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Twenty-four DS0 channels make up one DS1 (total bandwidth is 1.544 Mbps). DS3 Digital signal level three. Equivalent of 28 DS1s and 672 DS0s (total bandwidth is 44.736 Mbps). DSR Data set ready. A signal on the DTE interface that indicates if a connection exists and if the devices are ready to start handshaking control signals so communications can begin. 61200659L1-1 MX2800 STS-1 User Manual Appendix D. Glossary DSU Data service unit. A device designed to transmit and receive digital data on digital transmission facilities. DTE Data terminal equipment. The end-user terminal or computer that plugs into the termination point (DCE) of a communications circuit. The main difference between the DCE and the DTE is that pins two and three are reversed. E1 Transmission rates of 2.048 Mbps are available on T1 communication lines. See also T1. end device The ultimate source or destination of data flowing through a network (sometimes referred to as DTE). end user Subscriber who uses (rather than provides) telecommunications services. ES Errored seconds. A second with one or more coding violations (CVs). ethernet Transmission protocol for packet-switching LANs. facilities The equipment used by carriers to provide communication services. far end The distant end to that being considered. Not the end where testing is being carried out. FCC Federal Communications Commission. The U.S. federal agency responsible for regulating interstate and international communications by radio, TV, wire, satellite, and cable. MX2800 STS-1 User Manual 61200659L1-1 Appendix D. Glossary FDL Facility datalink. FDL bits provide overhead communication between the terminal equipment in ESF framing. gateway A device which enables information to be exchanged between two dissimilar systems or networks. host computer The primary or controlling computer in a multiple computer operation. idle code In a T3 circuit, an idle code consists of a sequence of 1100 over the entire payload bandwidth. in-band Signaling (dialing, diagnostics, management, configuration, etc.) over the same channel used for data. IP Internet protocol. A protocol which provides for transmitting blocks of data between hosts identified by fixed-length addresses. LAN Local area network. A privately owned network that offers high-speed communications channels to connect information processing equipment in a limited geographic area. local loopback (LL) A type of test used to verify the operation of the local terminal equipment, the CSU, and the connection between the two. The signal from the DTE is looped back by the CSU and is sent back to the DTE. loopback The technique for testing the processing circuitry of a communications device. May be initiated locally or remotely via a telecommunications circuit. Device being tested will echo back received test data. The results are compared with the original data. 61200659L1-1 MX2800 STS-1 User Manual Appendix D. Glossary LOS Loss of signal. Defined as a line state in which no pulses are received for 175 bit positions. M13 DS1/DS3 multiplexer that combines up to 28 DS1 channels into one DS3 channel. Uses two-stage, bit synchronous TDM. Mbps Megabits per second (one million bits per second). MIB Management information base. A database of network management information used by SNMP. modem Acronym for modulator/demodulator. Equipment that converts digital signals to and from analog signals. Used to send digital signals over analog phone lines. monitor To watch or listen to a signal non-intrusively. multi-point circuit A single communications circuit that has more than two terminations. NC Normally closed. Relay switch contacts that remain closed when inactive. near end The unit on-site. NI Network interface. The demarcation point between the CPE and the PSTN. NO Normally open. Relay switch contacts that remain open when inactive. MX2800 STS-1 User Manual 61200659L1-1 Appendix D. Glossary NRZ Non return to zero. A mode in which the digital level is low for a 0 bit and high for a 1 bit, and does not return to zero between successive 1 bits. out-of-band Signaling that is separated from the channel carrying information (voice, data, video, etc.). Typically the separation is accomplished by a filter. The signaling includes dialing and other supervisory signals. point-to-point Type of communications link that connects a single device to another single device, such as a remote terminal to a host computer. POP Point of presence. Physical place within a LATA (local access and transport area) where a long distance carrier or a cellular provider interfaces with the network of the local exchange carrier (LEC). A POP is usually a building serving as the point of termination which houses switches and transmission equipment. protocol A set of rules controlling the orderly exchange of information between stations in data communications networks or systems. PSTN Public switched telephone network. Usually refers to the world-wide voice telephone network available f...

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