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COMSPHERE 3550 Series Data Service Units
Glossary-2 February 1995 3550-A2-GB20-10
CCITT The International Consultative Committee for Telegraphy and Telephony, a
committee of the International Telecommunication Union (ITU).
clamping A function of the DSU that forces the output signal to go low (Off) and causes the
DSU to ignore input signals.
CMI Control Mode Idle. A control signal sent over the DDS line to indicate that no data
activity is being sent.
collision A collision occurs when two tributary DSUs transmit data onto the network at the
same time. The transmissions interfere with each other and neither is successfully
received.
control A DSU or modem that is, for diagnostic purposes, at the logical head of a
hierarchical network. It is the unit from which tests and commands are issued to
other units on the same circuit. There is only one control per link.
Control Channel
(CC)
The diagnostic interface between the 6700 Series NMS and the SDU for a
Model 3551 DSU, and the Hubbing Device for the Model 3550.
core A function of the circuit card that provides data transmission capability. With
Model 3550 or Model 3551 DSUs, there are two cores – one for the DSU and one
for the DBM, and the data can be transmitted through either (also see active core).
CSA Canadian Standards Association.
CTS The state of the Clear-to-Send lead.
Data Communications
Equipment
(DCE)
A device, such as a DSU or modem, that provides an interface between a DTE
device and a digital or dial/analog network (also called data circuit-terminating
equipment).
data router A sophisticated circuit switch in the DSU that is capable of connecting several
communication interfaces in more than one way, redirecting or routing data to an
alternate path.
Data Service Unit
(DSU)
A DCE device that interprets, interfaces, and provides timing and signal control
between a DTE device and a digital network.
Data Terminal Equipment
(DTE)
A computer or peripheral device, such as a terminal or printer; a data source or sink.
DBM The V.32 dial backup module that can be ordered for the DSU. This module
operates at 14.4 kbps and provides an alternate data path in case of failure of the
digital connection through the dial network.
DDS
Digital Data Service, such as the ACCUNET Spectrum of Digital Services that
provides digital (not dial) communication circuits.
dedicated backup A dial backup module (DBM) assigned to a particular DSU that is continually
available for service restoration. The DBM switches to Dial Backup mode
automatically when the DDS line fails; no switching is required. An external dial
backup unit (DBU) can also provide dedicated backup.