B-14
Appendix B: Glossary
Dedicated Circuits A WAN access circuit that is reserved for the use of a single subscriber. When
the bandwidth is not in use, it remains idle.
Demarc Point of demarcation. The point at which the public carrier’s network ends
and the subscriber’s local network begins.
DES Data Encryption Standard. DES is a published encryption algorithm that uses
a 56-bit symmetric key to encrypt data in 64-bit blocks. IPSec, the industry
standard for VPNs, supports 3DES. See also 3DES, IPSec, and VPN.
DHCP Dynamic Host Configuration Protocol. A protocol that allows network admin-
istrators to set up a server that manages IP addresses, automatically assigning
IP addresses to devices on the network. For more information about DHCP,
see RFC 2131 (at http://www.ietf.org/rfc/rfc2131.txt).
Diffie-Hellman A secure method for generating a unique, shared key without sending it over
the connection and thus rendering it vulnerable to interception. Each host
selects a private value, which is then modified (using prime number
modulation) into a public value. Hosts exchange the public values. Each uses
the other’s public value and their own private value to compute a new value.
The computation function is such that these values will be the same.
DiffServ Differentiated Services. A QoS mechanism for classifying traffic and determin-
ing forwarding behavior. The DiffServ protocol redefines the Type of Service
(ToS) field in the IPv4 header as the Differentiated Services (DS) field. With
DiffServ, traffic can be assigned to one of 63 different traffic classes, and each
traffic class is granted service based on the priority assigned to its DiffServ
value. For more information about DiffServ uses and values, see RFC 3260 (at
http://www.ietf.org/rfc/rfc3260.txt).
Digital
Certificates
An electronic document that contains a public key and is digitally signed by a
third-party issuer such as a CA. Digital certificates are used for network
authentication. They contain the certificate holder’s name, a serial number,
the expiration dates, and a copy of the certificate holder’s public key (used
for encrypting and decrypting messages). See also CA.
Digital Signal
Hierarchies
Hierarchies that determine the combinations of channels that compose the
bandwidths for an E-, J-, or T-carrier line. In Europe, Asia (except Japan), South
America, and Australia, the CEPT hierarchy is used. In Japan, the J-carrier
signal hierarchy is used for voice transmissions. In the United States and
Canada, the DSX hierarchy is used.
DLC Digital Loop Carrier. Equipment that bundles a number of individual phone
line signals into a single multiplexed digital signal. This signal includes local
traffic moving between a CO and a business complex or other outlying service
area. See also CO.
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