ISDN Modems Glossary

A thru H	Definition of Terms
ASSP	Application-Specific Standard Product - high-integration chip or chipset for a specific application.
ATM	Asynchronous Transfer Mode: cell-based transmission protocol.  Independent of the medium, it can be run over ISDN.  Can contain any type of information (voice, video, data).
B (Bearer) Channel	A 64 kilobit-per-second (kbps) circuit switched channel used for voice or data.
Baseband	Using entire bandwidth of a medium to carry a single signal.
BRI (Basic Rate Interface)	Basic Rate ISDN services targeted at home and small business users. BRI service is delivered over a single twisted pair, the same wiring that is used to deliver POTS.  It includes three fully duplex data channels. Two of these, referred to as Bearer or B channels, are used to carry voice or data. The third, the D channel, is used to communicate control information between the central office switch and the ISDN terminal device.
Broadband	Sharing the bandwidth of a medium to carry more than one signal; typically data rates above 1.5/2.0 Mbps.
CHI	Concentration Highway Interface, a TDM scheme defined by Lucent.
Circuit Switching	A communications technology where a dedicated communications path is established between two stations.  The path consists of dedicated channels on each physical link between the stations.  The process of establishing these dedicated paths is referred to as signaling.
CO	Central Office - telephone company equipment to terminate and interconnect customer lines.
Codec - Coder/Decoder	Converts video signals to/from digital for transmission.
D (Delta) Channel	A 16 kbps (for BRI) or 64 kbps (for PRI) packet switched channel used for signaling and data.
Demodulation	Conversion of analog carrier signal to digital information.
Ethernet	10 Mbps LAN protocol.
ETSI	European Telecommunications Standards Institute - European telecom standards-setting organization.
FireWire	Standard high-speed serial bus.  Supports up to 400 Mbps today, going to 3200 Mbps, and plug-and-play.
Frame	In a data communications context this term refers to a variable length grouping of digital data transmitted between end stations.  These frames include a header containing addressing and control information.  In a telecommunications context, a frame is pattern appearing regularly, typically every 125 microseconds, in a transmitted data stream that is used to define the structure of the transmitted data and to carry control information.
HDLC	High-level Data Link Control, a transmission protocol used at the data link layer (layer 2) of the OSI seven layer model for data communications.  HDLC is an ISO standard.
I thru P
IDL	Inter-chip Digital Link, a five-wire TDM interface defined by Motorola.
IDSL	ISDN Digital Subscriber Loop (128kbps).
IEEE 1394	Formal name for FireWire.
IOM-2	ISDN Oriented Modular Interface, a TDM interface defined by Infineon.
ISDN (Integrated Services Digital Network)	Up to 144 kbps digital transmission over copper.  The official definition for ISDN (from ITU Study Group XVIII - 1988): A network evolved from the telephony Integrated Digital Network (IDN) that provides end-to-end digital connectivity to support a wide variety of services, to which users have access by a limited set of standard multipurpose customer interfaces.
LAN	Local Area Network - Small-area data communications network; typical protocols are Ethernet and Token Ring.
LAPD (Link Access Procedure for D channel)	The data link layer protocol that was defined for communication over the D channel.  It is based on HDLC and defined in the I.441/Q.921 specifications.
Loop	Twisted-pair copper telephone line.
MAC	Media Access Controller - The logic that controls access to the physical transmission medium (PHY) on a LAN.  Common MAC layer standards are the CSMA/CD architecture used in Ethernet and the token passing methods used in Token Ring, FDDI and MAP.
Modem	Modulator/demodulator converts digital data to/from analog signals for transmission over analog facilities.
NIC	Network Interface Card - Circuit board that interfaces between computer and the communications network.
NT1 (Network Termination Equipment for layer 1)	Equipment that terminates the ISDN network connection at OSI layer 1 (the physical layer). Specifically it terminates the U interface and converts it into an S/T interface.
NT2 (Network Termination Equipment for layer 2)	Equipment that terminates the ISDN network interface at OSI layer 2, (the data link layer). An example would be a PBX that terminates a PRI connection and provides several BRI interfaces. An NT2 interfaces to TAs or TE1s via an S interface and to an NT1 via a T interface.
OSI (Open Systems Interconnect) Reference Model	A framework that was developed by OSI, that is used to describe communications protocol standards. It describes protocols in terms of seven layers, each of which serves a specific function. The following table summarizes the layers:    Layer Number Function Physical 1 Encoding bits on the wire, connectors, etc. Link 2 Covers framing, synchronization, error control, and flow control Network 3 Routing data between end stations Transport 4 Guarantees reliable delivery between end stations Session 5 Arbitrating, establishing, and maintaining dialogs between applications  Presentation 6 Normalizing data syntax between applications Application 7 Services for applications
Packet Switching	Packet switching technologies are based on end stations collecting data to be transmitted into packets.  Packets may be variable in length or may be of a fixed size, as in ATM.  Packets may be transmitted at any time without the setup of a connection with the destination.  It is up to the network to determine how to route the data to the destination.  At the same time the network does not guarantee delivery and it is up to the end stations to provide mechanisms for reliable delivery.  Most data communications technologies are based on packet switching.  The use of packet switching is driven by the underlying assumption that computer data traffic is inherently bursty in nature, and not time-critical.
PBX	Private Branch Exchange, a private telephone network.
PCP	Parallel Control Port, used by Motorola for a standard microprocessor bus port.
PHY	Physical Layer Interface - Direct interface to the transmission medium.
PNA	Phone Networking Alliance - Home networking standard for 1-10 Mbps over phone wire.
POTS	Plain Old Telephone Service - analog phone service, takes the lowest 4KHz of bandwidth on loop.
PPP	Point-to-Point Protocol, a method of connecting a computer to the Internet.
PRI (Primary Rate Interface)	Primary Rate ISDN service is targeted at larger corporate customers.  PRI service consists of 23 B channels in North America and is transported across a standard T1 physical layer interface.  In Europe the service provides 30 B channels plus one 64 kbps D channel and uses an E1 physical layer. PRI requires two sets of twisted pair telephone lines.
PSTN	Public Switched Telephone Network.
Q thru Z
R (Rate) Reference Point	Provides a non-ISDN interface between user equipment that is not ISDN capable and ISDN adapter equipment. Examples include RS232, V.35, and X.21.
Router	Connects multiple computer networks.
RS232	Standard for serial transmission between a computer and peripherals for short distances.
S (System) Reference Point	An ISDN terminal or terminal adapter interface using four wires and alternate space inversion (ASI), sometimes referred to as pseudo-ternary, data coding. Up to eight devices can be connected in a multi-drop configuration to an S interface.
SAR	Segmentation and Reassembly - Segmenting packets into payloads for ATM.
T (Terminal) Reference Point	The interface between an NT1 and NT2.  It is functionally equivalent to the S interface.
TA (Terminal Adapter)	Adapts non-ISDN equipment to ISDN.  A TA provides an R interface for the non-ISDN equipment and an S/T interface for connection to the ISDN network.
TDM	Time Division Multiplexing, a type of multiplexing that combines data streams by assigning each stream a different time slot in a set.
TE1 (Terminal Equipment 1)	ISDN terminal equipment such as ISDN telephones.  These devices interface to the ISDN network by way of an S interface.
TE2 (Terminal Equipment 2)	Non-ISDN terminal equipment such as personal computers.  These devices interface to a TA by way of an R interface.
U (User) Reference Point	The interface between the ISDN customer premises equipment and the public ISDN network.  This interface defines a point to point connection using a single twisted pair and 2B1Q data coding.
USB	Universal Serial Bus - Standard for serial transmission between a computer and peripherals.  Supports up to 12 Mbps and plug-and-play.
UTOPIA	Universal Test & Operations Interface for ATM - Refers to an electrical interface between the sublayers of the PHY layer.
V Reference Point	Proprietary interface within central office used to connect the line cards to the ISDN switch.
WAN	Wide Area Network - Private network facilities usually offered by public telephone companies.

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