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EXFO Glossary

D (browse from .......... to)
D_ID...............DFDFB...............DNSDomain Name System (DNS)...............Dynamic Range
D_IDDBADeep Packet Inspection (DPI)
DAPIDBSDegree of Polarization (DOP)
DASDCCDelay Factor (DF)
Data CenterDCEDense Wavelength-Division Multiplexing (DWDM)
Data PlaneDDNDestination MAC Address
Data Service Unit (DSU)Dead ZoneDF
Data-Link LayerDedicated Connection
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Acronym for: Destination identifier


Acronym for: Destination access point identifier


Acronym for: Distributed antenna system

Data Center

A physical infrastructure housing computing equipment like rackmount servers, routers, switches, and structured cabling, as well as supporting components for data backup and cooling.

Data Plane

The data plane (also known as a user plane) is the component of a network that carries the user traffic.

Data Service Unit (DSU)

A network device that converts digital data frames from the communications technology used on a local-area network (LAN) into frames appropriate to the communications technology used on the wide-area network (WAN) and vice versa.

Data-Link Layer

Layer 2 of the OSI reference model. This layer takes data from the network layer and passes it on to the physical layer (layer 1). The data-link layer is responsible for transmission and reception of Ethernet frames, 48-bit addressing, etc. It includes both the media access control (MAC) and logical link control (LLC) layers.


Acronym for: Direct broadcast service


Acronym for: Data communications channel


Acronym for: Dynamic channel equalizer


Acronym for: Digital data network

Dead Zone

A peak or blind spot on an OTDR trace where no measurement can be made. This is caused by a Fresnel reflection and the subsequent recovery time of the OTDR detector. Dead zones are always prominent at the very beginning of a trace or at any other high reflectance event.

Dedicated Connection

A communication link that operates constantly and is not shared between users.

Deep Packet Inspection (DPI)

A type of computer network packet filtering that examines a packet's data section (and sometimes the header) as it passes an inspection point to detect any protocol non-compliance, viruses, spam, intrusions, or defined criteria, and thus identify, reroute or stop packets with undesirable code or data.

Degree of Polarization (DOP)

A quantity used to describe the portion of an electromagnetic wave, which is polarized. A perfectly polarized wave has a DOP of 100%, whereas an unpolarized wave has a DOP of 0%. A wave which is partially polarized, and therefore can be represented by a superposition of a polarized and unpolarized component, will have a DOP somewhere in between 0 and 100%. DOP is calculated as the fraction of the total power that is carried by the polarized component of the wave.

Delay Factor (DF)

A temporal value given in milliseconds that indicates how much time is required to drain the virtual buffer at the concrete network node and at a specific time. In other words, it is a time value indicating how many milliseconds’ worth of data the buffers must be able to contain in order to eliminate time distortions (jitter).

Dense Wavelength-Division Multiplexing (DWDM)

A technology that enables a single optical fiber to carry multiple data channels (or wavelengths). Commercial DWDM systems can have as many as 160 separate channels.

Destination MAC Address

Address identifying the station or stations on a LAN to which a frame is being sent.