Vodavi NomadIP, Руководство пользователя

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Glossary
108
December, 2005 Vodavi Telenium IP Product Guide
mobility ▪ presence ▪ collaboration ▪ convergence
CSMA/CD Short for Carrier Sense Multiple Access / Collision Detection, a set of rules determining how
network devices respond when two devices attempt to use a data channel simultaneously (called a
collision). Standard Ethernet networks use CSMA/CD to physically monitor the traffic on the line at
participating stations. If no transmission is taking place at the time, the particular station can
transmit. If two stations attempt to transmit simultaneously, this causes a collision, which is
detected by all participating stations. After a random time interval, the stations that collided
attempt to transmit again. If another collision occurs, the time intervals from which the random
waiting time is selected are increased step by step. This is known as exponential back off.
CSU/DSU Channel Service Unit/Data Service Unit- primarily used for connecting a router to a T1 or a T3 line.
The CSU terminates a T interface, while the DSU is essentially a digital modem.
Default
Gateway In an IP network, the default gateway is the router that forwards traffic to a destination outside of
the subnet of the transmitting device.
Delay The amount of time it takes for a packet of information to arrive at its destination. Usually
measured in milliseconds on LANs and WANs. Also called latency.
DHCP DHCP (Dynamic Host Configuration Protocol) is a communications protocol that lets network
administrators centrally manage and automate the assignment of Internet Protocol (IP) addresses
in an organization's network. Using the Internet Protocol, each machine that can connect to the
Internet needs a unique IP address, which is assigned when an Internet connection is created for
a specific computer. Without DHCP, the IP address must be entered manually at each computer in
an organization and a new IP address must be entered each time a computer moves to a new
location on the network. DHCP lets a network administrator supervise and distribute IP addresses
from a central point and automatically sends a new IP address when a computer is plugged into a
different place in the network.
DiffServ Differentiated Services: A protocol for specifying and controlling network traffic by class so that
certain types of traffic get precedence - for example, voice traffic, which requires uninterrupted
flow of data, might get precedence over other kinds of traffic. Differentiated Services is the most
advanced method for managing traffic in terms of Class of Service (CoS). For a given set of
packet travel rules, a packet is given one of 64 possible per-hop forwarding behaviors. A six-bit
field, known as the Differentiated Services Code Point (DSCP), in the Internet Protocol (IP) header
specifies the per hop behavior for a given flow of packets.
DNS The Domain Name System (DNS) is the way that Internet domain names are located and
translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-
remember handle for an Internet address.
DOCSIS Data Over Cable Service Interface Specification. Cable modem communications standard.
Domain A group of hosts which share the same network suffix.
DS-3 Digital Signal, level 3. Also called T-3. In North America, DS-3 is the equivalent of 28 T-1
channels, operating at a total signaling rate of 44.736 Mbps. In a channelized application, DS-3
supports 672 channels, each of 64 Kbps.
DSCP Differentiated Services Code Point: see DiffServ
DSL DSL (Digital Subscriber Line) is a technology for bringing high-bandwidth information to homes
and small businesses over ordinary copper telephone lines. xDSL refers to different variations of
DSL, such as ADSL, HDSL, and RADSL. Typically, connections will provide from 1.544 Mbps to 512
Kbps downstream and about 128 Kbps upstream.
EAP Extensible Authentication Protocol (EAP): authentication protocol for wireless networks. EAP can
support multiple authentication mechanisms, such as token cards, smart cards, certificates, one-
time passwords, and public key encryption authentication.