AIS
Alarm Indication Signal
AMI
Alternate Mark Inversion
ANSI
American National Standards Institute
ASCII
American Standard Code for Information Interchange
BITS
Building Integrated Timing Supply
Bits Clock
Building Integrated Timing Supply
BOM
Bit-Oriented Messaging
BPV
Bipolar Violation
CDMA
Code Division Multiple Access.
CEV
Controlled Environmental Vault
CO
Central Office
DCE
Data Communications Equipment
DDS
Direct Digital Synthesis
DS1
Digital Signal, level 1
DTE
Data Terminal Equipment
DUS
Do not Use for Sync
EIA-232
See RS-232
EMC
Electromagnetic Compatibility
EMI
Electromagnetic Interference
ESF
Extended SuperFrame Format
ETSI
European Telecommunications Standards Institute
FG
Frame Ground
Flash ROM
Flash Read Only Memory
FLL
Frequency Lock Loop
ITU
International Telecommunication Union
ITU-T
International Telecommunications Union-Telecommunications Standardization Sector
LED
Light Emitting Diode
LNA
Low Noise Amplifier
LO
Local Oscillator
LOF
Loss of Frame
LOS
Loss of Signal
Mbps
Megabits per second
NCO
Numerically Controlled Oscillator
NE
Network Element
NEBS
Network Equipment Building Standards
NTP
Network Time Protocol
NVRAM
Nonvolatile Random Access Memory
OOF
Out-of-Frame Error
PDOP
Position Dilution Of Precision
PLD
Programmable Logic Device
PLL
Phase Lock Loop
PQL
Priority Quality Level
PRC
Primary Reference Clock
PRR
Primary Reference Receiver
PRS
Primary Reference Source
RO
Remote Oscillator
SDH
Synchronous Digital Hierarchy
SNTP
Simplified Network Time Protocol
SSM
TCP/IP
Transmission Control Protocol/Internet Protocol
TSG
Timing Signal Generator
UTC
Universal Time Coordinated
UTP
Unshielded Twisted Pair
VCXO
Voltage Controlled Crystal Oscillator. Typically a component of a hardware PLL or FLL
vDC
Volts Direct Current. Also see Direct Current
1PPS
One pulse per second, which equates to approximately 86,400 times per day.
10BaseT
Ethernet local area network (LAN) using twisted pair wiring, the most commonly installed LAN.
Alarm Indication Signal (AIS)
Signal transmitted downstream to inform that an upstream failure has been detected. Replaces normal traffic signal when a maintenance alarm indication is activated.
Alternate Mark Inversion (AMI)
Signaling protocol in which ones are indicated by either a positive or a negative pulse, and zeros by no pulse. The ones alternate between positive going and negative going.
American National Standards Institute (ANSI)
Standards-setting, non-government organization that develops and publishes standard for transmission codes, protocols, and high-level languages for voluntary use in the United States.
American Standard Code for Information Interchange (ASCII)
The most popular character representation method used by personal computers to communicate with each other.
Ampere
The unit of measurement of electric current or the flow of electrons, mathematically equal to watts divided by volts.
Antenna Gain
Ratio, usually expressed in decibels, of the power required at the input of a loss-free reference antenna to the power supplied to the input of the given antenna to produce, in a given direction, the same field strength or same irradiance, at the same distance. Unless specified otherwise, gain refers to the direction of the maximum radiation.
Bellcore
Originally, Bell Communications Research, now Telcordia Technologies, Inc. An organization established by the AT&T divestiture, representing and funded by the Regional Bell operating companies for the purposes of establishing telephone-network standard, training materials and standards, and quality procedures.
Bipolar Violation
In the T carrier line coding system that inverts the polarity of alternate one bits, a bipolar violation (BPV) indicates the presence on the carrier line of two consecutive one bits of the same polarity.
Building Integrated Timing Supply (BITS)
A synchronization method in which the best clock in an office is designated to receive timing from references outside the office, while all other clocks in the office are timed from the designated BITS clock. The BITS clock provides a pulse stream (1-0-1-0-1-0-1-0) that synchronizes a SONET network
Bypass Relay Assembly
Used to bypass the normal electrical route should the power, signal, or other equipment fail.
Central Office (CO)
In telephony, the Local Exchange Carrier (LEC) switching facility. Also called Local Exchange or wire center. Refers to Class 5 switching office, at which subscribers’ local loops terminate. The Central Office handles a specific geographic area, identified by the first three digits of the local telephone.
Clock
Internal timing device that creates a signal, generated by an oscillator. The oscillator creates a uniform electrical frequency from which digital pulses can be created. The clock signal provides a timing reference or base for sampling of signal elements in a transmission link; creates signals to be used in a transmission system to control the timing of certain functions; generate periodic, precisely spaced signals that can be used for timing, relating processor operations, or generating interrupts.
Clock accuracy
The level of agreement of the frequency of a clock with the ideal frequency, specified as the magnitude of the fractional frequency offset from the ideal frequency. The fractional frequency offset is defined as the difference between the actual and ideal frequency divided by the ideal frequency. The frequency in this definition is generally the frequency averaged over a sufficiently long observation time (typically on the order of one hour to one day) to adequately determine the frequency.
Clocking
In synchronous communication, a periodic signal used to synchronize transmission and reception of data and control characters.
Clock signal
Uniform electrical frequency from which digital pulses can be created to provide a reference for transmission signal elements and for timing functions.
Coaxial Cable
Copper-wire cable consisting of a central wire conductor surrounded by dielectric insulator and encased in a wire mesh. Coaxial cable provides excellent high frequency transmission (50-100 MHz) and data rates to 45Mb/s. Commonly used as CATV transmission cable, 56kb/s data cables and Ethernet LAN connections.
Code Division Multiple Access (CDMA)
New form of digital cellular phone service. CDMA is a spread spectrum technology that combines the original information signal with a correlating code, resulting in a signal which occupies a much greater bandwidth than the original but allows several simultaneous conversations to share the same frequency allocation.
Configuration
Hardware and software arrangements that define a system and thus determine the system functionality and performance.
Connector
Device for electrically connecting wires or fibers in cable to equipment or other wires or fibers.
Controlled Environmental Vault (CEV)
Below ground temperature- and humidity-controlled housing for electronic or optical equipment.
Critical Alarm
Alarm message which signifies that the output reference is invalid or that the output cards have no clock source, unless otherwise specified by the user. If specified, a critical alarm activates the major alarm relays and the CRITICAL LED.
D4
The fourth-generation interface (between T-1 carrier system and analog premises device) in T-1 transmission technology.
D4 Framing
A T-1 framing format that uses the D-4 framing bit to identify both channel and signaling frame.
Data Communications Equipment (DCE)
As defined in the RS-232 specification, equipment to which DTE (Data Terminal Equipment) is connected, often to enable access to network facilities.
Data Terminal Equipment (DTE)
As defined in the RS-232 specification, equipment to which DCE (Data Communications Equipment) is connected, often to enable access to network facilities.
Decibel (dB)
A unit of measure of signal strength, usually the relationship between a transmitted signal and a standard signal source.
Delay
Time between events, such as the time between when an event occurs and when an alarm is generated.
Digital Signal, Level 1 (DS1)
Digital signal consisting of 24 DS-0s and a framing bit (193 bits) transmitted 8000 times per second, which may be carried on T1 or other transmission medium; 1.544 million bits per second in North America, and 2.048 million bits per second elsewhere (where it is called E-1).
Direct Current (DC)
A flow of electricity always in the same direction. Contrast with alternate current (AC). See Volt.
Direct Digital Synthesis (DDS)
DDS circuitry uses oscillator frequency to generate an analog output waveform of a specific frequency from a stable reference clock.
Download
To receive data into a computer or ROM from another computer, for example, a network element receiving updated software from a host computer into the OT-21 Flash ROM.
Do not Use for Sync
An SSM (sync status message) parameter not generated by the OT-21, but may be emitted in bypass mode.
Earth Ground
The connection of an electrical system to earth. This connection is necessary to provide lightning and static protection and to establish the zero-voltage reference for the system.
Electromagnetic compatibility (EMC)
The ability of equipment or systems to be used in their intended environments within designed efficiency levels without causing or receiving degradation due to unintentional EMI (electromagnetic interference). EMI can be reduced by using proper shielding techniques and grounding
Electromagnetic Interference (EMI)
Occurs when one device emits unwanted electrical noise, adversely affecting the operation of another device. EMI is reduced by copper shielding.
E-1
European equivalent of North American DS1. DS1 carries information at the rate of 1.544 million bits per second (Mbps) T-1. E-1 carries information at the rate of 2.048 Mbps.
Ethernet
A medium often used as a local area network to connect computers printers, terminals, servers, and other network devices within the same building or campus. Ethernet operates over twisted wire and over coaxial cable at speeds up to 100 Mbps.
European Telecommunications Standards Institute (ETSI)
European counterpart to the American National Standards Institute (ANSI), founded in 1988 as a result of an initiative of the European Commission, established to produce telecommunications standards for users, manufacturers, suppliers, Administrators, and Post Telephone and Telegraph (PTT) administrations.
Event History
Historical record of activities on a device, comprised of event messages indicating a change in the physical or logical state of the device or transmission.
Extended SuperFrame Format (ESF)
A modification of the Superframe (sometimes called D4) framing scheme for DS1. ESF extends the framing pattern from 12 frames to 24 frames. A frame is 192 data bits and one frame bit. The 24 frame bits are a unique pattern of 1s and 0s that allows for terminal alignment, frame count, CRC bits, and a 2K data channel. Framing allows receiving equipment to identify the start and sequence of data in the binary 1.544Mbps DS1 stream.
Facilities Data Link (FDL)
ESF allows 4 Kbps to be used for a facilities data link which supports the communication of various types of monitoring or diagnostic network information used for provisioning and maintenance. OT-21 units use FDL for PQL settings.
Fault
Hard failure or performance degradation serious enough to threaten network function.
Firmware
Software that is stored in semipermanent memory, so-called because it shares characteristics of software and hardware. Usually stored on Programmable Read Only Memory (PROMs) or Electrical (or Erasable) PROMs. The software code is said to be burned into a chip.
Flash Read Only Memory (Flash ROM)
Flash ROM (or Flash Memory) contains software known as firmware. FlashROM can be erased and reprogrammed but persists when power to the device is turned off. FlashROM can be updated by downloading new firmware into the FlashROM.
Form-C
Relay configuration consisting of a wiper, a normally open (NO) contact, and a normally closed (NC) contact. These terms typically refer to the non-energized state; the wiper close the NO contact and opens the NC contact when energized.
Frame Generator
Frame generators accept input SQL from the reference input and convert it to the appropriate sync status message (SSM) for output.
Frame Ground (FG)
Connected to the equipment chassis to provides protective grounding.
Framing
Error control procedure which inserts bits which can be used by the receiver to identify the time slots allocated to each sub-channel in multiplexed digital channels. Framing bits may also carry alarm signals.
Framing Error
Error which occurs when a receiver does not interpret frame bits correctly.
Frequency
Rate at which electromagnetic waveform alternates
Frequency Lock Loop (FLL)
Mechanism whereby a generated signal is locked to a precise frequency relationship with a reference clock signal. See PLL.
G.703
ITU-T Recommendation G.703, “Physical/Electrical Characteristics of Hierarchical Digital Interfaces." The G recommendations are a series of standards defined by the ITU-T for transmission facilities.
Generic Requirement (GR)
Telcordia Technologies (formerly Bellcore) document type that replaces Framework Technical Advisory (FA), Technical Advisory (TA), and Technical Reference (TR) document types. The GR is a living document representing Telcordia Technologies’ current view of a technology.
Global Positioning System (GPS)
System of satellites, that transmits its position and time (derived from on-board celestial navigation equipment and atomic clocks), and a pseudo random noise code (PRN).
Holdover Mode
Mode of operation in which an internal clock provides the synchronization reference in the event that the internal reference is lost and another suitable reference is not available.
Insertion Loss
The difference in the amount of power received before and after something is inserted into the circuit. In a coaxial cable, insertion loss is the power loss due to all causes, usually expressed as dB per foot. The loss varies depending on frequency and cable type.
Interactive ASCII Mode
Instrument control protocol whereby a user issues commands and the instrument responds.
International Telecommunication Union (ITU)
A United Nations Specialized Agency in the field of telecommunications.
International Telecommunications Union-Telecommunications Standardization Sector (ITU-T)
A permanent organ of the ITU. The ITU-T is responsible for studying technical, operating, and tariff questions and issuing recommendations of each with a view to standardizing telecommunications on a worldwide basis.
Jumper
Strictly speaking, a wire connection between equipment and cable on a distribution frame. This term has come to be used for the adapters located on a chassis, to which standard connections are made to the internal logic and circuits.
Keep Alive Signal
Signal transmitted when a circuit is idle to prevent the logical connections from timing out.
Light Emitting Diode (LED)
The OT-21 chassis has a number of LEDs which provide a visual indication of the current status or condition of a system component.
Local Oscillator (LO)
The internal oscillator. See Oscillator.
Locked Mode (Normal)
An operational mode in which the processor controls DDS on the clock inputs in order to maintain the output frequency with respect to the input reference. The processor measures the phase of each input and adjusts the control value based on phase changes of the reference. The processor also monitors all input signals for frequency and input signal errors such as Loss of Signal (LOS) or Out-of-Frame (OOF).
Login
Process by which users identify and authenticate themselves to a network system or interface. Users typically enter their username and password.
Loss of Frame (LOF)
Generic term which is used specifically in different signal domains. For example, in the SONET domain, LOF is a condition that indicates that a valid framing pattern could not be obtained
Loss of Signal (LOS)
Generic term which is used specifically in different signal domains. For example, in the SONET domain, LOS is a loss of signal condition which is detected physically at the receiver
Low Noise Amplifier (LNA)
Typically a parametric amplifier.
Major Alarm
A failure within the unit that may require user intervention to clear the alarm. The output may be degraded.
Microprocessor Unit (MPU)
Electronic circuit, usually on a chip, which uses internal memory to perform arithmetic, log, and control operations.
Minor Alarm
An informational alarm that may or may not affect output. MINOR alarms may elevate to conditions that would degrade the performance of the unit and should be addressed as soon as possible
Network Element (NE)
Processor controlled entities of the telecommunications network that primarily provide switching and transport network functions and contain network operations functions.
Network Equipment Building Standards (NEBS)
Defines a rigid and extensive set of performance, quality, environmental and safety requirements developed by Telcordia Technologies (formerly Bellcore), a research and development standards organization.
Network Time Protocol (NTP)
Developed to enable world-wide Internet systems to use a common time relative to Greenwich Mean Time (GMT).
Nonvolatile Random Access Memory (NVRAM)
RAM that does not lose its memory when power to it is turned OFF.
Null Modem Cable
Crossover or cross-pinned wiring of an RS-232 cable such that a DTE (Data Terminal Equipment) device (such as a PC) can talk to another such device without the use of a modem, hence the term null, which means amounting to nothing. A null modem cable allows one PC to connect directly to another PC for transfer over maximum distances of 50 to 100 feet (depending on the quality of the cable) without the use of either a modem or a line driver. A null modem cable also can be used to connect one DCE (Data Communications Equipment) device to another. Essentially, a null modem cable reverses the TX (Transmit) and RX (Receive) signals and some handshaking lines on an RS-232 cable.
Oscillator
Device for generating an analog test signal or electronic circuit that creates a single typically precise frequency signal.
Out-of-Frame Error (OOF)
OOF (Out of Frame) designates an error condition in framing bits, declared when 2 of 4 or 2 of 5 framing bits are missed.
Output card
An optional card with four secondary clock signal outputs. The OT-21 may have up to two optional output cards installed at the factory.
Password
Word or string of characters which a user or system Administrator associates with a username, and which is entered by the user to authenticate the username login to the network.
Phase Lock Loop (PLL)
Mechanism whereby a generated clock is locked to a precise phase relationship to a reference clock. A signal that is phase locked is also frequency locked. See FLL.
Phase measurement
The relative position between two signals within one cycle of a waveform, usually quantified in units of degrees or radians in the scientific literature. In telecom phase is usually expressed in units of time, and may also be called time delay or time interval. It is the measured time difference between the significant instants (e.g., zero level crossings) of the signal waveform under test and those of a reference signal. Phase measurements are often used to find Time Interval Error (TIE), which is a history of phase reading over a measurement period, indicating the deviation from the desired phase. TIE is used to calculate frequency offset and stability of a timing signal.
Position Dilution Of Precision (PDOP)
Measure of the position accuracy available due to the geometrical configuration of GPS satellites. A PDOP value of 1 indicates optimum satellite positions for high-quality data. Data quality decreases as the PDOP value increases.
Primary Reference Clock (PRC)
Any device that provides a PRS quality output signal.
Primary Reference Source (PRS)
1. A timing signal with ANSI and Stratum 1, or ITU and ETSI PRC accuracy and stability.
2. A master clocking source in a system or network from which other distributed devices derive their clocking and which enables the system or network to maintain synchronization.
Primary Reference Receiver (PRR)
A radio receiver that provides a PRS quality output signal.
Priority Quality Level (PQL)
The PQL settings provide an editable translation table for provisioning Sync Status Messages. In the OT-21, PQL information is carried in the FDL of the ESF.
PRV
Abbreviation used by the OT-21 when displaying PORT data. The command associated with the "PRV" field is PORT [x] PROV [#].
Rack
Aluminum or steel rack onto which equipment is mounted. The telecom industry standard rack size is 19 inches (480 mm) wide at the front. Telecom equipment is mounted on the rack and cables are laid in and fastened to the rack.
Rack mounting ears
Adjustable brackets which attach to the sides of the equipment chassis to allow a 19-inch chassis to be mounted in a standard 23-inch rack.
Radio Frequency (RF)
Electromagnetic waves operating between 10 kHz and 3 MHz propagated without a guide such a wire or cable, that is, in free space.
Restart
Interactive ASCII command for restarting the unit.
RJ-45
The 9-pin connector used for data transmission over flat or twisted standard telephone wire. Flat wire is used for serial data communications up to 19.2 Kbps to PBX, modems, printers, or printer buffers. Twisted wire is used for connecting to a 10BaseT local area network. Connectors are keyed or non-keyed. Keyed male connectors have a key or small square bump on the end; keyed female connectors are shaped to accommodate the key.
RS-232
Also known as EIA/TIA-232-E. A set of standards specifying electrical, functional, and mechanical interfaces for communicating between computers, terminals, and modems. The interface established by EIA to specify functions of interchange circuits, electrical characteristics, and connectors.
S/A
Selective Availability. Refers to the ability of the Department of Defense (DOD) to purposely degrade the accuracy of GPS coarse acquisition codes to an accuracy of about 100 meters. OT-21 units use software PLL with a dynamic loop tau to minimize selective S/A from the GPS satellites and environmental effects of the unit.
Security access level
One of five access levels associated with each username that grants rights to some set of ASCII command functionality. The levels range from Idle (level 0), which grants rudimentary rights and login privileges, to Administrator (level 4), the highest level, which grants complete access to all system functions. Each higher security access level grants privileges of all lower levels and additional privileges available only to that level.
Shield
Metallic layer surrounding insulated conductors. Shielding reduces stray electrical fields, and provides a measure of safety for personnel handling cables.
Sine wave
Analog wave which varies continuously in terms of amplitude and frequency.
Simplified Network Time Protocol (SNTP)
Protocol that assumes the clock is always Stratum 1 or unavailable.
Slave Clock
A clock which is locked to a reference timing signal.
Software configurable
Hardware options which operators can set by entering software commands via a communications interface.
Square wave
Digital signal which is binary in nature (in contrast to an analog sine wave which varies continuously in terms of amplitude and frequency).
Stratum 1
A timing signal whose long term accuracy is maintained at 1 x 10 -11 or better with verification to coordinated universal time (UTC), and which may be used as the basis of reference for the control of other clocks within a network. Equipment which produces a Stratum 1 timing signal is also called a Primary Reference Source (PRS) or a Primary Reference Clock (PRC).
Stratum Levels
Clocks in a synchronization network are classified into four level based on their performance in terms of accuracy and stability. Stratum 1 is the highest and Stratum 4 the lowest level of performance.
Synchronization
Timing of network transmissions by a master clock.
Synchronous Digital Hierarchy (SDH)
A fiber-optic-based serial standards for use with SONET and ATM in Europe.
Synchronization Status Messages (SSM)
Identifiers embedded within the reference signals, and used as synchronization sources for Timing Signal Generators (TSGs) and other network elements (NEs). The identifiers carry information about the quality of the synchronization source to which the particular synchronization signal is traceable. Identifiers also indicate whether the signal is available for use as a synchronization source. SSMs are especially useful in avoiding timing loops, while allowing the TSG or NE to autonomously reconfigure to the most suitable synchronization source available.
Synchronization Supply Unit (SSU)
A logical function of reference timing signal selection, processing, and distribution that provides the frequency characteristics of slave clocks for telecommunications synchronization.
Synchronous Optical NETwork (SONET)
Optical interface standard that allows transmission products from vendors to work together. The SONET design standard defines fiber-optic transmission rates for transporting digital signals of different capacities
Timing Signal Generator
Device which generates and distributes network synchronization signals, generally in a variety of waveforms.
Tip and Ring
Two wires, positive and negative, needed for a connection.
Transaction Language 1 (TL1)
A machine to machine language that is a subset of ITU-T’s man machine language.
Transmission Control Protocol/Internet Protocol (TCP/IP)
Two of the protocols from a suite of networking standards developed by the U.S. Department of Defense in the 1970s to support a global system of interconnected networks.
Turn up
Power up.
Universal Time Coordinated (UTC)
Also known as UCT, Universal Coordinated Time. In the U.S., the official UTC is kept by the U.S. Naval Observatory. Globally, UTC is kept by a number of laboratories cooperating in the determination of UTC.
Unshielded Twisted Pair (UTP)
Transmission medium in which a pair of copper conductors, twisted around each other at intervals, are separately insulated, generally with plastic, to prevent shorting.
User Interface
Software-defined boundary mediating between machine and user.
Username
The name by which each user is known in the network administration. Each user must enter a username when logging in to identify the user to the network. Each username is also associated with a password, which validates the username, and an access level which determines the degree of access granted to the user.
Watchdog timer
Mechanism used to trigger an event or an escape from a process unless a timer is periodically reset. For example, a time may indicate the maximum period of time that a network connection will remain open before expiring.
Wire Wrap
Wire wrap adapters are designed to provide a temporary connection using standard jumper wire to cross-connect between a standard jumper header and a wire wrap post.