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Appendix D
Glossary
L
LAN
Local Area Network. High-speed, low error data network covering a relatively small geographic area.
LANs connect workstations, peripherals, terminals, and other devices in a single building or other
geographically limited area. Ethernet, FDDI, and Token Ring are widely used LAN technologies.
LCD
Liquid Crystal Display. An alphanumeric display using liquid crystal sealed between two pieces of glass.
LCDs conserve electricity.
Line layer
Refers to the segment between two SONET devices in the circuit. The line layer deals with SONET
payload transport, and its functions include multiplexing and synchronization. Sometimes called a
maintenance span.
Line timing mode
A node that derives its clock from the SONET lines.
Link budget
The difference between the output power and receiver power of an optical signal expressed in dB. Link
refers to an optical connection and all of its component parts (optical transmitters, repeaters, receivers,
and cables).
Link integrity
The network communications channel is intact.
Loopback test
Test that sends signals then directs them back toward their source from some point along the
communications path. Loopback tests are often used to test network interface usability.
LOW
Local Orderwire. A communications circuit between a technical control center and selected terminal or
repeater locations.
M
MAC address
Standardized data link layer address that is required for every port or device that connects to a LAN.
Other devices in the network use these addresses to locate specific ports in the network and to create and
update routing tables and data structures. MAC addresses are six bytes long and are controlled by the
IEEE. Also known as the hardware address, MAC-layer address, and physical address.
Maintenance user
A security level that limits user access to maintenance options only. See also Superuser, Provisioning
User, and Retrieve User.
Cisco ONS 15454 Installation and Operations Guide
D-7
November 2001
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