of light by molecules in the fiber — causing some of the intensity of the light to be lost from the signal. Usually measured in dB/km.

Automatic Protection Switching (APS)
The ability of a network element to detect a failed working line and switch the service to a spare (protection) line. 1+1 APS pairs a protection line with each working line. 1:n APS provides one protection line for every n working lines.

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B-ISDN
Broad band Integrated Services Digital Network

Backbone (1)
The part of a network used as the primary path for transporting traffic between network segments. (2) A high-speed line - or series of connections - that forms a major pathway within a network.

Backplane (B/P)
The high-speed communications line to which the MultiWave circuit packs are physically connected. Status information about the MultiWave modules (circuit packs) is communicated via the backplane (however, no fiber optic signals are carried over the backplane).

Bandwidth
Information-carrying capacity of a communication channel. Analog bandwidth is the range of signal frequencies that can be transmitted by a communication channel or network.

Bend Radius
The allowable limit a fiber cable can be bent.

BER (Bit Error Rate)
The number of coding violations detected in a unit of time, usually one second. BER is calculated with this formula: BER=errored bits received/total bits sent.

Bidirectional
Operating in both directions. Bidirectional APS allows protection switching to be initiated by either end of the line.

Bit
One binary digit; a pulse of data.

Bit Error Rate (BER)
(1)Percentage of bits in a transmittal received in error. (2) The number of coding violations detected in a unit of time, usually one second. (3) Specifies expected frequency of errors. compares the ratio of incorrectly transmitted bits to correctly transmitted bits.

BITS
Building Integrated Timing Supply. A single building master timing supply. BITS generally supplies DS1 and DS0 level timing throughout an office. The BITS concept minimizes the number of synchronization links entering an office, since only the BITS will receive timing from outside the office.

BLSR
Bi-directional Line Switched Ring

BPS (Bits Per Second)
The number of bits passing a point every second. The transmission rate for digital information.

Buffer - The protective coating over the fiber.

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C-band (Conventional Band)
In erbium doped fiber amplifiers, the region of amplification approximately between wavelengths of 1530nm and 1580nm.

CCITT
The United Nations technical specialized agency for telecommunications, now the International Telecommunication Union­Telecom. It functions through international committees of telephone administrations and private operating agencies.

CEPT
European Conference of Postal and Telecommunications Administrations. The CEPT format defines the 2.048Mbps European E1 signal made up of 32 voice-frequency channels.

Channel
The smallest subdivision of a circuit that provides a type of communication service; usually a path with only one direction.

Chirping
Rapid changing of a laser’s peak emission wavelength.

Circuit
A communications path or network; usually a pair of channels providing bi-directional communication.

Circuit Breaker
A mechanically resettable unit that disconnects a circuit at a specifically defined current.

Circuit Switching
Basic switching process whereby a circuit between two users is opened on demand and maintained for their exclusive use for the duration of the transmission.

CIT
Craft Interface Terminal

Cladding
The section of an optical fiber surrounding the core. The cladding’s lower refractive index serves to guide light within the core.

Cladding
The material surrounding the core of an optical fiber. The cladding must have a lower index of refraction in order to steer the light in the core.

CLEC
Competitive Local Exchange Carrier

Clock Free Run Mode
An operating condition of a clock in which its local oscillator is not locked to an external synchronization reference, and is using no storage techniques to sustain it's accuracy.

Clock Holdover Mode
An operating condition of a clock in which its local oscillator is not locked to an external synchronization reference but which is using storage techniques to maintain its accuracy with respect to the last known frequency comparison with a synchronization reference.

Clock Recovery/Timing Recovery
The extraction of clock information from an optical signal, used to know exactly when to sample the signal to look for a 1 or a 0.

CMIP (Common Management Information Protocol)
The network management protocol defined by OSI specifications. Used to convey CMIS defined operations over an OSI network.

CMIS (Common Management Information Services)
The portion of the OSI network management specification which defines the management services available to a network management system (works with CMIP).

CO
Central Office

Coarse wavelength-division multiplexing (CWDM)
A version of WDM that employs multiple, widely spaced wavelengths, lying anywhere in the transmitting region of an optical fiber (1260 to 1620 nanometers).

Collapsed Ring
A topology where the ring resides entirely within a single fiber bundle. In the event of a cable cut the ring is severed in two places.

Concatenate
The linking together of various data structures, for example, two bandwidths joined to form a single bandwidth.

Concatenated STS-Nc
A signal in which the STS envelope capacities from the N STS-1s have been combined to carry an STS-Nc Synchronous Payload Envelope (SPE). It's used to transport signals that don't fit into an STS-1(52Mbps)payload.

Concatenated VT
A virtual tributary (VT × Nc) that is composed of N × VTs combined. Its payload is transported as a single entity rather than separate signals.

Connector
A mechanical device used to align and join two fibers together to provide a means for attaching and decoupling it to a transmitter, receiver or another fiber. Commonly used connectors include the FC, FCPC, Biconic, ST Connector, SC, D4, SMA, 905 or 906.

COPS(Class of Protection Services)
Type of telecommunication service offered by carriers based on protection type required by customer service level agreement. AuroraTM empowered true shared mesh networks allows carriers to offer 4 levels or class of services, identified as dedicated, shared, unprotected and pre-emptible.

CORBA
Common Object Request Broker Architecture

Core Grooming
The aggregation and segregation of traffic in the long-haul portion of a carrier network. rates into 10Gb/s or higher traffic rates. This type of grooming is accomplished at the STS-48 granularity for the fastest, most scalable and efficient core network with the least complexity. (See also edge grooming)

CoS
Class of Services

Coupler - A device used to connect two similar cconnector types.

Cross-bar Switch
A switch that has a plurality of vertical paths, a plurality of horizontal paths, and electromagnetic means, i.e., relays, for interconnecting any one of the vertical paths to any one of the horizontal paths.

Cross-connection
Connections between terminal blocks on the two sides of a distribution frame, or between terminals on a terminal block. Also called cross-connect.

Crosstalk
One optical signal being adversely affected by the presence of another.

CV (Coding Violation)
A transmission error detected by the difference between the transmitted and the locally calculated bit-interleaved parity.

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DACS
Digital Access Cross-Connect System

Data Communications Channels
OAM&P channels in SONET that enable communications between intelligent controllers and individual network nodes as well as internode communications.

DB
Decibel — usually used as a figure of loss or gain in an optical network. Calculated as one tenth of the logarithm of the output power divided by the input power.

DBm
A unit of power, popular in optical networks, showing the power with respect to 1 milliwatt (0.001W). Uses the dB equation, with the input power set to 1 milliwatt. Zero dBm is a power of 1 milliwatt.

DCC
Data Communications Channel, in the section layer, 3 bytes (D1,D2,D3) are allocated in STS-1 number 1 of an STS-N signal for section data communications. These 3 bytes are treated as one 192kbs data channel for the transmission of alarms, maintenance, control, administration as well as other network element communication needs. In the line layer, 9 bytes (D4-D12) are used as a 576kbs data channel for similar purposes.

Degrade
The condition where one or more established performance parameters fall outside of predetermined limits, resulting in lower quality performance.

Demultiplexing
A process applied to a multiplexed signal for recovering signals combined within it and for restoring the distinct, individual channels of the signals.

Dense Wavelength-Division Multiplexing (DWDM)
A variety of WDM that uses multiple wavelengths (or channels) in the 1550-nanometer region of the infrared spectrum. The wavelengths are closely spaced — usually evenly, on a grid.

Deregulation
The removal of regulatory authority to control certain activities of telephone companies.

Diffraction
The deflecting of a light wave when it travels through an object such as a grating.

Digital Cross-Connect (DCS)
An electronic cross-connect that has access to lower-rate channels in higher-rate, multiplexed signals and can electronically rearrange (cross-connect) those channels.

Digital Loop Carrier (DLC)
A device similar to a channel bank which multiplexes a number of local voice lines into a smaller number of lines for transmission to a Central Office.

Digital Signal
An electrical or optical signal that varies in discrete steps. Electrical signals are coded as voltages; optical signals are coded as pulses of light.

Digital Subscriber Line (DSL)
A method of providing high-speed data services over the twisted pair copper wires traditionally used to provide POTS. Types of DSL include ADSL (asymmetric digital subscriber line), HDSL (high data rate digital subscriber line), SDSL (single line digital subscriber line), and VDSL (very high data rate digital subscriber line).

Dispersion
Different wavelengths of light travel at slightly different speeds in optical fiber, and this causes optical pulses to spread out as they travel through a system.

Dispersion-Shifted Fiber
Optical fiber that has a point of minimum dispersion moved towards its point of lowest attenuation — around 1550nm.

Distributed Feedback (DFB) Laser
Lasers giving out a very sharply defined color of light. Similar to Fabry-Perot design but with the addition of a corrugated structure above the active layer. This feeds back one specific wavelength into the cavity, which is then amplified and emitted.

Distribution Frame
A physical piece of hardware, where cross-connects are made.

Drop and Broadcast
A cross connect typically used to enable a broadcast transmission. A signal in the high speed time slot is used to provide simultaneous drops at more than one node. A distance learning application would use drop and continue to feed multiple classrooms.

DSX-1
May refer to either a cross-connect for DS1 rate signals or the signals cross-connected at DSX-1.

DSX-3
May refer to either a cross-connect for DS3 rate signals or the signals cross-connected at DSX-3.

Dual Ring Internetworking
A topology where two rings are connected at two a different nodes providing traffic an alternate path from one ring to another.

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Edge Grooming
The aggregation and segregation of traffic just outside the avenues of a carrier network. This type of grooming is typically accomplished at the lowest possible levels of Granularity (currently STS-1) for ease of service provisioning and support of legacy phone traffic. (See also core grooming)

Electrostatic Discharge (ESD)
The discharge of high voltage caused by static charging.

Electrostatic Discharge Strap
ESD-guard wristband worn by technicians that protects the technician and system from electrostatic discharge.

Element Management System (EMS)
A platform supporting multiple WDM spans to provide Network Management services.

Envelope Capacity
The number of bytes the payload envelope of a single frame can carry. The SONET STS payload envelope is the 783 bytes of the STS-1 frame available to carry a signal. Each virtual tributary(VT) has an envelope capacity defined as the number of bytes in the VT less the bytes used by VT overhead.

Erbium Doped Fiber Amplifier (EDFA)
Optical amplifiers made of short lengths of optical fiber doped with the element “erbium.” A pump laser excites erbium ions in the fiber, which can then give their energy to optical signals passing through.

Errored Seconds (ES)
A performance monitoring parameter. ES "Type A" is a second with exactly one error, ES "Type B" is a second with more than one and less than the number of errors in a severely errored second (SES) for the given signal. ES by itself means the sum of the type A and B ESs.

Eye Diagram/Eye Pattern
1 and 0 signals in an optical system are displayed on an oscilloscope to show how clearly they are defined. An “open” eye shows a good quality signal with clear differences between 1s and 0s. A “closed” eye means that some 0s could be confused for 1s and vice versa, and therefore is a sign of a poor transmission system.

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Fabry-Perot Laser
The most basic design of laser, consisting of two specially designed slabs of semiconductor material on top of each other, with another material between them forming what is known as the “active layer” or “laser cavity.” Electric current flows through the device from the top slab through to the bottom, and the emission of light occurs in the active layer.

Failure
A termination of the ability of an item to perform a required function. A failure is caused by the persistence of a defect.

Fiber Bragg Gratings (FBGs)
Small sections of optical fiber that act like selective mirrors — only reflecting back specific wavelengths. This reflection is caused by a periodic change of refractive index in the fiber core, which reflects mainly at the Bragg wavelength.

Fiber Plant
Building, or underground fiber optic cable.

FIT rate
A measure of reliability for a device — the number of failures in one billion device hours.

Forward Error Correction (FEC)
Additional bits added to a signal that can be used to detect and correct any errors that occur during transmission through a system.

Four Wave Mixing
FWM is basically an intermodulation and cross talk phenomenon that occurs in WDM systems due to the non-linear nature of the fiber optic cable. The effect occurs in areas of zero dispersion as the signals need to be traveling at the same velocity in the fiber for the effect to occur. FWM does not occur in the 1550nm window unless the fiber is dispersion shifted.

Four-Wave Mixing
A nonlinear Kerr effect in which two or more signal wavelengths can interact to create a new wavelength.

Framing
Method of distinguishing digital channels that have been multiplexed together.

Frequency
The number of cycles of periodic activity that occur in a discrete amount of time.

Fuse
A unit that detects current flow and opens a circuit at a preset current flow.

Fusion Splice - A permanent splice where the two fiber ends are welded together.

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Gain
The ratio of output optical power to input power, usually given in units of dB. Usually represents an increase in an optical signal; a negative gain means a loss of power.

Gain Flattening
The art of getting equal amounts of amplification over a range of wavelengths in an optical amplifier.

Grating
A device designed to allow specific wavelengths to be reflected, while others pass through it.

Grooming
The aggregation, segregation and/or re-organization of traffic used to improve the efficiency of network transport.

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Hot Swapping
The process of replacing a module without bringing down the equipment. This process occurs by sliding an active module into a fully powered up unit.

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IEEE (Institute of Electrical and Electronics Engineers)
A U.S. professional organization active in the creation, promotion, and support of communications specifications and standards.

In Fiber Bragg Grating
An optical fiber grating is an optical fiber component consisting of a length of optical fiber wherein the refractive index of the core has been permanently modified in a periodic fashion, generally by exposure to an optical interference pattern as generated by an ultraviolet laser.

Insertion Loss
The loss introduced into a system by the connection of a device. Usually given in dB.

Integrated Optical Circuits
Similar in principle to electrical integrated circuits, but with the combining of many tiny versions of current optical components onto single silicon wafers.

Interexchange Carrier (IXC)
(1) Any individual, partnership, association, joint-stock company trust, governmental entity or corporation engaged for hire in interstate or foreign communication by wire or radio, between two or more exchanges. (2) A long-distance telephone company offering circuit-switched, leased-line or packet switched service or some combination thereof.

Interleave
The ability of SONET to mix together and transport different types of input signals in an efficient manner, thus allowing higher-transmission rates.

Intermediate Reach
IR optical interfaces refer to optical sections with system loss budgets from 0 db to 12 db. Typically low power, e.g. 50uW or -13 dbm, SLM or MLM lasers are used.

Internet Protocol (IP)
A set of rules for how data gets transmitted from one place to another on the Internet. IP is a connectionless protocol, in which data gets broken down into a number of small bundles known as packets, and each packet gets transmitted to the destination separately, possibly along a different route than other packets from the same message.

Interoperability
The process whereby computers can operate interactively with each other across a network without data conversion or human intervention.

ISO(International Standards Organization)
An organization that promotes the development of standards for computers. Developers of the OSI model.

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Jack - The female receptacle.

J0
Section trace bytes.

Jitter
Rapid changes in an optical signal — usually referring to changes in the time interval between optical pulses.

Jumper
Fiber optic cable that has connectors installed on both ends.

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Kerr Effect
Optical Kerr-effect is where the index of refraction of a fiber optic varies with the intensity of the transmitted light. This is a non-linear process that occurs when the product of the laser power and the effective system length becomes a significant fraction of the nonlinearity coefficient y. At 1550 nm, 1/y ranges from 700 mW-Km for unshifted single mode fiber to 500 mW-Km for NZDSF (Non Zero Dispersion Shifted Fiber). In systems with milliwatt transmitters and hundreds of Km span lengths nonlinear diffraction will occur. The main effect of this is self phase modulation of the signal

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L-band (Long band)
In erbium doped fiber amplifiers, the region of amplification approximately between wavelengths of 1580nm and 1610nm.

Laser Cavity/Active Layer
The layer in a laser that is designed to confine the light and allow it to build up before being emitted.

Laser/Laser Diode/Laser Chip
Light Amplification by Stimulated Emission of Radiation. Tiny salt-grain sized semiconductor devices giving out intense light at one specific color when an electric current is passed through them. Used to transmit information in an optical network.

Leased Line
A physical line that a single subscriber leases from a carrier, giving the subscriber exclusive rights to the line’s capacity.

Light Amplification by the Stimulated Emission of Radiation (LASER)
A device that produces a single frequency light.

Light Emitting Diode (LED)
A device used in a transmitter to convert information from electric to optical form. It typically has a large spectral width. A semiconductor diode which emits light when forward biased to an optical signal.

Light Emitting Diode (LED)
A semiconductor diode that emits light when a current is passed through it. In lightwave transmission systems, light emitting diodes or lasers are used as sources of light. LEDs are also used on circuit pack faceplates to show failure (red) or service state. In addition, LEDs are used to the alarm and status condition of the system.

Line
One or more SONET sections, including network elements at each end, capable of accessing, generating, and processing Line Overhead.

Line AIS
Is generated by the section terminating equipment upon loss of an input signal, loss of frame, or equipment failure. The line AIS maintains operation of downstream regenerators preventing generation of unnecessary alarms.

Line Amplifier
Also called an OLA or Optical Line Amplifier. A MultiWave device consisting of a common shelf only. It does not multiplex or demultiplex signals but instead amplifies signals; it does so to maintain signal strength over long distances.

Link - The entire span between two optical devices.

Local Exchange Company (LEC)
A telephone company that provides customer access to the worldwide public switched network through one of its central offices.

LOH (Line Overhead)
18 bytes of overhead accessed, generated, and processed by line-terminating equipment. This overhead supports functions such as locating the SPE in the frame; multiplexing or concatenating signals; and handling performance monitoring, automatic protection switching, and line maintenance.

Long Reach
LR optical interfaces refer to optical sections with system loss budgets from 10 db up to 28 db at OC-3, to 24 db at OC-12, and to 20 db at OC-48. Typical of long haul telecommunications systems, LR interfaces are based on high power, e.g. 500uW or -3dbm, Multi-Longitudinal Mode (MLM) or Single-Longitudinal Mode (SLM) lasers.

Long-haul Communications
In public switched networks, pertaining to circuits that span large distances, such as the circuits in inter-LATA, interstate, and international communications.

Long-haul Communications
In public switched networks, pertaining to circuits that span large distances, such as the circuits in inter-LATA, interstate, and international communications.

Long-haul Communications
In public switched networks, pertaining to circuits that span large distances, such as the circuits in inter-LATA, interstate, and international communications.

Loss Budget - The maximum amount of power that is allowed to be lost per optical link.

Loss of Frame (LOF)
A failure to synchronize to an incoming signal.

Loss of Signal (LOS)
The absence of an incoming signal.

LTE (Line-Terminating Equipment )
Network elements such as add/drop multiplexers or digital cross-connect systems that can access, generate, and process Line Overhead.

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Mandrel - The fiber wrapping device used to cause attenuating within a fiber cable.

Map/Demap
A term for multiplexing, implying more visibility inside the resultant multiplexed bitstream than available with conventional asynchronous techniques.

Mapping
The process of associating each bit transmitted by a service into the SONET payload structure that carries the service. For example, mapping a DS1 service into a SONET VT1.5 associates each bit of the DS1 with a location in the VT1.5.

Mechanical Splice - A mechanical means of connecting two ffibers.

Mesh Network
The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network. A mesh network's topology has at least two nodes with two or more paths between them.

Micro-electro-mechanical Systems (MEMS) Mirrors
Mirrors, no larger in diameter than a human hair, which can be arranged on special pivots so that they can be moved in 3 dimensions. Several hundred such mirrors can be placed together on mirror arrays no more than a few centimeters square in size, to form an optical crossconnect.

Micrometer/Micron
A length of 0.000001 meters.

Micron (um)
Another term for micrometer. One millionth of a meter. 10exp-6 meter.

Misalignment Loss
The loss of power resulting from angular misalignment, lateral displacement, and end separation.

MTBF
Mean Time Between Failures: An indicator of expected system reliability calculated on a statistical basis from the known failure rates of various components of the system.

Multi-protocol Label Switching (MPLS)
A method used to direct data traffic in networks in which IP over ATM is being used. In MPLS, IP routers at the edge of the network label packets in a way that greatly facilitates their handling by ATM switches at the network core.

Multimode Fiber
An optical fiber in which more than one mode is allowed to be transmitted through the core.

Multiplex (MUX)
To transmit two or more signals over a single channel.

Multiplexer
A device for combining several channels to be carried by one line or fiber.

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Narrowband
Services requiring up to 1.5 Mbps transport capacity.

Network Element (NE)
Any device that is part of a SONET transmission path and serves one or more of the section, line, and path-terminating functions.

Network Management System (NMS)
A system responsible for managing at least part of a network. NMSs communicate with agents to help keep track of network statistics, resources and performance.

Non-blocking Switch
A switch that has enough paths across it that an originated call can always reach an available line without encountering a busy condition.

NRZ
The optical line coding used in SONET systems. A one or zero are designated by a constant levels of opposite polarity.

NZDSF
Non Zero Dispersion Shifted Fiber. This type of fiber was designed to introduce a small amount of dispersion without the zero point crossing being in the WDM passband. With this type of fiber you can eliminate, or at least greatly reduce the degradation due to four wave mixing , a distortion mechanism that requires the spectral components to be phase matched along the fiber.

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OAM&P (Operations, Administration, Maintenance, and Provisioning)
Provides the facilities and personnel required to manage a network.

OC-1 (Optical Carrier Level 1)
The optical equivalent of an STS-1 signal.

OC-N (Optical Carrier Level N)
The optical equivalent of an STS-N signal.

Open Systems Interconnection (OSI)
A logical structure for network operations standardized by the International Standards Organization (ISO). The OSI model organizes the communications process into seven different categories and places the categories in a layered sequence based on their relationship to other users. Layers, seven through four, deal with end to end communications between the message source and the message destination, while layers three through one deal with network access.

Operations Support System (OSS)
A network management system used for a single specific purpose, such as billing or alarm monitoring.

Optical Amplifier
Device that boosts the power of an optical signal without any conversion of the light into an electrical signal.

Optical crossconnect (OXC)/Optical switch
Device that can move optical signals between different optical fibers, without the need for conversion to electrical signals.

Optical Excitation
In a laser, the achievement of population inversion through light from another laser exciting electrons into higher energy states.

Optical Fiber
A filament of transparent dielectric material, usually glass or plastic, and usually circular in cross section, that guides light.

Optical Network
A communications network in which data is transmitted over fiber optic lines as pulses of light.

Optical Path
The optical transmission medium made up of the individual fiber sections traversed by the multi-wavelength optical signal.

Optical switch/Optical crossconnect (OXC)
Device that can move optical signals between different optical fibers, without the need for conversion to electrical signals.

Optical Time-Division Multiplexing (OTDM)
The interleaving of optical signals from different sources to make a higher composite bit-rate, e.g., combining four 10-Gbit/s signals to give one 40-Gbit/s signal.

Orderwire
A channel used by installers to expedite line provisioning.

OS (Operating System)
Sophisticated applications software that overlooks the entire network.

OSI Seven-layer Model
A standard architecture for data communications. Layers define hardware and software required for mult-ivendor information processing equipment to be mutually compatible. The seven layers from lowest to highest are: physical, link, network, transport, session, presentation, and application.

OSS
Operation Support System

Overhead
Extra bits in a digital stream used to carry information besides traffic signals. Orderwire, for example, would be considered overhead information.

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Packet Switching
An efficient method for breaking down and handling high-volume traffic in a network. A transmission technique that segments and routes information into discrete units. Packet switching allows for efficient sharing of network resources as packets from different sources can all be sent over the same channel in the same bitstream.

Passive Device
A device that does not require a source of energy to function, unlike active devices.

Passive Optical Network (PON)
Enables a single fiber access line to support a cluster of buildings through use of a passive splitter close to the cluster, so that light from a single fiber can be split into different wavelengths and steered to individual buildings via short lengths of fiber.

Path
A logical connection between a point where an STS or VT is multiplexed, to the point where it is demultiplexed.

Path Overhead (POH)
Overhead accessed, generated, and processed by path-terminating equipment. Path overhead includes nine bytes of STS POH and, when the frame is VT-structured, five bytes of VT POH.

Path-Terminating Equipment (PTE)
Network elements, such as fiber-optic terminating systems, that can access, generate, and process Path Overhead.

Payload
The portion of the SONET signal available to carry service signals such as DS1 and DS3. The contents of an STS SPE or VT SPE.

Payload
The data in an SONET cell or IP packets that subscribers want to access (the message, conversation, file, etc.). The term payload is used to distinguish the subscriber’s data from the "overhead," which is data in an SONET cell or IP packet that network equipment tacks on to the payload to help guide its transmission across the network.

Performance Monitoring (PM)
Measures the quality of service and identifies degrading or marginally operating systems (before an alarm would be generated).

Photodiode
A diode designed to produce photocurrent by absorbing light. Photodiodes are used to detect optical power and convert optical power into electrical power.

Plain Old Telephone Service (POTS)
Plain Old Telephone Service (POTS) Analog voice transmission over twisted pair copper wires, without any of the more recently added amenities such as caller ID or call waiting. POTS was invented over a century ago, and is still used widely in public telephone networks.

Plug - The male connector.

PMD
Polarization Mode Dispersion. Light transmitted down a single mode fiber can be decomposed into two perpendicular polarization components. Distortion results due to each polarization propagating at a different velocity. PMD causes pulse spreading as the polarizations arrive at different times. The longer the span the worse the PMD. Total PMD = PMDc x (L)^1/2, where PMDc is the PMD coefficient and L is the length of the fiber. PMDc has the units of ps/(Km)^1/2, that is pico-seconds per root Km. PMD is generally not a factor at OC-48 but will be a factor at OC-192. Corning has stated that they have conducted field measurements on various installed SMF-28 fibers and have typical installed link centered at less than 0.1ps/(Km)^1/2. Beginning in 1994 Corning also implemented a fiber PMD specification of <0.5ps/(Km)^1/2 for SMF-28 and Titan single mode fibers. For OC-192 this level of PMD probably will meet most common span engineering requirements.

Polarization
The direction of the electric field in an electromagnetic wave.

POP (Point-of-Presence)
A point in the network where interexchange carrier facilities such as DS3 or OC-N meet with access facilities managed by telephone companies or other service providers.

Power Budget/Loss budget
The amount of optical power launched into a system that will be lost through various mechanisms, e.g., insertion losses and fiber attenuation. Usually given in dB.

Pre-amplification
Amplification of optical signals at the end of the system just before they reach the detectors.

Protocol
The rules or conventions used to govern the exchange of information between networked nodes.

Provisioning
The setting in place and configuring of the hardware and software required to activate a telecommunications service for a customer; in many cases the hardware and software may already be in place and provisioning entails only configuration tasks such as creating (or modifying) a customer record in a database and associating it with the service(s) and service level for which the customer has subscribed.

Pulse Density
At all digital interfaces, digital bit streams must contain sufficient energy for self extraction of a timing signal. The level of energy is controlled by ensuring that the signal has a sufficient number of pulses as specified by a pulse density. In general as the bit rate increases the desired level of pulse density also increases, resulting in different requirements being applied to different levels in the digital hierarchy.

Pump Laser
A laser used to excite ions in a material, usually used in optical amplifiers.

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Raman Amplification
Optical amplification process throughout the actual transmission fiber in an optical network, caused by a carefully selected pump-laser wavelength scattering from atoms in the fiber and changing its wavelength to that of the optical signal. Performs stimulated Raman scattering.

Rayleigh Scattering
Light scattering in an optical fiber due to slight changes in the core’s refractive index.

Refraction
The change in direction of light due to its passing between two different materials.

Refractive index
A property of a material that determines how fast light travels through it.

Regeneration(3R )
The process of amplifying (correcting loss), reshaping (correcting noise and dispersion), retiming (synchronizing with the network clock), and retransmitting an optical signal.

Regenerator
Device that restores a degraded digital signal for continued transmission; also called a repeater.

Repeater/Amplifier/Optical Amplifier
Device that boosts the power of an optical signal. An optical amplifier does this without any conversion of the light into an electrical signal.

Restoration
Action taken to repair it and return its services to an impaired (degraded) or unserviceable telecommunications service or facility.

Return Loss - The ratio of the power launched into a cable and the power of the light returned down the fiber. This measurement is expressed in positive decibel units (dB). A higher number is better. Return Loss = 10 log (incident power / returned power)

Ring
A configuration of nodes comprised of network elements connected in a circular fashion. Under normal conditions, each node is interconnected with its neighbor and includes capacity for transmission in either direction between adjacent nodes. Path switched rings use a head-end bridge and a tail-end switch. Line switched rings actively reroute traffic over a protection line

Ring Network
A network topology or circuit arrangement in which every node has exactly two branches connected to it.

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Scattering - A second cause of attenuation. Scattering occurs when light collides with individual atoms in the glass.

SDH (Synchronous Digital Hierarchy)
The ITU-T defined world standard of transmission whose base transmission rate is 52 Mbps (STM-0) and is equivalent to SONET's STS-1 or OC-1 transmission rate. SDH standards were published in 1989 to address interworking between the ITU-T and ANSI transmission hierarchies.

Section
The span between two SONET network elements capable of accessing, generating, and processing only SONET Section overhead. This is the lowest layer of the SONET protocol stack with overhead.

Section Overhead
Nine bytes of overhead accessed, generated, and processed by section- terminating equipment. This overhead supports functions such as framing the signal and performance monitoring.

Section-Terminating Equipment (STE)
Equipment that terminates the SONET Section layer. STE interprets and modifies or creates the Section Overhead.

Semiconductor Laser
Tiny salt-grain sized semiconductor devices giving out intense light at one specific color when an electric current is passed through them.

Semiconductor Optical Amplifiers (SOAs)
Similar to regular lasers, but with non-reflecting ends and broad wavelength emission. An incoming optical signal stimulates emission of light at its own wavelength, therefore amplifying it.

Severely Errored Seconds (SES)
A second in which a signal failure occurs, or more than a preset amount of coding violations (dependent on the type of signal) occurs.

Short Reach
SR optical interfaces refer to optical sections having system loss budgets from 0 db to 7 db. Depending on the SONET hierarchical level , SR transmitters may be either LEDs or low power MLM (multi-longitudinal Mode) lasers.

Signal-to-noise Ratio (SNR)
Ratio of the amplitude of the optical signal to the amplitude of the noise.

Singlemode Fiber
A mode is one of the various light waves that can be transmitted in an optical fiber. Each optical signal generates many different modes, but in singlemode fiber the aim is to only have one of them transmitted. This is achieved through having a core of a very small diameter (usually around 10 micrometers).

Soliton Pulse
A specially designed optical pulse that takes advantage of nonlinear effects to reverse the effects of dispersion, and travel through a system while maintaining its shape and integrity.

SONET (Synchronous Optical Network)
A standard for optical transport that defines optical carrier levels and their electrically equivalent synchronous transport signals. SONET allows for a multi-vendor environment and positions the network for transport of new services, synchronous networking, and enhanced OAM&P.

SPE (Synchronous Payload Envelope)
The major portion of the SONET frame format used to transport payload and STS path overhead. A SONET structure that carries the payload (service) in a SONET frame or virtual tributary(VT). The STS SPE may begin anywhere in the frame's payload envelope. The VT SPE may begin anywhere in a floating mode VT, but begins at a fixed location in a locked-mode VT.

Spontaneous Emission of Light
Light given out by ions or electrons naturally falling from excited states to ground states.

Stratum
Level of clock source used to categorize accuracy.

STS Path Overhead (STS POH)
Nine evenly distributed Path Overhead bytes per 125 microseconds starting at the first byte of the STS SPE. STS POH provides for communication between the point of creation of an STS SPE and its point of disassembly.

STS Path-Terminating Equipment (STS PTE)
Equipment that terminates the SONET STS Path layer. STS PTE interprets and modifies or creates the STS Path Overhead. An NE that contains STS PTE will also contain LTE and STE.

STS-1 (Synchronous Transport Signal Level 1)
The basic SONET building-block signal transmitted at 51.84 Mbps data rate.

STS-N (Synchronous Transport Signal Level N)
The signal obtained by multiplexing integer multiples (N) of STS-1 signals together.

Submarine Systems
Optical fiber links connecting countries through the world’s oceans.

Synchronous
A network in which transmission system payloads are synchronized to a master (network) clock and traced to a reference clock.

Synchronous Digital Hierarchy (SDH)
A format for packaging data to send through an optical network. U.S. version is called Sonet.

Synchronous Digital Hierarchy (SDH)
A format for packaging data to send through an optical network. U.S. version is called Sonet.

Synchronous Optical Network (Sonet)
The U.S. version of SDH. A format for packaging data to send through an optical network.

Synchronous Transfer Module (STM)
An element of the SDH transmission hierarchy. STM-1 is SDH's base-level transmission rate, equal to 155 Mbps. Higher rates of STM-4, STM-16, and STM-48 are also defined.

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T1X1 Subcommittee
A committee within ANSI that specifies SONET optical interface rates and formats.

Telecommunications Management Network (TMN)
A concept where all OMCs (Operations and Maintenance Centers) are linked together to form a network. A centralization occurs to facilitate control, monitoring and management of all devices in the communications network.

Termination - The process of mechanically installing a connector onto a fiber cable

Time Division Multiplexing (TDM)
A method for transmitting multiple calls over a single line; each call is assigned a recurring timeslot on the line, and a small portion of that call gets transmitted over the line each time its assigned timeslot is available.

Timing Recovery/Clock Recovery
The extraction of clock information from an optical signal, useful to know exactly when to sample the signal to look for a 1 or a 0.

Transmission Control Protocol/Internet Protocol (TCP/IP)
(1) A family of IP-based protocols which facilitate the transmission of data packets over various media in various circumstances. TCP/ IP provides the basis of the Internet and also of many subscriber services. (2) A set of protocols developed to link dissimilar computers across many kinds of networks.

Transmission Delay
To control echo and to minimize the effect on digital throughput, the maximum (one way absolute delay for steady state operation of a 100 mile transport system with no intermediate terminals is 1ms. This applies for all interface options provided. The required maximum delay for shorter systems is to be decreased in direct proportion to the route mileage.

Transmission Loss
Total loss encountered in transmission through a system.

Tunable Lasers
Lasers that can be adjusted to emit one of several different wavelengths, usually on the ITU-Grid.

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Unidirectional Path Switched Ring (UPSR)
A method of providing redundancy for fiber optic lines on a SONET rings. The SONET ring consists of two fiber optic lines, each carrying the same traffic, but transmitting it in opposite directions around the ring. If one line fails, the backup line is already carrying the same traffic.

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Vertical Cavity Surface Emitting Lasers (VCSELs)
Lasers with a vertical cavity that emit light from their surface, in contrast with regular “edge emitters.”

Virtual Private Network (VPN)
A network service which employs encryption and tunneling to provide a subscriber with a secure private network that runs over public network infrastructure.

Virtual Tributary(VT)
A signal designed for transport and switching of sub-STS-1 payloads.

VT Group
A 9 row × 12 column structure (108 bytes) that carries one or more VTs of the same size. Seven VT groups can be fitted into one STS-1 payload.

VT Path Overhead (VT POH)
Four evenly distributed Path Overhead bytes per VT SPE starting at the first byte of the VT, SPE. VT POH provides for communication between the point of creation of an VT SPE and its point of disassembly.

VT Path Remote Defect Indication (RDI-V)
A signal returned to the transmitting VT PTE upon detection of certain defects on the incoming path.

VT Path Remote Failure Indication (RFI-V)
A signal, applicable only to a VT1.5 with the byte-synchronous DS1 mapping, that is returned to the transmitting VT PTE upon declaring certain failures. The RFI-V signal was previously known as the VT Path yellow signal.

VT Path-Terminating Equipment (VT PTE)
Equipment that terminates the SONET VT Path layer. VT PTE interprets and modifies or creates the VT Path Overhead. An NE that contains VT PTE will also contain STS PTE, LTE, and STE.

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Wander
Long-term variations in a waveform.

Wavelength
The length of one complete wave of an alternating or vibrating phenomenon, generally measured from crest to crest, from trough to trough of successive waves. The distance between two crests of an electromagnetic waveform.

Wavelength Division Multiplexing (WDM)
(1) A technique in fiber-optic transmission for using multiple light wavelengths (colors) to send data over the same medium. (2)Two or more colors of light on one fiber. (3) Simultaneous transmission of several signals in an optical waveguide at differing wavelengths.

Wideband
Services requiring 1.5 to 50 Mbps transport capacity.

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Yellow Signal
See Remote Alarm Indication (RAI) and VT Path Remote Failure Indication (RFI-V).

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