Glossary-F - Industrial Ethernet switches|Ethernet|USB|RS485|RS232|media converter|optic fiber modem|protocol converters|video converters
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FAQs list and answer the most common questions on a particular subject.


Fast Mode

Fast mode means no interleaving takes place and transmission is faster (a "fast channel"). This is suitable for a good line where little error correction is necessary.


Fax Pass-through

Fax pass-through is where a VoIP device applies the G.711 codec to fax messages before sending them over the Internet. See also G.711.



A WiMAX mode in which a mobile station (MS) dynamically switches between base stations, assessed on signal strength.



The FCC (Federal Communications Commission) is in charge of allocating the electromagnetic spectrum and thus the bandwidth of various communication systems.



The Frame Check Sequence is the four octets in an Ethernet frame that contain the CRC-32 check.



In frequency division multiplexing (FDM), individual data sub channels each occupy a specific portion of the communication stream's frequency bandwidth, and can transmit at any time. Subcarrier waves at differing frequencies modulate each sub channel. FDM is used in radio communications.



A Fast Fourier Transform (FFT) is a mathematical algorithm used to perform the Discrete Fourier Transformation (DFT) that describes a complex waveform (such as an audio or radio signal) in terms of the trigonometric functions (sine and cosine) that comprise its elementary waves. FFT is widely used in digital signal processing applications.


Filtering Database

The filtering database shows how frames are forwarded or filtered across a switch ports. The switch uses the filtering database to determine how to forward frames.



Filters decide whether or not to allow passage a data packet and/or make a call. There are two types of filter applications: data filtering and call filtering. Data filtering screens data to determine if the packet should be allowed to pass. Call filters prevent packets from triggering calls.



 A program that tells you the name associated with an email address.



A hardware or software "wall" which restricts access in and out of a network. Firewalls are most often used to separate an internal LAN or WAN from the Internet. Is a security scheme that prevents unauthorized users from gaining access to a computer network or that monitor transfers of information to and from the network.



Firmware is software that is embedded in a hardware device. It often contains processing and management instructions for your device.


Flash memory

A nonvolatile storage device that can be electrically erased and reprogrammed so that data can be stored, booted and rewritten as necessary.



The Flexworker system lets a person use any IP phone connected to a Flexworker-compatible IP PBX and retain telephone account-specific settings such as personal phonebook, speed dial, call forward, block list, account name, user.


Flow Control

Flow control is used to manage the sending of traffic so the sending device does not transmit more than the receiving device can process. This helps prevent traffic from being dropped and having to be resent. See also IEEE802.3 Flow Control and Back Pressure Flow Control.


Forced User Authentication

Forced user authentication automatically displays the login screen whenever users who have not logged in yet try to send web (HTTP) traffic.


Forward Delay

In RSTP (or STP), this is the maximum time (in seconds) a device waits before changing states. This delay is required because every device must receive information about topology changes before it starts to forward frames.


Forward Error Correction

Forward Error Correction (FEC) is a system where the sender adds redundant data to its transmissions that allows the receiver to correct errors without the need to ask the sender to resend the data.



An FQDN consists of a host and domain name and includes the top-level domain. For example, is a fully qualified domain name, where "www" is the host, "level1" is the second-level domain, and "" is the top level domain.



These are packets less than 64 octets long, and with either CRC (Cyclic Redundant Check) or alignment error(s).



Breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.


Fragmentation Threshold

A Fragmentation Threshold is the maximum data fragment size that can be sent in a wireless network before the AP fragments the packet into smaller data frames.


Frame Rate

Frame rate is the number of images that are displayed per second = fps. The higher the number of video frames per second, the smoother the video playback. Lower rates may result in choppy playback.


Frame Relay

Frame relay is a form of packet-switching technology that routes frames of information from source to destination over a switching network owned by a carrier. Frame sizes are not fixed.


Frame Type

Each frame type is a separate logical network, even though they exist on one physical network. Frame Types are 802.2, 802.3, Ethernet II (DIX) and SNAP (Sub-Network Access Protocol).


Frame and WiMAX

In WiMAX, a frame is the transmission unit that is transmitted using a fixed interval of 5 milliseconds (that is, a frame length equals to 5ms).


Free-space optics

Free-space optics uses line-of-sight transmissions of visible or infra-red light through Earth's atmosphere or outer space to communicate between devices. An everyday example of free-space optics is the IrDA standard that allows mobile devices such as cellphones or PDAs to exchange information across short distances. Longer-range free-space optical connections are often deployed for building-to-building communications, but can be susceptible to disruption by meteorological interference (such as clouds and rain).



The frequency of a wave or signal is the number of times it cycles, or repeats itself, over a certain period of time. A wave with a low frequency has a long wavelength (because it cycles slowly) and a wave with a high frequency has a short wavelength (because it cycles quickly). Frequency is usually measured in Hertz (Hz), or number of cycles per second. A 1Hz wave cycles one time a second.


Friendly AP

A Friendly Access Point (AP) is a wireless access point detected in your network that is approved by the network administrator.



A Fiber Service Gateway (FSG) is an all-in-one Internet Access Device (IAD) that uses fiber optic cables to deliver services, including broadband Internet connectivity, VoIP, wireless or wired home networking and sharing.



File Transfer Protocol is an Internet file transfer service that operates on the Internet and over TCP/IP networks. A system running the FTP server accepts commands from a system running an FTP client. The service allows users to send commands to the server for uploading and downloading files.



Fiber To The Building (FTTB) refers to network infrastructure that provides broadband services over fiber-optic cables from the central office to a building. See also PON.



Fiber To The Curb (FTTC) refers to network infrastructure that provides broadband services over fiber-optic cables from the central office to a curb-side unit. Another network medium is used for connections between the curb-side unit and the subscribers. See also PON.



Fiber To The Home (FTTH) refers to network infrastructure that provides broadband services over fiber-optic cables from the central office to subscribers homes.



Fiber-To-The-x (FTTx) refers to networking infrastructure that extends from a service provider to the x, where x can be one of many locations: Office (FTTO), Home (FTTH), Desk (FTTD), Building (FTTB) or even Curb (FTTC), to name a few. In an FTTO connect



A Fiber Termination Unit (FTU) is a device that converts fiber optic signals in order to deliver Fiber to the Home (FTTH) network services such as data, voice and video (through Ethernet, coaxial, and so on).


Full Archive Backup

A full archive backup copies all of the source files. This provides the most protection but also requires the most storage space.


Full Cone NAT

In full cone NAT, all requests from the same private IP address and port are mapped to the same public source IP address and port. Someone on the Internet only needs to know the mapping scheme in order to send packets to a device behind the NAT router.


Full Duplex

The ability of a network device to receive and transmit data simultaneously.


Full Tunnel Mode

In SSL VPN full tunnel mode, a virtual connection is created for remote users with virtual private IP addresses in the same subnet as the local network. This allows them to access network resources in the same way as if they were part of the internal network.



A Foreign eXchange Office (FXO) is a port on a PBX or an IPPBX device that connects to the PSTN or a telephone company.



A Foreign eXchange Subscriber (FXS) is a port on a PBX or an IPPBX device. The PBX/IPBPX device uses an FXS port to connect with an analog phone through a telephone cable.


FXS Extension


An extension number assigned to an analog phone directly connected to an FXS port on a PBX or an IPPBX device.