CCNA Cisco Certified Network Associate Study Guide - FTP Server

Glossary 669
data frame Protocol Data Unit encapsulation at the Data Link layer of the
OSI reference model. Encapsulates packets from the Network layer and prepares
the data for transmission on a network medium.
datagram A logical collection of information transmitted as a Network
layer unit over a medium without a previously established virtual circuit. IP
datagrams have become the primary information unit of the Internet. At various
layers of the OSI reference model, the terms cell, frame, message,
packet, and segment also define these logical information groupings.
Data Link control layer Layer 2 of the SNA architectural model, it is
responsible for the transmission of data over a given physical link and compares
somewhat to the Data Link layer of the OSI model.
Data Link layer Layer 2 of the OSI reference model, it ensures the trustworthy
transmission of data across a physical link and is primarily concerned
with physical addressing, line discipline, network topology, error
notification, ordered delivery of frames, and flow control. The IEEE has further
segmented this layer into the MAC sublayer and the LLC sublayer. Also
known as the Link layer. Can be compared somewhat to the Data Link
control layer of the SNA model. See also: Application layer, LLC, MAC,
Network layer, Physical layer, Presentation layer, Session layer, and
Transport layer.
DCC Data Country Code: Developed by the ATM Forum, one of two ATM
address formats designed for use by private networks. Compare with: ICD.
DCE data communications equipment (as defined by the EIA) or data
circuit-terminating equipment (as defined by the ITU-T): The mechanisms
and links of a communications network that make up the network portion
of the user-to-network interface, such as modems. The DCE supplies the
physical connection to the network, forwards traffic, and provides a
clocking signal to synchronize data transmission between DTE and DCE
devices. Compare with: DTE.
D channel 1) Data channel: A full-duplex, 16Kbps (BRI) or 64Kbps (PRI)
ISDN channel. Compare with: B channel, E channel, and H channel. 2) In
SNA, anything that provides a connection between the processor and main
storage with any peripherals.