FSO Primer
FSO Guide
Laser Guide
FSO Comparisons
White Papers
Application Notes

a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z

3G A short term for third-generation wireless, it refers to near-future developments in personal and business wireless technology, especially mobile communications.

ANSI   American National Standards Institute

Availability   Link availability is the fraction of time a link is useable in specific weather encountered in various climates, assuming no outages due to equipment failure or other system problem. Availability is typically quoted in nines. For example, 99.9%, or three-nines (3-9's) availability, means, on average, the link is expected to be not available 0.1% of the time, or an average of 43 minutes per month. Four-nines (4-9's) availability translates into only four minutes per month of down-time and five-nines averages just 30 seconds of downtime per month.

Backbone   The part of the communications network that connects main nodes, central offices or LANs. When speaking of the Internet, the backbone refers to the set of paths that local or regional networks connect to for long-distance interconnection.

Backhaul   In cellular/PCS systems, the transmission links between cell sites and the system operator's switching center. In general, transmitting data from remote locations to a point from which it can be distributed over a network.

Bandwidth   In analog communications, bandwidth referred to the width of the frequency range allocated for transmission.  In the digital world, it is more common to talk about bandwidth in terms of the number of bits transmitted per second (bps).

BER   Bit Error Rate. 

A way to measure data transmission integrity.  The bit error rate (BER) is a ratio of bad bits to total bits.

Bit   Binary Digit.

A unit of data represented as a one or a zero. Memory or data transferred per unit of time is measured in bits. Bits are lowercase (b) when used in abbreviations.

Broadband   The original meaning for broadband was incorporating more than one channel into a communications transmission.  T1 is a broadband communications protocol because it carries 24 conversations over four wires. Cable TV is also broadband because it carries many TV channels over one coax. Currently, broadband refers to communications technologies capable of transmitting over 45 Mbps over any type of media.  For example, a 155 Mbps Free Space Optics link would be considered broadband even though only one channel is being transmitted in either direction.

Byte   Eight bits. Memory storage is measured in bytes. Bytes are uppercase (B) when used in abbreviations.

Carrier   A telephone or other company that sells or rents telecommunication transmission services. A local exchange carrier (LEC) is a local phone company and an inter-exchange carrier (IEC or IXC) carries long-distance calls.

Cost/bit   The cost to transmit one bit.

Dark Fiber   Dark fiber refers to unlit and therefore unused fiber-optic cable. Often, companies lay more fiber lines than are needed at the time, and defer the cost of the associated fiber-optic components until increased network traffic justifies the extra investment.

DWDM   Dense Wavelength Division Multiplexing

An optical technology used to increase bandwidth over existing fiber. DWDM combines and transmits multiple signals simultaneously at different wavelengths on the same fiber.

EMI   Electromagnetic Interference

Interference caused by a radio signal or other electromagnetic field.  Any device or system that generates an electromagnetic field in the radio frequency spectrum has the potential to disrupt the operation of electronic components, devices and systems in its vicinity.

Ethernet   One of the oldest communication protocols for networking personal computers, and the most widely-used local area network (LAN) technology. Generally refers now to 10BASE-T systems, operating at 10 Mbps.

Fast Ethernet    Fast Ethernet is a local area network (LAN) transmission standard that provides a data rate of 100 megabits per second (referred to as "100BASE-T").

FDDI   Fiber-Distributed Data Interface

A set of ANSI protocols for sending digital data over fiber optic cable. Typically used as a LAN backbone protocol. 

Fixed Wireless   The operation of wireless devices or systems in fixed locations such as homes and offices.

FSO   Free Space Optics (FSO), also called Free Space Photonics (FSP) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain broadband communications. FSO systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, communication is theoretically possible, given enough power.

Giga   (G) Engineering notation for one billion.

Gigabit   One billion bits. 

In data communications, a gigabit is one billion bits. Commonly used for measuring the amount of data that is transferred in a second between two telecommunication points.

Gigabit Ethernet   A transmission technology based on the Ethernet frame format and protocol used in local area networks (LANs), provides a data rate of 1 billion bits per second (one Gigabit). Gigabit Ethernet is carried primarily on optical fiber (with very short distances possible on copper media).

Gigabyte   One billion bytes

GPS   Global Positioning System.

A system of low Earth orbiting satellites used to measure location on the ground or in the air. A GPS receiver contains a computer that "triangulates" its own position by measuring its distance from at least three of the 24 GPS satellites. The result is the longitude and latitude of the receiver, accurate to within about 10 meters for most receivers.

HFC   Hybrid Fiber Coax

When the cable companies wanted to start providing services that required more bandwidth than their coaxial cable networks could handle, they laid fiber and the resulting networks were referred to as HFC.

Mbps   Megabits per second

Mbps stands for millions of bits per second or megabits per second and is a measure of bandwidth (the total information flow per unit time) in a telecommunications medium.

OC-x   Short for Optical Carrier; a prefix for SONET carrier hierarchies, which is followed by a number. 

See table below for specific speeds:

OC bps
OC-1 51.84 Mbps
OC-3 155.52 Mbps
OC-12 622.08 Mbps
OC-24 1.244 Gbps
OC-48 2.488 Gbps

Optical Wireless   Free Space Optics (FSO), also called Free Space Photonics (FSP) or Optical Wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to carry broadband communications. FSO systems can function over distances of several kilometers. As long as there is a clear line of sight between the source and the destination, communication is theoretically possible, given enough power.

OSI   Open Systems Interconnect

The OSI model for communications protocols is a global ISO standard for communications that contains protocols in seven layers. Control is passed from one layer to the next, starting at one end, proceeding through the layers to the other and back again. The following chart names the layers and their functions:

Layer 7 Application Layer Connects an application or program to a communications protocol
Layer 6 Presentation Layer Encodes and decodes the data to be transmitted
Layer 5 Session Layer Establishes and maintains connection to the communications processes in the lower layers
Layer 4 Transport Layer Responsible for error correction and direction of flow (transmit/receive)
Layer 3 Network Layer Switching and routing layer
Layer 2 Data-link Layer Receives and transmits data over the physical layer
Layer 1 Physical Layer The transmission medium itself (twisted pair, fiber optic, free-space optics, etc.)

Protocol   A set of processes and rules that communications equipment use to transfer bits and bytes(data).

Reliability   Refers to the expected failure rate of the equipment.

Router   On the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination.

SDH   Synchronous Digital Hierarchy

Standardized by the ITU, SDH is a family of digital carrier rates. SDH is the term used by the ITU to refer to SONET OC rates, as they are called in the United States. The basic SDH building block is a rate of 155.52 Mbps, called STM-1.

 SNMP   Simple Network Management Protocol

An IETF-defined standard for network management across network management systems and network components. Another definition is: Protocol that governs network management and monitoring of network devices and their functions.

SONET   Synchronous Optical Network

Proposed by Bellcore in the 80s, SONET has become an ANSI (American National Standards Institute) standard as well as an ITU international standard named SDH that defines interface standards at the physical layer 1 level.  It allows data streams of differing rates to be multiplexed. It is generally implemented over fiber optic cable and is often configured in a ring allowing it to reroute traffic with no interruption of service, should a cable be cut.

STM   Synchronous Transfer Mode

STS   Synchronous Transport Signals; the electrical  version of OC (Optical Carrier)

Telco   Abbreviation for telephone company

Transceiver   A combination transmitter/receiver in the same device

WDM   Wavelength Division Multiplexing

Multiplexing technology developed for use on optical fiber. WDM modulates each of several data streams onto a different part of the light spectrum.