User guide

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Glossary
DTMF (Dual-Tone MultiFrequency): A generic push-button
concept made popular by AT&T TouchTone.
E
E&M: A telephony trunking system used for either switch-to-
switch, or switch-to-network, or computer/telephone system-to-
switch connection.
EIA: The Electronics Industries Association is a trade
organization in Washington, DC that sets standards for use of its
member companies. (See RS-232, RS-422, RS530.)
Encapsulation: A technique used by network-layer protocols in
which a layer adds header information to the protocol data unit
from the preceding layer. Also used in “enveloping” one protocol
inside another for transmission. For example, IP inside IPX.
Errored Seconds (ES): Any second of operation that all 1.544M
bits are not received exactly as transmitted. Contrast “Error Free
Seconds”.
Error Free Seconds (EFS): Any second of operation that all
1.544M bits are received exactly as transmitted. Contrast
“Errored Seconds”.
ESF Error Event: A T1 error condition that is logged when a
CRC-6 error or an Out-Of-Frame (OOF) error occurs.
Ethernet: A 10-megabit baseband local area network that allows
multiple stations to access the transmission medium at will
without prior coordination, avoids contention by using carrier
sense and deference, and resolves contention by using collision
detection and transmission. Ethernet uses carrier sense multiple
access with collision detection (CSMA/CD).
Excess Zeros: A T1 error condition that is logged when more
than 15 consecutive 0s or fewer 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. Both ESF and
B8ZS are typically 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
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 (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, an
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 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 nonprofit organization of 300+ vendors
and service providers, based in Foster City, CA, that are
developing and deploying frame relay equipment.