ACU See Automatic Call Unit.

ACU configuration An AG ISDN protocol stack configuration in which the protocol stack implements all ISDN layer 2 and layer 3 functionality, but no channelizer is present. The application communicates directly with the ACU using the AG ISDN Messaging API.

AG Access One of the NMS telephony application programming interface products.

AG board See Alliance Generation board.

AG configuration file A text file containing configuration information for the AG boards in a system. When agmon runs, it configures the boards as described in this file.

AG ISDN Messaging API
An API supplied with the AG ISDN software which allows an application to gain direct access to Q.931 (layer 3) call control. Switch- and country-invariant D channel messages are exchanged with the application at this interface.

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

Alliance Generation board (AG board)
A member of Natural MicroSystems' Alliance Generation family of telephony and voice processing hardware products.

ANI See Automatic Number Identification.

asynchronous programming
Enables concurrent processing between hardware boards and the host CPU. The application initiates telephony functions on the AG board and continues its own processing instead of waiting for events from the AG board to arrive. CT Access and AG Access support this configuration.

Automatic Call Unit (ACU)
An entity within layer 3, directly above the network layer. When the protocol stack is in ACU configuration, the application uses the Messaging API to communicate with the ACU, sending message sequences and handling network responses. When the protocol stack is in NCC configuration, the TCP instances communicate with the ACU.

Automatic Number Identification (ANI)
A network service that provides a called party with the phone number of the calling party. ANI information 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.

B channel See bearer channel.

bearer channel (B channel)
One of the timeslots on an E1 trunk or T1 trunk over which voice data and in-band signaling is passed.

blocking Call control action taken by an application to refuse any further incoming calls. Depending on the protocol, blocking calls either tells the Central Office or switch not to offer any calls, or to reject every call that is being offered (not answer, or play busy, etc.).

call control The act of setting up, monitoring and dismantling a telephone call.

call progress analysis Functions that allow the application to control call placement. Call progress monitors in-band energy to detect network tones, voice, and other tones such as modems.

CAS See Channel Associated Signaling.

CCITT Comite Consultatif Internationale de Telegraphique et Telephonique; an international organization, based in Geneva, that recommends standard practices for communications. Now publishing under the name of its parent organization - ITU.

CCS See Common Channel Signaling.

CEPT Conference des administrations Europeenes des Postes et Telecommunications, a standards body that sets standards for services and interfaces.

chained layers In the OSI protocol layering model, the chained layers are the lowest three layers: the physical layer, the data link layer and the network layer.

channel An electronic communications path. In digital telephony, a channel usually refers to a separate connection carried on a digital trunk. Channel information is carried in timeslots, time-division multiplexed into a single continuous stream of information.

channelizer An entity on the protocol stack between the ACU and the TCP. It routes D channel information between the lower ISDN layers through the state machine implemented by the ISDN TCP to the CTA contexts.

Channel Associated Signaling (CAS)
A signaling system in which signaling information is sent for all channels at regular intervals, regardless of whether each channel's state changes or not. The information for each channel consists of a set of bits (called the ABCD bits). Whenever a channel's state changes, the ABCD bit pattern for that channel changes. On T1 trunks, this information is "buried" in the voice information using robbed-bit signaling. On E1 trunks, this signaling is carried in a separate channel.

Common Channel Signaling (CCS)
A signaling method where signaling information is provided for a number of channels in data-packet form sent over a separate link.

connection id 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 ISDN protocol stack. It is used to identify the call in all communications between the ACU and the application.

CT Access One of the NMS telephony application programming interface products.

D channel The timeslot on an E1 trunk or on a T1 trunk in which common channel signaling information is passed.

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

Digital Signal Processor (DSP)
A microprocessor that is designed to perform the calculations required for voice processing.

DSP See Digital Signal Processor.

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

DTMF Dual-Tone-Multi-Frequency; an in-band signaling system that uses two simultaneous voice-band tones for dialing. Also called touchtone.

E&M Ear and Mouth; a telephone signaling system used between two switches that uses two wires called the E lead and the M lead. In analog E&M, the M lead of one switch is connected to the E lead of the other, and vice versa. In digital E&M signaling, a single bit is used to convey signaling states. A common mnemonic is that E stands for ear-lead and M for mouth-lead.

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

e1stat A utility that lets you monitor the status of an E1 trunk, including alarm states, errored and failed seconds, bit error rate violations, framing slips and framer synchronization state.

end-to-end layers In the OSI protocol 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, etc.

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 by national documents. The register signaling is either carried by in-band DTMF tones (not compelled) or by out-of-band decadic pulses.

glare 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.

H.100 bus A PCM digital bus standard for integrating various board vendors. Allows boards to share data, signaling, and switching information.

inbound application An application designed to receive inbound calls.

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

Integrated Services Digital Network (ISDN)
A standard for providing voice and data telephone service with all digital transmission and message based signaling.

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

ISDN protocol stack Software running on the AG board which implements ISDN layer functionality. The stack can run in NCC configuration, ACU configuration, or LAPD configuration, depending upon how the application is to access the protocol stack.

ISO See International Organization for Standardization.

LAPD See Link Access Procedures for the D Channel.

LAPD configuration An AG ISDN protocol stack configuration 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.

layer In the OSI protocol layering model, a level of digital communication. Each layer generally has one or more protocols associated with it.

LE An ISDN equipment category. LE is Local Exchange equipment.

line A logical telephone connection on which a call can take place.

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

MFC-R2 ITU standard line protocol for E1 lines and T1 lines using compelled MF tones and channel-associated signaling. Almost every country has a variant of this standard.

MVIP Multi-Vendor Integration Protocol; a PCM digital bus standard for integrating various board vendors. An interoperable subset of the H.100 bus standard.

NAI See network access identifier.

NCC configuration A protocol stack configuration in which the protocol stack implements all ISDN layer 2 and layer 3 functionality. A channelizer is also present. ISDN TCP instances communicate with the application and with the channelizer entity in the protocol stack.

network access identifier (NAI)
A 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 is CCITT recommendation Q.931.

NT1 An ISDN equipment category. Equipment in this category physically terminates the local loop.

NT2 An ISDN equipment category. Equipment in this category is network terminating equipment, class 2.

off-hook The active state of a customer telephone circuit. The term is derived from old telephone sets where the receiver, when in use, was lifted from a hook attached to a switch. The opposite condition is on-hook.

Open System Interconnect (OSI)
A model for digital communication, developed by the International Organization for Standardization (ISO). In OSI, seven separate layers of communication are defined.

OSI See Open System Interconnect.

outbound application An application designed to place outbound calls.

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

overlap receiving mode
When the ACU is in this mode, when an inbound call arrives, the ACU sends ACU_CONN_IN 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.

physical layer In the OSI protocol 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 is CCITT recommendation I.430/I.

PRI See primary rate.

primary rate An ISDN term used to describe a trunk configuration consisting of 23 B channels and one D channel running at 1.544 Mbit/s (or 30 B channels and 1 D channel at 2.048 Mbit/s in Europe).

primitive Messages used by a layer to request services from an adjacent lower layer.

protocol A scheme for communication. Many different protocols for digital telephony, and variations of these standards, are in use around the world.

Pulsed E&M See E&M.

Q.921 See Link Access Procedures on the D Channel.

Q.931 CCITT recommendation Q.931 describes a protocol for the network layer (layer 3 in the OSI protocol layering model).

runfile A module of basic low-level software which an AG board requires to operate. 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.

S point The service access point between TE1 and NT2 equipment.

SAP See service access point.

SAPI See service access point identifier.

service access point (SAP)
In the OSI protocol layering model, the point at which a layer provides services to the layer directly above it. With each SAP is associated a unique Service Access Point Identifier (SAPI).

service access point identifier (SAPI)
In the OSI protocol layering model, a unique identifier for a service access point (SAP).

showsig A utility which monitors the signals on all lines on a trunk simultaneously.

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

Special Information Tone (SIT)
A sequence of three tones which indicate to a calling party that a network-provided announcement will follow.

stream A group of timeslots. Typically, this term refers to the entire set of timeslots on a trunk, or the mapping of those timeslots onto the MVIP bus.

SW Utility A utility program for configuring and controlling MVIP boards. MVIP-90 compliant. (For use with AG Access only.)

swish A utility program shipped with CT Access for configuring and controlling MVIP boards. MVIP-95 compliant. (For use with CT Access only.)

SwitchPath A switching library provided by Natural MicroSystems for MVIP-90 compliant device drivers. (For use with AG Access only.)

synchronous function A function that does not return until its operation is complete.

T point The service access point between NT2 and NT1 equipment.

T1 A standard for telephone transmission that multiplexes up to 24 channels on a single 1.544 Mbit/s carrier.

t1stat A utility that lets you monitor the status of a T1 trunk, including alarm states, errored and failed seconds, bit error rate violations, framing slips and framer synchronization state.

TCP See Trunk Control Program.

TE1 An ISDN equipment category. Equipment in this category is ISDN end-user terminating equipment, class 1, which terminates a single ISDN trunk.

timeslot On a digital trunk and on the MVIP bus, information in each channel is time-division multiplexed into a single continuous stream of data. The interval in which each channel broadcasts is called a timeslot.

trunk A transmission channel connecting two switching machines.

Trunk Control Program (TCP)
A software module designed to run in an AG board's on-board memory, which interfaces a host application with an analog or digital trunk running a certain protocol. The TCP to use is specified in the AG configuration file, and is transferred to the AG board by agmon.

U point The service access point between NT1 and LE equipment.

unsolicited events Events that can occur at any time, regardless of the application's current activities.