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MultiModem ZPX User Guide 37

Default Pipe: the message pipe created by Universal Serial Bus

system software topass control and status information between

the host and a Universal Serial Bus device’s Endpoint 0.

Device: a logical or physical entity that performs a function. The

actual entity described depends on the context of the reference.

At the lowest level, device may refer to a single hardware

component, as in a memory device. At a higher level, it may refer

to a collection of hardware components that perform a particular

function, such as a Universal Serial Bus interface device. At an

even higher level, device may refer to the function performed by

an entity attached to the Universal Serial Bus; for example, a

data/FAX modem device. Devices may be physical, electrical,

addressable, and logical. When used as a non-specific reference,

a Universal Serial Bus device is either a hub or a function.

Device Address: the address of a device on the Universal Serial

Bus. The Device Address is the Default Addresswhen theUniversal

Serial Bus device is first powered or reset. Hubs and functionsare

assigneda unique Device AddressbyUniversal Serial Bus software.

Device driver: Software that controls how a computer

communicates with a device, such as a printer or mouse.

Digital Cross-connect System (DCS): The CO device which splits

and redistributes the T1 bandwidth. the DCS takes time slots

from various T1 lines and alters them to provide the needed

connectivity. DCS connections are made with software at an

administrator’s workstation.

Digital Data: Information represented by discrete values or

conditions (contrast “Analog Data”).

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 intoa DIP (dualin-line package), used for setting

configurable parameters on a PCB (printed circuit board).

Downstream: The direction of dataflow 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 termwhichusually refers

to PCs, terminals, printers, etc.

DTMF (Dual-Tone MultiFrequency): A generic push-button concept

made popularby 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 thehostisin operation.

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.

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.

Glossary

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