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MultiFRAD 100-Series User Guide
Excess Zeros: A T1 error condition that is logged when more than 15 consecutive 0s or less than one 1 bit in 16 bits
occurs.
Exchange: A unit (public or private) that can consist of one or more central offices established to serve a specified area.
An exchange typically has a single rate of charges (tariffs) that has previously been approved by a regulatory group.
Exchange Area: A geographical area with a single uniform set of charges (tariffs), approved by a regulatory group, for
telephone services. Calls between any two points within an exchange area are local calls. See also "Digital PBX", "PBX".
Exchange Termination (ET): The carrier's local exchange switch. Contrast with "Loop Termination - LT".
Explicit Congestion Management: The method used in frame relay to notify the terminal equipment that the network is
overly busy. The use of FECN and BECN is called explicit congestion management. Some end-to-end protocols use FECN
or BECN, but usually not both options together. With this method, a congestion condition is identified and fixed before it
becomes critical. Contrast with "implicit congestion".
Extended Super Frame (ESF): One of two popular formats for framing bits on a T1 line. ESF framing has a 24-frame
super-frame, where robbed bit signaling is inserted in the LSB (bit 8 of the DS-0 byte) of frames 6, 12, 18 and 24. ESF has
more T1 error measurement capabilities than D4 framing. ESF and B8ZS are typically both offered to provide clear channel
service.
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 56 Kbps (DS0 rate) and 1.544 Mbps (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 64 Kbps multiples, usually
up to 768 Kbps.
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 (i.e., 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 connection must be configured.
Forward Explicit Congestion Notification (FECN): A bit that tells you that a certain frame on a particular logical
connection has encountered 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 1024 Kbps) 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 nonprofit organization of 300+ vendors and service providers, based in Foster City, CA, that are
developing and deploying frame relay equipment.
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