Multi-Tech Systems Multivoip 200 Model Mvp200 Voice/fax Over Ip Networks User Guide

							81 Appendix C - Regulatory Information
EMC, Safety and Terminal Directive Compliance
The CE mark is affixed to this product to confirm compliance with the following European Community Directives:
Council Directive 89/336/EEC of 3 May 1989 on the approximation of the laws of Member States relating to
electromagnetic compatibility.
and
Council Directive 73/23/EEC of 19 February 1973 on the harmonization of the laws of Member States relating to
electrical equipment designed for use within certain voltage limits:
and
Council Directive 98/13/EC of 12 March 1998 on the approximation of the laws of Member States concerning
telecommunications terminal and Satellite earth station equipment. 
						

							82 MultiVOIP 200 User Guide 
						

							Voice / Fax over IP Networks
Glossary 
						

							84 MultiVOIP 200 User Guide
A
Access:   The T1 line element made up of two pairs of wire that the phone company brings to the customer premises. The Access portion
ends with a connection at the local telco (LEC or RBOC).
Accunet Spectrum of Digital Services (ASDS):   The AT&T 56K bps leased (private) line service. Similar to services of MCI and Sprint.
ASDS is available in 
nx56/64K bps, where n=1, 2, 4, 6, 8, 12.
ACK (ACKnowledgement code) (pronounced ack):  A communications code sent from a receiving modem to a transmitting modem to
indicate that it is ready to accept data. It is also used to acknowledge the error-free receipt of transmitted data. Contrast with NAK.
Adaptive Differential Pulse Code (ADCPM): In multimedia applications, a technique in which pulse code modulation samples are com-
pressed before they are stored on a disk. ADCPM, an extension of the PCM format, is a standard encoding format for storing audio informa-
tion in a digital format. It reduced storage requirements by storing differences between successive digital samples rather than full values.
Address:  A numbered location inside a computer. Its how the computer accesses its resources, like a video card, serial ports,  memory, etc.
AMI line coding:   One of two common methods of T1 line coding (with B8ZS). AMI line coding places restrictions on user data (B8ZS does
not).
Analog signal:    A waveform which has amplitude, frequency and phase, and which takes on a range of values between its maximum and
minimum points.
Analog Transmission:  One of two types of telecommunications which uses an analog signal as a carrier of voice, data, video, etc. An
analog signal becomes a carrier when it is modulated by altering its phase, amplitude and frequency to correspond with the source signal.
Compare with digital transmission.
Application Program Interface (API):  A software module created to allow dissimilar, or incompatible applications programs to transfer
information over a communications link. APIs may be simple or complex; they are commonly required to link PC applications with mainframe
programs.
ASCII (American Standard Code for Information Interchange) (pronounced askey):  A binary code for data that is used in communica-
tions and in many computers and terminals. The code is used to represent numbers, letters, punctuation and control characters. The basic
ASCII code is a 7-bit character set which defines 128 possible characters. The extended ASCII file provides 255 characters.
Asynchronous Transfer Mode (ATM):  A very high-spped method of transmission that uses fixed-size cells of 53 bytes to transfer informa-
tion over fiber; also known as cell relay.
AT Commands:  A standard set of commands used to configure various modem parameters, establish connections and disconnect. The AT
is used to get the attention of the modem before the actual command is issued.
Availability:   The measure of the time during which a circuit  is ready for use; the complement of circuit outage (100% minus % outage =
% available).
B
B7ZS (Bipolar 7 Zero Suppression) line coding:  One method of T1 line coding (see also B8ZS and AMI). B7ZS  line coding does not
place restrictions on user data  (AMI does).
B8ZS (Bipolar 8 Zero Suppression) line coding:  One of two common methods of T1 line coding (with AMI). B8ZS  line coding does not
place restrictions on user data  (AMI does). A coding method used to produce 64K bps clear transmission. (See also B7ZS and AMI  line
coding)
Backbone:  1. A set of nodes and their interconnecting links providing the primary data path across a network. 2. In a local area network
multiple-bridge ring configuration, a high-speed link to which the rings are connected by means of bridges. A backbone may be configured as
a bus or as a ring. 3. In a wide area network, a high-speed link to which nodes or data switching exchanges (DSEs) are connected. 4. A
common distibution core that provides all electrical power, gases, chemicals, and other services to the sectors of an automated wager
processing system.
Background:  An activity that takes place in the PC while you are running another application. In other words, the active user interface does
not correspond to the background task.
Bandwidth:  The transmission capacity of a computer channel, communications line or bus. It is expressed in cycles per second (hertz), the
bandwidth being the difference between the lowest and highest frequencies transmitted. The range of usable frequencies that a transmission
medium will pass without unacceptable attenuation or distortion. Bandwidth is a factor in determining the amount of information and the
speed at which a medium can transmit data or other information.
Backward Explicit Congestion Notification (BECN):  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 opposite direction of
the received frame. See also FECN (Forward Explicit Congestion Notification).
Basic Rate Interface (BRI):  An ISDN access interface type comprised of two B-channels each at 64K bps and one D-channel at 64K bps
(2B+D). 
						

							85 Glossary
Bell Operating Companies (BOC): The family of corporations created during the divestiture of AT&T. BOCs are independent companies
which service a specific region of the US. Also called Regional Bell Operating Companies (RBOCs).
Bell Pub 41450:  The Bell publication defining requirements for data format conversion, line conditioning, and termination for direct DDS
connection.
Bell Pub 62310:  The Bell publication defining requirements for data format conversion, line conditioning, and termination for direct DDS
connection.
Binary Synchronous Communication (BSC):  A form of telecommunication line control that uses a standard set of transmission control
characters and control character sequences, for binary synchronous transmission of binary-coded data between stations.
Bit (Binary digIT):  A bit is the basis of the binary number system. It can take the value of  1 or 0. Bits are generally recognized as the
electrical charge generated or stored by a computer that represent some portion of usable information.
Bit Error Rate Test (BERT):A device or routine that measures the quality of data transmission. A known bit pattern is transmitted, and the
errors received are counted and a BER (bit error rate) is calculated. The BER is the ratio of received bits in error relative to the total number
of bits received, expressed in a power of 10.
Bit robbing:  The use of the least significant bit per channel in every sixth frame for signaling. The line signal bits  robbed from the speech
pat conveys sufficient pre-ISDN telephony signaling information with the remaining line signal bits  providing sufficient line signaling bits for
recreating the original sound. See robbed bit signaling.
Blue Alarm:  An error indication signal consisting of all 1s indicating disconnection or attached device failure. Contrast Red Alarm and
Yellow Alarm.
Bps (bits per second):  A unit to measure the speed at which data bits can be transmitted or received. Bps differs from baud when more
than one bit is represented by a single cycle of the carrier.
Bridges:  1. A functional unit that interconnects two local area networks that use the same logical link protocol but may use different medium
access control protocols. 2. A functional unit that interconnects multiple LANs (locally or remotely) that use the same logical link control
protocol but that can use different medium access control protocols. A bridge forwards a frame to another bridge based on the medium
access control (MAC) address. 3. In the connection of local loops, channels, or rings, the equipment and techniques used to match circuits
and to facilitate accurate data transmission.
Buffer:  A temporary storage register or Random Access Memory (RAM) used in all aspects of data communications which prevents data
from being lost due to differences in transmission speed. Keyboards, serial ports, muxes and printers are a few examples of the devices that
contain buffers.
Bus:  A common channel between hardware devices either internally between components in a computer, or externally between stations in a
communications network.
Byte:  The unit of information a computer can handle at one time. The most common understanding is that a byte consists of  8 binary digits
(bits), because thats what computers  can handle. A byte holds the equivalent of a single character (such as the letter A).
C
Call Setup Time:  The time to establish a circuit-switched call between two points. Includes dialing, wait time, and CO/long distance service
movement time.
Carrier Group Alarm (CGA):  A T1 service alarm generated by a channel bank when an OOF condition occurs for a predefined length of
time (usually 300mS to 2.5 seconds). The CGA causes the calls using a trunk to be dropped and for trunk conditioning to be applied.
Carrier signal:  An analog signal with known frequency, amplitude and phase characteristics used as a transport facility for useful informa-
tion. By knowing the original characteristics, a receiver can interpret any changes as modulations, and thereby recover the information.
CCITT (Consultative Committee for International Telephone and Telegraph):  An advisory committee created and controlled by the
United Nations and headquartered in Geneva  whose purpose is to develop and to publish recommendations for worldwide standardization of
telecommunications devices. CCITT has developed modem standards that are adapted primarily by PTT (post, telephone and telegraph)
organizations that operate telephone networks of countries outside of the U.S. See also ITU.
Central Office (CO):  The lowest, or most basic level of switching in the PSTN (public switched telephone network). A business PABX or any
residential phone connects to the PSTN at a central office.
Centrex:  A multi-line service offered by operating telcos which provides, from the telco CO, functions and features comparable to those of a
PBX for large business users. See also Private Branch Exchange, Exchange.
Channel:  A data communications path between two computer devices. Can refer to a physical medium (e.g., UTP or coax), or to a specific
carrier frequency.
Channel bank:  A device that acts as a converter, taking the digital signal from the T1 line into a phone system and converting it to the
analog signals used by the phone system. A channel bank acts as a multiplexer, placing many slow-speed voice or data transactions on a
single high-speed link.
Circuit-switched Network:  A technology used by the PSTN that allocates a pair of conductors for the exclusive use of one communication
path. Circuit switching allows multiple conversations on one talk path only if the end-users multiplex the signals prior to transmission. 
						

							86 MultiVOIP 200 User Guide
Circuit switching:  The temporary connection of two or more communications channels using a fixed, non-shareable path through the
network. Users have full use of the circuit until the connection is terminated.
Clear Channel:   A transmission path where the full bandwidth is used (i.e., no bandwidth needed for signaling, carrier framing or control
bits). A 64K bps digital circuit usually has 8K bps used for signaling. ISDN has two 64K bps circuits, and a 16K bps packet service of which
part is used for signaling on the 64K channels.
Client-Server:  In TCP/IP, the model of interaction in distributed data processing in which a program at one site sends a request to a program
at another site and awaits a response. The requesting program is called a client; the answering program is called a server.
Cluster Controller:  A device that can control the input/output operations of more than one device connected to it. A cluster controller may be
controlled by a program stored and executed in the unit, or it may be entirely controlled by hardware.
Committed Burst Size: the maximum number of bits that the frame relay network agrees to transfer during any measurement interval
Committed Information Rate (CIR):  An agreement a customer makes to use a certain minimum data transmission rate (in bps). The CIR is
part of the frame relay service monthly billing, along with actual usage, that users pay to their frame relay service provider.
Compression: 1. The process of eliminating gaps, empty fields, redundancies, and unnecessary data to shorten the length of records or
blocks. 2. In SNA, the replacement of a string of up to 64-repeated characters by an encoded control byte to reduce the length of the data
stream to the LU-LU session partner. The encoded control byte is followed by the character that was repeated (unless that character is the
prime compression character). 3. In Data Facility Hierarchical Storage Manager, the process of moving data instead of allocated space during
migration and recall in order to release unused space. 4. Contrast with decompression.
COMx Port:  A serial communications port on a PC.
congestion:   A network condition where there is too much data traffic. The ITU I.233 standard defines congestion management in terms of
speed and burstiness.
congestion notification:   The function in frame relay that ensures that userdata transmitted at a rate higher than the CIR are allowed to
slow down to the rate of the available network bandwidth.
Consecutive Severely Errored Seconds (CSES):  An error condition that occurs when from 3 to 9 SES (Severely Errored Seconds) are
logged consecutively.
Customer Premise Equipment (CPE):  The generic term for data comm and/or terminal equipment that resides at the user site and is
owned by the user with the following exclusions: Over voltage protection equipment, inside wiring, coin operated or pay telephones, com-
pany-official equipment, mobile phone equipment, 911 equipment, equipment necessary for the provision of communications for national
defense, or multiplexing equipment used to deliver multiple channels to the customer.
D
D4:  the T1 4th generation channel bank.
D4 channelization:  Refers to the compliance with AT&T TR 62411 for DS1 frame layout.
D4 framing:  The T1 format for framing in AT&T D-Series channel banks, in which there are 12 separate 193-bit frames in a super-frame. A
D4 framing bit is used to identify the channel and the signaling frame. Signalling for voice channels is carried in-band for every channel, along
with the encoded voice.  See robbed-bit signaling.
Data Communications Equipment (DCE):  Any device which serves as the portal of entry from the user equipment to a telecommunications
facility. A modem is a DCE for the phone network (PSTN) that is commonly on site at the user’s premises. Packet Switched Networks have
another level of DCE which is most often located at a central office.
Data Link Connection Identifier (DLCI):  One of the six components of a frame relay frame. Its purpose is to distinguish separate virtual
circuits across each access connection. Data coming into a frame relay node is thus allowed to be sent across the interface to the specified
address. The DLCI is confirmed and relayed to its destination, or if the specification is in error, the frame is discarded.
Dataphone Digital Service (DDS):  A private line digital service that offers 2400, 4800, 9600 and 56K bps data rates on an inter-LATA basis
by AT&T and on an intra-LATA basis by the BOCs.
Data Service Unit (DSU):  A device that provides a digital data service interface directly to the data terminal equipment. The DSU provides
loop equalization, remote and local testing capabilities, and a standard EIA/CCITT interface.
Dedicated Line:  A communication line that is not switched. The term leased line is more common.
Default:  This is a preset value or option in software packages, or in hardware configuration, that is used unless you specify otherwise.
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 administrators worksta-
tion.
Digital Data:  Information represented by discrete values or conditions (contrast Analog Data). 
						

							87 Glossary
Digital Loopback:  A technique used for testing the circuitry of a communications device. Can be initiated locally, or remotely (via a telecom-
munications 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 (64K bps) for digital voice conversation using PCM (pulse coded modula-
tion).
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 64K bps 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 64K bps (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 computers 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).
Driver:  A software module that interfaces between the Operating System and a specific hardware device (i.e. color monitors, printers, hard
disks, etc.). Also known as a device driver.
Drop and Insert:  The process where  a portion of information carried in a transmission system is demodulated (Dropped) at an intermedi-
ate point and different information is included (Inserted) for subsequent transmission.
DTE (Data Terminating 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.
E
E&M:   A telephony trunking system used for either switch-to-switch, or switch-to-network, or computer/telephone system-to-switch connec-
tion.
EIA:  The Electronics Industries Association is a trade organization in Washington, DC that sets standard 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 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 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 phone services. Calls
between any two points within an exchange area are local calls. See also Digital PBX, PBX.
Exchange Termination (ET):  The carriers 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 capabili-
ties than D4 framing. ESF and B8ZS are typically both offered to provide clear channel service. 
						

							88 MultiVOIP 200 User Guide
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
phone lines (faxing). Fax transmission differs from data transmission in that the former is a bit-mapped approximation of a graphical docu-
ment 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 phone service from a CO outside of  (foreign to) the subscribers 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 phone 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 connec-
tion must be configured.
Forward Explicit Congestion Notification (FECN):  A bit that tells you that a certain frame on a particular logical connection has encoun-
tered 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 non-profit organization of 300+ vendors and service providers, based in Foster City, CA, that are developing and
deploying frame relay equipment.
Frame Relay Implementors Forum:   A group of companies supporting a common specification for frame relay connection to link customer
premises equipment to telco network equipment. Their specification supports ANSI  frame relay specs and defines extensions such as local
management.
Frame Relay Access Device (FRAD):  A piece of equipment that acts as a concentrator or frame assembler/dissassember that can support
multiple protocols and provide basic routing functions.
G
Gateway:  1. A functional unit that interconnects two computer networks with different network architectures. A gateway connects networks or
systems of different architectures. A bridge interconnects networks or systems with the same or similar 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.
High-level Data Link Control (HDLC):   An ISO standard, bit-oriented data communications protocol that provides nearly error-free data
transfers. 
						

							89 Glossary
I
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.
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 less 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) whos central office provides the point of reference for T1 access.  Any
common carrier authorized by the FCC to carry customer transmissions between LATAs.
Internet:  Refers to the computer network of many millions of university, government and private users around the world. Each user has a
unique Internet Address.
 Internet Address (IP Address):  A unique 32-bit address for a specific TCP/IP host on a network. Normally printed in dotted decimal format
(e.g., 129.128.44.227).
Internet Protocol (IP):  A protocol used to route data from its source to its destination in an Internet environment. The Internet Protocol was
designed to connect to local area networks. Although there are many protocols that do this, IP refers to the global system of interconnecting
computers. It is a highly distributed protocol (each machine only worries about sending data to the next step in the route).
Internetwork Packet Exchange (IPX):  A NetWare communications protocol used to route messages from one node to another. IPX packets
include network addresses and can be routed from one network to another. An IPX packet can occasionally get lost when crossing networks,
thus IPX does not guarantee delivery of a complete message. Either the application has to provide that control, or NetWares SPX protocol
must be used.
Interoperable:  Devices from different vendors that can exchange information using a standards base protocol.
I/O Addresses:  Locations within the I/O address space of your computer used by a device, such as an expansion card, a serial port, or an
internal modem. The address is used for communication between software and a device.
IRQ Level (Interrupt Request Level):  The notification a processor receives when another portion of the computers hardware requires its
attention. IRQs are numbered so that the device issuing the IRQ can be identified, and so IRQs can be prioritized.
ISA (Industry Standards Architecture) (pronounced ice a):  The classic 8 or 16-bit architecture introduced with IBMs PC-AT computer.
ISDN (Integrated Services Digital Network):    An International telecommunications standard for transmitting voice, video and data over a
digital communications line. ISDN is a  world-wide telecommunications service that uses digital transmission and switching technology to
support voice and digital data communications. Frame relay was partially based on ISDNs data link layer protocol (LAPD). Frame relay can
be used to transmit across ISDN services offering circuit-switched connection at 64K bps and higher speeds. Contrast Public Switched
Telephone Network (PSTN).
ITU-TSS (formerly CCITT):  International Telecommunications Union-Telecommunications Sector; the United Nations organization that
prepares standards (Recommendations) for resolving communications issues and problems.
K
Key Telephone System (KTS):  Phone devices with multiple buttons that let you select incoming or outgoing CO phone lines directly. Similar
in operation to a PBX, except a KTS you dont have to dial a 9 for a call outside the building.
Key Service Unit (KSU):  A small device containing the switching electronics for a business key telephone system (KTS).
 Key Set:  A phone set with several buttons for call holding, line pickup, intercom, autodialing,  etc. Also called a touchtone phone (Ericsson)
and a KTS (Key Telephone Set).
L
LAPB:  Link Access Procedure Balanced; based on the X.25 Layer 2 specification.  A full-duplex point-to-point bit-synchronous protocol
commonly used as a  data link control protocol to interface X.25 DTEs. LAPB is the link initialization procedure that establishes and maintains
communications between the DTE and the DCE.
LAPD:  Link Access Protocol for the D-Channel; based on the ISDN Q.921 specification. A full-duplex point-to-point bit-synchronous  link-
level protocol for ISDN  connections; different from LAPB in its framing sequence. Transmission is in units called frames, and a frame may
contain one or more X.25 packets.
Line Coding:  The representation of 1s and 0s on a T1 line. The two methods of line coding commonly used, B8ZS and AMI, differ in the
restrictions placed on user data. T1 line coding ensures that sufficient timing information is sent with the digital signal to ensure recovery of all
the bits at the far end. Timing information on the T1 line is included in the form of 1s in the data stream; a long string of 0s in the data stream
could cause problems recovering the data. 
						

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Line Termination (LT):  The electronics at the ISDN network side of the user/network interface that complements the NT1 at the user side.
The LT and the NT1 together provide the high-speed digital line signals required for BRI access.
Listed Directory Number (LDN):  The main number assigned by the telco; the number listed in the phone directory and also provided by
Directory Assistance. Some devices  can have more than one LDN, such as ISDN devices that have one LDN for voice and another LDN for
data.
Local Area Network (LAN):  1. A computer network located on a users premises within a limited geographical area. Communication within a
local area network is not subject to external regulations; however, communication across the LAN boundary may be subject to some form of
regulation. 2. A LAN does not use store and forward techniques. 3. A network in which a set of devices are connected to one another for a
communication and that can be connected to a larger network.
Local Access and  Transport Area (LATA):  A post-divestiture geographical area generally equivalent to a Standard Metropolitan Statistical
Area. At divestiture, the territory served by the Bell system was divided into approximately 161 LATAs. The Bell Operating Companies (BOCs)
provide  Intra-LATA services.
Local Exchange Carrier (LEC):  The local phone company which provides local (i.e., not long distance) transmission services. AKA telco.
LECs provide T1 or FT1 access to LDCs (unless the T1 circuit is completely intra-LATA). Inter-LATA T1 circuits are made up of a combination
of Access and Long Haul facilities.
Local Management Interface (LMI):  A specification for frame relay equipment that defines status information exchange.
Local Loop:  A transmission path, typically twisted-pair wire, between an individual subscriber and the nearest public telecommunications
network switching center. The wires provide ISDN service, but require an NT1 at the user end and an LT at the network end. (AKA, loop or
subscriber loop.)
Logical Link Control (LLC2):  In a local area network, the protocol that governs the exchange of transmission frames between data stations
independently of how the transmission medium is shared. The LLC2 protocol was developed by the IEEE 802 commitee and is common to all
LAN standards.
Logical Unit (LU):  A type of network accessible unit that enables end users to gain access to network resources and communicate with each
other.
Long Haul:  The T1 element that connects to the Access portion of the long distance companys (LDCs) central office. The LDC is commonly
called the point of presence (POP). Each LDC has a number of POPs, located throughout the country. The LDC is also called an IEC (Inter
Exchange Carrier).
Long Haul Communications:  The  type of phone call reaching outside of a local exchange (LE).
M
Management Information Base (MIB):  A database of network management information used by the Common Management Information
Protocol (CMIP) and the Simple Network Management Protocol (SNMP).
Megacom:   An AT&T service with a normal WATS line (typically T1) between the customer premise and the AT&T serving class 4 CO  are
the customers responsibility.
MegaLink:    BellSouths leased T1 service.
Message:  Associated with such terms as packet, frame, and segment. 1. In information theory, an ordered series of characters intended to
convey information. 2. An assembly of characters and sometimes control codes that is transferred as an entry from an originator to one or
more recipients.
Modem:  A communications device that enables a computer to transmit information over a phone line. It converts the computers digital
signals into analog signals to send over a phone line and converts them back to digital signals at the receiving end. Modems can be internal
and fit into an expansion slot, or external and connect to a serial port.
Multiplexer (Mux):  1. A device that takes several input signals and combines them into a single output signal in such a manner that each of
the input signals can be recovered. 2. A device capable of interleaving the events of two or more activities or capable of distributing the
events of an interleaved sequence to the respective activities. 3. Putting multiple signals on a single channel.
Multiprotocol:  A device that can interoperate with devices utilizing different network protocols.
Multithreading:  The ability of a software system to be able to handle more than one transaction concurrently. This is contrasted to the case
where a single transaction is accepted and completely processed before the next transaction processing is started.
N
Nailed Connection:  A permanent or dedicated circuit of a previously switched circuit or circuits.
Nailed-up Circuit:  A semipermanent circuit established through a circuit-switching facility for point-to-point connectivity.
NAK (Negative Acknowledgment):  Communications code used to indicate that a message was not properly received, or that a terminal
does not wish to transmit. Contrast with ACK.