MultiModemISDN User Guide
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.
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.
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.
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, pro vided 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 information is stored.
SS7 (Signaling System 7)—An ITU-T and ANSI standard for digital out-of-band signalling between central offices that provides much o f the network switching intelligence to support many ISDN functions
stop bit—One of the variables used for timing in asynch- ronous 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 support, etc.
switched 56—A circuit-switched (full duplex digital synchronous data transmission) service that lets you dial a number and transmit data to it at 56 Kbps. It is a relatively low cost service, widely used in North America for telecommuting, videoconferencing and high speed data transfers. Many phone companies are phasing out switched 56 in favor of ISDN service.
switched line—In communications, a physical channel established by dynamically connecting one or more discreet segments. This connection lasts for the duration of the call after which each segment may be used as part of a different channel. Contrast with leased line.
switched network—A network in which a temporary connection is established from one point via one or more segments.
synchronous transmission—The transmission of data which involves sending a group of characters in a packet. This is a common method of transmission between computers on a network or between modems. One or more synchronous characters are transmitted to confirm clocking before each packet of data is transmitted. Compare to Asynchronous Transmission.
