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Glossary
GL-7
Cisco 10008 Router Hardware Installation Guide
OL-0659-13
IR
Intermediate reach. SONET/SDH specification for transmit power and receive sensitivity that achieves
a 9.3-mile (15-km) reach.
ISP
Internet Service Provider. A company that provides Internet access to other companies and individuals.
ITU-T
International Telecommunication Union Telecommunication Standardization Sector. International
body that develops worldwide standards for telecommunications technologies. The ITU-T carries out
the functions of the former CCITT.
L
LAN
Local-area network. High-speed, low-error data network covering a relatively small geographic area
(up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in
a single building or some other geographically limited area. LAN standards specify cabling and
signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are
widely used LAN technologies. Compare with MAN and WA N.
Line card
Any I/O card that can be inserted in a modular chassis.
LMI
Local Management Interface. A set of enhancements to the basic Frame Relay specification. LMI
includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism,
which provides the network server with its local DLCI and the multicast DLCI; global addressing,
which gives DLCIs global rather than local significance in Frame Relay networks; and a status
mechanism, which provides an on-going status report on the DLCIs known to the switch. Known as
LMT in ANSI terminology.
Local-area network
See LAN.
Loopback test
A test in which signals are sent and then directed back toward their source from some point along the
communications path. Loopback tests are often used to test network interface usability.
LOS
Loss of signal. A SONET port status indicator that activates when an LOS defect occurs and does not
clear throughout the alarm integration period, which is typically 2.5 seconds. An LOS defect occurs
when the OC-3 port receives all zeros for 20 microseconds (+.3 ms). This occurrence begins the alarm
integration period. If this period elapses without the detection of two consecutive frames in which there
are no 20-ms periods of signal loss, the LOS indicator activates. The LOS indicator clears when an LOS
defect is not detected for an interval equal to the alarm deactivation period (typically 10 seconds).
M
M13
Generic term for equipment that multiplexes DS1s into DS3s. Sometimes used to describe a specific
DS3 multiplex format. Some standards use this term to describe a synchronous multiplexing format
also know as SYNTRAN. In many cases M13 does not refer to the SYNTRAN format, but instead
refers to the format also known as M23.
M23
A method of multiplexing four DS1 signals into a DS2 signal, then multiplexing seven DS2 signals into
a DS3 signal.