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Glossary

data circuit-terminating equipment

DCE is used to provide clocking to

DTE equipment.

data compression

See: compression

data direct VCC

A bidirectional point-to-point virtual control connection

(VCC) set up between two LECs in ATM and one of three data connections
defined by Phase 1 LAN emulation. Because data direct VCCs do not guar-
antee QoS, they are generally reserved for UBR and ABR connections. Com-
pare with: control distribute VCC and control direct VCC.

data encapsulation

The process in which the information in a protocol is

wrapped, or contained, in the data section of another protocol. In the OSI
reference model, each layer encapsulates the layer immediately above it as
the data flows down the protocol stack.

data frame

Protocol Data Unit encapsulation at the Data Link layer of the

OSI reference model. Encapsulates packets from the network layer and pre-
pares 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 var-
ious 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 com-
pares somewhat to the Data Link layer of the OSI model.

Data Link layer

Layer 2 of the OSI reference model, it ensures the trust-

worthy transmission of data across a physical link and is primarily con-
cerned with physical addressing, line discipline, network topology, error
notification, ordered delivery of frames, and flow control. The IEEE has fur-
ther 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.

data terminal equipment

See: DTE.

DCC

Data Country Code: Developed by the ATM Forum, one of two ATM

address formats designed for use by private networks. Compare with: ICD.

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