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B-12

Appendix B: Glossary

CVoDSL Channelized Voice over DSL. An ADSL feature that eliminates the need to use

IP or ATM to encapsulate voice. CVoDSL is transmitted directly to the voice

switch at the public carrier’s CO.

D4 A superframe format used on T1-carrier lines. The D4 frames consists of 12

193-bit frames combined into a single superframe.

DACS Digital Access and Cross-connect System (US). In the United States, a DACS

is a telecommunications device used to route T1-carrier lines. A DACS uses

D3/D4 framing to cross-connect any T1 DS0 channel (or a complete T1-carrier

line) in the system with any other T1 DS0 channel or line also in the system.

DACS can also be used with SONET.

DACS Digital Access Carrier System (UK). A digital system in the UK that provides

two subscriber lines over one copper twisted pair wire. DACS works by

digitizing the analog signal and sending the combined digital information for

both lines over the same copper pair between the exchange and the pole. The

cost of the DACS equipment is significantly less than the cost of installing

additional copper pairs; however, the maximum speed of an analog modem is

reduced on a line that uses DACS. This is because DACS involves an additional

conversion between analog and digital signaling.

Data Link Layer Layer 2 of the OSI model. At this layer, data frames are encoded and decoded

into bits. The Data Link Layer is divided into two sublayers: The Media Access

Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC

sublayer controls how a computer on the network gains access to the data

and permission to transmit it. The LLC layer controls frame synchronization,

flow control, and error checking. See also OSI.

Data Link Layer

Protocols

A protocol that operates at the Data Link Layer of a network. Data Link Layer

Protocols provide service for Network Layer operations.

DBU Dial Back-Up. DBUs provide connection recovery and dial-up redundant

connectivity in case a primary WAN connection circuit fails.

HP ProCurve 7000dl Series User Manual

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