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Appendix A

Glossary


A-law
An encoding scheme that determines how an analog speech signal is converted to a digital signal. A-law encoding is used in Europe. The other algorithm, mu-law, is used in North America and Japan. See also mu-law.

ACU
Automatic Call Unit; an ISDN entity directly above the network layer. When the AG ISDN protocol stack is in ACU stack mode, the application uses the AG ISDN Messaging API to send message sequences to the ACU and handle network responses. When the AG ISDN protocol stack is in Channelized stack mode, the TCP instances communicate with the ACU. See also ACU stack mode, ISDN, LAPD stack mode, Channelized stack mode, protocol stack.

ACU stack mode
An AG ISDN protocol stack mode in which the protocol stack implements all ISDN layer 2 and layer 3 functionality, but no channelizer is present. Without a channelizer, one application performs call control for all channels; with a channelizer, a separate application instance can perform call control for each channel. The application communicates directly with the ACU using the AG ISDN Messaging API. See also ACU, LAPD stack mode, Channelized stack mode.

address
In telephony, the number dialed by a calling party which identifies the party called. Also known as the telephone number.

ADI service
A CT Access service that provides all AG board device-level functionality. Functions are provided for establishing and maintaining network connections, determining call status, playing and recording voice messages, and generating and detecting DTMF and other tones. Note that the call control functions in the ADI service have been superseded by the NCC service. See also CT Access, NCC service, service.

ADSI
Analog Display Services Interface; a specification for sending display information over ordinary telephone lines. For example, used in caller ID. See also ANI, caller ID.

ADSL
Asymmetric Digital Subscriber Line; a method for moving data over regular phone lines at broadband rates (above 1 Mbyte/s). ADSL permits data to be uploaded and downloaded at different rates of speed, hence, asymmetric. ADSL can be considered as an alternative to ISDN, allowing higher speed data transmissions in cases where the connection is always to a known terminal which can support the specified speed.

AG
Natural MicroSystems' Alliance Generation product line of telephony and voice processing hardware.

AG configuration file
Text file (usually named ag.cfg) that provides configuration information for all AG boards in a system. The AG configuration file also specifies runtime software such as DSP files and TCPs to download to the AG board(s) as part of board initialization. agmon uses the AG configuration file to initialize and load the AG boards in the system. See also agmon, DSP file, TCP.

AG ISDN Messaging API
An API supplied with AG ISDN which enables an application to communicate directly with Q.931 (layer 3) call control in the ISDN protocol stack. Switch- and country-invariant D channel messages are exchanged with the application at this interface. See also D channel, ISDN, protocol stack, Q.931.

agmon
Utility program which reads a configuration file and uses it to load and monitor AG hardware.

ANI
Automatic Number Identification; a network service that provides a called party with the phone number of the calling party. It is typically available to the called party in R1, R2, and ISDN signaling systems. The implementation of ANI can vary between different telephone companies and even different central office switches. See also ADSI, caller ID.

API
Application Programming Interface; a library of function calls that allow an application developer to access functionality in a uniform and consistent way.

asynchronous
Refers to circuitry and operations without a common timing or clock signal.

asynchronous function
Enables concurrent processing between hardware boards and the host CPU. In telephony, an application initiates functions on a telephony board and continues its own processing as it waits for the results of those functions. See also synchronous function.

Automatic Call Unit
See ACU.

Automatic Gain Control
See AG configuration file.

B channel
A timeslot on an E1 trunk, T1 trunk, or telephony bus that carries voice data and in-band signaling. B channel is an abbreviation of bearer channel. See also D channel, ISDN.

blind transfer
Call transfer method in which a call control function places a second call and then disconnects its port from the PBX before call placement is resolved, connecting the original call.

blocking (telephone call)
Call control action taken by an application to refuse any further incoming calls. Depending on the telephony protocol, blocking calls on a line will tell the CO (Central Office) or switch not to offer any calls, or the line will reject every call that is being offered. The rejection method also varies according to the telephony protocol being used. Some protocols allow an application to designate a particular rejection method, such as playing a busy signal or a reverse-make busy signal. See also CO.

BRI
Basic Rate Interface; in ISDN, a configuration that consists of two B channels and one D channel at 16 kbit/s.

buffer
A data area that can be shared by hardware devices or program processes. It functions as a "midpoint holding place."

bus (telephony)
A physical system which permits the interchange of data. A telephony bus has three basic elements: lines for the data, bit synchronization (clocks), and frame synchronization (frame strobe). Most telephony buses also have a network reference - an 8 kHz timekeeper. See also H.100 bus, MVIP.

call control
Any part of telephone call establishment, including setting up, blocking, monitoring, transferring, releasing, or tearing down the telephone call.

call progress
In CT Access, functions that allow the application to control and supervise call placement. Call progress monitors in-band energy to detect network tones, voice, and other tones such as modems.

caller ID
A telephone company service that delivers the calling party's number to the called party. For example, in one method, the data is delivered to the called party in the interval between the first and second incoming rings using an ADSI modem. See also ADSI, ANI.

CAS
Channel Associated Signaling; a signaling method where signaling information is provided on a line-by-line or channel-by-channel basis. Signaling information is sent for each channel at regular intervals, regardless of state changes. Each transmission channel is associated with one or more transmission paths. In-band signaling is a type of channel associated signaling. See also Common Channel Signaling (CCS).

CEPT
Conference of European Postal and Telecommunications administrations; a European telephony standards committee.

CEPT E1
A standard used in Europe for digital telephone carriers. CEPT E1 is similar to T1 but operates at 2.048 Mbps and has 32 channels instead of T1's 24. See also T1.

chained layers
In the OSI layering model, the chained layers are defined to be the lowest three layers: the physical layer, the data link layer and the network layer. See also ISDN.

channel
An electronic communications path. In digital telephony, a channel usually refers to a separate connection carried on a digital trunk.

Channel Associated Signaling
See CAS.

Channelized stack mode
An AG ISDN protocol stack mode in which the ISDN protocol stack implements all OSI layer 2 and layer 3 functionality. A channelizer is also present. AG ISDN TCP instances communicate with the application and with the channelizer entity in the protocol stack. See also ACU stack mode, LAPD stack mode, layer, TCP.

channelizer
An entity on the AG ISDN protocol stack between the ACU and the ISDN TCP. It routes D channel information between the lower ISDN layers through the state machine implemented by the ISDN TCP to the application. Without a channelizer, one application performs call control for all channels. Using a channelizer enables a separate application to perform call control for each channel. See also ACU, D channel, TCP.

client/server model
A model for distributed computing in which one program, the client, makes a service request from another program, the server, which fulfills the request. In a network, the client/server model provides a convenient way to interconnect programs that are distributed across different locations.

In telephony, a periodic reference signal used for synchronization on a transmission facility, such as a telephony bus.

CO
Central Office; the location of the public network switch.

Common Channel Signaling (CCS)
A signaling method that sends data packets of signaling information for a group of associated transmission channels over a separate link. This separate link is usually another channel of the same digital trunk, called the D (for data) channel in ISDN service. CCS sends signaling data only when one or more channels in the designated group experiences a state change. See also B channel, CAS, D channel.

connection ID
In ISDN, a handle to a call on a B channel. The connection ID is assigned to outbound calls by the application, and to inbound calls by the AG ISDN protocol stack. It is used to identify the call in all communications between the ACU and the application. See also ACU, B channel.

CPE
Customer Premise Equipment; customer-owned equipment connected to telephone company lines.

CSA
Canadian Standards Association; CSA certification is required for most electrical equipment used in Canada.

CT Access
Natural MicroSystems' development environment for telephony applications.

CTA context
In CT Access, an entity that organizes services and accompanying resources around a single processing context. Usually represents an application instance controlling a single telephone call. Some contexts are not associated with a call; an application performing voice conversions does not require a telephone line.

ctahd
The handle returned by ctaCreateContext that identifies a specific CTA context. See also CTA context.

D channel
The timeslot on an E1 trunk, a T1 trunk, or telephony bus in which common channel signaling information is passed. See also B channel, BRI, CAS, Common Channel Signaling (CCS), ISDN.

data link layer
In the OSI layering model, the data link layer (layer 2) is above the physical layer. Protocols for this layer describe methods for error-free communication between devices across the physical link. One protocol used in this ISDN layer is CCITT recommendation Q.921, also known as Link Access Procedures on the D Channel (LAPD). See also ISDN, Link Access Procedures on the D Channel (LAPD), Open System Interconnect (OSI).

DCE
Data Communications Equipment.

default channel
In AG ISDN, the B channel bound to the same CTA context as the AG ISDN TCP instance. The AG ISDN TCP will always request use of this channel when attempting to place an outbound call. In Non-Exclusive Mode, the ISDN TCP instance will accept any B channel that the network assigns. In Exclusive Mode, the TCP aborts the call. See also CTA context, Exclusive Mode, Non-Exclusive Mode, TCP.

DID number
Direct Inward Dial number; the called number which is collected by the trunk control program and is passed to the application.

DNIS
Dialed Number Identification Service; a telephone company service that reports the number that the caller was trying to reach. to the called party. For example, a company with multiple 800 numbers would use this service to determine how to respond to an incoming call.

DoC
Department of Communications; the Canadian government agency that regulates communications and the use of the electromagnetic spectrum.

DSP file
A low-level program, downloaded to an AG board at initialization, that enables an AG board's DSPs to perform tasks such as DTMF signaling, voice recording, and playback.

DSP program file
A software module that programs an AG board's DSPs to perform certain functions. The DSP program files for an AG board to use are specified in the AG configuration file, and are loaded to on-board memory by agmon.

E1
See CEPT E1.

end-to-end layers
In the OSI layering model, layers above layer 3 (the network layer). These layers describe how information is exchanged and delivered end-to-end. They also define process-to-process communication, and describe application-independent user services, user interfaces, and applications. See also International Organization for Standardization (ISO), network layer, Open System Interconnect (OSI).

error macros
Macros used by service API functions to ensure consistent error handling across all CT Access services.

ETSI
European Telecommunication Standards Institute.

EUC protocols
EUropean digital Channel associated signaling protocols. A protocol family including special channel associated signaling protocols used in certain European countries. The protocols use two-bit line signaling, not as specified by CCITT, but as specified by national documents. The register signaling is either carried by in-band DTMF tones (not compelled) or by out-of-band decadic pulses. Also know as EuroCAS.

events
In CT Access, data structures that contain notification of certain conditions or state changes. Events can be sent from the hardware or from another software module to the application program. All events are represented as C data structures. The event structure contains information about the specific event, including a timestamp, associated CTA context, specific data, error codes, or reason codes. For example, when a voice play operation completes, a completion event is returned to the application.

event queue
In CT Access, the single queue created by calling ctaCreateQueue where the application receives all of its events from the telephony hardware. NMS software is event-driven. CT Access provides functions to wait for and retrieve events from the event queue.

Exclusive Mode
One of two modes which determines how the AG ISDN TCP responds if the telephone network denies the AG ISDN TCP use of its default channel. The default channel is the B channel bound to the same CTA context as the ISDN TCP instance. In Exclusive Mode, the TCP aborts the call. See also Non-Exclusive Mode, default channel.

glare
In telephony, the simultaneous occurrence of an attempt to place a call and the appearance of an incoming call on the same line. In general, the incoming call must be given precedence. Also known as call collision.

H.100 bus
A PCM digital bus standard for integrating hardware from various PC board vendors which enables boards to share voice data, signaling data, and switching information. The H.100 bus is an interoperable superset of the H-MVIP and MVIP-90 telephony buses. It can be addressed using the MVIP-95 switch model.

HDLC
High Level Data Link Control; a link layer protocol for point-to-point and multi-port communications.

inbound application
An application designed to receive inbound calls.

inbound call
A call received by an inbound application, placed by a remote party.

informational event
In CT Access, an event which does not indicate an internal state change and does not require any action from the application. Informational events are not automatically generated, but can be made available via an eventmask parameter.

International Organization for Standardization (ISO)
The standards organization that developed the OSI seven-layer protocol model.

International Telecommunications Union
See ITU.

ISDN
Integrated Services Data Network; a standard for providing voice and data telephone service with all digital transmission and message-based signaling.

ISO
See International Organization for Standardization (ISO).

ITU
International Telecommunications Union; an international standards body for telecommunications.

LAPD
See Link Access Procedures on the D Channel (LAPD).

LAPD stack mode
An AG ISDN protocol stack mode in which the protocol stack implements layer 2 functionality only. No channelizer or ACU is present. The application communicates directly with the data link layer. See also ACU stack mode, Channelized stack mode.

layer
In the OSI seven-layer protocol model, a level of digital communication. Each layer generally has one or more protocols associated with it. Communication networks for computers can be organized as a set of independent protocols, each in a different layer (or level). The lowest layer governs direct host-to-host communication between the hardware at different hosts; the highest layer consists of user applications. For each layer, programs at different hosts use protocols appropriate to the layer to communicate with each other. See also ACU stack mode, data link layer, end-to-end layers, LAPD stack mode, Channelized stack mode, network layer, physical layer.

LE
Local Exchange equipment; an ISDN equipment category.

Link Access Procedures on the D Channel (LAPD)
CCITT recommendation Q.921; a protocol for communication at the data link layer. See also data link layer.

mu-law
One of two algorithms used in telephony to logarithmically compress or expand digitized speech. mu-law is used in North America and Japan. A-law is the other algorithm used in European networks. See also A-law.

MVIP
Multi-Vendor Integration Protocol; PCM digital bus standard for integrating various board vendors. Facilitates software-controlled digital switching within the PC chassis. MVIP interconnects switching and telephony processing boards on a PC. An interoperable subset of the H.100 bus standard. See also H.100 bus.

NAI
See NCC service.

NCC service
A CT Access service which performs call control. NCC service features include a protocol-independent API, separate call and line state machines, call hold/retrieve, and the ability to query a protocol's capabilities. The NCC service supersedes the call control functions provided by the ADI service.

network access identifier (NAI)
A software handle used to refer to a trunk.

network layer
In the OSI protocol layering model, the network layer (layer 3) is the layer above the data link layer. Protocols for this layer describe methods for transferring information between computers. They also describe how data is routed within and between networks. One protocol used at this layer for ISDN applications is CCITT recommendation Q.931. See also data link layer, Q.931.

NFAS
Non-FAcility Signaling; an AG ISDN stack mode in which a single D channel on a T1 trunk carries the signaling for all B channels on more than one trunk. This leaves the 24th channels on the trunks free for use as B channels. NFAS is not supported on E1 trunks. See also ACU stack mode, B channel, D channel, LAPD stack mode, Channelized stack mode, T1.

NOCC
NO Call Control; the trunk control program used when the application will not use protocol-independent call control. NOCC is a stateless protocol which does not generate any call control events. It is typically used with low-level functions to perform call control from the host. Also known as the NULL protocol. See also protocol (telephony), TCP.

Non-Exclusive Mode
One of two modes which determine what the ISDN TCP does if the network denies the ISDN TCP use of its default channel. The default channel is the B channel bound to the same CTA context as the ISDN TCP instance. In Non-Exclusive Mode, the TCP will accept any B channel that the network assigns. See also default channel, Exclusive Mode.

NT1
Network Terminating equipment, class 1; an ISDN equipment category. Equipment in this category physically terminates the local loop.

NT2
Network Terminating equipment, class 2; an ISDN equipment category.

Open System Interconnect (OSI)
A model for digital communication, developed by the International Organization for Standardization (ISO). The OSI model defines seven separate layers of communication. ISDN follows this protocol model to ensure end-to-end connectivity.

OSI
See Open System Interconnect (OSI).

outbound application
An application designed to place outbound calls.

outbound call
A call placed by an application to a remote party.

overlap receiving mode
An AG ISDN ACU mode, in which an inbound call causes the ACU to send a ACU_CONN_IN message to the application even if the called number and/or calling number are not complete (i.e. the "Sending Complete" IE is not present). The ACU then sends any additional incoming digits in ACU_DIGIT_IN messages. See also ACU stack mode.

parameter
A variable that dictates the behavior of functions.

parameter structures
Multiple parameters that are grouped together in C language structures.

PBX or PABX
Private (Automatic) Branch telephone eXchange; a system providing local telephone switching in an office or building.

.pf file
Parameter definition file; used to automatically generate parameter source and header files.

physical layer
In the OSI layering model, the physical layer (layer 1) is the electrical and mechanical layer. Protocols for this layer describe, on an electrical and mechanical basis, the methods used to transfer bits from one device to another. One protocol used at this layer in ISDN is CCITT recommendation I.430/I. See also data link layer, end-to-end layers, layer, network layer, Open System Interconnect (OSI).

point
An interface between ISDN equipment categories.

PRI
Primary Rate Interface; a term used to describe a trunk configuration consisting of 23 B channels and one D channel running at 1.544 Mbyte/s (or 30 B channels and one D channel at 2.048 Mbyte/s in Europe). It is an ISDN interface equivalent to a T1 circuit. Also known as primary rate. See also ISDN.

primitive
An abstract, implementation-independent representation of an interaction; in the OSI protocol layering model, a layer requests services from an adjacent lower layer using primitives. In AG ISDN, messages used by a layer to request services from an adjacent lower layer.

protocol (telephony)
Defined procedure for call setup and call teardown.

protocol-independent
Consistent for all available protocols.

protocol stack
The AG ISDN protocol stack; software running on the AG board which implements OSI layer functionality. The ISDN protocol stack can run in Channelized configuration, ACU configuration, or LAPD configuration, depending upon how the application is to access the ISDN protocol stack. See also ACU stack mode, ISDN, LAPD stack mode, Channelized stack mode.

PSTN
Public Switched Telephone Network; a public telephone network.

Q.921
See Link Access Procedures on the D Channel (LAPD).

Q.931
CCITT recommendation Q.931 describes an ISDN protocol for the network layer (layer 3 in the OSI layering model). See also network layer, OSI.

runfile
Mandatory low-level runtime software which is downloaded to an AG board as part of its initialization. The runfile for a board is specified in the AG configuration file. When agmon runs, it transfers the runfile from the host into on-board memory. See also agmon.

S point
In ISDN telephony, the service access point between TE1 and NT2 equipment. See also NT2, SAP, TE1.

SAP
Service Access Point; in the OSI layering model, the point at which a layer provides services to the layer directly above it. A unique Service Access Point Identifier (SAPI) is associated with each SAP. See also ISDN, OSI, SAPI.

SAPI
Service Access Point Identifier; in the OSI layering model, a unique identifier for a service access point (SAP). See also ISDN, OSI, SAP.

service
In CT Access, a group of logically related telephony functions. A service may be implemented on multiple hardware boards. No matter what hardware is providing the functionality, all services with the same functionality have a standard API. This enables device-independent programming.

signaling
Information relayed between parties that is related to the process of a call (e.g., the status of the line, call progress and control information, etc.) rather than the content of the call (e.g., data or voice information).

solicited event
An event that occurs as a consequence of some function call.

stream
A grouping of timeslots that usually corresponds to a particular bit-stream of time-domain multiplexed (TDM) serial data on an individual track or wire of a bus.

supervised transfer
A call transfer method in which the application controls the transfer process. See also blind transfer.

swish utility
CT Access utility which controls MVIP switches. swish is a tool for interactive or text-file-driven control of MVIP switches. It provides a convenient way to manually try out connections during development to verify the commands that will be given to switches from within CT Access applications that use the Switching service.

synchronous function
A function that does not return until the operation it initiated has completed. See also asynchronous function.

T point
The service access point between NT2 and NT1 ISDN equipment. See also NT1, NT2, SAP.

T1
A standard for telephone transmission that multiplexes 24 digital voice channels on a single 1.544 Mbyte/s carrier.

TCP
Trunk Control Program; a downloadable module which contains the low-level code to interface with an analog or digital trunk running a certain protocol. TCPs are specific to a trunk protocol, for example, one-way inbound with wink start (which is used for DID and DNIS). .

TE1
An ISDN equipment category; ISDN end-user terminating equipment, class 1, which terminates a single ISDN trunk.

timeslot
Specifies a particular 64 kbit/s subdivision of a TDM bus stream. Timeslots number from zero (0) to n where n is stream-dependent.

transitional event
A protocol-independent call control event which causes a transition in a state machine.

transport layer
In the OSI protocol layering model, the transport layer (layer 4) is the layer above the network layer. Protocols for this layer describe methods for maintaining reliable end-to-end communication across a network. See also network layer, OSI.

trunk
A transmission channel connecting two switching machines.

With regard to NMS products, a trunk is defined as the physical interface between the telephone network and the board. It can be used interchangeably with line because it could be connected to either a trunk or a line.

In telephone networks, a trunk is a shared connection between two switches. It differs from a line in that it is not dedicated to one subscriber or extension. Trunks should have good machine-to-machine interfaces. Compared to lines, trunks have different signaling requirements, including possibly billing information.

Trunk Control Programs
See TCP.

U point
The service access point between NT1 and LE ISDN equipment. See also LE, NT1, S point, SAP.

unsolicited events
Events that are not generated in response to a command.



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