Multitech Multivoip 100 Model Mvp120 Voice/fax Over Ip Networks User Guide

							91 Glossary
Multi-Tech Systems, Inc. MultiVOIP User Guide
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.
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.
CODEC (COmpression/DEcompression): The term is used to describe the conversion of voice signals from their analog form to
digital signals acceptable to modern digital PBXs and digital transmission systems. It then converts those digital signals back to
analog so that you can hear and understand what the other person is saying. In some phone systems, the CODEC is in the PBX
and shared by many analog phone extensions. In other phone systems, the CODEC is actually in the phone. Thus the phone itself
sends out a digital signal and can, as a result, be more easily designed to accept a digital RS-232-C signal.
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 user data 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, company-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 telecom-
munications 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 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 (64K bps) 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 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
intermediate 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
E1:  The European equivalent of the North American 1.544M bps T-1, except that E-1 carries 2.048M bps. It is characterized by
thirty 64 Kbps digital channels for voice or data calls, plus a 64 Kbps channel for signaling and a 64 Kbps channel for framing
(synchronization) and maintenance.
E&M:   A telephony trunking system used for either switch-to-switch, or switch-to-network, or computer/telephone system-to-switch
connection. 
						

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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.
Endpoint: The clients in an H.323 network. They are typically video conferencing, audio conferencing, or other multimedia systems
implemented by end users to communicate in real time. The H.323 standard requires that every endpoint support certain functions
and codecs (Coder/Decoder) that have previously been defined by the ITU.
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 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. ESF and B8ZS are typically both 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 phone 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 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, an  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
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 non-profit organization of 300+ vendors and service providers, based in Foster City, CA, that are develop-
ing 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/dissassembler that
can support multiple protocols and provide basic routing functions.
G
Gatekeeper: An H.323 entity that provides address translation, control access, and sometimes bandwidth management to the LAN
for H.323 endpoints.
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. 3. An H.323 entity that provides real-time, two-way communications between H.323 terminals on the
LAN and other ITU terminals on a WAN, or to another H.323 Gateway.
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
H.323: An umbrella recommendation from the International Telecommunications Union (ITU) that sets standards for multimedia
communications over Local Area Networks (LANs) that do not provide a guaranteed Quality of Service (QoS).
H.323 Endpoint: The clients in an H.323 network. They are typically video conferencing, audio conferencing, or other multimedia
systems implemented by end users to communicate in real time. The H.323 standard requires that every endpoint support the
G.711 ITU standard for speech compression, H.245 protocol for controlling media between H.323 endpoints, Q.931 signal protocol
for establishing and terminating calls, RAS (Registration/Admissions/Status) channel data stream used to communicate with a
gatekeeper (optional), and RTP/RTCP (Real-Time Protocol/Real-Time Control Protocol) for carrying packetized real-time media on
IP networks.
H.323 Entity: Any H.323 component, including terminals, Gateways, Gatekeepers, Multipoint Controllers (MCs), Multipoint
Processors (MPs), and  Multipoint Control Units (MCUs).
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.
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. 
						

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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.
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. Communica-
tion 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 telecommuni-
cations 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
committee 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.
Multicast: A process of transmitting from one source to many destinations. The actual mechanism may be different for different
LAN technologies.
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.
Multipoint Conference: A conference between three or more terminals, which may be on the LAN or on the Circuit Switched
Network.
Multipoint Control Unit (MCU): An H.323 endpoint on the LAN which enables three or more terminals and Gateways to participate
in a multipoint conference. The MCU includes a mandatory Multipoint Controller and optional Multipoint Processors.
Multipoint Controller (MC): An H.323 entity which provides for the control of three or more terminals in a multipoint conference.
Multipoint Processor (MP): An H.323 entity which provides for the processing of audio, video, and/or data streams in a multipoint
conference. The MP provides for the mixing, switching, or other processing of media streams under the control of the MC.
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. 
						

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Network:  A group of computers connected by cables or other means and using software that enables them to share equipment,
such as printers and disk drives to exchange information.
Node:  Any point within a network which has been assigned an address.
O
Object-Orientated:  A method for structuring programs as hierarchically organized classes describing the data and operations of
objects that may interact with other objects.
Office Channel  Unit - Data Port (OCU-DP):   The CO channel bank used as the interface between the customers DSU and the
channel bank.
Off-hook:  The condition of a device which has accessed a phone line (with or without using the line). In modem use, this is
equivalent to a phone handset being picked up. Dialing and transmission are allowed, but incoming calls are not answered.
Contrast on-hook.
Off Premise Extension (OPX):  An extension or phone that terminates in a location other than that of the PBX.  Commonly used to
provide a corporate member with an extension of the PBX at home.
Ones Density:  the measure of the number of logical 1s on a T1 line compared to a given total number of bits on that line; used for
timing information in data recovery in AMI and B8ZS.
On-Hook:  The condition of a device which has not accessed a phone line. In modem use, this is equivalent to a phone handset
that has not been picked up. In other words, it can receive an incoming call. Contrast off-hook.
Open Shortest Path First (OSPF):  A hierarchical Interior Gateway Protocol (IGP) routing algorithm for IP that is a proposed
standard for Internet. OSPF incorporates least-cost routing, equal-cost routing, and load balancing.
Outage:   The measure of the time during which a circuit  is not available for use due to service interrupt. Outage is the comple-
ment of circuit availability (100% minus  % available = % outage).
Out-of-band:  Signaling that is separated from the channel carrying the information (i.e., the voice/data/video signal is separate
from the carrier signal). Dialing and various other supervisory signals are included in the signaling element. Contrast In-band
signaling.
Out of Frame (OOF):  A T1 alarm condition that is logged on the loss of 2, 3 or 4 of 5 consecutive FT framing bits.
P
Packet:  1. In data communication, a sequence of binary digits, including data and control signals, that is transmitted and switched
as a composite whole. The data, control signals and, possibly, error control information are arranged in a specific format. 2.
Synonymous with data frame. 3. In TCP/IP, the unit of data passed across the interface between the Internet layer and the link
layer. A packet includes an IP header and data. A packet can be a complete IP datagram or a fragment of an IP diagram. 4. In
X.25, a data transmission information unit. A group of data and control characters, transferred as a unit, determined by the process
of transmission. Commonly used data field lengths in packets are 128 or 256 bytes. 5. The field structure and format defined in the
CCITT X.25 recommendation.
Packet Assembler/Dissembler (PAD):  Used by devices to communicate over X.25 networks by building or stripping X.25
information on or from a packet.
Packet Data:  The information format (packetized) used for packet-mode calls.
Packet Mode:  Refers to the switching of chunks of information for different users using statistical multiplexing to send them over
the same transmission facility.
Parity bit:  An extra bit attached to each byte of synchronous data used to detect errors in transmission.
PBX (Private Branch Exchange):  A phone exchange located on the customers premises. The PBX provides a circuit switching
facility for phone extension lines within the building, and access to the public phone network. See also Exchange.
Permanent Virtual Circuit (PVC):  A connection between two endpoints dedicated to a single user. In ISDN, PVCs are established
by network administration and are held for as long as the user subscribes to the service.
Physical Unit (PU):  The component that manages and monitors the resources (such as attached links and adjacent link stations)
associated with a node, as requested by an SSCP via an SSCP-PU session. An SSCP activates a session with the physical unit in
order to indirectly manage, through the PU, resources of the node such as attached links. This term applies to type 2.0, type 4, and
type 5 nodes only.
Point-of-Presence (POP):  The central offices end points of the long distance carriers.
Point-to-Point Protocol (PPP):   A protocol that lets a PC user access TCP/IP (Internet member) using an ISDN terminal adapter
or a high-speed modem over a standard phone line.
Port:  A location for input or output data exchange. Computers, muxes, etc. have ports for various purposes. 
						

							PRI (Primary Rate Interface):  Used on ISDN. In North America, and Japan, PRI is one 64Kbps D channel and 23 B channels.
Elsewhere, it is one D channel and 30 B channels. PRI is the ISDN equivalent of a T-1 circuit.
Primitive:  An abstract representation of interaction across the access points indicating that information is being passed between
the service user and the service provider. The OSI Reference Model defines four types of primitives: Request, Indication, Response
and Confirm.
PROM (Programmable Read Only Memory - pronounced prom):  A permanent memory chip that can be programmed or filled
by the customer after by the manufacturer has set initial values. Contrast with ROM.
Protocol:  1. A set of semantic and syntactic rules that determines the behavior of functional units in achieving communication. 2.
In Open Systems Interconnection architecture, a set of semantic and syntactic rules that determine the behavior of entities in the
same layer in performing communication functions. 3. In SNA, the meanings of and the sequencing rules for requests and re-
sponses used for managing the network, transferring data, and synchronizing the states of network components. 4. Synonymous
with line control discipline.
PSTN (Public Switched Telephone Network):  A worldwide public voice phone network that is used as a telecommunications
medium for the transmission of voice, data and other information.
Public Data Network (PDN):  A packet-switched network that is available to the public for individual (subscriber) use. Typically,
controlled by a government or a national monopoly.
Public Switched  Telephone Network (PSTN):  The group of circuit-switching voice carriers, which are commonly used as analog
data communications services.
Pulse Code Modulation (PCM):  1. In data communication, variation of a digital signal to represent information; for example, by
means of pulse amplitude modulation (PAM), pulse duration modulation (PDM), or pulse position modulation (PPM). 2. Transmis-
sions of analog information in digital form through sampling and encoding the samples with a fixed number of bits.
Pulse dialing:  One of two methods of dialing a phone, usually associated with rotary-dial phones. Compare with tone dialing.
Q
Quality of Service (QoS): Guarantees network bandwidth and availability for applications.
Quantizing:  The process of analog-to-digital conversion by assigning a range, from the contiguous analog values, to a discrete
number.
R
Random Access Memory  (RAM):    A computers primary workspace. All data must be stored in RAM (even for a short while),
before software can use the processor to manipulate the data. Before a PC can do anything useful it must move programs from disk
to RAM. When you turn it off, all information in RAM is lost.
RAS Channel: An unreliable channel used to convey the Registration, Admissions and Status messages and bandwidth changes
between two H.323 entities.
Rate Enforcement:  The concept in frame relay where frames sent faster than the CIR are to be carried only if the bandwidth is
available, otherwise they are to be discarded. (The frame relay network assumes that anything exceeding the CIR is of low priority.)
Rate enforcement makes sure that the network will not get so congested that it isnt able to meet the agreed on CIR
Recognized Private Operating Agency (RPOA):  A corporation, private or government-controlled, that provides telecommunica-
tions services. RPOAs, such as AT&T, participate as non-voting members in the CCITT.
Red Alarm:  A T1 error condition generated when a local failure (e.g., loss of synchronization) exists for 2.5 seconds, causing a
Carrier Group Alarm (CGA). See also Blue Alarm and Yellow Alarm.
Request for Comment (RFC):  A set of papers in which Internet standards (published and proposed),  along with generally-
accepted ideas, proposals, research results, etc. are published.
Ring Down Box:  A device that emulates a CO by generating POTS calls for testing and product demos.
Ring Down Circuit:  A tie line connecting phones where picking up one phone automatically rings another phone. A feature used
for emergencies to alert the person at the other phone of the incoming call.
RJ-11:  An industry standard interface used for connecting a phone to a modular wall outlet; comes in 4-and 6-wire packages.
RJ-45:  An 8-wire modular connector for voice and data circuits.
Robbed Bit Signaling: The popular T1 signaling mechanism where the A and B bits are sent by each side of the T1 termination
and are buried in the voice data of each voice channel in the T1 circuit. Since the bits are robbed infrequently, voice quality is
remains relatively uncompromised. See bit robbing.
The robbed-bit signaling technique is used in D4 channel banks to convey signaling information. The eighth (least significant) bit of
each of the 24 8-bit time slots is robbed  every sixth frame  to convey voice-related signaling information such as on-hook, off-
hook, etc., for each channel. 
						

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Router:  A device that connects two networks using the same networking protocol. It operates at the Network Layer (Layer 3) of the
OSI model for forwarding decisions.
Routing Information Protocol (RIP):  A distance vector-based protocol that provides a measure of distance, or hops, from a
transmitting workstation to a receiving workstation.
RS-232-C:  An EIA standard for a serial interface between computers and peripheral devices (modem, mouse, etc.). It uses a 25-
pin DB-25, or a 9-pin DB-9 connector. The RS-232 standard defines the purposes, electrical characteristics and timing of the
signals for each of the 25 lines.
RS-422:   The EIA standard for a balanced interface with no accompanying physical connector. RS-422 products can use screw
terminals, DB-9, various DB-25, and DB-37 connectors.
RS-530:  The EIA standard for the mechanical/electrical interface between DCEs and DTEs transmitting synchronous or asynchro-
nous serial binary data. RS-530 provides for high data rates with the same connector used for RS-232; however, it is incompatible
with RS-232.
S
Serial Port:  The connector on a PC used to attach serial devices (those that need to receive data one bit after another), such as a
mouse, a printer or a modem. This consists of a 9- or 25-pin connector that sends data in sequence (bit by bit). Serial ports are
referred to as COMx ports, where x is 1 to 4 (i.e., COM1 through COM4). A serial port contains a conversion chip called a UART
which translates between internal parallel and external serial formats.
Service:  The requirements offered by an RPOA to its customers to satisfy specific telecommunications needs.
Severely Errored Seconds (SES):  Refers to a typical T1 error event where an error burst occurs (a short term,  high bit-error rate
that is self-clearing). Per the ITU-T (CCITT) G.821: any second in which the BER is less than 1x10
-3.
Signaling:  The process of establishing, maintaining, accounting for, and terminating a connection between two endpoints (e.g., the
user premises and the telco CO). Central office signals to the user premises can include ringing, dial tone, speech signals, etc.
Signals from the users phone can include off-hook, dialing, speech to far-end party, and on-hook signals. In-band signaling
techniques include pulse and tone dialing. With common channel signaling, information is carried out-of-band.
Simple Network Management Protocol (SNMP):  TCP/IP protocol that allows network management.
Simultaneous Voice Data (SVD):  A technology for letting a user send data via a modem, and use a handset to talk to another
user at the same time over the same connection. The alternative, making a second call, can be expensive or even impossible. The
uses for SVD are telecommuting, videoconferencing, distant learning, tech support, etc.
Stop Bit:  One of the variables used for timing in asynchronous data transmission. Depending on the devices, each character may
be trailed by 1, 1.5, or 2 stop bits.
Superframe (D4):  A T1  transmission format that consists of 12 DS1 frames, or 2316 bits. A DS1 frame consists of 193 bit
positions. A frame overhead bit is  in the first position, and it is used for frame and signaling phase alignment only.
Subscriber Loop:  See Local loop.
Switched 56:  A circuit-switched (full duplex digital synchronous data transmission) service that lets you dial a number and transmit
data to it at 56K bps. It is a relatively low cost service, widely used in North America for telecommuting, videoconferencing and high
speed data transfers. Many phone companies are (or will be) phasing out Switched 56 in favor of ISDN service.
Switched Virtual Circuit  (SVC):  A type of data transmission where the connection is maintained only until the call is cleared.
Switched Line:  In communications, a physical channel established by dynamically connecting one or more discreet segments.
This connection lasts for the duration of the call after which each segment may be used as part of a different channel. Contrast with
leased line.
Switched Network:   A network in which a temporary connection is established from one point via one or more segments.
Synchronous Data Link Control (SDLC):  A discipline conforming to subsets of the Advanced Data Communications Control
Procedures (ADCCP) of the American National Standards Institute (ANSI) and High-level Data Link Control (HDLC) of the Interna-
tional Organization for Standardization, for managing synchronous, code-transparent, serial-by-bit information transfer over a link
connection. Transmission exchanges may be duplex, or half-duplex over switched or nonswitched links. The configuration of the link
connection may be point-to-point, multipoint, or loop.
Synchronous Transmission:   The transmission of data which involves sending a group of characters in a packet. This is a
common method of transmission between computers on a network or between modems. One or more synchronous characters are
transmitted to confirm clocking before each packet of data is transmitted. Compare to Asynchronous Transmission.
Systems Network Architecture (SNA):  The description of the logical structure, formats, protocols, and operational sequences for
transmitting information units through, and controlling the configuration and operation of networks. 
						

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T
Tariff:  The rate/availability schedule for telephone and ISDN services from a regulated service provider.
TCP/IP:  A set of communication protocols that support peer-to-peer connectivity functions for both local and wide area networks.
TCP/IP was developed by the US Department of Defense to link dissimilar computers across dissimilar and unreliable LANs.
T Carrier:  The generic name for a digitally multiplexed carrier system. In the North American digital hierarchy, a T is used to
designate a DS (digital signal) level hierarchy. Examples: T1 (DS1) is a 1.544 M bps 24-channel designation.  In Europe, T1 is
called E1.  The T Carrier system was originally designed for transmitting digitized voice signals, but has since been adapted for
digital data applications.
T1:  A digital transmission link capable of 1.544M bps. T1 uses two pairs of normal UTP, and can handle 24 voice conversations,
each digitized at 64K bps. T1 is a standard for digital transmission in the U.S., Canada, Japan and Hong Kong. T1 is the access
method for high-speed services such as ATM, frame relay, and SMDS. See also T Carrier, T1 line and FT1.
T1 Channel Tests:  A set of diagnostics that vary by carrier, used to verify a T1 channel operation. Can include Tone, Noise Level,
Impulse Noise Level, Echo Cancellors, Gain, and Crosstalk testing.
T1 Framing:   To digitize and encode analog voice signals requires 8000 samples per second (twice the highest voice frequency of
4000  Hz). Encoding in an 8-bit word provides the basic T1 block of 64K bps for voice transmission. This Level 0 Signal, as its
called, is represented by DS-0, or Digital Signal at Level 0.   24 of these voice channels are combined into a serial bit stream
(using TDM), on a frame-by-frame basis. A frame is a sample of all 24 channels; so adding in a framing bit gives a block of 193 bits
(24x8+1=193). Frames are transmitted at 8000 per second (the required sample rate), creating a 1.544M (8000x193=1.544M)
transmission rate.
T1 Line:   A digital communications facility that functions as a 24-channel pathway for data or voice. A T1 line is composed of two
separate elements: the Access element and the Long Haul element.
T1 Mux:   A device used to carry many sources of data on a T1 line. The T1 mux assigns each data source to distinct DS0 time
slots within the T1 signal. Wide bandwidth signals take more than one time slot. Normal voice traffic or 56/64K bps data channels
take one time slot. The T1 mux may use an internal or external T1 DSU; a channel bank device typically uses an external T1
CSU.
Terminal: 1) The screen and keyboard device used in a mainframe environment for interactive data entry. Terminals have no box,
which is to say they have no file storage or processing capabilities. 2) An H.323 endpoint that provides for real-time, two-way
communications with another terminal, gateway, or H.323 MCU. An H.323 terminal must provide audio and may also provide video
and/or data.
Terminal  Adapter (TA):  An ISDN DTE device for connecting a non-ISDN terminal device to the ISDN network. Similar to a
protocol converter or an interface converter, a TA connects a non-ISDN device between the R and S interfaces. Typically a PC
card.
Tie line:   A dedicated circuit linking two points without having to dial a phone number (i.e., the line may be accessed by lifting the
phone handset or by pushing a button).
Time-Division Multiplexing (TDM):  Division of a transmission facility into two or more channels by allotting the common channel
to several different information channels, one at a time.
Time Slot:  One of 24 channels within a T1 line. Each channel has a 64K bps maximum bandwidth. Time slot  implies the time
division multiplexing organization of the T1 signal.
Toll Call:   A call to a location outside of your local service area (i.e., a long distance call).
Tone dialing:  One of two methods of dialing a phone, usually associated with Touch-Tone® (push button) phones. Compare with
pulse dialing.
Topology:  Physical layout of network components (cables, stations, gateways, and hubs). Three basic interconnection topologies
are star, ring, and bus networks.
Transmission Control Protocol (TCP):  A communications protocol used in Internet and in any network that follows the US
Department of Defense standards for internetwork protocol. TCP provides a reliable host-to-host protocol between hosts in packet-
switched communications networks and in interconnected systems of such networks. It assumes that the Internet protocol is the
underlying protocol.
Transport Layer:  Layer 4 of the Open Systems Interconnection (OSI) model; provides reliable, end-to-end delivery of data, and
detects transmission sequential errors.
Transport Protocol Data Unit (TPDU):  A transport header, which is added to every message, contains destination and source
addressing information that allows the end-to-end routing of messages in multi-layer NAC networks of high complexity. They are
automatically added to messages as they enter the network and can be stripped off before being passed to the host or another
device that does not support TPDUs.