RS-232◆ Universally accepted Electronics Industries Association standard that defines the signals between data terminal equipment and data communications equipment. Uses a 25-pin connector; theoretically limited to distances of 50 feet; functionally identical to standards V.24/V.28.

RS-422◆ Electronics Industries Association standard for balanced transmission at distances greater than 50 feet. Compatible with V.11.

RTS (Request To Send) ◆ RS-232 (V.24) control signal, sent from the data terminal equipment to the data communications equipment on pin 4. Indicates that the DTE has data to transmit. (See RS-232.)

Rx ◆ Abbreviation meaning receive, receiver, or reception.

SAP ◆ Service Access Point

SAPI (Service Access Point Identifier) ◆ Part of the address in an ISDN signalling frame. Identifies the service that the signalling frame is intended for.

SDLC ◆ See Synchronous Data Link Control (SDLC).

Serial Transmission ◆ Technique in which each bit of information is sent sequentially on a single channel. Serial transmission is the normal mode for data communications. Contrast with parallel transmission.

SDU (Service Data Unit) ◆ User data passed through a SAP between the layers of the OSI or a similar model.

Signalling ◆ An ATM connection procedure that dynamically implements explicit routes through switches to establish a communication link with another station on the network.

S Interface ◆ The interface point between an ISDN device and the user premises network termination.

SDLC ◆ See Synchronous Data Link Control.

SNA ◆ IBM’s Systems Network Architecture. The part of a user- application network that conforms to the formats and protocols of Systems Network Architecture. It enables reliable transfer of data among users and provides protocols for controlling the resources of various network configurations. The SNA network consists of Network Accessible Units (NAUs), boundary function, gateway function, and intermediate session routing function components, and the transport network.

SNMP (Simple Network Management Protocol) ◆ Ahigh-level,stan-dards-based protocol for network management, usually used in TCP/ IP networks. An SNMP manager controls and measures the activities

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