Multitech MultiModem MT5634ZPX User Manual page 54

Digital Loopback: A technique used for testing the circuitry of a
communications device. Can be initiated locally, or remotely (via a
telecommunications device). The tested device decodes and
encodes a received test message, then echoes the message
back. The results are compared with the original message to
determine if corruption occurred en route.
Digital PBX: A Private Branch Exchange that operates internally
on digital signals. See also "Exchange".
Digital Service, level 0 (DS0): The world-wide standard speed
(64 Kbps) for digital voice conversation using PCM (pulse coded
modulation).
Digital Service, level 1 (DS1): The 1.544M bps voice standard
(derived from an older Bell System standard) for digitized voice
transmission in North America. The 1.544M bps consists of 24
digitally-encoded 64 Kbps voice channels (north America) and
2.048M bps (30 channels) elsewhere.
Digital Signal: A discrete or discontinuous signal (e.g., a
sequence of voltage pulses). Digital devices, such as terminals
and computers, transmit data as a series of electrical pulses which
have discrete jumps rather than gradual changes.
Digital Signaling Rates (DSn): A hierarchical system for
transmission rates, where "DS0" is 64 Kbps (equivalent to ISDN B
channel), and DS1 is 1.5 Mbps (equivalent to ISDN PRI).
Digital Transmission: A method of electronic information
transmission common between computers and other digital
devices. Analog signals are waveforms: a combination of many
possible voltages. A computer's digital signal may be only "high" or
"low" at any given time. Therefore, digital signals may be "cleaned
up" (noise and distortion removed) and amplified during
transmission.
Digitize: To convert an analog signal to a digital signal.
DIP switch (pronounced "dip switch"): A set of tiny toggle
switches, built into a DIP (dual in-line package), used for setting
configurable parameters on a PCB (printed circuit board).
Downstream: The direction of data flow from the host or away
from the host. A downstream port is the port on a hub electrically
farthest from the host that generates downstream data traffic from
the hub. Downstream ports receive upstream data traffic.
Driver: When referring to hardware, an I/O pad that drives an
external load. When referring to software, a program responsible
for interfacing to a hardware device; that is, a device driver.
Drop and Insert: The process where a portion of information
carried in a transmission system is demodulated ("Dropped") at an
intermediate point and different information is included ("Inserted")
for subsequent transmission.
DTE (Data Terminal Equipment): A term used to include any
device in a network which generates, stores or displays user
information. DTE is a telecommunications term which usually
refers to PCs, terminals, printers, etc.
DTMF (Dual-Tone MultiFrequency): A generic push-button
concept made popular by AT&T TouchTone.
DWORD: Double word. A data element that is 2 words, 4 bytes, or
32 bits in size.
Dynamic Insertion and Removal: the ability to attach and
remove devices while the host is in operation.
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.)
Multi-Tech Systems, Inc. MT5634ZPX User Guide
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.
End User: The user of a host.
Endpoint: See Device Endpoint.
Endpoint Address: The combination of a Device Address and an
Endpoint Number on a Universal Serial Bus device.
Endpoint Number: A unique pipe endpoint on a Universal Serial
Bus device.
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 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.
Glossary
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