Cisco 10000 Series Configuration Manual page 355

Loss of Frame. A SONET port status indicator that activates when an LOF defect occurs and does not
LOF
clear for an interval of time equal to the alarm integration period, which is typically 2.5 seconds. An
LOF defect occurs when an out-of-frame (OOF) condition occurs and does not clear for more than
3 microseconds (ms). This occurrence begins the alarm integration period. (OOF occurs when four
consecutive frames do not contain a valid frame word. OOF clears when two valid consecutive frames
are detected.) The LOF indicator clears when an LOF defect is not detected for a time interval that is
equal to the alarm deactivation period (typically 10 seconds).
A test in which signals are sent and then directed back toward their source from some point along the
Loopback test
communications path. Loopback tests are often used to check network interface usability.
Loss of signal. A SONET port status indicator that activates when an LOS defect occurs and does not
LOS
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, however, M13 does not refer to the SYNTRAN format; it
refers instead 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.
Media Access Control. The lower of the two sublayers of the data link layer defined by the IEEE. The
MAC
MAC sublayer handles access to shared media.
Standardized data link layer address that is required for each port or device that connects to a LAN.
MAC address
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 6 bytes long and are controlled by
the IEEE. Also known as a hardware address, MAC-layer address, or physical address.
See MDL.
Maintenance data
link
One of a group of alarm conditions that are considered the second most severe of all reportable alarms.
Major alarm
Major alarms affect several subscribers who connect to the reporting node. You can use the show
facility-alarm status
alarm
See MTU.
Maximum
transmission unit
Maintenance data link. Embedded communications channel in C-bit parity DS3 framing. Used to
MDL
convey message-oriented signals.
OL-8834-04
IOS command to obtain more information about the problem. See also
and Minor alarm.
Cisco 10000 Series Router Line Card Configuration Guide
Glossary
Critical
GL-5