E1 Glossary

5 E1 Daughter Card

RAI: Remote Alarm Indication; a field of all ones (1) used as a “keep-alive” signal.

AMI: Alternate Mark Inversion; a type of line coding for E1 spans.

HDB3: High Density Bipolar Order 3 Encoding.

CAS: Channel Associated Signaling. A form of circuit state signaling in which the circuit state is indicated by one or more bits of signaling status sent repetitively and associated with that specific circuit.

bps: Bits per second; the serial digital stream’s data rate (e.g., 2.048M bps equals 2,048,000 bits per second).

BPV: Bipolar Violation (two pulses of the same polarity in a row).

CEPT: Conference on European Posts and Telecommunications (a body that sets telecommunications service and interface policies).

CFA: Carrier Failure Alarm; detection of a red (local) or yellow (remote) alarm.

CO: Central office (the telephone company switch; the other end of a local loop from the CP).

CP: Customer premises (user or customer-related operations, as opposed to telephone company-related operations).

CPE: Customer premises equipment (user’s communications equipment, as opposed to telephone company-related equipment).

CSU: A communications device that terminates the local loop and provides a digital interface to the E1 line.

DNIS digits: Dialed Number Identification Service. DNIS is a feature of R2MF E1 lines that provides the number the caller dialed to reach the attached computer telephony system (manual or automatic).

DS-0: Digital Signal, level 0 (the 64K bps worldwide standard speed for PCM digitized voice channels).

DS-1: Digital Signal, level 1 (the standard speed for PCM digitized voice channels; 1.544M bps in North America; 2.048M bps in ITU standards).

DS-2: Digital Signal, level 2 (the standard speed of four E1s used in Japan).

DS-3: Digital Signal, level 2 (the standard speed of 28 E1s; 44.736M bps).

DSL: Digital Subscriber Line (an ISDN BRI line).

DSU: The digital communications device used to convert an RS-232 to DSX-1 interface.

E-1: The European digital signal level 1; 2.048M bps.

ESS: Electronic Switching System (a CO switch).

Frame: A method of error control where bits are inserted into the data stream for the receiving device to identify the time slots allocated to each sub-channel.

FXO: Foreign Exchange, Office; an interface at the end of a private line connected to a switch that, along with FXS, allows the phones to act as if connected locally to the main PBX, but without the cost.

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