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Firewall User Guide

Router: A device that connects two networks using the same networking protocol. It operates at the Network Layer

(Layer 3) of the OSI model for forwarding decisions.

Routing Information Protocol (RIP): A distance vector-based protocol that provides a measure of distance, or hops,

from a transmitting workstation to a receiving workstation.

RS232-C: An EIA 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.

RS-422: The EIA standard for a balanced interface with no accompanying physical connector. RS-422 products can

use screw terminals, DB9, various DB25, and DB37 connectors.

RS-530: The EIA standard for the mechanical/electrical interface between DCEs and DTEs transmitting synchronous

or asynchronous serial binary data. RS-530 provides for high data rates with the same connector used for RS-232;

however, it is incompatible with RS-232.

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 (i.e., COM1 through COM4). A

serial port contains a conversion chip called a “UART” which translates between internal parallel and external serial

formats.

Service: The requirements offered by an RPOA to its customers to satisfy specific telecommunications needs.

Severely Errored Seconds (SES): Refers to a typical T1 error event where an error burst occurs (a short term, high

bit-error rate that is self-clearing). Per the ITU-T (CCITT) G.821: any second in which the BER is less than 1x10 -3 .

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.

Simple Network Management Protocol (SNMP): TCP/IP protocol that allows network management.

Simultaneous Voice Data (SVD): 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.

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.

Superframe (D4): A T1 transmission fromat that consists of 12 DS1 frames, or 2316 bits. A DS1 frame consists of 193

bit positions. A frame overhead bit is in the first position, and it is used for frame and signaling phase alignment only.

Subscriber Loop: See “Local loop”.

Switched 56: A circuit-switched (full duplex digital synchronous data transmission) service that lets you dial a number

and transmit data to it at 56K bps. It is a relatively low cost service, widely used in North America for telecommuting,

videoconferencing and high speed data transfers. Many phone companies are (or will be) phasing out Switched 56 in

favor of ISDN service.

Switched Virtual Circuit (SVC): A type of data transmission where the connection is maintained only until the call is

cleared.

Switched Line: In communications, a physical channel established by dynamically connecting one or more discrete

segments. This connection lasts for the duration of the call after which each segment can 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 Data Link Control (SDLC): A discipline conforming to subsets of the Advanced Data Communications

Control Procedures (ADCCP) of the American National Standards Institute (ANSI) and High-level Data Link Control

(HDLC) of the International Organization for Standardization, for managing synchronous, code-transparent, serial-by-

bit information transfer over a link connection. Transmission exchanges may be duplex, or half-duplex over switched or

nonswitched links. The configuration of the link connection may be point-to-point, multipoint, or loop.

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.

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