off-hook—The condition of a device that has accessed a phone line (with or without using the line). In modem use, this is equivalent to a telephone handset being picked up. Dialing and transmission are allowed, but incoming calls are not answered.
on-demanddialing—A cost-saving feature of ISDN that sets up, transfers, and then closes a call only when the ISDN device detects a data packet addressed to the remote network, but will not perform setup/transfers ofjust administrative (non-user data) packets.
out-of-bandsignaling—A system that uses a separate communications channel or frequency outside the voice band for signaling. Modern systems use a separate channel, either TDM or virtual. SS7 uses messages for signaling that are carried on signaling links distinct from voice channels. ISDN uses messages for signaling that are carried on the
D-channel distinct from the voice carried on the B- channels. Frame Relay and ATM use messages that are carried on a separate virtual connection reserved for signaling.
on-hook—The condition of a device which has not accessed a phone line. In modem use, this is equivalent to a telephone handset that has not been picked up. In other words, it can receive an incoming call.
P
packet data—Packet-mode calls.
packet mode—The switching of chunks of information for different users using statistical multiplexing to send them over the same transmission facility. ISDN packet mode capabilities are based on the ITU-TSS Recommendation X.25 procedures.
PAP(Password Authentication Protocol): (RFC 1334)
parity bit—An extra bit attached to each byte of sync—hronous data used to detect errors in transmission.
PBX (private branch exchange)—A telephone exchange located on the customer’s premises. The PBX provides a circuit switching facility for tlephone extension lines within the building, and access to the public telephone network. See also exchange.
P-channel(PCHAN)—The ISDN physical channel identification; contrast logical channel or virtual channel.
PDN (public data network)—A packet-switched network that is available to the public for individual (subscriber) use. Typically, controlled by a government or a national monopoly.
port—A location for input or output data exchange. Computers, muxes, etc. have ports for various purposes.
PPP(Point to Point Protocol)—A protocol that lets a computer user access a TCP/IP address using an ISDN terminal adapter or a highspeed modem over a standard telephone line.
PRI (Primary Rate Interface)—One
of two forms of ISDN service. PRI provides 23 64 Kbps B-channels for video, voice or data, and one 64 Kbps D-channel for control
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
R reference 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.
