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EXFO Glossary

V (browse from .......... to)
Variable Bit Rate (VBR)...............VLANVOA...............VT
Variable Bit Rate (VBR)VectoringVirtual Local Area Network (VLAN)
VBRVery-high-bit-rate digital subscriber line 2 (VDSL2)Virtual Private LAN Service (VPLS)
VCVery-High-Data-Rate Digital Subscriber Line (VDSL)Virtual Private Network (VPN)
VC_RDYVFVirtualized Network
VCATVFLVisual Fault Locator
VDSLVideo-on-Demand (VoD)VLAN
VDSL2Virtual Concatenation (VCAT)
from Variable Bit Rate (VBR)... to VLAN

Variable Bit Rate (VBR)

A term used in telecommunications and computing that relates to the bit rate used in sound or video encoding. As opposed to constant bit rate (CBR), VBR files vary the amount of output data per time segment.


Acronym for: Virtual container


Acronym for: Virtual circuit ready (Class 4)


Acronym for: Very-high-bit-rate digital subscriber line generation 2


DSL technology of noise cancellation to increase effective bandwidth.

Very-high-bit-rate digital subscriber line 2 (VDSL2)

Very-high-bit-rate digital subscriber line 2 (VDSL2) is an access technology that exploits the existing infrastructure of copper wires that were originally deployed for traditional telephone service as a way of delivering very high speed internet access. The main high-speed link (e.g. a fiber optic connection) terminates at a hub near the customers' location. The existing copper wire infrastructure is then used to carry the high speed connection for the short remaining distance to the customers. It can be deployed from central offices, from fiber-optic connected cabinets located near the customer premises, or within buildings. It has been defined in standard ITU-T G.993.2

Very-High-Data-Rate Digital Subscriber Line (VDSL)

A developing technology that promises much higher data rates over relatively short distances (up to 52 Mbit/s over lines up to 1,000 ft or 300 m in length). It is envisioned that VDSL may emerge somewhat after ADSL is widely deployed and coexist with it. The transmission technology (CAP, DMT, or other) and its effectiveness in some environments have not yet been determined; however, a number of standards organizations are currently working on it.


Acronym for: Video frequency

Video-on-Demand (VoD)

A pay-per-view television service in which a viewer can order a program from a menu and have it delivered instantly to the television set, typically with the ability to pause, rewind, etc.

Virtual Concatenation (VCAT)

Process enabling transport pipes to be "right-sized" for various data payloads by allowing SONET/SDH channels to be multiplexed in arbitrary arrangements. VCAT breaks down data packets and maps them into the base units of TDM frames. This data is then grouped in multiple data flows of varying size to create larger, aggregate payloads optimally sized to match available SONET/SDH pipe capacity. VCAT is applied at the end-points of the connections, which permits each channel used to be independently transmitted through a legacy transport network.

Virtual Local Area Network (VLAN)

A method in which a port or set of ports in a bridge or switch are grouped together and function as a single "virtual" LAN.

Virtual Private LAN Service (VPLS)

A way to provide Ethernet-based multipoint-to-multipoint communication over IP/MPLS networks. It allows geographically dispersed sites to share an Ethernet broadcast domain by connecting sites through pseudo-wires.

Virtual Private Network (VPN)

One or more wide-area network links over a shared public network, typically over the Internet or an IP backbone from a network service provider (NSP), which simulates the behavior of dedicated WAN links over leased lines. The data traveling between two hosts is encrypted for privacy using both hardware and software solutions.

Virtualized Network

Network able to simulate hardware functionality in software as a virtual instance, which is supported on generic host hardware.

Visual Fault Locator

A handheld optical test device used to inject a highly visible laser light into a fiber; for detection of bends, faults, continuity or port identification.