information. Usually used to connect high-cpacity CPE, such as PBXs, to the network. Also called 23B+D in the U.S. and 30B+D in Europe.) See also ISDN and BRI.
primitive—An abstract representation of interaction accross 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.
PSTN (public switched telephone network)—The group of circuit- switching voice carriers, which are commonly used as analog data communications services. A worldwide public voice telephone network that is used as a telecommunications medium for the transmission of voice, data and other information.
pulse dialing—One of two methods of dialing a telephone, usually associated with rotary-dial phones. Compare with tone dialing.
PVC (permanent virtual circuit)—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.
Q
Q.921—The ITU-T recommendation for user-network interface layer 2 specifications for D-channel signaling. Similar to LAPD. See also ISDN.
Q.931—The ITU-T recommendation for user-network interface layer 3 specifications for D-channel signalling. See also ISDN.
R
Rreference point—Establishes the boundary between non-ISDN compatible equipment (TE-2) and the IDN network. TAs are used to convert the communication protocol used by the non-ISDN termnials to the desired BRI or PRI protocol. Non-ISDN (TE2) terminal equipment connects to IDN at the R-Reference point with a TA. (This interface may follow the RS232 or V.35 specification.) Also called the R interface. (Contrast S reference point.)
RAM (random access memory)—A computer’s 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.
reference point—A connection point between ISDN equipment classes (rather than the specific protocol of the interconnection). Can include R, S, T, and U reference points.
RFC(Request for Comments)—Name for the IETF document that provides internet standards.
RJ-11—An industry standard interface used for connecting a telephone to a modular wall outlet; comes in 4-and 6-wire packages.
RJ-45—An 8-wire modular connector for voice and data circuits.
RPOA (recognized private operating agency)—A corporation, private or government-controlled, that provides telecommunications services. RPOAs, such as AT&T, participate as non-voting members in the ITU-T.
RS-232—An EIA/TIA 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. Similar to the ITU-T V.24 standard.
S
S reference point—Provides the connection between NT2 equipment and the TA or TE-1. Can provide both primary and basic rate
services. Also called the S-interface. (Contrast R-reference point.)
SAP (service access point)—A point at which the services of an OSI layer are made available to the next higher layer. See also SAPI.
SAPI (service access point identifier)—A logical point at which data link layer services are provided by a data link layer entity to a layer 3 entity. See also SAP.
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 (e.g., COM1 through COM4). A serial port contains a conversion chip called a UART that translates between internal parallel and external serial formats.
service—The requirements offered by an RPOA to its customers to satisfy specific telecommunications needs.
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 user’s telephone 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. In ISDN, signaling includes the call establishment, call progress monitoring, call termination and enhanced telephone features provided typically by the D-Channel. See also SS7, out-of-band signaling, and in-band signaling.
SPID (service profile identifier)—In North America, the ISDN network parameter for logical terminal identification and tracking, provided by the ISDN provider. The voice SPID and data SPID identify a particular set of service or feature parameters. They are assigned by the ISDN service provider, in the form of a string of up to 20 characters, at subscription time. The SPID actually points to a specific location in central office memory where the relevant informartion is stored.
SS7 (Signaling System 7)—An ITU-T and ANSI standard for digital out-of-band signalling between central offices that provides much of the network switching intelligence to support many ISDN functions
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.
subscriber loop—The pair of wires that connect the end user to the telephone network. These wires provide ISDN service, but also require an NT1 at the enduser location as well as the LT at the network end. See also local loop.
supplementary services (SS)—ISDN functions beyond the basic requirements; includes videoconferencing, fast dialing, call waiting, call forwarding, calling line ID.
SVC (switched virtual circuit)—A type of data transmission where the connection is maintained only until the call is cleared.
SVD (simultaneous voice and data)—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 sup- port, etc.
switched 56—A circuit-switched (full duplex digital synchronous data transmission) service that lets you dial a number and transmit
