Symmetricom SyncServer S100 User Manual page 136

SyncServer S100
L1 Band, L2 Band
Each Navstar GPS satellite currently transmits in two dedicated frequency bands: L1 and L2,
which is centered on 1227.6 MHz. L1 carries one encrypted signal, as does L2, both being
reserved for the military. L1 also carries one unencrypted signal, for civilian use.
LAN
Local area network (LAN): A data communications system that (a) lies within a limited spatial
area, (b) has a specific user group, (c) has a specific topology, and (d) is not a public switched
telecommunications network, but may be connected to one. Note 1: LANs are usually
restricted to relatively small areas, such as rooms, buildings, ships, and aircraft. Note 2: An
interconnection of LANs within a limited geographical area, such as a military base, is
commonly referred to as a campus area network. An interconnection of LANs over a city-wide
geographical area is commonly called a metropolitan area network (MAN). An
interconnection of LANs over large geographical areas, such as nationwide, is commonly
called a wide area network (WAN). Note 3: LANs are not subject to public
telecommunications regulations.
LDAP
The Lightweight Directory Access Protocol is the standard Internet protocol for accessing
directory servers over a network.
Leap Seconds
Today's scientists and engineers have perfected clocks based on a resonance in Cesium
atoms to an accuracy of better than one part in 10 trillion. These clocks keep pace with each
other to within one two- or three-millionth of a second over a year's time. The earth, on the
other hand, can accumulate nearly a full second of error during a given year. To keep
coordinated with the rotation of the earth, this error is added to (or deleted from) UTC time as
a leap second, on the last day of the June or December in that year.
MD5
An algorithm for creating a cryptographic hash (or "fingerprint") of a message or of data.
Message Authentication Code (MAC)
A MAC is a function that takes a variable length input and a key to produce a fixed-length
output.
Message Digest
The hash of a message.
See also: Hash
MIB
Management Information Base, a database on the network that tracks, records, and corrects
performance for each device on the network.
MTBF
Mean Time Between Failure, a measure of reliability. The longer the time span between
failures, the more reliable the device.
128 S100 User Guide – Rev. D – June 2005