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Glossary
F
Failed Seconds: A test parameter where the circuit is unavailable for one full second.
Failed Signal: A T1 test parameter logged when there are more than 9 SES (Severely Errored Seconds).
Fax (facsimile): Refers to the bit-mapped rendition of a graphics-oriented document (fax) or to the electronic transmission of the image over
telephone lines (faxing). Fax transmission differs from data transmission in that the former is a bit-mapped approximation of a graphical
document and, therefore, cannot be accurately interpreted according to any character code.
Firmware: A category of memory chips that hold their content without electrical power, they include ROM, PROM, EPROM and EEPROM
technologies. Firmware becomes "hard software" when holding program code.
Foreground: The application program currently running on and in control of the PC screen and keyboard. The area of the screen that
occupies the active window. Compare with "background".
Fractional T1 (FT1): A digital data transmission rate between 56K bps (DS0 rate) and 1.544M bps (the full T1 rate - in North America). FT1
is typically provided on 4-wire (two copper pairs) UTP. Often used for video conferencing, imaging and LAN interconnection due to its low
cost and relatively high speed. FT1 rates are offered in 64K bps multiples, usually up to 768K bps.
Frequency: A characteristic of an electrical or electronic signal which describes the periodic recurrence of cycles. Frequency is inversely
proportional to the wavelength or pulse width of the signal. Long wavelength signals have low frequencies and short wavelength signals yield
high frequencies.
Foreign Exchange (FX): A CO trunk with access to a distant CO, allowing ease of access and flat-rate calls anywhere in the foreign
exchange area.
Foreign Exchange Office (FXO): provides local telephone service from a CO outside of ("foreign" to) the subscriber's exchange area. In
simple form, a user can pick up the phone in one city and receive a tone in the foreign city.
Connecting a POTS telephone to a computer telephony system via a T1 link requires a channel bank configured for the FX connection. To
generate a call from the POTS set to the computer telephony system, a FXO connection must be configured.
Foreign Exchange Station (FXS): See FX, FXO. To generate a call from the computer telephony system to the POTS set, a FXS connec-
tion must be configured.
Forward Explicit Congestion Notification (FECN): A bit that tells you that a certain frame on a particular logical connection has encoun-
tered heavy traffic. The bit provides notification that congestion-avoidance procedures should be initiated in the same direction of the
received frame. See also BECN (Backward Explicit Congestion Notification).
Frame: A group of data bits in a specific format to help network equipment recognize what the bits mean and how to process them. The bits
are sent serially, with a flag at each end signifying the start and end of the frame.
Frame Relay: A form of packet switching that uses small packets and that requires less error checking than other forms of packet switching.
Frame relay is effective for sending "bursty" data at high speeds (56/64K, 256K, and 1024K bps) over wide area networks. Frame Relay
specifications are defined by ANSI documents ANSI T1.602, T1.606, T1S1/90-175, T1S1/90-213, and T1S1/90-214. In using frame relay,
blocks of information (frames) are passed across a digital network interface using a "connection number" that is applied to each frame to
distinguish between individual frames.
Frame Relay Forum: A non-profit organization of 300+ vendors and service providers, based in Foster City, CA, that are developing and
deploying frame relay equipment.
Frame Relay Implementors Forum: A group of companies supporting a common specification for frame relay connection to link customer
premises equipment to telco network equipment. Their specification supports ANSI frame relay specs and defines extensions such as local
management.
Frame Relay Access Device (FRAD): A piece of equipment that acts as a concentrator or frame assembler/dissassember that can support
multiple protocols and provide basic "routing" functions.
G
Gateway: 1) A functional unit that interconnects two computer networks with different network architectures. A gateway connects networks or
systems of different architectures. A bridge interconnects networks or systems with the same or similar architectures. 2) A network that
connects hosts.
Graphical User Interface (GUI): A type of computer interface consisting of a visual metaphor of a real-world scene, often of a desktop.
Within that scene are icons, representing actual objects, that the user can access and manipulate with a pointing device.
H
Handshaking: A process that two modems go through at the time of call setup to establish synchronization over the data communications
link. It is a synchronization and negotiation process accomplished by the exchange of predefined, mutually recognized control codes.
High-level Data Link Control (HDLC): An ISO standard, bit-oriented data communications protocol that provides nearly error-free data
transfers.