Specifications

December 2008 Page C–5
Appendix C — Glossary
itself to insure that it is functioning properly.
Sidetone The transmission and reproduction of
sounds through a local path.
Single-Mode Fiber A fiber waveguide that
supports the propagation of only one mode. The
small core radius approaches the wavelength of
the source; consequently, only a single mode is
propagated.
Slave Aterminal which derives its reference clock
from the master terminal.
Slip The loss of a data bit on an T1/E1 link due to
a frame misalignment between the timing at a
transmit terminal and timing at a receive terminal.
Snell’s Law When light is passed from a given
transmission medium to a less dense medium, its
path is deviated away from normal.
Step-Index Fiber Afiber where there is an abrupt
change in the refractive index between the core
and the cladding along a fiber diameter.
Synchronization The process of ensuring that
network elements maintain timing relationships.
Network Timing Synchronization A network
where all communication T1/E1 links are
synchronized to a common clock table between
the terminals to assure no slips occur.
Frame Synchronization Delimiting frames
within the 1.544 Mbps T1/E1 signals.
Synchronous Data A transmission method of
synchronizing bits to a clock. Bit transfers are
controlled by clock signals at the sending and
receiving stations. Characters are formed by
counting the bits. Special ‘sync’ characters in the
data stream are uniquely recognizable and reset
the counter to the beginning of a new character.
T1 Link A circuit that is used as a time division
link between multiplexers to transmit T1/E1
formatted digital signals at a rate of 1.544 Mbps
(full T1 rate). Also referred to as T1 trunk or DS1
circuit.
Terminal A FOCUS chassis that constitutes the
source and termination of a channel
Time Slot Any time interval that can be recog-
nized and uniquely defined.
TSIC Time Slot Interchange Circuit. A device that
switches digital highways in PCM based
switching systems.
Timing Refers to the source of clock signals used
to synchronize the network (e.g., internal timing,
external timing).
Transceiver The combination of transmitting and
receiving equipment on a single module.
Trip Arelay closing as a result of a stimulus from
the remote terminal.
Voice Digitization Techniques that convert
analog voice signals to digital (e.g., PCM).
Yellow Alarm An alarm signal sent back towards
the source of a failed signal due to the presence of
an Loss of Sync Alarm.
Zero Bit Insertion A process in bit-oriented
protocols where a zero is inserted into a string of
ones by the sender to prevent the receiver from
interpreting valid user data (the string of ones) as
control character (a Flag character for instance).
This is not the same as pulse stuffing used in E1
networks.
Zero Suppression The insertion of a logical one
to prevent the transmission of eight consecutive
zero bits. Primarily used to ensure sufficient ones
density.