B-16
Appendix B: Glossary
DSCP Differentiated Services Code Point. Six bits in the DiffServ header that can be
set with values that define up to 63 traffic classes. For more information about
DSCP values and usage, see RFC 2983 (at http://www.ietf.org/rfc/rfc2983.txt).
See also DiffServ.
DSL Digital Subscriber Line. A broadband technology, DSL provides high-speed
WAN connections over existing local loops. Two types of DSL technologies
are available: symmetric DSL, which dedicates the same amount of data to
upstream and downstream transmissions, and asymmetric DSL, which
dedicates most of the available bandwidth to downstream transmissions.
DSLAM Digital Subscriber Line Access Multiplexer. A network device, usually at a
service provider’s central office (CO), that receives signals from multiple
customer DSL connections and puts the signals on the high-speed infrastructure
backbone using multiplexing techniques.
DS0 Digital Signal Zero. DS0 is a digital channel operating at 64 Kbps, the amount
of bandwidth required to transmit a single analog voice call through a digital
telecommunications network. DS0 is the fundamental unit of bandwidth—the
fundamental channel—in all copper-based T-, E-, and J-carrier systems. In E-
carrier systems, DS0 is called E0, and in J-carrier systems, DS0 is called J0.
However, the basic signal is virtually identical in all three carrier systems.
DS1 Digital Signal at the First Level. A bipolar signal combination of 24 DS0s that
is transmitted at 1.544 Mbps. Also called T1.
DSU Digital Service Unit. The DSU accepts data from the router at the customer’s
premises and translates it from the signaling format used on the LAN to the
format necessary for transmission on the WAN. In the United States and
Canada, the public carrier may provide the DSU in conjunction with the CSU.
In this case, it is referred to as the CSU/DSU.
DSS Digital Signature Standard. A DSA used to create digital signatures, which
authenticate electronic documents such as digital certificates. DSS creates
and verifies a digital signature using a pair of asymmetric keys. The private
key in the pair, which is known only by the signer, transforms and “signs” the
certificate. The public key, which can be distributed to any host, verifies the
signature.
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