User guide

38 MultiModem ZPX User Guide
Contrast with “Loop Termination - LT”.
Explicit Congestion Management: The method used in frame relay
to notify the terminal equipment thatthe network is overly busy.
The use ofFECN and BECNis 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 congesion”.
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 56
Kbps (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 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, 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 initiatedin the same
direction of the received frame. See also BECN (Backward Explicit
Congestion Notification).
Function: A Universal Serial Bus device that provides a capability
to the host. For example, an ISDN connection, a digital
microphone, or speakers.
G
Gateway: 1. A functional unit that interconnects two computer
networks with different network architectures. A gateway
connects networks or systemsofdifferent architectures.A bridge
interconnects networks orsystems with the same orsimilar
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.
Hexadecimal: A base 16 numbering system used to represent
binary values. Hex uses the numbers 0-9 and the letters A-F:
usually notated by an “h” (e.g., “4CF h”, read “four charley fox,
hex”). The result is that one hex digit represents a 4-bit value.
High-level Data Link Control (HDLC): An ISO standard, bit-
oriented data communications protocol that provides nearly
error-free data transfers.
Host: The host computer system where the Universal Serial Bus
host controller is installed. This includes the host hardware
platform (CPU, bus, etc.) and the operating system in use.
Host Controller: The host’s Universal Serial Bus interface. A
hardware device that provides the interface to the Host
Controller Driver (HCD) and the USB bus.
Host Controller Driver (HCD): Software that provides an interface
to the USB Driver and the Host Controller. (The interface to the
Host Controller is defined by the OHCI spec.)
I
Implicit congestion management: A method of informing the
terminal that the network is busy. This method relies on the end-
system protocol to detect and fix the congestion problem. (TCP/
IP is an example of a protocol using only implicit congestion
management.) See also “explicit congestion management”.
In-band: Refers to the type of signalling over the conversion path
on an ISDN call. Contrast “out-of-band”.
Insufficient Ones: A T1 error condition that is logged when fewer
than one 1 in 16 0s or less than 12.5 % average 1s density is
received.
Inter Exchange Carrier (IEC): The long distance company (LE) who’s
Glossary