150-359-100-01, Revision 01
Appendix D - Glossary
HXU-359 List 1
October 27, 2000
57
DDS
Digital Data Service
DS1
Digital Signal Level 1
DSU/CSU
Digital Service Unit / Channel Service Unit — Converts digital
data frames
DSX-1
Digital System Cross-connect frame
ES
Errored Seconds
ESF
Extended Superframe
EXZ
Excessive Zeroes
FCLT
Facility Loopback
GND
Ground
HDB3
High Density Binary 3 — An E1 line code.
HDSL
High-bit-rate Digital Subscriber Line
HXU
HiGain Multiplexer Unit
LBO
Line Buildout — Software-configured LBO allows selection of
correct cable length for a particular location.
LINE
One or more SONET sections, including network elements at
each end, capable of accessing, generating, and processing
Line Overhead.
LOF
Loss of Frame — An LOF occurs when the OOF state exists for
a specified time in milliseconds.
LOP
Loss of Pointer — An LOP occurs when a specified number (8,
9, or 10) of consecutive invalid pointers or consecutive new
data flags are received.
LOS
Loss of Signal — An LOS is generated when the synchronous
signal level drops below the threshold at which a BER of 1 in
103 is predicted. It can occur due to a cut cable, excessive
attenuation of the signal, or equipment fault.
LSS
Loss of Sequence Synchronization
MDF
Main Distribution Frame
Multiplexer (MUX)
A device for combining several channels to be carried by one
line or fiber.
NDU
Network Doubler Unit
